Dirtys 2nd 6DOF - AASD - M4S Controller - SFS1620

hi @Dirty, did you do your actuators with 70mm rods on your rebuild and if you did, how did it go. I am a newbie here and will be starting my build or purchase as soon as I have learnt enough to start ordering parts. My main aim is to make low noise actuators and your 2020 ball screws idea should help with that. I also at this time intend to build using plastic pressure pipe for the actuator housing and push rod with the sole aim of reducing noise. In addition to that I am trying to think of ways of isolating the ball screw, which if I have understood correctly is the main source of noise, from all of the other component parts. Any help appreciated and of course whatever I eventually do I will share with the community.

I love your actuator build. Its what i have in mind for my extreme version after my initial version works haha

Your explanation of various solutions for the linear actuator was extremely helpful. I am still struggling with one piece and haven't found solution if you (or anybody on this forum) can advise:

How to stabilize the ballnut in the shaft. Ballnut needs to be moving up and down without rotating when ballscrew rotates. I understand there has to be some kind of "rail" that prevents the ballnut from rotating while allowing it to slide up and down and have seen few commercial examples but nothing DIY friendly).

Is there a documentation anywhere how it's done?

Thank you.

P.S. I have seen standard SFX150 design which works with 80/20 but I am using a square tube, same as in this design from @Dirty

Yes, the ball nut needs to be freely moving in the linear direction while being locked in the angular direction. So something has to take the reaction force of the motor turning the screw. There are two possibilities:

1. Use a square tube and some sort of slider that moves linearly inside the tube but blocks rotary movement. In this case you can use simple ball joints to attach the pushrod to the rig as all torque is handled internally.
2. Use a round tube (like @Dirty did) and ommit the anti-torque feature (at least internally). In this case there has to be a U-joint at the end of the pushrod that can take the torque and stop the nut from rotating.

Solution #2 introduces a small error as the Pushrod and the nut will rotate a little bit when the rig moves around the yaw axis. You could theoretically compensate that error by mixing yaw into the position formulas of all actuators (I think, FlyPT Mover could do that). But in practice this is not really necessary. 20° of yaw will translate to ~1mm heave error with 20mm pitch screws. You won't feel that.

Thank you, @Aerosmith.

I understand the theoretical concept, but what would be the practical implementation of either 1 or 2? Pictures or description with parts used, etc. I have seen commercial implementation on an actuator, it was very well done but not suitable for DIY. It was using Igus bearings and some proprietary parts.

Also, @Dirty has description of the ball-nut housing but what would be acceptable print material for it? I would imagine PETG would wear out within the first hour and then that ball-nut housing will be banging against the outer square tube?