Blackbird - Land speed record breaking car
These guys have supplied goods FOC
Congleton Propshafts (part of the FIROW group)
These guys have generally supplied goods at cost
Glebe engineering (gearboxes)
Congleton Laser cutting
Alan at the Forge (fantastic welding artistry).
Brothers John (Icecreams & wheel bearings) and Bill (space facilities & backup).
Martyn and Richard at work, sounding boards, work with motors and drives.
Rob Green in Maltby, outstanding machining and knowledge of things mechanical
I have been contacted by Jeremy at Greenpower with an intriguing idea; try to break the UK land speed record for electric cars. What a brilliant idea!. So this is henceforth my hobby... Initial thoughts are;
1) there's nowhere long & straight in UK to go for the record
2) use BLDC aero engines for RC planes, light cheap & powerful
3) use lithium batteries - light & "high-C" discharge rates possible
I bought a couple of motors from www.hobbycity.com - only £30 each with 2.5kW output. I did a simulation with 4 wheel drive & 200kW, geared for 230mph. With 0.6m2 cross section and Cd = 0.15 we ought to be able to exceed 300mph on an 8 mile track(!) - or reach nearly 170mph over 1km at elvington (3km track suitable for kilometer record), and well over 200mph at Pendine sands (5 mile straight beach suitable for 1 mile record).
I started thinking about drives for the motors. I can't afford a drive each (there are 80 of them....) and there are question marks about starting the motors with back emf sensorless control, so I reckon I'll make my own controllers. Making a big PWM controller like this also looks a bit daunting so I plan to have an input synchronous buck converter feeding the bridge as a current source, with the bridge switched at fundamental frequency from shaft sensor feedback. So far, I've made prototype PCBs for the sensor and for a single motor drive: I'll make these work on a 2 seat training car for the CAUC team (2.5kW should suit them just fine) & then move on up to a 10kW version for Blackbird. My plan is to have each wheel driven independently, and each wheel to have its own battery pack and 5 independent 10kW drive spindles. This will give modularity and redundancy in the drive system. The BLDC motors will be geared for about 200mph in UK from about 36V (note we are talking BIG currents here)
Looking at other stuff I'll need, I was encouraged to find "off the shelf" dragster tyres rated at 300mph(!), heard encouraging noises from "lifebatt" - a supplier of lithium batteries, and "ondrives" gearboxes, and have determined that vauxhall corsa uprights look like the thing to use on all 4 corners. Next weekend will see me down at the scrapyard to furnish myself with 4 of these. I will start talking to APracing to try and get some carbon/ceramic brake discs.
I have also spoken to Dr. Kenji Takana at Southampton University aerodynamics department and we might be able to get some help from that quarter (note the Cd = 0.15 above.........)
I have started a 3D design project with a "safety cell" for the driver & battery pack outlines & motor mockups to start working towards target weights & packaging.
It all looks very encouraging, with all-up weight around 700kg. Physically we should be able to get it much smaller than "Dieselmax", and a world record might also be on the cards (note that UK record is presently 137mph, world is ~315, an altogether different kettle of fish). If everything goes to plan in the UK, it's a logical next step & would be much more interesting for any sponsors!
I bought a couple of Corsa front uprights from the scrapyard for £60 - I'll get down there again when the weather is nice for a couple more. The bottom balljoints look usable. I also took away the driveshafts & will use part of them. I spoke to a local propshaft company, Congleton Propshafts, on the industrial estate where I work & they put together a suitable package of hooke joints & splined shaft for the driveshafts. These are quite small because there are no shock loads with the electric drive. The hooke joints are light and efficient when compared to CV joints & my steering angles will be infinitesimal. So I have to engineer the Vauxhall hub spline onto the UJ - piece of cake - drill & weld! I'll leave a bit of the CV joint on there so the wheel will stay on if the weld breaks.......
The uprights cleaned up quite well, I've measured them up carefully & used a geometric suspension program to determine wishbone lengths & chassis pickup locations to give me a stable geometric roll centre over 3 inches of bump and 3 degrees of roll. The roll centre is about 30mm higher at the back than the front.
All upper wishbones are 190mm so these can all be made on the same jig. Similarly all the lower wishbones are 300mm, Chassis pickup points are:
front: bottom pivots 183mm from ground and 320mm apart. Uppers 200mm higher and 84mm further apart.
rear: bottom pivots 223mm from ground and 320mm apart. Uppers 195mm higher and 54mm further apart.
At the rear, a turnbuckle from the rear upper wishbone pivot on the chassis to the steering arm will be used to set the tracking. Springs and dampers will be acuated via pullrods from the upper balljoint mounting brackets on the uprights.
I bought another pair of corsa uprights, these were SO much easier to remove now I've done it before! The idea of using the old corsa driveshafts was a complete non- starter (they're made of the hardest metal known to man.....), so I've had some machined, splines, threads and all, out of billet EN8 steel by a very nice man in Rotherham. He's done a lovely job, very prompt & very reasonable; they're being welded to the hooke joint carriers I got from Congleton Propshafts (I turned them up in myself). They said they'd preheat prior to welding. I should be able to put that lot together fairly soon. I have solid models of the uprights & the required extra brackets to make the uprights work with double wishbones; all looking good. I need to source some billet steel to mill out these brackets; 8 to make, I have the material for 2....
I've added a couple of pictures showing the wishbone geometry for the car. This will allow the use of the same wishbones front & rear & the geometric roll centres stay fixed w.r.t. the chassis, within a centimetre or so, for 2" bump, 1" droop and a few degrees of roll. The overall width is 1.2m
It's been a while since i added to this diary. I've done most of the milling on the suspension brackets (dug out of billet EN8 steel) and started making the wishbones and wishbone jigs. I've designed the composite motors and gearboxes in detail and begun the manufacturing. This has mandated a reduction in the wishbone lengths.
