) I did not understand this and that gave me the idea to use the info that was listed online provide by Vex. When I inputted that info into the equation, I was given a much different stall torque then what is listed online. That brings me to my question. How does VEX find the stall torque of a motor? And what is the tolerance?
The equation that I have been using for the test is:
T=(5252Hp)/rpm
Hp=(AmpsV)/745.7
Using the info given online this will give a torque of 2.43ft-lbs or 29.16in-lbs. This is not the 14.76in-lbs listed
So I assume what you tried was something like.
Hp=(4.8 * 7.2) / 745.7 = 0.0463Hp
T = (52520.0463)/100 = 2.43 (which really should be T=(52520.0463)/0 = INF, rpm is 0 when stalled).
or perhaps at half speed.
Hp=(2.4 * 7.2) / 745.7 = 0.0232Hp
T = (5252*0.0232)/50 = 2.43
You cannot do the calculations that way, it completely ignores motor efficiency.
Instead of writing a long explanation of how to measure motor torque, have a read of this.
Thanks for the info. So I just finished asking in the official post, is there another equation that I could use to find the torque, or am I limited to the one with the scale
One way that’s been used before is to measure motor speed as a number of known weights are raised using a fixed diameter pulley. Motor speed is usually measured using a quadrature encoder, the number of counts in a given time interval can be used to calculate speed.
For example, a 1lb weight is attached to a string would around a VEX wheel with a radius of 2 inches. The torque created by this would be 2 in-lbs. The motor speed is measured when lifting this weight and found to be 85rpm. The test is repeated with a 2lb weight (torque created by this is 4 in-lbs), speed measured is 72 rpm. more measurements are made, however, by the time a 5lb weight is used the motor will not run for long enough as the internal thermal fuse (the infamous PTC) trips before any measurements can be made. If this data is plotted then the stall torque can be extrapolated.
This “sort of” works but there are some problems. I mentioned the PTC protection device inside the motor, as tests are performed this will heat up and create increased resistance in series with the motor, this reduces the total current and therefore reduces torque which then reduces motor speed. You will probably find measurements do not fall on a completely straight line as the theory would suggest.
The best way to do this is with a dynamometer and the PTC removed from the motor (an illegal modification with safety implications so don’t actually do this).