EDIT: here are some useful links for getting the basics of torque
for the readers (from reply #2)
for the watchers (starting at 3:20 he goes into the specifics of a practical torque calculation)
(Jeremy Fielding, highly recommend him, has some really beginner friendly videos)
Hello,
I'm working on a project where I'd like to use a stepper motor.
I've done some research to get an idea of the torque required and I've seen the following in the arduino forums:
Torque is how much you "weight" you can pick up by wrapping around a shaft. (the amount of Horsepower determines how fast you can move it).
Torque is Measured in "distance/weight" -- "inch/lbs" or "cm/kg" or "foot/lbs" or even "mile/tons" (but that is kind unrealistic, but theoretically possible) The metric world has a N/m or Newton/meters, but I've never felt it was practical.
Torque is a pretty straightforward equation: (think of a cable wrapping around a drum on a shaft)
Torque is [how far you are from the center of the shaft] divided by [how much you are trying to lift by rotation]
So if torque = 10 cm/kg, then you can pick up 10kg that 1cm away from the center of the shaft OR>>OR>OR>> 1kg that is 10cm from the center of the shaft OR>> any "math" that makes the equation true:
2kg that is 5cm away
3kg that is 3.33cm away
.01kg that is 1000cm awaysince the farther you get away from the center of the shaft, the "linear speed" increases, so (if HP stays constant) then the weight you can move must decrease
and also
A simple method to get a rough measurement of the required torque.
Attach some sort of wheel or drum to the shaft that the stepper motor will be required to turn. Wrap some strong thread or fine string around the drum and suspend a small plastic beaker from it. This will obviously only work if the shaft is horizontal.
Add coins to the beaker until the weight is just sufficient to make the drum rotate. Weigh the beaker with the coins in it.
Measure the diameter of the drum where the thread is wrapped and calculate the radius. Suppose the radius in 2cm and the weight is 100grams. Then the torque is 200gm-cm.
Repeat the measurement several times and take an average. Choose a motor with perhaps twice that amount of torque to provide a good safety margin.
I have a rough understanding that if the lever arm decreases, the weight can increase.
With this in mind it would be possible to select the correct torque required.
My question is, how do I calculate the torque available if I choose not to use a lever arm and just mount the project directly to the motor shaft?
The way I see it:
I'll take the 10cm/kg example.
It states that at 1cm I should be able to lift 10 kg, and torque is measured in distance/weight but this doesn't make sense if I use it as follows:
Known load to calculate torque required.
- A distance off 0.01 cm as I'm working directly from the shaft
- The load of let's say 50kg
Torque = distance/ mass = 0.01cm/50kg = 0.0002 cm/kg?
Known torque to calculate maximum load
- A distance off 0.01 cm as I'm working directly from the shaft
- The load of let's say 50kg
Torque = distance/ mass --> mass = distance / torque = 0.01 cm/ 10cm/kg = 0.001 kg ?
Both of the calculation results don't make sense to me hence why I'd like to call in the forum help.
I've been staring at the examples* and something tells me that it's really simple but I can't seem to grasp it.
2kg that is 5cm away
3kg that is 3.33cm away
.01kg that is 1000cm away
Thank you
rgds