The motors have been partially dismantled and the stock connections separated (the motors were hard wired in delta connection) So I now have 6 wires coming out of each motor, meaning that I can wire the 4 motors on a shaft in series (for perfect load sharing). In conjunction with switching to star connection, this will lead to the drives being much higher voltage and lower current. This will allow a big reduction in the amount of copper (wiring) and silicon (power switching). Previously we required 36V; this has now gone up by 4*sqrt(3) to 250V. Note this is now a potentially dangerous voltage. Furthermore the slotted opto disc for position feedback has been abandoned in favour of hall effect sensors mounted between stator poles. This gives guaranteed fixed indexing and continues working in sunshine!! The inverter part of the drive has been run up to 10A (the limit of my power supply), but the current source front end has not been run yet.
The gearboxes: I have been in contact with Glebe engineering in Stoke & they say they will manufacture gears and spurs at cost for the 1st stage of the car (UK record attempt). They were talking about £60 per gear. Rob in Rotherham (who made the driveshafts) says he can do the gearbox casings for £125 each (I'll need 8); so that's looking like about £2500 for all four gearboxes complete. I have a source of the PTFE lined steel rod end bearings for the wishbones, whom I now owe about £400.
Still no word on wheels, though to be honest I don't see why I can't use stock corsa steel wheels, at least for the UK runs!
Once more, a long time since i've updated the diary...
Plenty happened too: where to start???
Motors: I did quite a lot of design work based on the Towerpro motors. Eventually I managed to get into contact with the manufacturers only to be told they've stopped making that motor & are getting out of the 'big' motor sector. Nil desperandum - design in some alternative motors. I got some turnigy C6374-200. These looked splendid on the face of it, nice design with the open end of the bell also supported on a ballrace. However, these turned out to be impossible to separate the windings. I will use the motors I bought by removing the existing windings entirely & rewinding them to build up a spindle. Other problems were lack of power data and poor build quality (machining flash and windings literally hanging out of the stator slots!). Meanwhile I've been in contact with another potential supplier who seems very keen to help - same diameter motor so no design work lost.
I got the aluminium motor parts laser cut and bent by KMF - the samples arrived quickly & seem to be perfectly accurate - the first spindle metalwork has gone together beautifully. The front flange is too thick for laser cutting so another local firm, Tec Mat in Macclesfield has done them (including a few "spares") by water jet cutting.
Suspension: With the motor outline fixed I've been able to make progress with chassis and suspension. Main change to the suspension as that the old design with spring/dampers jointed to the top of the uprights, would have necessitated a high chassis mounting. This would lead to unacceptably large frontal area. So I've put some rockers in; these will allow the spring/dampers to sit horizontally towards the middle of the car, much lower. I used a local firm, Congleton Laser Cutters to make all the required parts in steel & they supplied in just a couple of days at very reasonable cost. These guys are next door to Congleton Propshafts, just down the road from work - most convenient! They also laser cut the rocker bearing blocks in 20mm steel - I've been finishing the machining of these on my lathe tonight; bore out to 26mm & thread the bolt holes M10x1.25 - easy job, done 4 of 'em.
Wheels: Nobody has come up with a convincing argument against using standard corsa steel wheels - so I'll try to liberate some at the scrappies in due course. It turns out that Hoosier tyres UK reps are based in Padiham (where I'll be building up the chassis) & they do high speed tyres for dragster fronts... Excellent!
Chassis: With motor/suspension units all modelled, and some representative battery blocks; I've been able to progress with the chassis. First up I redesigned the driver safety cell in 40mm x 3mm square and round tube, so it fit round a seat and driver; ensured there was enough room for entry/exit; then extended some tubes to pick up on the front & rear motor/axle subframes. This has resulted in a surprisingly compact vehicle (2.7m wheelbase).
Body: With chassis & drivetrain laid out it has been possible to start on the body design. The first iteration is now going through the aerodynamics simulations, It certainly looks the part. Aero results are good and bad, good - drag is low (about 1700N at 250mph. That's less than 200kW - my power budget. Bad - a load of downforce at the back and (even worse) 1500N of lift at the front (reducing from 5000kg for the car's weight....) - that might end up a little on the light side. The level of downforce at the rear is massive (3000N) - enough to make the car squat down on its suspension. So - some work to do there then.... I really need the car to stay in control with a couple of degrees of pitch up: I haven't begun looking at its yaw stability!
I can see the body design being a long long process.. fortunately chassis & drivetrain can be built & tested during this time so progress will continue apace. I'll try to leave shorter gaps between diary entries in future too!!!
Test venues: I called in at BAE at Salmesbury to see if I could borrow their runways for testing ;^). The man on the gate said "what runway? - it's a car park now & we're going to start building on it" so I went away. However, a look on google maps shows that it's a very short 'cross' runway that's a car park & it looks as though they still have 2 that are about a mile long. I'll check again when passing one day.
Motors: tried a couple of times to rewind the turnigy motors; failed due to the varnish on the wire being too soft & getting short circuits to the stator. Serves me right for trying to use transformer wire. I bought more robust motor wire (off ebay) and the first winding has gone on without any shorts.
The water jet cut parts arrived, also looking beautiful - the cut faces look like sandpaper (weirdly). So the gearbox blanks have gone off to Rob in Maltby for machining and one spindle end flange has been welded to the spindle frame. Looking good for a spindle assembly in the near future: I've taper reamed the "bell ends" ready for when the windings are done.
All the rocker bearing blocks have been machined, and all the wishbones are fully TIG welded and painted in grey primer.
Body aerodynamics work has taken a back seat to the school greenpower car aerodynamics design - I'm simulating a range of body shape options - but I'll get back on with this in a week or so. I have a plan to reduce the car's nose up - tail down predilections & need to see what it costs in absolute drag terms.
