The Electric Kitten

February 2007

Time to start this up again. I originally started in 1999 but unfortunately the control hardware I chose (chosen because I was able to blag a development system including an in circuit emulator) turned out to have a faulty pulsewidth modulator. This would all invert itself at random if you went into overmodulation; this would have killed the inverter pretty quickly. So I gave up with that and basically didn't get any further with anything until December 2006 when I bought an old basket case kitten for £82 off ebay. I made a trailer & went to get it the next day.

OK the car's a shed - it's been in a field for the past 15 years by the look of it - but most of the bits are there & the shell looks as though it can be made reasonable. So my plan is to take everything off the shell, renovate and paint the fibreglass part, take the engine and gearbox off the chassis & sort that out: Get the motor rewound & fit that; reassemble everything at the Forge then trail it round to Knutsford to finish off the electrics and installation. I can of course be working on the electronics during the week & on the car at the weekend. Once again a big job! On the plus side I've got Rich Kenney at work interested too (he wants to electrify a mini) so I've given him the battery charger job! He's a good lad & his input will be very welcome & make shorter work of the large number of circuits which will have to be developed.

The overall aim is to develop some "electric vehicle modules" which anybody could cobble together into an electric vehicle. It may even work out to be commercially interesting. The overall system I decided on 5 years ago is still the way I'll go I think, not a lot has changed. There is still no real alternative to lead acid "accumulators" and an induction motor is still quite a convenient motive power source. It's not the most efficient, or the lightest, or the most compact, but it is easy to drive, has a large 'field weakening' range and is in cheap and plentiful supply. So there will be a battery charger module - a 1kW item which can be configured to charge 5 to 10 12V cells. For faster charging, buy more modules! And there will be an inverter module (which will contain the micro), a dash/display module and an auxiliary 12V module.

The kitten is an estate version in turquoise. Nice. The dismantling has started. So far no major bolts have come out using a spanner, and the seat belt bolts have broken a 17mm spanner. But the little ones and screws have come off OK. Here are some snaps of it.

April 2007

Not spent as much time on the project as I would have liked, but have taken off all the trim and windows to do up the shell, and removed a lot of the bolts holding shell & chassis together. When they're split I'll get the chassis in bits & de- rusted and try to renovate the brakes etc. Looks like all new will be required - the backplates are rusted completely through & the back axle feels decidedly ropey.

July 2007

Finally split chassis & body; (been busy on house & enormous new shed etc.) (see 4th pic above). I'm a bit depressed about the chassis, can't see how I'll get the lower front wishbones apart without totally ruining them. A bloke in Clitheroe says he'll tart up the body for ~£500. This is like -serious money & makes me think I should maybe start with something a little less knackered already. Having said all that, the chassis would be OK with 3 or 4 plates welded on & I can get the lot galvanised pretty cheap. I'll give it some thought. I also need to source ball joints & TREs & all the void bushes.

September 2007

Decided chassis is not too bad. I'll remake the wishbones. I found "the kitten register" & Brian there seems to know all about these things & is helpful and stocks many of the things which are hard to find. So I've bought a set of rubber bushes from him (£98). I've bought some mini TREs and maxi bottom balljoints (to see if they fit - OK they don't - by miles). I've also spent about £350 on a complete set of mini brakes. I'll start assembling them tomorrow (everyone swears they won't fit...). The chassis is being sandblasted so I will be able to weld plates on it tomorrow ready to be galvanised. I'll get some spitfire top balljoints too, just in case they fit. I've been told metro ones might be worth a look too. The body is completely bare now - I just need to weld new ends onto the steel hoop in the B pillars where they bolt to the chassis - the chassis bit is still there but the hoop has rotted off. And I'll get the wheels tarted up. The back axle has been stripped & actually looks OK inside, so I'll put it back together with hylomar & threadlock & some fresh EP type oil (I'll try to find a low viscosity one). Only serious work on this is handbrake cable ends - I may be able to simplify things by pulling from the leaf spring, rather than remake the corroded pulleys on the axle - we'll see. Hopefully I'll make a lot of progress relatively quickly now. And I must remember to get some pictures...

