At long last I have finally got my moco rig working, thanks to a busy weekend with Roos Mattaar. It's a 6 axis rig with a crane arm and a 1.5m track. Connecting everything up has been quite a challenge, and I probably will be modifying some of the gears to improve performance.

But the ArcMoco interface with Dragonframe is excellent. We managed to produce a couple of moves, which have exciting potential. These are just the rough videos made from the live view, not proper shots, and we just slung some scenery and props in there to point the camera at not to create a particular scene.

http://www.youtube.com/watch?v=EjBSb_7-uUo

http://www.youtube.com/watch?v=cNsCpiBA7ok

We had to forego the focus control, as the driver was playing up and I managed to fry one (don't buy the Chinese copies!), and the tilt also took a holiday. Severe backlash from the rotation, which will be addressed somehow. Any suggestions gratefully received.

The track operates with a ballscrew, a bit slow but very positive. Rotation is via 25:125 gears. Crane uses belt drive, which seems good once tensioned. Pan and tilt are 25:100 gears and focus uses a 40 tooth gear onto a flexible 0.8mod gear ring.

But the great news is, after all this time it works!

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I'm curious to know more about your keyframe problem. I have an understanding of mo-co gear, and programming with the dragonframe interface. It's simple enough to program an arc into the speed of a move - to ease in and out smoothly with the bezier handles - so I assume you mean you're having trouble programming an arc through physical space? Are you seeing the weird acceleration changes on the velocity graph in the ARC window before you run the move?

Hi Evan Thanks for your reply. 

It's unfamiliarity with creating a move using several different motors. After a couple of tries it is already improving by shifting keyframes around. But perhaps you could explain how one might programme in a complex move? Do you set the start and end points first, then create a mid-point to pull an arc, or do you go sequentially through the move and set keyframes as you go?

I think the weird acceleration changes were due to the program putting in eases before and after each keyframe. To be honest, we did not set up those first couple of shots with the greatest care! I did see the changes in the velocity graph, but did not do anything about them. Can you suggest an approach for smoothing them out?

Thanks in advance. Any tips greatly appreciated!

The key to a smooth move, as far as I've figured out, is minimal keyframes. Each axis should really only have 2 keyframes, one at the start and end of the move. There would only be another keyframe needed if the axis changes direction at some point, or if the move pauses in the middle.

My advice would be: set the start and end keyframes (as smooth bezier keyframes) for all axis', then instead of adding more keyframes in the middle, adjust the bezier handles until the camera is looking where you want in the middle of the move. Move the playhead inbetween your 2 keyframes, then click the blue "send to playhead" button to send the machine to the middle of the move. If the middle of the move is off, adjust the beziers, then "send to playhead" again until it's corrected. There's some blind calculation needed for this- if you're in the middle, and the camera is tilted too low (for eg.), you would adjust the beziers on your tilt axis to either speed up or delay the tilt move. Your rig won't move when you adjust the beziers, so you need to adjust a little, send to playhead, see if it's right, keep adjusting. If you're dragging out the beziers too far in order to delay a move, you might try moving the actual keyframe in time, offsetting it a little from your other axis'.

Hope that makes sense. Please post more tests as you go- really cool to see the rig in action.

That's great advice. Thank you. It will save a load of frustration, as I was trying to put keyframes in at every significant change of movement, and it was just getting worse. Then we took all of them out, and the rig moves the shortest distance between start and end! I haven't yet made use of the blue playhead button, but that looks like being really useful.

I've just received some new drivers, so will post further tests once I've got them installed and working.

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