Motors: 2 motors now rewound with 8 turns of 7 strand wire. These were vacuum impregnated with varnish & the first spindle has now started to come together; all looking very good. The gearbox casings have come back, they look fabulous; Tony has done a lovely job, plus I've got all the bolts - I foresee many happy hours in the shed working on that little lot. Now I know the motor revs and target speed I can get the gear cutting under way.
Steel has been ordered for the safety cage and chassis. I need to finish the design of the cross members holding the suspension rockers and spring/dampers & get the drawings to the laser cutters.
I've decided how to do the driveshafts: I'll buy ball spline nuts and get the shafts made for me: I can then incorporate whatever fixing mechanisms I want. The issue was always the supplied driveshafts - whether they could be machined or welded etc - If I get some made I can do whatever I want.
The drag force results suggest 150kW power into aero drag at 250mph, hence a top speed from 250kW over 300mph. The car is starting to get light at the front already at 250mph. The pressure/streamlines render shows the turbulence behind the car and the pressure/vortices due to the tyres.
The drag/aero figures are plotted against time, the simulation has to settle before results can be used. In this case a reverse average suggsets it settles half way through the simulation. Notice the large oscillating lateral forces: these are at a frequency around 50Hz.
Making plenty of progress at the moment. Motor - the first test spindle is complete and ready for testing; looks exactly like the solid model. The dyno design is complete and the frame is made for it. I have 'found' an unused 2 pole 11 kW induction motor and 4 quadrant drive (sinamics G120 PM250) (I design 'em) at work. I'll put a design render on here - it's amazing just how big and heavy the induction motor is compared to the blackbird spindle - if the motor stays together it should prove to be a good choice!
The steel has come for the chassis; I've started cutting and tacking up the main frame rails. Maybe next weekend I'll have something 3 dimensional to try and put the seat into! I got CDS tube for the "head protection" part of the frame, but it looks as though the piece is too short - we'll see.
CFD work continues on the mk1 shape, I've been modelling it with its front wheels a few inches up in the air (pointing up 1 degree at the front). The thing stays firrmly planted on the ground, but what attracted my notice was the massive reduction in drag, from 1400N down to 1200N. What was going on? with its nose in the air surely drag should increase???
Then the penny dropped - induced drag! I've been looking at friction and form drag, and neglecting the large amount of downforce that the shape produces. But that downforce comes with an induced drag penalty, and when it is reduced by 1 degree of nose up, the drag is reduced pro rata. This is great - I now know just where to attack the shape to get the drag down. Meanwhile the lift I'm getting at 250mph (or reduction in downforce......) is still relatively small compared to the weight of the vehicle. Also reducing the aerodynamic downforce will stop attitude (trim) changes due to aerodynamic forces at speed, and stop drag increases on sand (due to sinking in further) at speed (if we run at Pendine).
Another day at the Forge, I wasn't able to get much done today. I finished and painted the frame for the motor development dynamometer (which will be needed for motor performance verification and drive electronics development) and tacked some more tubes into the chassis. The picture below (sorry about the quality - it's a moby picture) shows it right way up pointing towards the camera. Yes of course I sat in the chassis & made car noises... it's just something you have to do ;^)
This week I ordered the spring/damper units from protech (www.protechshocks.co.uk) - they agreed to supply at cost. I've ordered their 400 series 1.9" units with 13" open length and 275lb/in springs. I don't think I have to be too fussy about suspension, the car might only ever go as little as 30 miles, but the Protech stuff is good kit. I'm still having difficulty communicating with the guys I'm getting the ball splines for the driveshafts from: (no sponsorship, no names....). At the Forge today I made the jig that will space out the motor/gearbox unit mounting holes; this has to be accurate, and come apart in the middle; it looks pretty good (all triangulated & welded up bolted to one of the casings). I also cut up & bored out all the steel bobbins to bolt the gearboxes to the frame. I'll have to get 4 long lengths of 12mm studding to jig that little lot up in the chassis.
I've had another think about the motor drive & am redesigning with just six transistors, sorry can't help myself! It's still controlled in current mode by a current mode SMPS control IC, but the PWM is now done by the bridge transistors, it should work I think...
End of May now & it's been a good month for the project. Scorpion systems are now supplying some big RC aircraft motors for the next stage in motor and drive development. THK are on board and organising some manly ball splines at cost. I had to send the spring/dampers back as I had miscalculated & bought ones that were too long, but that's all in hand. Congleton laser made me some front and rear chassis cross members to hold the suspension and front and rear motor subframes - they are now tacked in place on the chassis. I've made the big removable cross- brace over the second front battery compartment; this has conical section bolting surfaces for positive location. I also made all the suspension brackets for the chassis. These are laser cut from 3mm mild steel and bent in a special jig. They have a 4mm countersunk locating screw at the back so they can be rotated in place before welding properly to prevent the rose joints binding.
It is interesting that now the chassis is looking so purposeful, massively sturdy, many suppliers are taking a much more serious view of the project & seem happier that it is 1) being done properly and 2) actually being done at all!!!!
I've also been looking into batteries. Once again the best answer seems to come from the model aircraft world: the lithium polymer batteries from the likes of turnigy via hobbycity seem to have the most potential. They come with 30C or 40C discharge rating. This suits me absolutely perfectly (I only have to go 2 or 3 miles) (really fast...) so I don't end up lugging a load of unnecessary capacity around. I seem to be looking at less than 20kg per corner for the batteries:- still a few thousand pounds though. For a charging system I'm going to make a load of completely independent, fully isolated current limited 4.2V power supplies & just wire one up across each cell. A BMS is too much work, this looks (once again) like more hardware but a MUCH simpler, indeed idiot- proof solution. I've read the horror stories about peoples' EVs burning themselves out while on charge... I'll go for the KISS solution!
