Dual-motor Austin Mini

88363 Views 168 Replies 42 Participants Last post by galderdi, Feb 27, 2017

MalcolmB

Discussion Starter · Nov 29, 2010 (Edited)

I've been talking about this for long enough and I've changed my mind about how to do it countless times, but I've finally made a start on my Mini conversion.
I've got to come clean first and say it's not a completely authentic Mini, as it was rebodied some years ago with a glass fibre shell. Otherwise it's a Mini through and through, complete with leaks, ageing 1275 A-series engine and gokart handling.

She's currently buried outside under 12 inches of snow, but I've bought a spare front subframe so that I can get the motors mounted and refurbish the front running gear over winter. I found a couple of Prestolite 7" motors a while back, via an ebay contact. They're rated at 130A continuous at 36V. I've advanced them by eight degrees and plan to run them at around 120V each.

The motors have actually been shortened by around 40mm since I took the photo below. This was done by removing the internal fan, and machining back the alloy "legs" on the drive end. It was the only way I could get the two motors to fit across the subframe and also gave me a decent length of plain shaft to mount the drive sprocket on. I'm not going to worry about whether it's unbalanced the motors yet...
Each of the motors will drive a chain sprocket mounted on the inboard ends of the half shafts, so no gearbox, no diff. I'm busy making up two pairs of bearing carriers that will each support a short shaft with a sprocket on one end and a CV joint on the other. I'll post some photos in a few days when I've got something worth showing.

Now to the first of many daft questions: I want to keep this conversion as simple (and hopefully cheap) as possible. I've been looking at options for providing vacuum and 12V power and the simplest way I can see to do that would be to use the tail shaft on one motor to drive a mechanical vacuum pump, and use the tail shaft on the other to drive a lightweight alternator. The question is, if I have the motors wired in series to a single controller, is the small difference in load on each motor likely to cause any problems?

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major

· #2 · Nov 29, 2010

MalcolmB said:
The question is, if I have the motors wired in series to a single controller, is the small difference in load on each motor likely to cause any problems?

Hi Malc,

I assume they are series motors, identical designs. Then when in series, they will be forced to have the same load; that is current therefore the same torque. So if you take more torque from one motor shaft for accessories than the other, one of your drive wheels will get a little less torque. I don't really have any idea if that would be noticeable to you or not

Which Prestolite motors are those?

major

MalcolmB

Discussion Starter · #3 · Nov 29, 2010

major said:
Which Prestolite motors are those?

I've searched high and low for more information, but no luck. All I have is from the rating plate: Part no. LKAR4002, Class H, 3.6 kW, Class H windings. They have a 33 bar comm. Pretty sure they're series wound. They were Army surplus.

major

· #4 · Nov 29, 2010

MalcolmB said:
I've searched high and low for more information, but no luck. All I have is from the rating plate: Part no. LKAR4002, Class H, 3.6 kW, Class H windings. They have a 33 bar comm. Pretty sure they're series wound. They were Army surplus.

My experience with Prestolite dates way back. I didn't know they did any "Army" motors and the LKAR prefix is post my time. Also, Prestolite went bankrupt and split apart, and there was also an Asian Prestolite (non-related from what I can tell) and divisions in the UK.

But if they are the 7.2 inch diameter frame with the 33 slot and bar armature (from the old design), they are very good machines. If you can post some photos of the guts, I may be able to tell you more.

major

MalcolmB

Discussion Starter · #5 · Nov 30, 2010

Yes I've read some of your earlier comments about the Prestolite motors. This one is labelled Ametek-Prestolite, so it would have been after the split, but it looks to me to be similar in construction to the earlier ones I've seen. The stack is shorter though, at around 5 1/2 inches. Here are a couple of photos I posted ages ago in the fork lift motor thread.

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major

· #6 · Nov 30, 2010

MalcolmB said:
Yes I've read some of your earlier comments about the Prestolite motors. This one is labelled Ametek-Prestolite, so it would have been after the split, but it looks to me to be similar in construction to the earlier ones I've seen. The stack is shorter though, at around 5 1/2 inches. Here are a couple of photos I posted ages ago in the fork lift motor thread.

Kool

Ametek-Prestolite. I think they ended up with the Prestolite factories and tooling. Then it might just be MGP lamination. Likely a 5" stack. And they look like series field coils. And dual double shunt brushes. About the same brush as a Warp9 or 11

I think you have a couple of keepers

MalcolmB

Discussion Starter · #7 · Nov 30, 2010

That's good to hear, especially from you Major. One thing that's been nagging me is whether I'll have enough torque for decent bottom end performance. Obviously that depends on the gear ratio, but space is so tight in a Mini that the practical upper limit is about 4.5:1 with a single-stage reduction. These motors produce 10.5 ft lbs of torque at 130A (5 hp at 2500 rpm), which doesn't seem much when you compare it with some of the brutes that others are playing with here.

