I have the screw machine “working” with the new 16MM screw that is more appropriate than the 20MM I was using before.
I decided to use a servo motor and gecko drive to increase speed and torque at high speeds. A servo motor should be able to accelerate faster and run faster as well as having high torque at high speeds as opposed to a stepper that has a much worse torque curve and difficulty accelerating fast.
In spite of the fact that the servo is supposed to be better in the above mentioned respects, I am having a very difficult time getting it to perform well. I think I am slowly figuring out how to get decent performance but it has been a long road of trial and error and guessing. It seems that the stepper motors drivers would just ignore impossible moves. With no feedback they would do the best they could and not get upset. Some steps might be missed in rapid accelerations. The servo has feedback from the shaft encoder and it goes into fault mode for 1 second each time the error count exceeds a set threshold. This is great for a milling machine or other machine where position is critical at every point. For a fucking machine, this just gets in the way of progress.
So I am experimenting with processing of the joystick encoder data before sending it to the motor driver. I have made significant progress but no to the point that the machine will accelerate as rapidly as I demand. If I could get a faster lead ballscrew I am sure the way it is working now would be adequate. I am not sure if these are easy to find. High lead screws are available but I am just not sure if this can be done in a ballscrew due to the way the balls need to recirculate.
I will keep working on the step pre-processing to get the best performance. It looks like the highest pitch for a 16MM ballscrew is 10MM which is twice the common standard of 5MM. Unfortunately it looks like they are only made by companies like Thompson and are very expensive.
My internet connection is very slow so I can not do a lot of searching. It would be great if somone with a better connection could research this matter. A low cost 16MM screw with a pitch of 10MM or greater would be ideal. There are higher pitch screws but only in much larger diameters. Also it might be possible to find a non ball nut type. I have one that is very fast but it is only 12 MM or maybe even smaller and would probably not last very long. I can experiment with it if it turns out that my step processing alone can not produce fast enough acceleration.