102 replies to this topic

[mk3 Cooper S]

Lithium Iron would be the way to go in terms of cost and range and thermal control.

I have concerns your twin motors with a single controller running them at the same speed will act more as a locked diff.
Have you considered running through a transmision locked in gear and therfore using a convesional Diff?

[MalcolmB]

The batteries I linked to are lithium iron phosphate.

Yes, I did consider running through a transverse gearbox and diff. That's a proven method, but in the end I decided to try it this way to see how it works out. I like the simplicity of direct drive and it eliminates losses in the gearbox and diff. We'll see...

[mk3 Cooper S]

Good luck with the project.

Don't forget the E stop button if you are going direct drive!!

[MiniLandy]

The batteries I linked to are lithium iron phosphate.

Yes, I did consider running through a transverse gearbox and diff. That's a proven method, but in the end I decided to try it this way to see how it works out. I like the simplicity of direct drive and it eliminates losses in the gearbox and diff. We'll see...

I thought i'd already posted on here, apparently not. This is something i've given quite a lot of thought to, in various daydreams...

The two motors, run off one speed controller, should give an LSD action. I used to compete in RC Rock Crawling, and when my twin motored rig had one speed controller and two motors, the rear motor would "stall" on inclines, with all power being directed to the motor of least resistance, the front.

With a differential action, you get the same kinda thing, just make sure you wire them parallel. If you wire them series, you "split" the voltages, and end up with a slow car.

As for the battery situation, have you considered something like Top Gear's Eagle iThrust or whatever it was called? A small, diesel powered generator would fit nicely in the boot, and would keep you going, needing only a small battery.

As has been said, be sure to wire in a kill switch. I once had a speed controller melt at full throttle, and so lost control of the car. I certainly wouldn't want to be in a car with the esc welded open.

Good luck

[MalcolmB]

Thanks MiniLandy, it's good to get comments from someone who's played with these systems before. There's a lot of good information feeding back from the RC field, especially on batteries and battery management.

I've heard so many conflicting views on whether it's a good idea to connect the motors in series or parallel that I'll probably try both just to find out for myself. Wiring them in parallel would be easier in some ways because of the lower voltage, but a couple of people (including someone earlier in this thread) have said that wiring them in parallel will exaggerate any slight differences between the motors and lead to low-speed steering problems and possibly damage to the controller/motors.

Wiring them in series seems to be the most reliable option, though it does mean higher voltage like you say. I'm planning to run at around 100V per motor, so 200V total. The controller will be good for 300V. Electrical safety is obviously a big factor, so the pack will be split into three or four lower voltage packs and all connections between them will be very well insulated. The controller will be connected via a couple of high-voltage DC contactors and I have an enormous DC circuit breaker that will serve as the final on/off switch.

[MiniLandy]

Thanks MiniLandy, it's good to get comments from someone who's played with these systems before. There's a lot of good information feeding back from the RC field, especially on batteries and battery management.

I've heard so many conflicting views on whether it's a good idea to connect the motors in series or parallel that I'll probably try both just to find out for myself. Wiring them in parallel would be easier in some ways because of the lower voltage, but a couple of people (including someone earlier in this thread) have said that wiring them in parallel will exaggerate any slight differences between the motors and lead to low-speed steering problems and possibly damage to the controller/motors.

Wiring them in series seems to be the most reliable option, though it does mean higher voltage like you say. I'm planning to run at around 100V per motor, so 200V total. The controller will be good for 300V. Electrical safety is obviously a big factor, so the pack will be split into three or four lower voltage packs and all connections between them will be very well insulated. The controller will be connected via a couple of high-voltage DC contactors and I have an enormous DC circuit breaker that will serve as the final on/off switch.

To be honest mate, it'd cost you nothing but time to try both setups, and that's what i did. I noticed the "stalling" effect was actually worse when in series, but i don't know if it's just because the motors were turning more slowly that it was more noticable... Either way, a lot of this project will be trial and error no doubt, so try both

I assume you're keeping the regular mini (non servo) braking system? As it'll probably weigh roughly the same as standard, all things considered...

