Moco Rig 7 – March 2017

I wish I could say I have made a lot of progress recently, but sometimes thinking about what to do is the most important thing. I knew I had to come up with a better rotation bearing – a lazy susan – but couldn’t seem to get it right. Now I have a solution, so some visible progress should soon happen!

Basically, there will now be a 400mm diameter disc resting on 14mm stainless bearing balls, which are held in position with a simple cage, a flat disc with oversize holes that permit the balls to rotate easily but hold them in alignment. The disc will rotate on a central spindle. It will be held down by some bearings on brackets mounted around the perimeter. In order to have a flat surface for the balls to move on, I am using some polycarbonate that I have available. This is probably not the ideal plastic, being a bit soft, but it is what I have. So the change from the previous post is that I have eliminated the need for machining a groove, and have a better running surface.

Around the perimeter of the disc I will mount a flexible plastic gear strip (1.0 MOD) that will engage with the motor’s pinion, and should give nearly 180 degrees rotation in each direction. I have not been able to find (at a reasonable price) either large pulleys or gears that would do the job, but as long as the strip can be firmly attached, it should be fine.

On top of the disc (birch ply screwed to the polycarbonate running surface) the whole crane is mounted. This can now incorporate the support for the ballscrew that raises and lowers the arm, increasing rigidity and therefore accuracy.

Although I am pretty confident that this will stop the stiction problems, inevitably someone else seems to have come up with an even better solution. Edu Puertas has posted a YouTube video of improvements to his rig, in which he changed from a ballscrew for jib arm raising to a straight linear rack. This was because he was experiencing some side-to-side wobble caused by friction with the ballscrew mechanism. It seemed to me that it was amplified by his choice of attachment point, right at the camera end. My ballscrew not only is nearly upright, but is attached at only around 250mm from the fulcrum, so I think this may not be an issue for me.

But I won’t find out until it’s made, so here goes….

PS The ungeared stepper motors I tried last month just wouldn’t pull the load on the pan and tilt. Maybe it was down to me trying to move them too fast, not sure. So I have gone back to the geared ones, and just have to live with the backlash in the gearboxes. I need to improve the adjustability of the motor mount so I can get the closest possible meshing of the gears. Another little job!