12v ride on modification query?

Vr6woes · May 24, 2021

Hey, im attempting to further modify my kids 12v quad and need some advice.
I have swapped the original motors for a a pair of 65w 35000rpm 12 dc motors.
Originals were 45w 12000rpm.
Motors run and seem a lot quicker with the rear wheels off the ground however on the floor and under load have no power and just bog down.
Battery has already been upgraded from the poxy 7ah stock to a generator 12v battery, not ideal but it was free and has lasted nearly 2 years now.
It is 12v 30amp.
My questions are as follows.
Are the new motors demanding too much power from the battery thus the lack of power under load?
Are the motors too high a rpm and thus not torquey enough?

I have managed to fit another 12v 30amp battery at the front, Would running this in parallel with the original, Doubling the amps provid sufficient power or would wiring them in series going it 24v do the job?

Just want a few pointers on what the issue could be?

Thanks in advance,

Max

[ElectriciansForums.net] 12v ride on modification query?

Lucien Nunes · May 24, 2021

Are the motors too high a rpm and thus not torquey enough?

Probably. Power is proportional to speed x torque. If the numbers are to be believed, the new motors have (65/35000) / (45/12000) = 0.49 times the torque of the originals. With only half the torque you can only climb half the gradient or carry half the weight etc. The motor torque and speed are no longer matched to the load torque and speed because the gear ratio is incorrect for the new motors.

Adding more batteries in parallel will allow it to run for longer but won't increase the torque. Connecting them in series will likely destroy the controller.

Vr6woes · May 24, 2021

Lucien Nunes said:
Probably. Power is proportional to speed x torque. If the numbers are to be believed, the new motors have (65/35000) / (45/12000) = 0.49 times the torque of the originals. With only half the torque you can only climb half the gradient or carry half the weight etc. The motor torque and speed are no longer matched to the load torque and speed because the gear ratio is incorrect for the new motors.

Adding more batteries in parallel will allow it to run for longer but won't increase the torque. Connecting them in series will likely destroy the controller.

Thanks for replying, kind of what I feared.
I've heard that these things can handle 24v fairly well, would throwing double the volts improve the torque significantly or in your opinion are these motors just too far off?
Other options are stick with 24v and fit stock motors?
Stick with current motors and see what happens?
Source lower rpm motors, around 20k but with similar w.
Source higher rpm gearbox?

Soo many options lol, little boy just got a revvi electric bike for his birthday so now need to mod this so the daughter can keep up, lol.

Lucien Nunes · May 24, 2021

Speed is proportional to voltage, torque to current. By doubling the voltage you enable the motors to run faster, but add nothing to their rated torque. In reality you will get more torque but not much and only by overloading the motors.

Better to get a matched drivetrain. Full size vehicle makers optimise the gear ratios to the last percent to get the most out of an engine. Your ratio is currently half of what it should be. Imagine having a car permanently stuck in 5th gear, where you try to improve the acceleration from standstill by fitting a nitrous oxide system to the engine.

12v ride on modification query?

Vr6woes

Lucien Nunes

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Vr6woes

Lucien Nunes

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