Electric Quad?

[Black Forest]

I want to build an electric 4 wheeler. My first thoughts were to build a 4 wheel bicycle and put an electric e-bike kit on each rear wheel. Do you all think it would be better to mount the two motors close driving a rear axle with a chain drive differential or drive each rear wheel? This could be a pedal assisted type verses a just electric drive. It will be mostly for off-road use around my farm. It doesn't have to go fast. 15 to 20 km/h is plenty. It needs torque though.

Bad idea?

[chipmaker4130]

Sounds like a boatload of fun to me! Go for it.

[Michael Edwards]

Like this with an electric motor would be a hoot.

[OKChipmaker]

Have you thought about a golf cart? Its already made and a used one may be lower cost than the parts to build one.

[achtanelion]

I'd go with driving each wheel separately. If you were going to a diff, a single beefier motor would make major sense.

[3 Phase Lightbulb]

I want to build an electric 4 wheeler. My first thoughts were to build a 4 wheel bicycle and put an electric e-bike kit on each rear wheel. Do you all think it would be better to mount the two motors close driving a rear axle with a chain drive differential or drive each rear wheel? This could be a pedal assisted type verses a just electric drive. It will be mostly for off-road use around my farm. It doesn't have to go fast. 15 to 20 km/h is plenty. It needs torque though.

Bad idea?

I made a self balancing electric 2 wheeler several years ago for fun. It will drive about 8mph. I'm only using a pair of 12V 12aH SLA batteries but I could really hop it up if I went with a LiPo power source. If you're interested in building one, I can give you all of the details and provide you my software/firmware that brings it to life.

Schematics:

[CCWKen]

I would go with one motor and a differential. Otherwise, controlling two motors will be expensive and you risk burning one out in a turn. Go-Kart differentials are common and cheap on this side of the pond. I'm pretty sure they're made in China so they should be available over there. Or use a transaxle out of an old lawn tractor. You could even use the change gears and have reverse.

[Dan Dubeau]

Pick up an old 90's Suzuki king quad 250/300 (I assume they had those over there). They had a hi-low-super low range gearbox, and locking differential. Would go anywhere (except deep mud), and pull anything, but had an independent (wishbone rear) suspension and didn't ride like a lumber wagon. Pull the old one lunger out of there, and insert your electric power source of choice. You would be hard pressed to design and build a more durable, and bullet proof drive system than those things, and starting from there you'd be 80% of the way to a finished product.

Sold mine a couple years ago, and regret it. $500 would get you a good doner over here.

Edit, for some reason I had it in my mind the gearbox and engine were separate on these, but they were a unit construction so you'd have a hard time "splicing" in your electric motor to take advantage of the gear box.

[mattthemuppet]

one motor, one differential and a BIG battery I'd skip the pedal assist for a 4 wheeler, can't really see how that would work. I'm guessing this is to get around on your property and perhaps tow a small trailer too (for hay etc)? There are also a fair number of eMTBs out there that might suit you if hauling stuff isn't needed. Then again, you have horses, so that aspect is probably covered!

For a starting point find out what DC motors, battery chargers and battery management systems/ controllers are available. Go with the biggest you can find, then build a battery that will give you the run time that you need. Mike Amick just built a battery with a tab welder, so he'd be a good person to ask. I'll be rebuilding mine this summer.

[Yondering]

I have a couple thoughts, speaking as someone who actually owns and rides four wheelers.

- There are very good reasons why commercial quads do not use bicycle wheels and other parts. Side loading on the wheels is a big one. Flotation in off road conditions is another.

- You'd be way ahead to buy a cheap used 4 wheeler with a bad motor to convert, rather than building from scratch yourself. I've built that sort of thing myself, and there's a huge amount of work and expense that goes into the chassis and suspension without even touching on the drive system.

- I recommend a chain drive to a solid rear axle, no differential, if you're going to use it for off road use around the farm. The big advantage of the chain drive is reducing unsprung weight, and the solid axle is for traction. Driving each wheel independently sounds fun in theory, but in a situation with little or no weight on one driving wheel, the ability to transfer 100% (as opposed to 50%) of the power to the other wheel makes a huge difference. If you do use a differential, you'll want some method of locking it, but that's even more complex and expensive.

[MattiJ]

I want to build an electric 4 wheeler. My first thoughts were to build a 4 wheel bicycle and put an electric e-bike kit on each rear wheel. Do you all think it would be better to mount the two motors close driving a rear axle with a chain drive differential or drive each rear wheel? This could be a pedal assisted type verses a just electric drive. It will be mostly for off-road use around my farm. It doesn't have to go fast. 15 to 20 km/h is plenty. It needs torque though.

Bad idea?

Easier to use differential unless you feel like to inventing your own drive electronics or some sort of control system for the rear wheel motors.
Many e-bike kits offer sort of torque control combined with speed control and that would work kind of ok also in the corners.

[BCRider]

If you use bicycle hub motors you can start off with a two motor rear drive and see how it goes. If all is well you could look at a coupe of more hub motors for the front wheels.

