Rpm Vs Torque

[dw5555]

Let me start this by saying that I realize that without proper testing equipment this will be difficult to answer so I guess your thoughts are in order.

If you have 2 identical motors but 1 motor spins 3K higher in rpm, does the torque necessarily increase with the higher rpm motor?

[chrisguyw]

No,.............In 2 identical motors, if one spins quicker it could be that it has a straighter motor shaft, the bushings are aligned better, the armature has better balance, , it has a bit more advanced timing of the commutator, or, the brush springs/brushes have more/less tension on the comm., so there are many variables to how fast identical motors spin...........torque is however, unrelated to how fast an armature spins, and it does not change just because one motor revs a bit more.

Torque is a function of......the # of turns, and the gauge of the wire, the magnet strength and air gap from the magnet face to the armature stack. Commutator advance does have an affect on torque, but, on the motors commonly used for 1/32 plastic car racing there is no timing on the comm.

There are several other little design details on higher end motors (commercial) that affect motor performance......the number of laminations and their shape and size, stack length and diameter, etc etc but, again on the motors commonly used by the folks on this forum, these factors are do not apply.

Cheers
Chris Walker

[Brumos RSR]

Chris, also if I remember peak torque is also at 0 RPM with most motors. So is it safe to say a motor can accelerate as fast or faster if it produces more torque and turns 3000 RPM less?

[chrisguyw]

Hi Tony, The answer is yes..........bear in mind that we are talking about the motor by itself,....gear ratio and the rear tire diameter significantly affect the performance of the car and are used to compensate for the motor's characteristics.......eg. a 20K FK180 motor, with its long stack and long magnets (lots of torque) can typically be geared in the 2:5 to 1 range, while a 30K "S" can motor, with smaller less powerful magnets, and a shorter stack ,will typically be geared in the 3:5 to range, yet both will exhibit similar acceleration.

Cheers
Chris Walker