Looking around at other motors of similar size and rating I've been using a guesstimated figure of 70 ft lbs from each motor at 500A. Does that sound too optimistic?

Huff

· #8 · Nov 30, 2010

Hi,
I saw the word Mini and had to investigate

(have owned 2 of the things!)

Why don't you remove the vacuum assisted brake servo and change it for an older type (1990 or earlier from memory) non assisted cylinder? Surely that would simplify matters.

I was looking to do a similar conversion. Perhaps with a Mini Estate/Van for more battery space.
2 (or 4!) agini motors. With one or two proving direct drive to each driveshaft. Not sure if it would fit?! Can agini motors be stacked up or 'siamised'?

N

MalcolmB

Discussion Starter · #9 · Nov 30, 2010

Huff said:
Hi, I saw the word Mini and had to investigate

Welcome Huff!
Removing the servo would make things a lot easier like you say. Unservoed brakes can be very good on a Mini, but my wife has arthritic ankles so I fitted the servo for her. She wants to drive this car as well, and she's been very tolerant of my obsession for all things electrovehicular, so I reckon it's a concession well worth making

A Mini van or estate would make a great conversion, though it's becoming hard to find a good one. The company that made my glass fibre shell (Domino) also made a pick-up version, and I'd really like to get one of those.

I believe the Lynch motors can be stacked, not so sure about the Agni motors. The man to ask would be Jozzer (a member here). He has lots of experience with them.

DIYguy

· #10 · Nov 30, 2010

MalcolmB said:
Now to the first of many daft questions: I want to keep this conversion as simple (and hopefully cheap) as possible. I've been looking at options for providing vacuum and 12V power and the simplest way I can see to do that would be to use the tail shaft on one motor to drive a mechanical vacuum pump, and use the tail shaft on the other to drive a lightweight alternator. The question is, if I have the motors wired in series to a single controller, is the small difference in load on each motor likely to cause any problems?

Hi Malcolm,... just a comment on the ideas for vacuum and 12 volt power. I don't see your method as being the simplest way. Perhaps "simple" and "cheap" are mutually exclusive...not sure...but in my little brain a vacuum pump and DC/DC (or even just a battery with enough Ah) is much simpler. Vacuum pumps can be relatively inexpensive...depends on how much noise you like to put up with. DC/DC's aren't all that much either. I would say these devices are on the lower end of the cost spectrum for what you need. Perhaps you should just let the motors drive the car....??

Anyways, good luck!

MalcolmB

Discussion Starter · #11 · Dec 1, 2010

DIYguy said:
...a vacuum pump and DC/DC (or even just a battery with enough Ah) is much simpler

I'm not sure – it would definitely be lighter, which is good. I guess it depends to some extent on the skills you have. I don't have a great deal of electrical experience but I worked in heavy fabrication for a few years, so it seems easier to make up some new mountings for a mechanical pump and alternator and just hook them up to the original connections.

Part of the reason I've taken so long to make a start on this build is that I'm torn between two approaches. On the one hand I want to make it as simple as possible by reusing as many original/familiar parts as possible. When people look under the bonnet (hood) I want them to understand how it works straight away. On the other hand I want to do it right

I did buy a Saab electric vacuum pump on ebay a while back, but haven't found a vacuum switch for it yet. I've also looked around for DC converters, but I'm planning a pack voltage of around 220V and there doesn't seem to be much choice at that end. I could run a pair of isolated 110V converters but that's getting more complicated and more expensive... Any other suggestions are very welcome

Anyways, good luck!

Thanks!

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DIYguy

· #12 · Dec 1, 2010

MalcolmB said:
I'm not sure – it would definitely be lighter, which is good. I guess it depends to some extent on the skills you have. I don't have a great deal of electrical experience but I worked in heavy fabrication for a few years, so it seems easier to make up some new mountings for a mechanical pump and alternator and just hook them up to the original connections.

Part of the reason I've taken so long to make a start on this build is that I'm torn between two approaches. On the one hand I want to make it as simple as possible by reusing as many original/familiar parts as possible. When people look under the bonnet (hood) I want them to understand how it works straight away. On the other hand I want to do it right

I did buy a Saab electric vacuum pump on ebay a while back, but haven't found a vacuum switch for it yet. I've also looked around for DC converters, but I'm planning a pack voltage of around 220V and there doesn't seem to be much choice at that end. I could run a pair of isolated 110V converters but that's getting more complicated and more expensive... Any other suggestions are very welcome

Thanks!