Forgot the pictures but; good news, the spitfire top balljoints are perfect and so are all the mini backplates. The mini drums are almost perfect, but not quite. I have to machine the drums to have one 13mm hole and a 3.25" inner hole (easy job on the lathe) and machine the wheel hubs slightly to not foul the inside of the drum - no big deal as the parts are all in bits anyway. I've emailed quinten hazel to ask if a spit top balljoint can also be used at the bottom: I'm still struggling to find a replacement for the bottom ball joint. It's a bit controversial because the weight of the car is hanging off the bottom balljoint.... I got the tyres taken off the wheels today so I can start to refurbish then (maybe I should have just bought new.......) I need to get a wire brush for the angle grinder & some mini rear taper roller bearings (oil seal disappeared). I'd better decide how I'm going to route the handbrake while the axle's off too.

October 2007

Plenty progress.... First the good news: The chassis has been sandblasted & all broken, mangled and rusted- away bits cut out and patched. It is now waiting to be galvanised - which is good because it means it can then live outside & start to be reassembled. I determined that the herald top balljoints are unsuitable as bottom balljoints - they are too bulky & hit things as they rotate - but alfa 164 bottom balljoints are perfect. So I've bought a couple & am now designing wishbones to suit. My only regret is that Quinten Hazel actually destructively tested one of the herald BJs for me (failed at 2300kg) which was fantastic customer service.

The bottom balljoint taper needed opening out a little so I spent a while trying to source a taper reamer. Dormer wanted 200 notes AND it was the wrong taper. Thankfully axminster did one for £3.45 (bit of a saving there) so this was purchased, ground to the correct taper, and used with perfect results - thanks to the locostbuilders forum for that gem & the alfa 164 balljoint tip!

I got hold of proper kitten front wheel bearings & so have started doing up the front uprights, The mini brake backplates fit perfectly and will only require the bleed nipple repositioning. However the bad news is that mini drums don't quite fit, so I set to work machining one 'til it did (basically opening out the centre hole to 3.25" & one wheel stud hole to 13mm) But if you do this  the drum hits the backplate before tightening flush to the flange - it's about 2mm too close; and there is also an internal clash on the outer periphery of the kitten flange. So my plan is to modify the hubs so they have a mini sized "central hole locating feature" turned into the existing kitten drum "central hole locating feature" - all 3mm further out & cut a 3mm steel spacer to pack out the drum. So - still a work in progress & I've scrapped a drum.

I completely dissembled the back axle, cleaned the gungy old oil out (nice job) and replaced the wheel bearings. On putting it back together again I found to my surprise  that most of the backlash had disappeared and the thing felt smooth and nice. How come has it got better? - I dunno! But I'm not complaining. I now have to do the same machining on the wheel flanges that I'm doing at the front (so that mini drums fit), but it's a little easier to set up the back flanges on the lathe. Mini rear backplates fit perfectly too, they are clearly original equipment on the kitten. Why did they not use mini drums too.... For the handbrake I'll use a nylon pulley on one of the spring clamp U-bolts.

I've measured the front springs for when I replace them. The wire diameter is 8.5mm, the coil diameter is 65mm and there are 9 active coils - that means 120 lbs/inch. I also assembled the rear springs onto the newly galvanised chassis (+ the back axle, just for the photo) see picture 5 above. The chassis picked up about a degree of twist while it was being dipped in the zinc, not too bad I reckon; bolting it to the body should sort that out (it was never going to be the best handling car in the world...)

November 2007

Quite late November actually... Today I took the old bodyshell to be tarted up & painted. It drew quite a crowd at the bodyshop & I got questions like "are these a classic then?". I suppose they are in way. I've been making shims for the brake drums (to make mini drums work unaltered). I bought some cheap mini drums and they were SO heavy. I've actually turned quite a lot metal off the rim of the drum as there was so much that the wheel rim wouldn't go over them! I need to find the right steel tube to make my new wishbones next - need to get that chassis rolling! I also have to sort out the other 3 wheels. As Richard did such a nice job on the last one I'll have to prey on his good nature some more  ;^)

If you ask the experts, they will say that mini brakes don't fit on a kitten. In fact they do but you have to do some work. The backplates fit perfectly, unaltered (though I expect bleeding issues with the rears in the fullness of time....) To make the drums fit you have to make some adapter plates.These are annular rings of 3mm thick steel plate, outside diameter 120.4mm, inside diameter 82.6mm. Drill 4 10.5mm holes on a 101.6mm PCD for the wheel studs. Mini brake drums (10" rim versions) now fit perfect.

