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?
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?
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
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.
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.
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
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?
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'?
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.
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....??
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 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..
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.
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.
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.
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...
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.
Spent most of the weekend tidying up the garage as there was barely room to swing a ferret. But I did manage to fit the cross-member and tack up the mounts for one of the turnbuckles for tensioning the chain.
There was some wobble in the driven sprocket when I tried spinning it in the bearings. I'm not sure whether this comes from the taper hub mounting or whether the platewheel itself is distorted, so I've asked a mate who has access to a measuring machine to check it out. I want this to run smooth as butter!
Just a small update. I've been stripping the running gear off the Mini, cleaning it up and transferring it to the new subframe. Replaced all the steering ball joints and one CV joint. The Mini normally has one long and one short drive shaft, which is handy, as it means I can use two of the short shafts, so there's no need to make up custom shafts.
I got a local machine shop to cut keyways in the motor shafts, the drive sprockets and the stub shafts that carry the driven sprockets.
The CV cups actually sit about 20mm further forward now than they would normally. I had to do this to provide enough clearance for the driven sprockets at the back of the subframe. I was a little worried this would cause the drive shafts to foul the sides of the subframe where they pass through it, but it turns out there's just enough clearance. Phew.
Now that I've checked everything fits I can weld the CV cups to the stub shafts, then mount the motors and start running the brushes in.
Thanks for the pictures. This is a great project. I am planning a very similar dual wheel drive. My plan is for a rear wheel VW drive setup (belt or chain?). I am in the gathering parts mode. I want to try and use as many off the self parts as possible for pulleys, axles, and cv joints, since my machining abilities are limited and I may want to repeat the process. I will be using two synchronous AC motors out of a prius transaxle with two homemade controllers. This might give me the opportunity for traction control since my motor is synchronous I already know the speed of each motor. I might also be able to push the outer turning motor harder through a turn if it helps handling. However, I have to complete my single motor conversion before I start on my dual motor project or my wife will know that I am insane. Everything I am learning on my first project should apply nicely. I just finished fabricating one of my drive axles that connects the prius tripod to the inner racer of the VW CV joint and next weekend hopefully the other. Looking at your design I was also picturing the larger chain sprocket might be a nice place to put disc brakes.
Was reading your post on putting brake caliper on drive sprocket. One simple suggestion is to make a replaceable rotor surface, so you don't need to replace the drive sprockets when the brake wear's out the rotor surface. Unless these sprockets need to be changed on a regular basis like motor cycle sprockets from wear. Just a thought I looked into doing this on my 57 Harley for simplicity sake of a few less parts to maintain.I think you are on the right track for using belt drive a lot quieter drive system and just as strong and plenty of gear ratios to fit your drive arrangement. I am going to use a 12v DC vacuum pump for my brake's as my wife wants to drive MY 63 Falcone. Much to my displeasure since she has her own 65 Fairlane. It does require power brake's since she like your wife has problems with her ankle's. oh well just one more fabrication hurdle to overcome and the switch you are going to need is called a hobb's switch and a vacuum chamber like a metal travel canteen/bottle. Have seen it used on one of the kiwi guy's site's. the hobbs switch can be set to maintain a set vacuum for break booster and I have seen several extremely small booster's for aftermarket hot rod applications to save room for those other items we find to add as we go along our way to EV bliss.
Thanks for that Duke, I'd not come across that name before. It brings up a few more likely candidates. I've found a source for new ones but don't like paying retail price
Thanks Jeff. I've been watching your project with the Prius motors. You really have something there if you can get that motor working reliably with your controller. A pair of them driving a little VW should prove very efficient, and relatively cheap. Hope it all goes well for you.
