So i want to build a robotic arm using stepper motors with harmonic drive to increase their torque.
For design reasons i also need to put belt and pulleys to link motors to joints.
Should i put the harmonic drive before the belt/pulley to the joint or after ?
In fact, harmonic drives have no or very less backslash but the pulley might add some if it's after the drive to the joint. Another problem might be that the harmonic drive delivers a high torque so the pulley might not resist long if it's after the drive.
So puting the drive after the pulley might be the option but is it the usual way tot go ? (As harmonic drives are beter suited to be just after the motor)
Google showed me that "harmonic drive" Is a product name. It is also a gearing system. The OP needs to be clear in what they want to use in their project, not just pick out interesting names. I wonder if the OP actually has one in mind that fits their project.
Have you actually used a harmonic gear drive? Actually, a direct drive servo is the best for a robotic arm. Next best would be a stepper motor and worm/gear drive. Do you have an arm that has proper bearings for the joints?
Bearings to support the weight and the movement. Your harmonic drive does not include either thrust bearings nor radial bearings, so what bearing are you using for your arm joints? Have you computed the weight that your joints will have to support?
How do you know that my harmonic drive does not include either thrust bearings nor radial bearings ? It looks like radial bearing.
At first glance, i will use the same bearings as the ones for the harmonic drive :
Also, how do you determine the exact distance between the motor axle and the pulley so that the belt is correctly stretched.
How do people usually do ? Do they permit the motor to slide before fixing it to adjust the belt tension ?
There is no exact distance since the temperature of the belt and other components will change along with the temperature. To allow for that the usual scheme is an idler pulley on a pivot with a spring to force the idler to keep the belt at the right tension. If the motor is moved to a new position, temperature will still make the belt length get shorter or longer.
My build is a home-made little robot arm, i don't think the temperature will really have a significant impact here, everything will be at around ambiant temp 25°C except de motor core which can rise at 50°C. But even that will not have an impact on the general structure which is made out of PMMA.
Also, here are my belts : (makeblock belt on google)
I will build my pulley like the image at the bottom left of my last message. There's no idler pulley in this case, how do i make the belt correctly stretch?
No, i rely on the fact that the maximum torque that the motors can handle will be larger enough than the maximum torque released on each joints by the load at the end of the arm (taking the reductor from the different pulley size on each side of the belt into account).
So that the stepper motors will not skip any step so i know at any time the angles of the joints.
I'll be making a sync at each starting of the robot with limit switches on each joints to initialize the position of the arm.
If the torque of my motors isn't enough, i'll switch to harmonic drives, which are commonly used in robot arm's joints to significantly increase motor's torque while being relatively compact and no backslash.
