I am seeking to collect data for my IB Physics IA (internal assessment). My question seeks to establish the relationship between speed and torque by adjusting gear ratios. (I am aware that gear ratios add mass and thus increase the stall torque and makes data less imprecise). I am using a Vex gear shaft, Vex motor, along with Vex gears and sprockets.
I am aware of the basics of torque: (Power = torque * angular velocity) and (Torque = Force * radius). Also, I am aware that: (Centripetal Force = Velocity squared * mass / radius).
I can easily calculate the tangential or angular velocity of the moving shaft, but need to measure the torque.
I have already researched possible methods for measuring that could do this:
- Torque sensor or gauge - Very expensive but is the most precise of the devices I have already researched. Will not buy, above $100.
- Stress gauge - Two problems: (1) it seems to be a device that will only work on shafts with large diameters - a Vex shaft is square with side length 3-4 mm. Would it even work?; (2) stress is very loosely relative to torque. It is cheap, however, is desirable if accurate.
- Torque wrench - In theory, you would use it until the shaft no longer moves and you can find the torque that way. It is harmful to the motor (and thus it would no longer be a consistent control). I am unable to find a small torque wrench - can anyone find one that is precise enough. This would, in theory, be cheap. Could I make my own and how? - if this is a good idea.
- Similiar to 3 - Resistance encoder. Not sure if these exist but might work well. Any thoughts?
- Add mass to the end of the shaft until it stops - With the centripetal force equation (or it slightly modified) I can calculate the necessary tangential force required to rotate the shaft (thus the torque by multiplying by radius). (Note: I am not certain that using the centripetal force equation would be correct - is there a better equation?). Cheap, but perhaps less accurate.
- Other ideas?
What would be the best method for measuring the torque of the shaft? As I am collecting data to analyze, accuracy is the highest preferred trait, although I do not want to spend a lot of money.
If necessary, I can use an Arduino to collect data from electronic devices.
Any help would be very appreciated. Thank you. Feel free to ask more specific questions.