More components being made at the forge; I've been making the top wishbone brackets. These bolt onto the outside of the gearboxes. To flatten the tube I heated them in the forge & got brother John to do the striking with the sledge. Anyway the upshot of this is that 2 of them have been made with a bit of smithy breeze trapped inside - they'll rattle forever - doh! The brackets are done with threaded holes to take the wishbone U brackets, so these can be held on with a wee screw & rotated to the best position before welding. That's how I'll avoid rose joint binding.
Protech have replaced the spring/damper units with 10.5" open ones - these look much more like it, big thanks to Protech for not asking me to pay for my mistake! I've made the shock brackets for the centre mounting point. These are threaded M10x1.25 as well as the 1/2 inch hole to relieve the bolt of most of the bending stress.
The Forging continues: I got to use Sandbach High School's milling machine last Wednesday and dug the final upper wishbone bracket from its chunk of EN8. A pretty big chunk of steel has become quite a small bracket and a huge pile of swarf.... I also "boxed in" the suspension rockers so they're ready to rock & roll; pictures above. THK bearings have found a set of 4 ball splines and a load of shaft for £800 so they should be on their way.
Plenty of work done but I've not been taking my camera to the forge so no pictures... The chassis has been fully welded now. I completely replaced all the wheel bearings (OK my brother John insisted that the old scrapyard bearings were past their prime...) I got lots of spacers made by Martyn's dad's mate Ernie (lovely job) so I'm close to getting it on its wheels. I'm on the lookout for a golf mk1 steering rack on ebay - no luck so far. No work on the car this weekend, I'm doing Cholmondeley Pageant of Power with the Sandbach Greenpower team & visiting another brother & family. I got a couple of Li poly batteries (they were on offer) and am keen to run the greenpower car on them with data logging active to see how they behave with a big load. Should flatten 'em in 5 minutes.
I got a "evaluation board" lithium battery charger from MAXIM using their max1737 li charger IC. looks ideal for my purposes, built in diagnostics and a couple of LEDs with charging progress - so I'll be putting a large number of them together in the fullness of time!
Mid- month; I spent today putting a front corner together (sort of properly) in order to determine rack size & position to get rid of bump steer. So I need an 18inch rack (460mm) and it has to be 18cm up from the bottom of the gearbox. Now - where will I find an 18" rack.... Actually that's the size of the one in the locost which was a cut down escort rack; I think the old golf might be about right - who knows. Maybe I should get back down to the scrappies, I need some corsa steel wheels as well as a rack, maybe I'll get lucky. I used my aldi special "tape measure with a laser in it" and string and G-clamps - all worked fine & I was able to demonstrate the considerable "bump steer" consequences of a millimetre rack height error, all good stuff! Now I need to do the same at the back!
Scorpion have shipped my first 4 trial motors; these are OK to 8000rpm. Now 250mph with a 75" circumfrence is 3520rpm so I need a gear ratio of 2.27:1
If I have 1.5 module gears and 90mm centres, that's 42:18 teeth (near enough).
Still not tried the batteries; waiting for the power connectors. The charger eval board was wired to an old switchmode & worked beautifully - charges a cell then all the lights go out - job done! I need to do some experiments with the mains transformer kit I got - maybe tomorrow - though I am a bit short of big electrolytics & diode bridges.....
I did a test with lithium poly batteries in the greenpower car, these were 20C rated 2.2Ah. The test was very successful; the batteries happily supplied more than the 2.2Ah on the case at the 20C rate. At the end of the test the batteries were quite warm (60C) and one seemed slightly swollen. Interestingly the series resistance seemed to reduce as the battery emptied meaning that the on load output voltage stayed very constant at near 3.4V.
For the battery charger, I've got the first transformer and designed a single cell charger PCB based on the TI BQ24600 chip. Each transformer will run 6 single cell chargers - I'm going to have to make a lot of these.... The PCB design has been sent off for prototyping. (and 1st batch of components bought).
I bought a golf rack off ebay & it was immediately, obviously the wrong thing. So I did what I should have done in the first place and bought an escort rack - 99p (plus a tenner for postage...) - bargain. This was duly sawn up & re- threaded 3.5" shorter and a couple of inches taken out of the housing. And I discover I can fit VW golf track rod ends directly to the track rods with no need for extenders or adapters - in short the front suspension is now complete!
I bought some steel 15" corsa wheels (again off ebay - £15 per corner). These are brand new, but will probably need to be cut in half and narrowed for the final car. Ahh.... tyres. I finally got in touch with Hoosier but they were wary of involvement in this kind of thing after the Richard Hammond incident. SO I've emailed them in US but I don't hold out much hope. Shame, it would have been handy to have local guys on the job. Better start looking at goodyear again...
So now the front end of the car is all together; I ground and machined the rallydesign ally rack clamps to fit my rack & positioned it to zero bump steer, and moved the chassis members that were getting in the way a bit. Only the spring/damper and rocker to pop on now. The final 3 ball spline nuts have arrived and look jolly lovely (should do at £60 a pop). And I started making enquiries about goodyear tyres and stroud drag chutes. I'm a little bit loth to assemble the rear suspension as I would not be able to lift the rear end of the car to stand it on end to put it away; I need to get a 20ft container for it so it's away from the grinding dust of the workshop environment - I don't think that does the ball joints any favours! Must get some pictures for this blog.....OK here goes, the rear suspension is mainly together including the spring damper units & rockers, a tiny bit of angle grinder work required to stop things rubbing. Front end is together too, all looking pretty businesslike.
OK I got some scrapyard wheels for a tenner apiece just so I could push the car around. With the front end together I had to sit in it......
slightly worried that the car was designed by that idiot....
