Has anyone tried having a dual motor board where each wheel has different gear ratios. Where one motor is geared for torque while the other it’s geared for top end. Could this broaden the acceleration curve of a dual motor board?
yes. many people have. most notable is @lowGuido well actually, @lowGuido used 2 different kV’s. would accomplish the same thing as what you’re talking about. think the biggest problem with different gear ratios is that when going full speed, one motor would just become a generator and all it would do is increase drag.
nice enough @Sender? was tempted to just say use the search button
I wouldn’t do it. The “trick” behind this is that you use one of your two motors in an operation mode that has high power output but a crappy efficiency. The motor will get hot, and you waste a hughe amout of energy. The max speed of your board shoud be ~90% of the no load speed. Then you have the highest torque and the highest efficiency. If your board can’t reach the theoretical speed, your problem is too little power, not too low KV. Get a bigger motor, or more motors.
What about using a hub gear from a bike? Has anyone tried that?
I think it would be cool to run a 170kv 16/40 and 190kv 16/36 or any other differing kv/gearing.
If the firmware would take it into account it could be a viable option for more versatility and efficiency…
I don’t believe that you can increase efficiency. As I said. The maximum efficiency is at KV as low as possible. The closer BOTH of your motors run to the 90% of the no load speed (before the efficiency drops again) the better. There is an optimum for a certain max speed. Having one motor to higher: you lose (too high torque load). Having one motor lower: even worse! You have NEGATIVE power output from that one…
But the firmware can transfer power from one to the other, when it becomes more efficient and the other not so much, you see? I understand the problem you are outlining, I’m proposing the firmware solve it dynamically…
What problem? My point is that the highes torque and the highest efficiency is bot there for the lowest possible KV. Adding one motor with higher KV both is worse. Nothing to gain there except for output power at crappy efficiency. “Transferring” the power from one motor running above no load speed happens automatically but is also nothing you can gain from. In best case if you had 100% efficiency you lose nothing, but that’s not the case. I don’t see how there’s anything to gain here.
You need a motor that delivers enough power at low torque load. Uneven drive is a workaround for motors that are operating beyond their capabilities.
I’ve done it. Like @GrecoMan says, at high speed, one just acts as a generator and slows the other one down. So it doesn’t really work as intended, not to mention you risk blowing your vesc by forcing the lower geared one over the ERPM limit.
That’s not to say it doesn’t “work”. My gearing was set-up 13/36 on one motor and 16/36 on the other motor. The theoretical top speed when using only 13/36 gearing was 32 mph. I was able to achieve 35 mph using on 13T and one 16T gear. So in that sense it works.
However, due to the generator effect, the board could barely reach 35mph and took forever to get there, making the improved top speed essentially useless unless you’re drag racing on an airstrip. Basically it doesn’t really make sense, because you never use the top speed and risk damaging your electronics/motors
Why not run a one-way bearing on the lower rated motor?
I suppose you could, although then you wouldn’t get the braking benefit of both motors. although then you’d have to figure out a way to mount the bearing within the motor pulley, which could get complex
I have a chain drive with freewheels…done…lol
Although there are no conclusive results, some think that uneven drive is actually quicker than same geared. Some people prefer a high kv high gear ratio because it’s sort of like a “running” start, the motor is already turning quickly. And then the lowest kv motor provides the torque needed. All of this is discussed in the threads linked above
This. If you adjust the firmware to turn off one motor when it becomes inefficient then everything should be fine. Hope you know calculus and C99
I don’t know that you can just “turn off” a motor. Maybe open all the FETs on the Vesc so the phase wires are all open-circuit, but the motor is till going to turn and generate a back EMF. And there’s a good chance that the back EMF will eventually build up to the point where it’ll jump and potentially short out the VESC.
This is part of the reason why you shouldn’t push-ride or down-hill with the board turned off.
If that was the case, you could spin the motor with the wires unhooked and if you spun it long enough, the wires would arc through the air
I think the main reason for that is because MOSFETs typically have a lower Gate-to-Source voltage limit than they do for Drain-to-Source. But I could be wrong.
Opening the FETs is exactly what I meant when I said “turn off”
I think it is the case that the voltage will arc eventually. However the air acts as a dielectric, and it takes a lot of voltage for it to experience dielectric breakdown, somewhere like 1 million volts/meter. So until that happens, basically now current flows, since the resistance is too high. Also, it would be basically impossible to generate 1 million volts/meter by spinning the motor. But if a certain component on the vesc has a lower dielectric breakdown, like PCB might (I’m not really sure if it does or not), you could risk shorting it.
I don’t think it does that