I have a box of geared motors here, complete with encoders that i think could make a good robotic arm from, but how can i find out the torque of the output shaft. I have looked at some online calculators for robot arms, but they are more concerned with making sure you have enough torque to lift a desired mass rather than calculate the motor torque itself.
Thanks
A guy could guess all
A guy could guess all day…
generally the torque is often represented in grams or kilograms - cm…
So ,To get some idea ,probably the roughest means would .be to put a arm on the shaft ,and on that arm, 1cm from the center of the shaft ,drill a hole to hang a weight of it… apply your working voltage to the motor…when the motor can no longer rotate the load 90degrees left or right from the bottom …that your stall torque…what ever weight @ 1cm…
One you get a base line …a guy can figure out the amount of torque at 10cm or whatever…general rule of thumb would be to reduce your findings by 20% as you do not want the motors running at max …
be very careful pushing motors with plastic gears …they will split…trustme I know 
Its crude…but if you really need something…with no info what so ever …thats probably your best bet…
Ok, i will try that, it
Ok, i will try that, it sounds reasonable but i think i should put the weight on the end of a 1meter bar, as i have sofar been unable to stall the motor using an 18" breaker bar (for fitting wheels to a car?) attached to the output, i had to let go before it snapped my arm, lol.
Should i take into account the weight of the lever arm or will it be insignificant. I dont need exact figures, just something rough will do. Thanks for the help thus far.
You will have to take into
You will have to take into acount the weight of the arm…
by the sounds of it…torque dosent seem to be an issue.
to really throw you for a loop ,and to provide more accurate calculation’s …try and wrap your head around " load momment "
Thanks, i will look into
Thanks, i will look into torque moments, i knew i had lots of torque, but when you start extending arms a meter or so, the required torque goes exponential :o
first its maybe look online
first its maybe look online about the specs of the motor itself.
I know a fait bit about the
I know a fait bit about the motor, for example its a bosch motor, stalls at 38 amps, has built in temperature, step and direction signals. Its purpose is controlling torque through the transmission system of a 4x4 vehicle. I have an 8 page specsheet, but unfortunatly torque is not covered, but it does tell me how to interface with all the other signals. It also does not specify the gear ratio 
It is driven by a worm gear, an the overall weight of it is about 3kg including the gearbox. I will try and do some measurements tonight. I want to try building an arm with gripper that can actually be useful in the workshop.
