Another mini conversion

Have you made or bought a converted vehicle if so this is for you
MalcolmB
Posts: 423
Joined: Sat Jun 23, 2007 8:07 pm

Another mini conversion

Postby MalcolmB » Sun Aug 03, 2008 10:24 am

I bought a mini a few weeks ago with the express purpose of doing an electric conversion. My motorbike is great fun and I learned a lot building it, but I eventually plan to sell it and put the proceeds towards lithium batteries.

I haven't actually started the conversion yet as I still have lots of questions to answer, so I'm hoping I can get some advice here before I get out the grinder.

So far I have the donor car and a pair of series wound motors I was lucky to get cheap
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The motors are 14 inches long, 7.25 inches in diameter and weigh 40 kg each. Although they're only rated at 36V I've been told on pretty good authority that it should be possible to run them at up to 120 volts by advancing the brushes around 10 degrees. This means rotating the brush plate counter to the direction of rotation of the motor, which looks to be fairly easy to do.

The plan so far is to use two of the motors at 108V, probably with a 750A controller. I’d like to stick with the existing front wheel drive and get rid of as many oily bits as possible, including the gearbox. I’m hoping that by using two fairly powerful motors I can get sufficient torque for takeoff. Final vehicle weight should be no more than 700 kg.

The options I’ve been looking at so far are:

a) Driving each front wheel independently with belt drives to the inner ends of the drive shafts. The motors would be connected in parallel and act as a limited slip differential.

b) Coupling the motors side by side with a timing belt drive, and using a second belt to take drive to an enclosed differential, like this: http://www.westhouse.plus.com/chaindrive1.htm
The motors would be connected in parallel again.

c) Either option a or b, but with a system of contactors that allows the motors to be switched from series to parallel. This effectively provides an electric gear change, switching the motors from high torque / low speed to low torque / high speed.

Although c) sounds good, I’m a bit worried about the complexity and cost of the contactor arrangement required, so I’m leaning towards a) or b).

Sorry this is so long, but I’d be really grateful if anyone could tell me which of these options is likely to work or if they have any alternative suggestions.

Malcolm
Last edited by MalcolmB on Sun Aug 03, 2008 7:13 pm, edited 1 time in total.

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Peter Eggleston
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Joined: Tue Apr 10, 2007 9:12 pm
Location: Tyne Valley Northumberland

Postby Peter Eggleston » Sun Aug 03, 2008 3:09 pm

I would get a Suzuki jeep or Jimney and drive one axle with each motor. The suspension would also be better able to cope with the weight of batteries.
Peter

MalcolmB
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Joined: Sat Jun 23, 2007 8:07 pm

Postby MalcolmB » Sun Aug 03, 2008 7:08 pm

Hi Peter

Yes, the Jimny would make a good base for a lead conversion (you're not trying to get rid of yours are you :P), but I'm aiming for a lightweight lithium conversion with good power to weight ratio. The Jimny is about 400 kilos heavier than the mini. I only need a two seater for most journeys, so if needs be I'll use the rear seat space for battery storage. The battery pack shouldn't weigh much more than 100 kilos.

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nino500
Posts: 63
Joined: Tue Jul 08, 2008 11:24 pm
Location: Isleworth, Middlesex

Postby nino500 » Sun Aug 03, 2008 11:42 pm

Hi, those motors look great. Are there any more where they came from?

I'm too green to give any help with the mini, I'm afraid, but it sounds like a sound idea to me. I've got a Zapi twin motor controller in my cupboard which is designed to run two motors with differential power control. It's rated way too low for your needs (300amp total @ 48v) but they might make bigger ones.

All the best,
Nino

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nino500
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Location: Isleworth, Middlesex

Postby nino500 » Mon Aug 04, 2008 12:42 am

I've got a Zapi twin motor controller in my cupboard which is designed to run two motors with differential power control.


I meant the controller, not the cupboard. In case my lack of punctuation left you wondering.

MalcolmB
Posts: 423
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Postby MalcolmB » Mon Aug 04, 2008 6:55 am

Hi Nino

The motors came from a seller of army surplus (http://stores.ebay.co.uk/Senitor). Another northern BVS member bought one and passed on the news that there were a few more for sale, so two of us bought a pair each. I've not seen any more for sale recently but it might be worth contacting the seller.

I've not taken a look at the Zapi controllers recently, I'll take another look. So far I've been looking at Logisystems and Kelly. The Kelly controllers are attractive for their programmability and torque control, but their ratings seem to be a little optimistic.

MalcolmB
Posts: 423
Joined: Sat Jun 23, 2007 8:07 pm

Postby MalcolmB » Thu Aug 07, 2008 1:42 pm

After reading around a bit more, I’ve just about convinced myself that I can get decent performance without a transmission and without messing about with clever stuff like series/parallel switching. There’s a good thread putting both sides of the argument here: http://www.diyelectriccar.com/forums/sh ... rect+drive

With the motors in parallel at 108V a single reduction ratio of between 4:1 and 5:1 should give the 70 mph top speed I want. I’d really like to use a belt drive for low noise and reliability, but the diameter of the final sprocket just gets too big above a ratio of around 3:1. Quaife make a very nice reduction gearbox with differential and reverse gear that would make things very easy, but the price is very nice too… http://www.quaife.co.uk/Quaife-CD-axle- ... riven-cars

Anyway, I’m actually looking for more advice :roll: The business end of my motor has a keyed taper that starts off at 22.0 mm and increases to 24.2 mm over a length of 20 mm. Does anyone recognize this as a standard taper? Just wondering If I’m likely to get anything to fit off the shelf or whether I’ll need to get a sprocket machined to fit?
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EVguru
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Postby EVguru » Wed Aug 27, 2008 8:45 am

Have you pulled the brushgear yet?

On many of the Prestolite motors I've dealt with in EV's the brushes were angled over about 15 degrees in the direction of rotation.
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
http://www.compton.vispa.com/the_named

MalcolmB
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Joined: Sat Jun 23, 2007 8:07 pm

Postby MalcolmB » Wed Aug 27, 2008 10:03 am

Yes the brushes are angled like you say. I did wonder if this would pose a problem to changing the direction of rotation, but Jim Husted has said on EVDL that it's not a problem. I'd value your opinion as well.

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EVguru
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Postby EVguru » Wed Aug 27, 2008 11:13 am

Well, Jim is 'the motor guy'.

I know that there has sometimes been a problem with twin motor setups in getting the motors to match. Garry Flo had a lot of trouble years ago with a twin drive Porsche 944, but I have a feeling that was ADC giving miss-information about their motors brush timing.

Sometimes motors seem to need different ammounts of advance in different directions. Permenant magnet motors are much more fussy becuase they want to run at a fixed rpm per volt. With these angled brushes, the motors do respond defferently IF the commutator is not in perfect condition. If the commutator is out of round or has a raised bar, then in one direction the brush is more inclined to 'bounce'.

Just something to bear in mind.

Put in some brush temperature sensors. The commutator and brushes are going to be what overheat first and fastest. I'd probably measure exit air temperature too at least initially and see how the motors are sharing.
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
http://www.compton.vispa.com/the_named


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