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Posted (edited)

I think the current XL motor already has way too much torque. We need one that's really fast but not much torque, like the motors from the control centre sets 8049 and 8485 but with a bit more power for the sake of prgress!

Edited by allanp
Posted

Yes, the XL motor has enough torque.

What is needed is to provide that same torque at between 5 and 10 times the speed: 1000-2000rpm.

That way, speeding up by x3 or x5 gives enough torque for a propeller.

Reducing by /3 or /5 provides high torque with enough speed for a ground vehicle.

I have used 4x 4000rpm motors with a dual contra-rotating rotor system. It takes a total of 1.3 Amps but needs more speed, maybe 3x as I was aiming for 7000rpm input. A 135W drill didn't work as it melted the axle!

RC Car and plane motors use up to 40 Amps at 7.4V (car or 11.1V (aircraft) using the latest LiPo packs.

One snag is that RC car and plane motors are usually rated in turns (maybe 17 to 27 turns), not in real units like torque.

40 Amps is a bit much for LEGO models but I'd go with 5 Amps at 9.0 Volts to get 40Ncm of torque at 2000rpm. That's 45 Watts, 1/3 of the drill power nut 3x the 1.7A stall current of an XL motor. It might need a bit more current than 5 Amps to get both torque and speed.

Other electrical things I would like, to complement motor speed and torque:

11.1V LiPo and PWM controller to give 9.0V output instead of the measly 7.4V from the LiPo, which is half the power.

Slave motor drivers (1-5 Amps output) to overcome the motor driver current limit of 400mA per channel.

128-channel control, either IR or radio.

If it needs the voltage to rise in order to get the power without excessive current (and thicker wires), to 14.8V or 18.5V then that's OK, as long as kids would be safe to use it. The limit is usually 30 or 36VDC for safety but perhaps toy regulations are tighter than that. 11.1V is also a widely used standard for laptops and RC models so that might be cheaper - it has to be commercially sound. Unfortunately the AFOL market is comparatively small. Perhaps it should be like third party NXT sensors, where AFOLs could get TLG sponsorship with the cases and make the internals themselves?

Mark

  • 4 weeks later...

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