And any thoughts on implementing a generator? In my imaginary design, that's what made it viable to use day-to-day, as charging up batteries will get tiresome very fast.

Also, have you looked into what system electric fork lift trucks use? Could be some useful info.

[MalcolmB]

any thoughts on implementing a generator

No, it'll be pure electric. One of the main attractions for me is simplicity. I want to keep this light and have as few failure points as possible. 50-60 mile range will cover most of my driving needs. Anything outside that I'll use the fossil burner (Alfa 156).

I don't see that charging will be a pain. It takes a few seconds to plug in and a full charge will take 3-4 hours from a standard mains outlet. Nissan will be producing the Leaf up this way so a lot of charging points are being installed in and around Newcastle.

Fork lifts can be useful as a source for motors, but they generally use low-voltage systems (36-48V) so the rest of the components aren't much use.

Edited by MalcolmB, 17 January 2011 - 05:07 PM.

[MiniLandy]

any thoughts on implementing a generator

No, it'll be pure electric. One of the main attractions for me is simplicity. I want to keep this light and have as few failure points as possible. 50-60 mile range will cover most of my driving needs. Anything outside that I'll use the fossil burner (Alfa 156).

I don't see that charging will be a pain. It takes a few seconds to plug in and a full charge will take 3-4 hours from a standard mains outlet. Nissan will be producing the Leaf up this way so a lot of charging points are being installed in and around Newcastle.

Fork lifts can be useful as a source for motors, but they generally use low-voltage systems (36-48V) so the rest of the components aren't much use.

That range is pretty impressive, actually. Does that also take into account using things like headlights, radio, satnav, and carrying fat people?? I'd be interested to see how this affected the battery life, and how you'll work a 'fuel gauge' type thing into it.

With all that in mind, you should end up with a very usable end result, my local tescos has a charging facility, even.

[MalcolmB]

Headlights and radio actually don't use much compared to the motors themselves. Weight will make a difference, though not so much in a relatively flat area like this. Mind you, that 60 mile range depends on me saving enough for the right lithium pack.

I've already found the fuel gauge: http://www.evworks.c...uct=INS-EVW-FGD

Oh yes the brakes – I'm using a servoed system as my other half wants to drive this and has a chronic ankle injury. There's obviously no vacuum from an electric motor, so I've got an electric servo pump from a Saab.

[clovus]

You might find the following link useful.

www.ausmini.com/forums/viewtopic.php?t=42150

There is a electric mini getting around Bathurst in Australia. He also has a bunch of youtube videos if you go looking.

Good luck, it sounds like a fun project.

[MalcolmB]

Thanks for that clovus! I was following his progress a while back but then he just dropped off the radar. Great to see he's still working on it and switching from lead to lithium.

Here's one of his videos:
g9BL0qtt8Gs

[MalcolmB]

Just a small update. I've been stripping the running gear off my mini, cleaning it up and transferring it to the new subframe. Replaced all the steering ball joints and one CV joint.

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 pot joint cups now sit about 20mm further forward 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. I'm using two short drive shafts so there was no need to get custom shafts made up. If anybody's looking for a pair of long drive shafts let me know...

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 motors in, which just involves running them for a day or so to fully seat the brushes.
 P1020281.jpg   504.89K   74 downloads  P1020287.jpg   531.51K   127 downloads
 P1020288.jpg   540.14K   105 downloads

[MalcolmB]

It lives! Admittedly the wheels turn in opposite directions, but that's just a minor oversight... There's also 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 electric motorcycle and the completed Mini subframe. If anyone local's coming to the fair, look out for the Weird Motors stand!

 P1020289.jpg   397.54K   66 downloads  P1020294.jpg   600.88K   149 downloads
 P1020295.jpg   583.65K   253 downloads

[freshairmini]

This looks awesome!! do you have any videos of it running?

[MiniLandy]

Forgot about this thread, what's the latest? Really interested in this