All the proper fastenings are now in place in the suspension so I can adjust the bump steer on the back. Unfortunately I forgot my laser so instead I tacked the tie rod mounting in what looked like the right place and went for a little roll in the car: http://www.youtube.com/watch?v=NsiCAFRmSVQ You can see a picture of the car on all its wheels above. I've ground a taper on the ballspline shafting pieces and bored a corresponding taper in the hooke joint ends & sent the lot off to Rob in Rotherham to get some woodruff keys put in. I need to organise a meeting with the steam record people over the next week or two - have a couple of days off work. Hopefully they will have lots of information on dealing with FIA! (spoke to the guy on the phone - he said he'd try to arrange something but it's all gone quiet....)
It's been a little while since I posted on here. Work has carried on of course..... The rear tie rods have been fixed properly in place. The steering "quickener" and UJs arrived from desert karts in US and this has been positioned to act as a steering "slowerer" over on the right of the chassis, leaving the biggest possible gap to fit batteries and drives in. The old brake calipers have been wire brushed up a little & given a thin coat of black. On one pair the discs and pads are new so I'll leave them, but I'll replace the others. I've bought a pair of 5/8" master cylinders and a balance bar so I can start working on a pedal box.
Brother Bill has got me a container to store the car and bits in - this will be handy for transport if we go abroad. To be honest it's rusty old & damp & the floor has sprung; I'll give it a few weeks to see if the floor dries enough to flatten it or whether I'll need to replace it - I'm actually thinking maybe of another decking 'kit'. I'll employ brother John's lads to wire brush & spray it to get it up to scratch - it should be possible to make it reasonable.
Meanwhile, Aldi have had the 3kW petrol generators on special offer, £150 each - so I bought a couple, I think they'll be needed for battery charger duties when record attempts are on. I got my Bro's old genny too - hopefully it just needs the regulator replacing to start producing electricity again... the spares should arrive this week. (yes - now working purrfect - swapped him for a little 2 stroke 750W job)
TRS harnesses have agreed to supply a 6 point racing harness for the car; I'll have to see if they do the HANS gear too & how it works. (yes they do & you can't use a HANS harness without the HANS collar/unit. So I'll start with a standard harness - get the HANS kit when we're doing silly speeds)
Goodyear have been in touch about their "landspeed" tyres, they don't recommend their dragster frontrunners, think they'll overheat when you go over the 1/4 mile... So I have altered the 3D model to suit the 23" OD, 5" wide tyres. He said they recommend 70psi in the tyres but their literature pairs that with a load of 1700lbs - that's nearly 4x my car; I don't think they're taking me seriously. Stroud safety (drag chutes) have recommended that I use a couple of dragster chutes - & deploy them both at the same time - interesting!
I've been looking at the position of the driver & have designed a steel seat (which is at the laser cutters) & reduced the height of the car quite a bit. A new model featuring these changes has been through the CFD and drag has gone down from 1400N right down to about 1000N - excellent! Tonight I incorporated wheel spats and a pointier nose; I'll run this through CFD over the next few days, and do another model with the nose up a foot or so; recheck for any propensity to take off!
The first battery charger PCB has been assembled & appears to do the job nicely. I have to do a little more work; in particular check it doesn't smoke on full current. I'd better start making progress on the drives/motors front too, now the dark nights are here.
I spent the weekend running CFD and drilling and tapping the gearbox housings & seating the bearings. Gearboxes looking nice - I really must get the cogs under way! CFD results are excellent; the new model with the wheel spats has only 850N drag at 250mph, that's not much more than a half the original model. Here are some pictures (1 and 2). I also modelled the car with its nose 8inches in the air at 250mph. Sure it's lighter on its wheels, but front and back are very much the same at about 2800N downforce on each axle (c.f. 4600N fr & 6200N rr when on its wheels). I think that's a good result - I've lost a lot less downforce on the front than the back; I guess with enough angle of attack the car might fly, but it seems unlikely to flip. Next job is to check aerodynamic stability by running the car 6 degrees sideways - watch this space....
We recently got a "3d printer" (an HP piece of kit) at work. This produces a 3 dimensional ABS model of whatever you want (based on an .stl 3d virtual model) Well I have the .stl file that I use for the CFD analysis, so I've got me a 1/20 scale model... if only the real thing were so easy... Actually, it's great having the model, makes it very easy & immediate when I'm trying to blag stuff (I mean arrange sponsorship...). I'm looking for a suitable plastic bottle to make into the cockpit canopy bubble.
I ran the battery charger module with full current into an empty battery today to see if anything got hot. It did. Not so hot that the smoke escaped, but too hot to be usable, the dual MOSFET package was up at 160C. So I'll have to bring the current limit down from 4A to 3A - should make everything rather less toasty. The input rectifier bridge was well over 100C too, and that's from a DC source. Easy fix, there's a pair of resistors for setting the charging current. The thermal imaging camera at work coming in very handy this lunchtime. I changed one of the resistors from 33k to 22k to reduce the current limit to 3 amps & this has reduced chip temperature to 95C & the rect. bridge now reasonably cool. To be honest 4A x 6 was rather a lot to take from a 100VA transformer anyway... Next job is to pop a couple of secondaries onto that transformer & complete and test the system before getting a job lot of PCBs made. PS - swapping the bootstrap diode from a junction to a shottky gives me a tad more gate voltage - this has also reduced chip temperatures to the 60s - job's a good 'un!
Somebody else talking about going for the record in the news today - Don Wales is the previous record holder (of 10 years) & has only to upgrade his batteries & motors to have another go. He's talking about next year too - lets see if anything materialises, talk is cheap & easy; witness Dave Vince & his electric lightning record attempt which was scheduled to happen this year. A bit of competition is no bad thing & the electric bluebird team have "been there" and "done that" already - makes them rather more credible than some (e.g. me)! He's also blithely talking about a wheel driven electric record in the 500mph region a year later, which has got to be, shall we say, "unlikely"!
