I recently learned about ODrive and it is a very exciting project
I was wondering whether anyone had managed to build a large ball or lead screw based system with ODrive. I am wondering what kind of speeds can be reached, as possible speeds (up to 7500 rpm considering the AMT102 encoder) would require very large screws or very small distances not to exceed the critical speed of the screw.
I was considering retrofitting an OpenBuilds-based system with ODrive, but based on critical speed calculations, and considering:
A 8 mm lead screw
A critical speed of 10,000 rpm (7,500 rpm usable considering a security factor of 0.75)
The maximum length of a system going at maximum speed would be 45 cm (~18"), which is not as much as I would need. If I were to build a 36" system, I would need a lead screw with a 32 mm diameterā¦!
Does anyone have any advice and/or positive/negative experience with fast screw based systems? I do not have any experience building these systems so maybe this is just theoretical babble?
My robot uses linear ball screws with ODrives. SFU1204 ball screws and 5060 380KV motors from hobbyking at 24V currently. Works just fine. I always assumed the ODrive/Sensor/Motor were the limiting factors, I havenāt looked into the wear/max speed of the (linear) bearings. In my system the maximum speed is limited by the electrical switching frequency of the ODrive and the number of poles in my motor. I have set the encoders to low enough resolutions that they are not the limiting factor.
Also Iāve noticed that at high velocity a serious limiting factor is safety. You really need strong end stops, especially in the beginning, and you need to test the system quite extensively. The motors can be really strong, especially after they are geared down by the linear screw. My system has āunscrewedā itsself quite spectacularly a few times.
Thanks for the information! Were these spectacular unscrewing events at the highest speeds? Do you still use these speeds without the system unscrewing? Iām thinking that maybe they were due to your screw resonating.
What is the length of your screw? With this motor + screw, you could go up to 467mm before reaching critical speed.
When my actuators went through their endstops they were usually moving at full speed. I have reinforced my endstops with springs, to absord some energy before the endstop is actually hit. Since then they have managed to prevent any further unscrewing!
I havenāt seen any resonance yet, but definitely something to look out for. Iāve attached a render so you have a basic idea of how i have mounted my screws. At the both ends of the screw I have installed collars+springs.