And the current "fat tire" wheels gives you some room for choice depending on the nature of your farm soil. If you have sandy areas or it gets mucky at some parts of the year the fat tires will really be a huge help for floatation on the soft stuff.

The one downside to the electric bicycle hub motors is that they need support on both sides of the axles. I don't know of any of those sort of motors that are intended for use on cantilevered axles such as you'd like to use for a quad style. On the other hand if you could make do with a suitable off road trike setup it would be easier and more natural to use the bike hub motors.

Perhaps steal a page from some of the electric scooters that are out there now? I'm thinking two front steering wheels that use "wheel chair" style large tubular axles and are cantilevered. Set these fairly wide. On the back set two bicycle style hub motors up with a slightly shorter footprint so the two bicycle style rear wheel support structures are enough smaller that the outer "chain and seat stays" are roughly the same width as the front steering wheels. So the track on the rear wheels might end up 8 to 12 inches smaller than the track of the front wheels.

This would allow you to use the rear hub style motors for an easy drive train setup. It would also somewhat reduce any differential torque steering by keeping those two wheels a little closer together. Yet it should still provide a quad style stability.

I'd also go with the fat tires for this sort of setup. Not only for the extra "floatation" they have on loose, sandy or muddy ground but also their ability to carry a bit more weight. The wheels will also want to be cambered a fair amount and likely laced up with dishing that is similar to the wheel setups used on competition wheel chairs used for paraplegic sports that need to withstand a higher than usual amount of side force.

Figuring out the chain drives to the wheels would be a nightmare. They don't make left hand drive stuff so if you want pedal assist it will have to be the cranks to some manner of jack shaft and then out to the two right side freehubs or freewheels. The good news is that you would not require a differential for this since the under driven wheel would simply freewheel faster than the drive. So the inside wheel in a turn would be the drive wheel and the outside wheel just spin. So no diff needed. And since at least half the power would be from the motors hardly any "power steering" would be evident.

Fitting the controllers would be interesting. To keep it simple I think you can just use the two independent controllers. At least initially to see if there's a need for a single combined controller. Fitting the pedal cranks with the two pedal sensors is easy. But the twist grip throttles is going to be a bit more trouble. You'll need some fancy mechanical "mixer" that rotates both together. But it may turn out that one needs to rotate a touch faster than the other. Depends on how much difference there is in the power from the motors compared to the movement of the twist grip.

All of this might be a good reason for not sweating on keeping the rear wheel track as wide as you can. The less distance between the two rear wheels the less you'll notice any power difference in the two sides. But of course you want to keep them fairly far apart for tipping stability. But I'm sort of thinking that if the rear wheels track was maybe 80%? of the front wheel track that it might be a nice compromise between stability and reducing the steering effects of power from the one side vs the other?

I got myself a fat tire electric off road bike a couple of years back. It's a 500w model and I can assure you that it's got really good power. It makes coming up the fairly steep hill I live on a piece of cake and uses a lot less power than I'd have thought. Like roughly 250 to 300 ft rise in about a half mile?

The bike I've got is 65 lbs with battery on board. Add me to the amount and we're up to around 280lbs. (trying to get down to a little trimmer 200'ish this year) Now your quad will be heavier. Probably 2.5 to 3 bikes worth due to the extra framing and steering setup. So probably around 160 to 180 lbs total in the end. Add your own weight to that. But with two such motors it would still have a better total power to weight ratio than the one bike with me on board. So powering up and climbing things should not be an issue if you use two 500's.

For off road it will also be subjected to more twisting then a road going pedal trike. So you're going to need a pretty fancy frame and suspension on all four corners just to avoid being beaten up badly. Which, come to think of it, totally changes how I was thinking about the rear wheel axle supports. I'm now thinking of two burly mountain bike swing arms and suspension components to do the job. And a fair amount of lightweight CrMo aircraft tubing in the middle of it all..... or at least thin wall hi tensile steel tube. Or... I wonder if an aluminium monocoque tub could be build up to mount the front steering "A" arms and the two mountain bike swing arms off the rear?

[danlb]

I made a self balancing electric 2 wheeler several years ago for fun. It will drive about 8mph. I'm only using a pair of 12V 12aH SLA batteries but I could really hop it up if I went with a LiPo power source. If you're interested in building one, I can give you all of the details and provide you my software/firmware that brings it to life.

Love the naming. I always wondered what PID stood for!

[3 Phase Lightbulb]

Love the naming. I always wondered what PID stood for!

My son was helping quite a bit when I was tuning the PI components of the PID. I'm so pissed that I can't locate a video that I took when my son was testing it out and it started to oscillate wildly. It started to rock him forward then backward, forward, backward each at around ~45 degrees. It looked sooo damn funny -- It was like he was riding a bull but it was like a rocking chair trying to fling him off but catching him each time. I'll keep looking for that footage.

[Black Forest]

One reason to still have pedals is I could still ride it in the forest that doesn't belong to me. Quads are not allowed or even horse buggy's. Ridden horses and bikes are allowed, E-bikes included. No cars or trucks unless you are specifically do forestry type work. Not and absolute deal breaker but if it is technically a bike it would be better.