Hi Malcolm,

You can likely use the Iota DLS-220-45. This is what I am using. These things work with DC input also. They tested this model for me to ensure it would work ok at my pack voltage. My charger cycles up to 250 volts and I have the DC/DC on too... no problems. You may want to confirm for your application. Mine is 192 nominal, 208 charged. http://www.iotaengineering.com/dls22045.htm
They are very helpful.

I'm more of a mechanical guy also, so...we are drawn to what we know. The DC/DC is very straight fwd. Go for it!

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MalcolmB

Discussion Starter · #13 · Dec 1, 2010

Thanks for the link DIYguy. I guess the Iota unit takes a DC input as well. I've just been reading through your thread, got to page 26 and I'm exhausted

You've done a really neat job so far. It's good to read all the little details like sorting out the tach input. I've got that to look forward to yet.

DIYguy

· #14 · Dec 1, 2010

MalcolmB said:
Thanks for the link DIYguy. I guess the Iota unit takes a DC input as well. I've just been reading through your thread, got to page 26 and I'm exhausted You've done a really neat job so far. It's good to read all the little details like sorting out the tach input. I've got that to look forward to yet.

Thanks Malcolm. Interestingly enough... the tach turned out to be 3 pulses/rev after all ...lol Having the Soliton1 made this a very simple adjustment. The tach output is programmable. I input 2 pulses/rev and output 3 to my tach..

Coley

· #15 · Dec 2, 2010

By not using a differential, I hope the steering is not to jumpy, especially when parking.

MalcolmB

Discussion Starter · #16 · Dec 2, 2010

Coley said:
By not using a differential, I hope the steering is not to jumpy.

Me too! It's a bit of a grey area so I'm looking forward to finding out. The accepted wisdom is that with motors connected in series to a single controller the car will behave as if it has a conventional diff, and if they're connected in parallel it will act as if it has a limited slip diff. I haven't found anyone who's tried both on the front wheels, apart from on radio control cars, so it'll be interesting to see how it feels.

A few people have warned that running the motors in parallel could be unsafe, with the risk of dangerous handling and damage to the controller/motors. I believe some golf carts drive both front wheels in parallel, but they have a narrow track and generally run on grass, which allows the wheels to slip relative to each other.

Wiring them in parallel would be easier in some ways as it requires a lower voltage pack, so there are fewer connections to make and parts like chargers, fuses and dc converters tend to be cheaper and more widely available.

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MalcolmB

Discussion Starter · #17 · Jan 8, 2011

It's been a while, but I've actually got some progress to show today, so Im celebrating with a drop of malt whisky. A belated Happy New Year to Everyone. Cheers!

Photos first:

This was just a trial fit of one of the two motors (affectionately known as "Righty"). It went well, with no unforeseen conflicts, which is unusual for me, though I will have to rotate the motor 60 degrees to avoid fouling the subframe with one of the terminals.

I'm going with 3/8" duplex chain drive for the time being, but the plan is to switch to belt drive if everything works out well. The Gates carbon belts and sprockets are bit too pricey to experiment with.

A 75x25mm rectangular section will go across the top of the subframe to stiffen everything up and provide a fixing point for the turnbuckles that will be used to adjust chain/belt tension.

I need to get some little machining jobs done next: boring out the motor sprockets and getting keyways cut, and turning the driven shafts so that they'll fit inside the CV cups. Very tempted to buy a small lathe and do it myself, as I know it would get plenty of use in the future.

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Woodsmith

· #18 · Jan 8, 2011

MalcolmB said:
Very tempted to buy a small lathe and do it myself, as I know it would get plenty of use in the future.

Nice work there.

If you are going to get a lathe get the biggest one you can afford and can find space for. You will always find a 'need' for a bigger lathe so start big and have fewer upgrades.

My lathe can just about accomodate a 10.5" diameter and I need 11" to make my motor DE cap!

If you have never used one before then a good book and guidance from an turner will be invaluable, especially before spending money.

MalcolmB

Discussion Starter · #19 · Jan 8, 2011

Thanks Woody
It's the space that's the problem when it comes to choosing a lathe. I'd love to get something like an old Harrison, but I have a typically tiny British garage measuring 2.4 x 4.8 metres, half-filled with kids bikes and my assorted junk, so I may have to compromise. This is why all my photos are wide-angle...

Woodsmith

· #20 · Jan 8, 2011

How about adding a 6'x4' shed out the back of the garage. All it need hold is the lathe.

I have thought about that on my front drive or at the side of the house as I wouldn't be able to get a decent sized lathe into the basement workshop. I figured I could place a lathe on the shed base and then build the shed around it. A 500w tubular heater underneath will keep it warm enough to stay dry.

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