dustman said:
In the future I want to build a touring trike to travel long distances. The issue is overheating on long steep hills considering that the whole setup including my own weight would be in excess of 300lbs, a lot to ask from a single motor.
Not if it's the right motor for the load and situation.
As long as the motor is kept in it's efficient speed range under the given load, and it's capable of handling that load, it shouldn't have a problem with it.
When you have to go slow under the same load it was meant to run at normal speed, or use a motor that's not capable of the load, that's when the motor may rapidly overheat.
Thinking of the possibility of using an all wheel drive setup using 3 identical motors, the idea being that each individual motor would see 1/3 of the load of the single motor. AWD would also be useful for the demanding off road situations I will likely find myself in.
Note that it will also add to the weight, which adds to the power required to go up those hills, which decreases your range or requires a larger heavier battery to compensate (which also adds to the weight, and thus increases power requirements and decreases range).
A typical DD hub/controller combo might be 15 pounds or more, so you'd add at least 10% more weight to a 300lb trike by going 3WD vs 1WD.
It does add redundancy, and could add various traction capabilities if your terrain/etc requires those. I use 2WD on my SB Cruiser trike partly for redundancy, but also because when I started it I didn't have money for a single controller that could handle the power required to run it on just one motor; using two smaller ones was a lot cheaper then.
Can hub motors be mounted on the front spindles of trikes?
Some can, such as the Grin All Axle motor--see Ecat's Catrike thread for some good info about that (there are others around the forums as well).
How can I set up a single controller and throttle to drive all 3 motors in unison?
One throttle is easy (signal goes from it to all three controllers, but it only gets power and ground from one controller), but you still need three controllers, unless you're going with old brushed motors that can be seriesed or paralleled on the same controller.
Note that each controller/motor pair will respond slightly differently to the throttle input, even if they are "identical", so you may want to tune each controller to respond the same, if they are programmable enough (most aren't). Alternatley you can setup a potentiometer on the input of each controller's throttle signal line, to fine tune the proportion of throttle each motor gets of the full signal, which does a similar job.
Would an AWD setup be less efficient?
Yes, because you have more motor mass with three separate motors than with a single motor that's three times as powerful (and other losses that are spread among three controller / motor systems that you'd only have perhaps a third of that with just one).
You can play with the http://ebikes.ca/tools/simulator.html to see how some of this works; it has a way to do two motor systems on one bike at the same time, which you can compare to a single larger motor setup that can do the same job it takes two smaller motors to do under the same conditions.
Would it be effective to use fans to cool the motors while climbing hills?
If they're inside the motor, like CowardlyDuck did with his (he has a thread on Cooling Fans in Hubmotors), they could at least circulate air around the interior to move heat from the windings to the rest of the motor so it cools faster after heat spikes, and if you also open up the casing in the right way they can force external air thru to cool as well...but you are using extra power to cool the motors, which either decreases your range or requires a bigger battery; if you use a motor (or motors) designed for the load and situation / speed, you shouldn't need to do that.
Justin_LE has a good thread about Definitive Testing of Heating and Cooling of Hubmotors that goes into some experimental detail about various cooling methods, as do some other threads.
What other potential problems might arise with a setup like this?
With DD hubmotors, you can have failures that lock up the motor (in the motor, the wiring, or the controller), so with three you have a higher chance of this happening in general, mitigated by the load-spreading of having the three, as long as you don't *require* all three to take that load in the first place for the system to do what it needs to.
DD hubmotors also always have some drag when unpowered, so if you're not using all three all the time, you may want to set them up to always at least be powered just enough to cancel out their own drag when moving.
Also with DD's, if your downhills exceed the normal unloaded speed of the motor at your full battery voltage, they'll begin generating voltage higher than your battery is intended to charge to. Results of that vary depending on system, but if the BMS is a single-port (common port) type, and it turns itself off to prevent battery overcharge, that voltage will now, with no load to dampen it, be placed on your controller(s), and if the FETs / LVPS / etc inside them can't handle that, they'll fail, sometimes in a way that can suddenly short the motor phases together, which can create significant uncontrolled braking forces (higher at higher speeds due to higher voltages making higher currents), which might cause you to crash.
I'm sure there's other things but those are all failures that can happen in a system with even one DD hubmotor; they're just exacerbated by three.