You also have to do some work on the flanges. Use an angle grinder to dress down the outside corners by the wheel studs so that the overall diameter is less than that of the adapter plates. The front hubs can also use some judicious grinding on the hub itself so that the drum inside  tightens flush with the adapter plate, and does not tighten onto the rough cast hub inside the  hubcentric rebate which centralises the kitten drums.

Finally, on the kitten hub studs, one has a larger diameter ring shrunk onto it so the drum can only go on one way round. Best to saw this off, though you could make various holes bigger instead...

February 2008

Bit of a gap since the last update. I've been waiting for other folk (body still at the body shop - they're treating it as a 'hobby' & doing a bit when they have spare time - and the motor is still being rewound) And I have been stuck trying to get hold of some suitable material to make the bush ends of the wishbones.

Anyway, last week I finally found the metal supermarket in trafford park (the website still shows their old address - they moved last march!) and got some suitable wishbone tube. I turned up the bush ends on the lathe (it's seamless tube - very nice!) And I've made the jig for the lower wishbones & all the plate parts & started welding them up. I'll do the upper bones over the next weekend or two.

Today I put one of the old wheels in the lathe & rotated it slowly while attacking it with the wire brush in the angle grinder. Frankly, they're all totally knackered, beat up and rusty as hell - they ain't never gonna seal again. So I'll buy new mini ones tomorrow.

I've visited the body shop a couple of times to see how they're getting on. They've glassed up all the crazed & split bits & have dug out the gelcoat cracks. In short they're doing a FAR lovelier job of it than it deserves. Dunno when it will be ready though!

Today I started to take the steering rack apart to do it up. I was surprised to discover it is in perfect nick - just needs new gaiters - another purchase for tomorrow!

Meanwhile I've bought a load of windscreen wiper bits from s-v-c, enough to put wipers on the seven and replace the ruined bits of the kitten system. To put a flare on the wiper rack bundy tube, hold it in the lathe chuck & push a drill bit into the end (drill held in tailstock chuck) with the lathe running backwards - works a treat!

I've been looking at the LiFebatt lithium batteries; I must say they look ever so nice. I have a cunning plan for battery conditioning with them: I can make a cell module with a wee AVR micro in and a shunt regulator - one for each cell. So the overall charger will just be a current source & each cell will do the bulk/float control itself. The cunning bit is that each micro will talk to the next lower voltage one to say what it's up to. This means no isolation is required as each cell is just 4V apart. The last cell at the bottom of the daisy chain sends all the information to the vehicle controller which will switch off the charger when all the cells are full. Oh yeah - the cell modules can contain a diode to prevent reverse charging & relay individual cell voltages during operation so weak cells can be detected early. Cool system - you saw it here first! Actually the trickiest bit of the cell module is the shunt power device - this will potentially blow off quite a few watts of heat (most of that can be done by a resistor). Anyway each cell module should be doable for 2 or 3 quid.

March 2008

Some progress; I bought a set of trailer wheels (mini pattern) (£13.95 each) and got new tyres fitted for 20odd quid apiece. And I have made my wishbones. I've got no idea what size shocks I need at the front, I think I'll have to fully assemble & then measure - may need to wait for the body. I'll stick some solid bars in meanwhile! Bottom bones are finished and painted but the top bones just need the pivot point tubes TIGging on - I'll let Alan do that! I need to get some rear shocks too - I feel another call to the "kitten register" coming on. The 'bones' look good - there seems to be no danger of clashing with the upright at extreme steering angles - it looks as though I might get the chassis rolling next weekend. I think I'll start transporting it to knutsford - I can assemble in my back garden & keep it dry under a tarp. Once the body is back it can live on the front drive.

April 2008

Well, the front suspension was all put together. unfortunately it became increasingly apparent that Captain Borlzup himself had been to town & left his calling card. 1st indication was that the first side had lots more left lock than right, then the tens of degrees of positive camber. Aha. I'd made the lower wishbones 40mm too short. So this week I've extended them. I still need to add a new lower shock mount. I'll turn them over so the old shock mount can stay there as a roll bar connection If I get that far. I also picked up the motor from ASK rewinds in Altham, all looking very posh with a new rating plate saying 70V and 100(ish)A. This has a 37.5mm shaft so I will start collecting drivetrain bits now. I will fix the motor and layshaft and use a propshaft with 2 UJs and a slidey extendy bit - they're only a few 10s of quid at the propshaft centre alond the road. I must remember to take my camera and get some more piccies next time I go to do a bit.

