Gas Gas TXT300 conversion

[down_under_builder]

Hi,

Been great reading and learning about all you builds. I have a TXT300 that did a gearbox on the weekend so am now looking into combinations to convert. Budget is reasonable and I have time and access to most tools I think I'll need to do the conversion.

To save on buying the wrong bits or those not suitable be great to get some advice. The following are my early thoughts on major components:

Motor: QS 138 V3 - I'm ok with no clutch on this one as I'm a very average rider lol and have kids electric trials bikes and they are plenty zappy enough.

Controller: Fardrive ND72530 - Could go bigger but trying to match to trials application, would like progressive regen braking and have seen conflicting reports if this is doable?

Throttle: Domino or Magura - Want high quality, really controllable low speed have read positive regarding both

Battery: A friend used Molicel 21700 P42A 4200mAh 45A in 16s6p but I'm wondering if 20s5or6p might be better with increased voltage?

Battery BMS: not sure of what to buy, want something that will support regen, quick charging and the required discharge rate to suit the motor.

Suggestions of suppliers also be great

Thanks

 

[amberwolf]

Throttle: Domino or Magura - Want high quality, really controllable low speed have read positive regarding both

That is more up to how the controller is setup to respond to the throttle, than the throttle itself. If it is an FOC controller it's usually already setup to be current (torque) controlled by the throttle. If it's not FOC, but still has the same throttle mode available, then that mode does the same basic job (if not necessarily as well as an FOC would; depends on the specific controller's firmware / hardware design in each case).

If the controller then also has adjustable throttle response curves, then you can setup controllability more finely; the more adjustable the more control over it you have.

A good smoothly operating throttle with more physical movement per electrical output amount will allow finer control, too, so the potentiometer throttles like Domino / Magura will generally have a better response than the average hall throttle would.

But you can get smooth response that is even a bit adjustable by using a cable-operated throttle, either hall or pot, if you don't mind the extra hardware and setup to do. (I use a COT for the thumb-controlled throttle on SB Cruiser, and also for the brake-lever-controlled variable regen, and I additionaly use the Grin Tech Cycle Analyst v3.x to match the output range of those to the input range of my controllers--if your controller has adjustable low and high voltages for throttle response then you wouldn't need that last device/feature, but it's handy when a controller doesn't have that).


(I don't have answers to your other questions)

 

[down_under_builder]

Thanks amberwolf makes sense.

I had thought about utilising the cable throttle then found the pot types that looked good. Best I can tell the domino has about 15deg less rotation between closed and open but otherwise does the same. Some people have been talking about getting best results where the controller was set up to linear response.

Today is first day starting the teardown on the gas bike so will get a better idea of room available. Also will order the motor/controller so that battery planning can actually start based on physical room. Weight is an issue, or at least trying to keep it down overall is.

Will post some pics of the donor bike

 

[amberwolf]

If you use a pot throttle (cable operated or direct), then if it is a linear pot and you use linear response in the controller, it will be entirely linear, the same amount of throttle movement anywhere in the physical movement range will give the same amount of change.

If the throttle uses a nonlinear (often a logarithmic response) pot and you use linear response in the controller, or vice-versa, then at one end of the throttle movement range it will have much less change in response than at the other. Which end that is depends on which end the more linear part of the curve is at. I recommend having that at the low end, the "off" end, rather than at the full end. I'd put the more-change-in-response-per-amount-of-movement at the farthest end of the throttle movement range (full throttle). Then you get good control at the low end, and quicker response as you engage the throttle more and more.