Had a short stint on the car today. I thought I'd wind the first battery charger transformer but found that the reel of wire I bought was only half as long as I'd understood, 25m instead of 50, so there was only wire enough for 3 secondaries. I've ordered another reel. I also ordered a steel enclosure, an IEC socket & some amphenol 12pole cable plugs & panel sockets which I will use as my standard charging interface. It all costs a bit mind you. The transformer is a 100VA kit from danbury electronics & each secondary is 45 turns of 0.75mm cu wire. The enclosure is reasonably compact at 180x97x75mm and about the cheapest one in RS.
I also took the steel seat I had laser cut & bent at Congleton Laser (£40), welded the seams and started welding the tube frames into the chassis. The seat and its frame have to be strong enough to hold a heavy body (like mine) in a very high speed crash - i.e. extremely sturdy! It belies its appearance by being surprisingly comfortable, and looks to have turned out about the right size for me too. Everyone asks if I'm going to upholster it – I don't plan to; a run will be over in a minute or so, how comfy do you have to be.....??
CFD tests with 6degrees of yaw now done. The car produces a lot of sideways aerodynamic force as you'd expect (2500N), and also produces 500N (per axle) of restoring torque: i.e. the fin is big enough to start to try to straighten the car up. This feels about right to me (I don't actually know...) so I'll leave the fin that size for now. Next CFD test is to put a "dieselmax" style airdam underneath and behind the front wheels; and to move the rear "diffuser" just forward of the rear wheels to try to reduce the vacuum between the back wheels. Hopefully this won't increase drag too much.
CFD results with the "dieselmax" airflow around the front wheels were rather disappointing; drag now nearly 1100N (up from 840). So I have decided to run with the simple original shape until it's clear from high speed running, that I actually need to change something. The rear "diffuser" area, I have got rid of altogether, resulting in slightly less rear downforce.
I contacted Glebe Engineering again and gave them the drawings for the gears. They are making them in 3 module out of EN24 steel, 18:42 ratio. Don't yet know about cost..... we'll see. The man suggested some oil & requirements for a "breather". You have to be careful with gears: it is all to easy to make a gear type oil pump which can produce enough pressure to damage itself - I think my design should be OK....
Back on the chassis, I've been making the sturdy box section seat supports & fitting them in the chassis. I'll weld them up properly when I've finally fitted the rollover structures for the survival cell. Speaking of which, I bought some chunky lumps of steel to make some rollers for the bender at the forge. I turned these on my lathe (that took a day or two...) & drilled some 3.5mm holes through the smaller ones to make the drive keyway. The excess material at the keyway chiselled out fairly easily. ( the picture below does not have the keyway finished)
I bought 38mm CDS tube for the rollcage ages ago, and the rollers bent this fairly nicely to the design dimensions.
I've designed a transporter trailer in angle iron & have started buying components; wheels, suspension units, drawbars, brake compensators & suchlike. Mostly because I noticed some braked 750kg braked susp. units really cheap on ebay.... I put the design into the FEA & it would appear to have a factor of safety of about 3 with the blackbird sat on it - looks good enough for me! Nice simple design using 2 sorts of angle iron, tandem wheels, all braked; I'll get it galvanised when it's done. The poncy bit of the design is that I'm using the on/off ramps as mudguards (these bits will be made of aluminium).
Week 2, I've finally installed the safety cage for the driver. This also completes the triangulation for the chassis sides & makes the whole car look much more complete. There were a couple of concerns: would I be able to put the seat in? would I be able to get in & out? Well it turns out that the answer is yes to both questions, but getting in is quite difficult for me (I have to dive in head first) and getting out is not very dignified.... It's rather snug in there & actually quite claustrophobic, which is a bit of a novelty for me, I've never experienced that before! Next step is to try and get in & out with a helmet on...
end of year: the weather has been incredibly cold, I've not been too well & what with Christmas & all - I've not made as much progress as I would have liked + I've sprained a pectoral muscle putting the chassis away; anyway I must buckle down and get the motors and drives working. I'll put the rest of the steering column in tomorrow & the bearings for the steering wheel. I got a detachable steering wheel boss off ebay (or I will not be able to get in/out). Speaking of which - it has got easier to get in and out, don't know why, & feels better when I'm in it; just getting used to it I suppose. Still undignified though!
This month I needed to start drives development. I put one of the spare turnigy outrunners into a bike for my nephew. The idea of this was to see how it behaved with RC (radio control) gear. The bike went together reasonably easily & the performance was remarkably good (so much so I decided to make an electric option for one of my own bikes). This persuaded me that sensorless control might be suitable for the LSR car, so I tried to find a supplier of a suitable drive. Kelly controllers appeared to make a sensorless product of suitable size but with insufficient speed capability. However they did not respond to my email. Furthermore, on consideration, it seems that no sensorless controller is going to work sensorless below about 10% speed, which in the case of the LSR car is over 30mph. This means that the push start begins to look a little impractical. (on the bike this threshold is reached after 1.5mph....) So it seems as though I'll have to use sensored control. Note the successful use of a home-made taperlock fixing on the motor - this is a sort of key technology for the car....
OK - fitting hall effect sensors - traditionally this is pretty tough, the motor has to be dismantled and the sensors epoxied into the stator slots. Then the wires somehow brought out (without breaking any) (or possibly chafing) (or shorting to each other). However on the turnigy motor plenty of field leaks outside the can so it makes a lot more sense to mount the halls on the outside: you can then optimise the high speed timing by physically moving the sensors. Once more there is a twist in the tail; the scorpion motors are much better quality and hardly any flux leaks. Will there be enough to get a good rotor position signal? The only possible way to find out is to make an external sensor rig and try it!