The pictures above show the chassis c/w new wheels, new wishbones, rack fixed &M10 studding in place of spring/dampers. Which tells me that at ride height my dampers must be 10inches from lower eye to top plate mount. So I'll be purchasing some suitable 1.9" spring damper units next week.

May 2008

Last week I bought a propshaft, a set of pulleys & belt for the primary reduction drive, and a set of dampers & front springs, in short spent a small fortune. The pulleys are 39 and 76 tooth HDT toothed belt jobs, 50mm wide. The large pulley in particular weighs a TON so I've spent the weekend drilling a lot of holes in it so now it weighs only 3/4 of a ton, I also got some 30mm plummer blocks for the layshaft. I determined final positions for the motor and layshaft and made a small subframe out of 25x25x2mm ERW and angle iron to hold them. I'll get this galvanised when it's finished so it fits in with the rest of the chassis.

Another couple of weekends messing with the car sees the prop bolted up & the layshaft output flange keyed onto a taper on the shaft (BTW don't fret about the taperlock photo - I do know how to fit the grubscrews honest....) I also spent some happy hours slotting 8mm microbore central heating pipe into the fins on my motor. These will be glued in with PU adhesive to liquid cool the motor. I'll use the same fluid (probably DERV) to cool he motor after it has already been used to cool the inverter. The fluid will be cooled by the kitten heater, who's warm air can either demist the screen or be vented outside. The fan on the motor has been removed. The fan cowl will be refitted as it is used to support the encoder.

Last picture above shows the chassis with its suspension virtually complete, motor propshaft and layshaft all in place (motor temporarily on blocks)

June 2008

With the chassis complete to all intents and purposes, it's time to look at the drivetrain. The plan for the battery charger is outlined above (with one or two extra special tweaks) and the plan for the inverter is unchanged. So really the only new thing I've done is to take the motor into work and put it on one of the big variacs. With just 50Hz available I should be able to work out the mag. current and measure its stator resistance. In fact I was able to go one better and use a programmable AC source which did harmonic analysis of the currents.

The graphs show various quantities plotted against phase-neutral voltage. The 1st graph shows power into the motor increasing sharply above 35V. The 2nd graph shows a large upsurge in 3rd harmonic current above 35V. Thus 2 independent factors point to 35V being a suitable off load voltage for 50Hz operation with a magnetising current of about 22Amps. (note there should be no 3rd harmonic component in the current of a balanced 3 phase load - it can only be there due to the non-linearity of magnetic saturation).

To measure stator resistance, a bench power supply was used to apply 2.0A d.c. to the motor windings between 2 phases. A voltmeter showed 148mV between motor terminals: therefore each phase has a stator resistance of 37mohm.

Meanwhile I've been simulating my inverter to decide how hard to switch the FETs.

The graph shows that in this low voltage (110V DC link) application it is not necessary to achieve  fast voltage edges, 1000V/us is plenty. The current switching should be reasonably fast though and I will aim for 2000 to 2500A/us. These figures dictate my choice of gate drive impedance. Essentially I want to switch as slowly as possible to reduce EMI, but not so slowly that my inverter melts....

August 2008

Last few weeks have been spent working on a cell bypass PCB for the battery charging and equalisation system. This is based on a AVRtiny44 (in 14 pin SOIC) , has serial links from the cell above and to the cell below, and includes bypass current measurement, cell voltage measurement and bypass transistor temperature measurement. I need to determine a suitable comms system so each cell will add a couple of bytes to the total message. I've downloaded the AVR development system free off the web & when my 3 prototypes are ready next week I'll be able to start writing and debugging code. I'll have to do the initial control testing from hyperterminal on a PC until the main car control board is done.

I've finally made the wee pulley pivot thingies for the handbrake cables today. I was expecting the body to be finished at the painters but apparently it's still in primer... Just checked back up the page - they've had it over a year. Lucky I wasn't in a rush !!!

September 2008

At the end of last month I got the main part of the car body back & have spent a couple of weekends bolting it back on the chassis, fitting glass & working towards having a car again. I've also got the first boards back for the battery charger cell control modules & these look pretty good, I just have to get used to the development system (AVR) now - which is making me swear a bit.... Anyway, here are some pictures...