[brian_]

The speed values may be different because of small errors in one or both (due to tire rolling radius not being exactly as expected, for instance). The speeds will also be different whenever the bike is turning a corner - the front goes further than the rear unless the rear is slipping significantly.

I agree that for the purpose of a speedometer, just use one of the two speeds. Is there some other reason to reconcile the speed calculations?

 

[brian_]

My hunch is that is a bad design. A better (though probably still not ideal) design would be to have two motor controllers getting input from the same throttle, but having a bit of a translation to account for the difference in RPM to speed mapping. Even with cheap non-programmable motor controllers that will be easy to accomplish by having a microcontroller taking the throttle input, then splitting it into two outputs with slight amplitude adjustment for the smaller wheel.

I don't think there's any problem with the design. The "throttle" input is normally interpreted as a torque request; in any road vehicle it is not a speed request, so there's no conflict between front and rear controllers taking the same request, even though their rotational speeds are different (as they would be in nearly any motorcycle). You don't need a translation of the throttle signal because it is not related to speed.

I think cds3302's only issue is determining the actual speed of the vehicle, not controlling it.

 

[brian_]

The two wheels can't be turning at different speeds unless one is slipping.

Maybe try reading this again:

The speed values may be different because of small errors in one or both (due to tire rolling radius not being exactly as expected, for instance). The speeds will also be different whenever the bike is turning a corner - the front goes further than the rear unless the rear is slipping significantly.

The will be turning at different rotational speeds if they are not identically sized (and they're not in most motorcycles, and not in this case). They will be running at slightly different road speeds (which can be ignored for speedometer purposes) if turning a corner or if either driven wheel (two in this case, which is not normal for a motorcycle) is slipping.

On motorcycles, OEMs use the front (not the rear as suggested) wheel for the speedometer.

But in cars, OEM's use whatever wheels are driven for a mechanically driven speedometer, regardless of whether they are front or rear, although I'm sure there were some weird antique things with a speedo gear on a non-driven front hub and a long cable to the speedometer. The difference in speeds is negligible for the purpose of a speedometer. With all new cars now having ABS they have a speed sensor for each wheel, and it's anyone's guess what speed is used for display on the instrument panel.

 

[brian_]

^ Maybe you should reread - rotational rate is not rotational speed.

Yes it is: rate of position change is speed; the rotational rate of an engine or a motor is routinely referred to - correctly - as speed. Rotational rate or speed is of course not linear rate or speed.

We're also talking about motorcycles, not cars, in this topic.

True, which doesn't matter even slightly.

Averaging the two, as proposed, is unnecessary, given the mice-nuts difference...

One tire, of known circumference, and its rotational rate can be used to derive a speedometer. In a motorcycle, every one I've seen is off the front wheel - whether electronic or mechanical.

I agree.

In a motorcycle, every one I've seen is off the front wheel - whether electronic or mechanical.

Again, that may be true but it it unimportant. Every motorcycle I've seen is only rear-wheel-drive, and almost all have gas engines; neither of those apply to this motorcycle, and that's okay, so why insist on using the front wheel speed? It really doesn't matter.

Cars use the driven wheel speed because the transmission was traditionally the easiest place to hook up a gear to drive a mechanical speedo cable. I don't know why motorcycles traditionally use the front hub... perhaps because the speedo is traditionally mounted on top of the front forks. All completely irrelevant to this electric motorcycle and its determination of speed from electronic signals from drive motors (or controllers).