2WD

Gio ,
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The guys at Power in Motion here in Calgary have controllers that will run two hub motors at once. I'm not really an expert on this stuff by any means although i'm doing the research as I go along, but it seems like this would just put a lot of weight on your bike for extra torque, but not much more speed.

Off roading is one of the things i'm looking to do with my project once its finished, but from personal experience having a front hub on those kinds of setups is bad. It pretty much negates the ability to have a suspension front fork, and makes front end manipulation much harder.

They did mention that they've been experimenting with using 2 batteries on a bike with a 72v controller, and adding a switching mechanism that would allow the rider to select between using the batteries at 36v for longer life, or 72v for increased speed and power (at least when he was talking about it, this is what it seemed like. He was saying something about being able to switch between parallel and serial easily). That kind of thing would be really great, as you could pack some serious range, or some high power. It would come with the price of having to buy a second battery array of course, but thats probably not much more than buying a second hub.

Could someone comment on if i'd picked up what he was saying correctly or not?

I've toyed with the idea of 2WD for my XM2K moped (not yet, when it get's older and I want to seriously "hack it"). I would imagine it would be more unwieldy on a bicycle than a moped/scooter/motorcycle - but I have zero experience with electric assisted bikes.

Another hub will get you more torque and that also means more acceleration as well as more hill climbing ability - so it has application on the mean urban streets as well as the mountain trail. Whether another hub gets you more top speed will mostly depend on what your current limiting factor is - opposing forces (wind resistance, rolling resistance etc.) or motor RPM limits (a motor has a max RPM for a given voltage). If you're already close to that RPM limit then another motor "helping out" won't help with more top speed - but would help with accel and hill climbing. Conversely if your top speed is limited through lack of power then doubling the power will surely help (this would be a good time to do a Tim the Tool Man Taylor "More power" impression)! However, remember that wind resistance increases as the square of speed so you won't get twice the speed!!!

So - the above comment on 36V for range or 72V for speed makes sense - as long as it fits within the parameters I described in the previous paragraph.

Hope this helps.

I know battery would be an issue, but I think it would be a cool idea for extreme trail riding.

I use two-wheel drive all the time: electric on the front, human on the back. If I were going to take an ebike off road this is probably what I would continue to do. Except I don't think I'd take an ebike off road. None of mine are tough enough to take it. The battery mounts are especially problematic. I'm certain a battery bag would fall apart. Something like the Bionx battery mount might be strong enough, but you would need to find room for two of them. You would probably want front shocks at least so then you hit the whole problem of motors and shocks not getting along very well.

There is also a certain amount of dead weight in a motor. It is easier to preserve the power to weight ratio by increasing the size of the motor rather than increasing the number of motors. By the time you are done this will be one heavy bike. The heaviness becomes a concern with frame strength, handling, and braking. Also I can't count the times I've had a 25lb mountain bike land on me. Now I'm trying to picture a 90lb mountain bike landing on me. Nope. Not a place I want to go.

As to the electrical design I am clueless. Maybe someone else will chime in.

use two-wheel drive all the time: electric on the front, human on the back. If I were going to take an ebike off road this is probably what I would continue to do. Except I don't think I'd take an ebike off road. None of mine are tough enough to take it. The battery mounts are especially problematic. I'm certain a battery bag would fall apart. Something like the Bionx battery mount might be strong enough, but you would need to find room for two of them. You would probably want front shocks at least so then you hit the whole problem of motors and shocks not getting along very well.

There is also a certain amount of dead weight in a motor. It is easier to preserve the power to weight ratio by increasing the size of the motor rather than increasing the number of motors. By the time you are done this will be one heavy bike. The heaviness becomes a concern with frame strength, handling, and braking. Also I can't count the times I've had a 25lb mountain bike land on me. Now I'm trying to picture a 90lb mountain bike landing on me. Nope. Not a place I want to go.

I guess there would actually be 2 sides to this story. Coming from a mountain bikers perspective, i'm still designing the 2nd variation on my bike but there are some major issues with front drive, personally experienced.. Trust me.

The first one as said before was shock strength, its one thing to mount a 15-16lb hub on your front shock and roll down a street, but to take it, try and even huck your hub over a log or do a drop is a recipe for a breakdown disaster. If you weren't planning on doing anything involving leaving the ground, front drive would probably do fine. You would just have to make sure that leaving the ground didn't happen. The other problem is that you'll lose a lot of technical agility for doing these maneuvers in the first place. That would mean dragging all that weight + your bike and supplies over and down these hazards though.

So far as the battery mounts are concerned, the best solution so far, I think, is to go with putting the batteries both on the rear rack and in the centre bag, splitting up the weight and distributing it more evenly. That helps from putting too much stress on either bag/rack.

In my personal opinion, if you built a bike like this you'd be looking at treating the bike more like an outdoor touring vehicle than a bike. Putting that much weight on a road bike is one thing, but you'd be hard pressed to properly ride out in the woods, it would handle more like a dirt bike but with none of the durability and not as much power.

I think davew's suggestion of power in motor > multiple motors is good. Found this on youtube the other day, this guy is using one of the Crystalyte 5303's http://youtube.com/watch?v=SZXI53-CISA
One of those higher wound series 5 motors would probably climb like a mountain goat.

The design in particular that i'm going to try out next, is a rear drive hub on full suspension, powered by a 48v lithium. Nothing overtly powerful, but with a 408 that would provide tons of climbing power and be light enough for using the bike in moderate technical cycling.

I once rode a bike with two hub motors... it was two Heinzmann's (?sp?) and had two separate throttles, separate controllers, one battery pack. That arrangement didn't seem to help except if one of the motors overheated you could use the other for awhile.

I think it's reasonable to have one pack, two motors, two controllers, and one throttle, and connect the throttle to both controllers. I've never tried it though.

I agree with the other comments about weight and sturdiness.

For anyone who might have been curious, here is that controller that they have at Power in Motion here in Calgary. Its a single controller which can control two hubs at once.

http://youtube.com/watch?v=wnwWpjXh5jc

These guys have a lot of interesting stuff actually.

That would be interesting. I've seen recumbent trikes with a motor in the rear before, but not 2 in the front. Or are you talking about a normal trike with 2 rear wheels and one front one? Apparenly there are some decent ATV trikes out there. Although i'm still not really sure on the effectiveness of 2 motors vs. 1 higher voltage/sized motor, a trike wouldn't suffer from the loss of ability that an upright would, as off-road trikers don't hop objects, and you'd still be able to have all of the stability. Might be hard to carry though..

Simple Design to Build your Own Ideas

One battery pack ,One throttle , One Speed Controller into Two Motor Driven to Wheel ..

Here is Deafscooter Draft this your Own Build Two wheel Drives by Front & Rear Motor.

Craig Uyeda
Deafscooter

One battery pack ,One throttle , One Speed Controller into Two Motor Driven to Wheel

If you go this route then you'll need to make sure that your controller's amp limit will support the load of two motors. Shouldn't be a problem - just something to consider. One controller is likely the best way to go - otherwise you should probably have some form of feedback between the two controllers - and then things would start to get really "interesting" (i.e. difficult) ...