In terms of inverter drive hardware, I'm now resigned to making my own. I'll be at ~150V and ~150A so it's not too daunting, and it looks as though Mitsubishi do a MOSFET 6pack just the right size. I will resurrect my old drive prototype from July 2009 & see if I can make something happen. The car frame is pretty much complete now so I have to start making real progress with the drive systems.
Congleton Propshafts have welded and skimmed the flanges on the driveshaft tubes; these can now have the ball spline nuts bolted on. Bizarrely the ball spline nuts appear to be drilled for 0BA cap screws - what is going on there? I'll drill them out to use M6 fine.
No progress finding MOSFET modules for the motor drives - it looks as though I will have to make something with discretes. Mitsubishi do a perfect module but 6 months lead time - bummer. I got the steel for the transporter trailer and started welding that up. I've made a hall sensor PCB to fit round the outside of the motor can - I'll be trying that out over the next few weeks. I also got an Atmel AVR motor control kit to look at BLDC motor control; I'll try to get to grips with that next week when I'm away on business.
Further searches and conversations with suppliers have revealed no suitable modules. There are some reasonable isolated package devices on RS from IXYS but they are £11 each and I need 360 in total - that's nearly £5k just for transistors. So I'm looking again at TO247s - this gets the transistor cost down to sub- £1k but I need to calculate how much heat I will need to soak up: because I'm only running for 45s, I'm hoping I can manage without heatsinks and just let thermal "slugs" heat up - but it all needs calculating to see what I need to do.
The transporter trailer for the car is progressing nicely. This is made of angle iron and tube and I will get it galvanised when it's done. It's quite long and narrow (like the car) and will weigh a couple of hundred kilos; but should be OK to carry 1.5tonnes (with FOS=3).
Not much to write up here, I've done most of the trailer but I can't finish it until I know what the wheels are going to be like (then I can set the tracks on the trailler).
On the car itself, I've fully welded most of the rollover structure and seat support (it was just tacked 'til now). I've got back on the drive development (I should be sending board designs to PCBtrain this week) and converted the first scorpion motor to 10mm shaft.
Oops - not been writing up on here, I've actually been a bit distracted by electric bicycles and the school car team. I've STILL not sent off the first drive PCB design. I really can't afford to fanny about like this. I got a load of surplus toroidal transformers FOC from Contract Purchasing, these will make excellent battery chargers, they'll do 5A apiece: I'll put them together like the school battery chargers - laser cut a suitable housing & hardwire to something like anderson connectors for the charging. They have 2 2.8A 9V secondary windings - these will nicely make 2 isolated single cell 5A chargers. At present I'm thinking I'll have 3 bulk chargers and 1 balance charger on the car, cycling the balance charge round the 4 wheels.
Oh yes - I forgot; the gearboxes are all made, assembled, filled with a few cc of ATF & plugged with a sintered bronze bung breather. The cogs were £2700 in the end from Glebe, look very nice. The sintered bungs were from RS components.
I was checking e-car motors (by my employers) as a possible "plan B" but they are too bulky and heavy for this car (and "not actually available"....)
This week I've stitch welded 2mm steel floor panels on the chassis. Next week I'll make up the brake pedal assembly.
End of month: I've fit the driver compartment front bulkhead (2mm steel) and tacked in place the twin master cylinder bracket. The brake pedal will be on a transverse tube shaft running in plummer blocks, so I have to make astrong adjustable pedal setup now. Still no progress on the wheels or motor drives. I might try to visit "Burtie" off "Endless Sphere" while I'm on holiday down south - he's developed an adjustable timing solution for BLDC motors which might just be worth a bunch of horsepower:
Other news, the Don Wales team "electric bluebird" are planning to run again at Pendine in a fortnight, & they have a fighting chance of making life more difficult for me.... Lets see how they get on! I hope they manage to make just slight progress.... :^)
Crikey - another big gap - happens when I'm doing a lot of CFD work because I run that on linux & don't boot this computer in windows. I've been looking at the aero again after noting with the school greenpower car that it is a lot more aerodynamic with a longer tail (they changed the rules allowing about a foot more length). What does this mean for Blackbird? Well a couple of feet of pointy tail has reduced the drag from 1200N to 625N - that's a crazy amount, it's about 50mph,more top speed. I had been going by mr. Kamm's theory that you can just chop the back off - CFD says different! I still have a flat back behind the driver's head - that will be where the parachutes live.
picture with the new tail piece on that makes so much difference
Don Wales high profile record attempt on Pendine Sands did not go well unfortunately, they broke the car before getting up to pace; Ah well, gives me a chance to set a mark if I can make some progress. Speaking of which, I've been talking to an ex- colleague who now works for a company that make EV drive modules, one of which may conceivably suit Blackbird pretty well. If I'm lucky we can strike some kind of deal - that would knock 4 or 5 months of my timescale! It's all early days & I've not had any official discussions with them yet, but I really hope this comes off, it would be a real shot in the arm for my project.
On the car itself, I've been working on the brake pedal and master cylinders. Having fit the brake pedal I discovered that I was not able to get my foot onto it, my legs were just too long. Clearly that wouldn't do, so I replaced 2 of the big square chassis tubes with slightly smaller round ones, and now I find that I fit once more (phew!). This weekend I'll fit the kunifer brake pipes and finally fit the master cylinders.
I have determined that I will need approximately 24 5s 5Ah Lipo bricks per corner, 40C batteries to get the power I need with some overhead. That's about $4500 total and 80kg - not bad
I made and fit the threaded inserts for the harness anchorages a while ago. It all fit fine except that the 2 crotch straps were rather too close together (might as well have been a 5 point..) so 2 extra anchorages have been welded in a couple of inches further apart.
