Nano/Tongxin motor "gearing" question.

[Andy Day]

These motors come in a range of speed options from the highest geared (I think) 160 rpm motors for 700c wheels to the lowest geared 260 rpm for the Brompton sized wheels (whatever they are).

Do the manufacturers, Tongxin actually make motors with differing internal mechanical ratios? I would find that very surprising, I would have thought it was more commercially viable to limit speed electronically within the controller.

 

[flecc]

I'm not sure of the answer to your question Andy, but the 260 rpm motor is for 20" wheels. The Brompton has 16" wheels and is therefore undergeared for the legal limit, having a maximum assist speed of 14 mph on a freshly charged battery, settling soon to more like 13 mph. Of course the upside to this is it's excellent hill climbing.
.

 

[frank9755]

Andy, Tongxin does in fact make 4 or 5 different speeds of motor. There is a 160 rpm which will give c15 mph in 700c wheels, to the 260, as you say, for small wheels. I believe the controller is the same regardless of motor speed.
Frank

 

[Jeremy]

To the best of my knowledge there are only two sensorless controllers, the 24V one and the 36V one. The latter has been subject to some modifications, I believe, as mine had a printed label giving a lower maximum current than it really has; the true 15A limit was written in biro on the label!

The motors come with different gear ratios depending on the intended wheel size. Mine is a 260rpm one, intended for use in 20" wheels.

I can't fault mine, it is light, quiet and pulls up hills very well. It doesn't give any significant assistance at my typical 20mph plus cruise speed (bear in mind this is on a 'bent, I'm most certainly not super-fit!), but comes into it's own on hills, where it performs extremely well indeed.

Jeremy

 

[john]

Do the manufacturers, Tongxin actually make motors with differing internal mechanical ratios?

My guess is that the different speeds are achieved by different windings, as Crystalyte do but until I can look at a different speed motor I cannot tell for sure. The three motors I have are rated around 260 rpm but actually run at different speeds. The gears are identical.

 

[Andy Day]

Ah yes, windings, that is the most likely solution. Model Airplane motors come with differing windings to give different RPM for the same applied voltage, the lower rpm per volt motors giving more torque and turning larger props at lower revs. Same as the Tongxin does for larger diameter wheels,

And the max speed must still be limited by the controller, but if the controllers are all the same it must be by current limiting, unless the controller has some complex algorithm to understand the motor it's connected to and set it's self up accordingly.

With regard to the rating of the controller, both I have had have been updated to 15A in biro! The latest replacement from Tony Castles, although he assures me it has differently spec'd components inside looks the same as the one that fried. Doesn't exactly fill one with confidence.

 

[john]

And the max speed must still be limited by the controller

The max speed is determined by the battery voltage (i.e. when the motor back EMF reaches this voltage), that's why you go faster when the battery is fresh.