S28-400 Mag Motor Torque/Speed/current draw Graph

19th August 2009, 12:59

I cant find any explicit data/graphs for the S28-400 magmotor, apart from some info on the robotbooks website, where it states the stall torque and max RPM, but there is no real correlation between the two.

Does anyone posses a Torque/Speed/current draw Graph for the S28-400? Or know where i can find one? Have emailed the manufacturer a while back but no reply

**terrorhurtz** · 19th August 2009, 17:15

Stall torque (and current) and peak (no load) RPM tell the whole story of the performance characteristics of PM DC motors.
The torque output of, and the current drawn by, the motor vary linearly with speed - maximum at stall (zero revs), minimum at peak revs.
Therefore peak output power is at half peak revs.
Note that the stall current given is assuming a perfect voltage source. You may want to take into account the resistance of your batteries to get a more realistic output torque. In heavyweight robots, the resistance of the batteries is quite often at least as much as that of the motor (particularly with high-power motors like the S28-400), so will half the stall current and torque.
See http://howto.killerhurtz.co.uk/boschspec.gif for a typical motor graph.

19th August 2009, 20:45

Cheers for the reply, valid points. I undertand the relationships, but i need to find out 2 points of the torpue speed curve in order to know the gradient. The problem i have is that the magmotor info i have only tells you the stall torque and max rpm independently. If that makes sense? Or have i got the wrong end of the stick?