I've assembled and fitted the bias bar assembly and master cylinders. I would have done the brake pipes too but it turned out that Bill's brake pipe flaring tool made the wrong sort of flares.... job for next week.
I got the corsa wheels back from Morespeed in Padiham. These had had 1.5" removed from the width and needed welding back together. So I made a jig at the laser cutters and on my lathe, and they went back together pretty well. A single MIG weld goes right round and seems to have penetrated right through (Alan at the controls & me slowly turning the wheel on command). I discovered that one of the wheels has a different offset so I'll have to try and find another spare from somewhere.
The hard brake pipes are in, I just need to find half a dozen or so more rubberised P clips to hold 'em firmly. The brake pedal, bias bar and master cylinders are all bolted up tight & looking good.
As I hinted in last month's blog entry, I was able to visit SEVCON just before Christmas. They make and apply EV drive modules in the northeast of England. They do indeed have modules which are very close to my requirements and are willing to supply me at cost; a factor which should get me mobile considerably quicker than the alternative of developing my own power modules from scratch. This is quite a weight off my mind and I'm now much happier about the probability of serious running fairly early next year. Indeed it feels like a bit of a breakthrough. So I have a low voltage brushless drive module from them which I will try to get to drive my motors. If it goes well I'll move up to higher voltage & therefore speed/power. In parallel, I need to build up a spindle with the 3 remaining scorpion motors I was donated; this involved dismantling, replacing bearings with 10mm, and machining the taper friction connection of the rotor front face, all pretty quick & straightforward (plus drilling & tapping M4 the 6 taper clamp fixings on the rotor face - slightly more of a pain to do to 60 motors....)
Now I have the wheels done, I know the exact track of the vehicle and so I can finish the transporter trailer. So I've welded the two "wheel tracks" in place and will fit wheels tomorrow.
Roll on 2012 - I have high hopes!
Motors: I have dissembled the remaining 3 scorpion motors and started the machining work to get them onto a spindle
Trailer: Main chassis now done including wheel mountings hitch and brakes I have to weld a few more brackets on then it can go off to be galvanised. I have bought the folded aluminium mudguard/offramps (£80 - expensive stuff aluminium these days).
Hall effect vane switches have been purchased and a motor spindle with 3 scorpions on a 10mm shaft has been assembled. The trailer is complete with wheels, galvanised and the mudguards/offramps have been fashioned from aluminium. Mudguards are now fitted and the trailer moved into the container. A full set of gearbox input shaft taper clamp plates have been laser cut and I've started putting the M4 threads in them. This is going to take ages and I need to buy a couple more tapping size drills and M4 taps - I'll try to do one or two every night.
Production work on duplex chain flexible couplings for the gearbox inputs. 20 couplings = 40 modified sprockets with taper-lock bore and 6inset boltholes for the socket cap M4 screws. Then I will need to make 80 tapered inserts for the motor and coupling taper locks. Rich said he'd help with that - the taper inserts on the motors aren't bad, but the coupling ones are double sided with taper in each direction.
Lots of work on the lathe making the motor couplings; the 2nd picture shows the gearbox input couplings complete with sprocket and threaded clamp plate, both taper bored with a matching brass olive. The trailer is now done and galvanised and you can see the offramps in the mudguard position. And the mighty winch - £13 on ebay....
Krikey - a while since I posted on here! Meanwhile Dave Vince of Ecotricity has run his car at 151mph at Elvington; so the goalposts have moved a tad Well done to those guys, they've had a couple of goes & it's not been plain sailing.
What have I been up to? Not enough I fear, I bought some Lipos to run up the test motor spindle on the Sevcon power module. I now have 5Ah at 125V with 30C rating - enough to trial a single spindle.
And I've pulled the gearboxes apart, twice now: first time it was that there wasn't enough room for a sufficiently strong taperlock on the gearbox inputs. Second time it was that the boxes were just too stiff & tight. I had put too much packing in there on all the input spindles, I need to leave a little play in there.
Meanwhile, I've done a lot of work on the new Sandbach Greenpower car, making a big 3d CNC router (1.5m x 0.5m x 70mm) as part of the process. This is great for making 3d styrofoam parts which can be vacuum bagged with a skin of fibreglass or carbon weave to make strong, dimensionally accurate and stable 3d shapes. It's how I'll make the nosecone of the car.
The running of "nemesis" will hopefully
galvanise me into making a proper effort to try and get this thing mobile; I'm
basically a year behind where I should be - time to get my finger out! Expect
more progress and reports in future!
Here are a couple of snaps: the brake lines have been run & there is the balance bar setup for the master cylinders.
Progress since last update:
1) I've mounted hall effect vane sensors on the scorpion spindle.
2) I've made a little progress with my own motor drive - this may be needed on the final thing if the sevcon can't do it (I'm a bit worried about maximum output frequency)
3) I've prototyped the dashboard. This will sit on the steering wheel so it has to be small & light. I used an arduino uno board (£9) with a 128x64 pixel graphics LCD display (£6). It all works rather well - a couple of days doing software & I had a reasonable practical running system.
What's the display? top left is speed in mph (there will be magnets on a wheel and a hall sensor pickup) Bottom left (also big numbers) is 1/100ths of a mile down the course - this will tell me where the measured mile is & show me braking points - there will be a button to reset this. The 4 bar graphs top right are battery volts for each of the 4 battery banks - should allow me to avoid over-discharging the LiPo's. The 2 bargraphs lower right are total battery current into the front and rear axles - I should be able to see if I lose one of the drives. The speed and distance numbers update slightly faster than once per second; the bargraphs about 15 times per second.
The arduino board was just the job for this - not a lot of
effort & nice clear, simple display - numbers big enough for even me to