AotPR part 6 - My God, I've created a monster!

It's alive!

The last few months of 2006 were really busy, with a whole series of projects ending at the same time, so although I'd managed to eke out some time to work on the motorised head, I'd not found the time or energy to write it up. :-(

Anyway, the head is semi-finished with all movements working and the programming side coming along. It's not been tested outside as the weather here in SW England has been appalling recently. And I was away on holiday in Madeira the week before Christmas, precisely to get away from the drizzle (insert smug grin).

Machine Shop

For several years I worked part-time for the University of Plymouth in the Faculty of Art & Design. I still have a lot of contact with the staff there, so was able to get access to the machine shop and do some of the more heavy duty machining. Which was handy, because I really don't have room for a power hacksaw or big pillar drill in my home office.

Power hacksaw, cutting the aluminium profile with a nice right-angle cut.

One of the large pulleys, clamped down under the pillar drill.

In comparison, a mini-vice and hand hacksaw at home.

Tasks done in the machine shop:

• Cut all the sections of alu frame to size, with 60x20mm profile used for the main U-frame and 40x20mm profile used for the inner rotating frame.
• Drill mounting holes in the pulley for the vertical movement, so that it can be bolted onto the side of the inner 'camera mount' frame.
• Drill out extra holes in both the large pulleys to reduce weight, currently unfinished.
• Drill holes in the inner frame sides and in the main uprights for the inner frame pivots.

Then, when I got home with a pile of roughly cut profile, it was time to dig out a file and make it all smooth enough to handle safely...

Construction

Overall construction, showing the outer frame plus the inner frame which holds the camera and rotates.

After a few false starts, I managed to get everything together, paying particular attention to getting what seemed about the right tension on the toothed belts. Everything is held together using hex bolts and t-slot nuts, so it's all adjustable.

View from overhead, with Canon 5D plus 70-200mm f4L lens.

In this photo the camera mounting arm coming out of the inner frame was a bit cobbled together, I've since replaced it with a macro focusing slide and quick release plate. The version you see here could point directly up as the camera mounting screw would have hit the belt!

Horizontal mount, with pulley, belt and roller bearing.

This arrangement is working OK for now, but having the roller bearing open to the elements is going to be a recipe for disaster in the long run. It's brass and stainless steel, so corrosion/rusting isn't really an issue, but dust getting between the surfaces would be a bad thing...

Viewed from the other side, showing the motor and geartrain.

The horizontal axis isn't geared down very much as it doesn't need to lift the weight of the camera. There's a bit more play in this axis than I would like, but there's enough resistance from the tension of the belt that it doesn't actually wobble.

The complete geartrain for the vertical axis.

LOTS of gearing down, this could easily cope with a heavier camera. If in doubt, over-engineer it.

Top pulley for the vertical movement.

In the top right of the photo you can see the head of one of the bolts clamping the pulley to the inner frame. The arm sticking out towards the lower left was for mounting the camera on, so that the lens is held in the correct position for the no-parallax point.

Mounting details for the vertical geartrain.

At the far end there are bolts going through the LEGO bars, then parallel to the belt pulley there are bolts sitting 'above' the rod, opposing the pull of the belt. This allows me to make crude adjustments to the tension of the belt by changing the position of the bolts.

Finally, the thing in action:

Click to see video.

To Do List

• Get outside and test it.
• Get a new enough mobile phone to run the Mindstorms control software.
• Dig into the Bluetooth protocol stuff so that the laptop can communicate directly with programs on the LEGO brick. This will allow a control program on the laptop to control the position etc. and build a rough PTGui project while shooting.

Ian