# Torque-speed-power charts

Hi Everyone,

I’ve been looking at VEX 393 Motor torque-speed-power charts, which show Speed (rpm) and Current (A) on the two Y axes, and Torque on the X axis. It graphically shows that the 393 runs most efficiently (100%) at 50-rpm and a corresponding Torque of 6.75-lb in. It also shows a current draw of 1.875-amps at the aforementioned Speed & Torque. It shows the corresponding Power output at the motor, and the input power from the battery as well. Most question is - do all the values come from measuring with instrumentation? Or are some variables (like Speed) measured and other simply calculated based on some info that VEX gives on these motors? For example, the VEX 393 has an optimal Watt rating of 3.98-W (roughly). Was this used to extrapolate other values in some way? Or are these curves completely built from measured data? Or is some of the data collected and the other data calculated from knowns?

These graphs

https://vexforum.com/index.php/attachment/56464d7f91a13_torque_speed_393.jpg
are all based on the numbers that VEX publishes, they have been backed up by some physical measurements.

edit: actually free current was modified from the VEX published number based on measurements that were made.

Hi
I have set up a winch to a 393 and am measuring the stall torque. If the stall torque published for the 393 is 1.67Nm and my winch has a radius of 1.25", then should the weight that will stall the motor be:

Torque = F * D
D= 1.25" = 0.032-m
Torque = 1.67 Nm
F = 1.67-Nm / 0.032-m
F = 52-N = 11.6-lbs

So theoretically speaking I should be able to suspend a 10-lb weight from the winch and the 383 could raise it correct? Assuming I’m supplying 7.2-Volts and approximately 5-amps.

The problem is that my motor driven winch won’t lift this weight at the 7.2-Volts.

If the radius is 1.25", then your divisor on line 4 is wrong (diameter is 2.5")