Using the sprockets as brake discs would be an elegant solution, but I may end up enclosing the sprockets and running them in an oil bath to prevent premature wear. The mini already has outboard disc brakes, so I'll leave them there and make life easy for myself
Well, I did think of just using that for reverse, as it would reduce the parts count even further
Seriously though, the motors were originally neutrally timed, so should work just as well in either direction at the rated voltage. I plan to run the motors at around 100V so I've advanced them by 8 degrees in their respective direction of rotation. To be honest I'm not sure advancing is really necessary, as most of the time I guess the motors will only 'see' around 60V. It's something else to test once I've got her running. I'll be putting temperature sensors close to each brush set to monitor temperatures.
The brushes on these motors are set at an angle, but according to Jim Husted this is simply to maximise brush area and doesn't affect the direction of rotation. I've measured the motor current with the motors running in both directions on the bench and couldn't see any significant difference using my rough and ready test setup.
Sorry Malcom: I was out working till 1:00am just got in and saw you responded. The Hobbs switches are not all that expensive and they are also adjustable for pressure or vacuum in several ranges I will check on the part number we used on our last alcohol injector it ranged from 5-20hg vacuum to inject alcohol into our fuel mix to cool under extreme turbo boost of 40-55 lbs on my four cyl 2300. that is now going in to an 80 pinto for a fun rocket ride, and fairly good fuel mileage around 40 mpg under lite load and around 25 under full boost. I guess we have to go to extreme's on our projects sometime's
Sorry Malcolm about the misspelling of your name just saw that I did that my apologies. the Hobbs company is now owned by Honeywell. That part number is a 5000 series, it is adjustable from 1hg vacuum to 30hg.
It lives! Admittedly the wheels turn in opposite directions, but that's just a minor oversight... There's a slight misalignment in one of the motor mountings, but easily remedied.
I've been working against the clock to make this presentable as there's a Maker Faire on here in Newcastle on 12/13 March and I'm planning to show my motorcycle and the completed Mini subframe.
It's 3/8" duplex, the largest pitch I could use and still get a reasonable reduction ratio. A side benefit of using such a small pitch (as I'm sure you know) is that it can run at higher rpm and generates less noise. I've also considered silent chain, which is expensive, although not too bad if you buy replacement chains for use in transfer cases
The colour is Mowog green (MOrris WOlseley Garages, I think). It's a high-temp engine paint.
I am planning on using 5/8" duplex on the back of the trike mainly because of the standard rear sprocket has a very large bore. I'm planning on putting two together to make a duplex to save machining one each time I change them. Back wheel will be running at 1130rpm at 80mph.
I've been playing with my motors a little today and noticed something odd. I have the motors wired in series with a 12 V battery, with both fields switched by a single reversing contactor. I found that one of the motors spins a good deal faster than the other, in either direction. When I measure the voltage across the armature I get around 7.5V across the faster motor, and around half that across the slower motor.
I expected a slight difference between the motors, but not this much. When I turn the hubs by hand the mechanical resistance feels very similar. It just occurred to me while writing this that I can easily check how similar they are by adding a torque arm to each hub and hanging a weight from it...
I'm just wondering if this difference is solely down to slight electrical and mechanical differences between the motors and drive trains, will it become less significant as I increase voltage and load?
It will happen while the motors and wheels are free-wheeling. The motor encountering the highest mechanical resistance will basically stall, giving most of the voltage to the other motor, which will allow it to spin faster.
The moment you drive on a road, the wheels will be connected to each other via the road, and things will even out. It is a good test to see which drive system has the highest resistance to turning, nothing else.
From elementary electrics I seem to remember that if two light bulbs were wired in series then one bulb would be brighter then the other due to the voltage drops as the first bulb acted as a resistor for the second.
I guess it would be the same thing and significant al low voltages but maybe negligable at high voltages.
From elementary electrics I seem to remember that if two light bulbs were wired in series then one bulb would be brighter then the other due to the voltage drops as the first bulb acted as a resistor for the second.
Elementary is about my level, but for me that begs the question how do they decide which one is first?
Yes, I plan to try parallel as well. I'm curious about the differences in steering feel. Ultimately though, series seems a little more efficient/simpler, as it means lower current and needs just one reversing contactor, I think.
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