MOTION RIG PROTOTYPE : DOLLY CART & TRACK

Marchand and Paul - with the support of Greg and Tarren from Festo Cape Town - have built and tested a motion control rig prototype (dolly cart & track) to be used for time-lapse photographic movies.

The prototype is composed of a dolly cart built with 6 mm aluminium plates and a series of 3.3 m long double rail aluminum tracks. We are using 6 lengths (almost 20 m) at the moment, that are easily joined together with 2 bolts & butterfly nuts.

Each track is mounted at about 1-m height from ground level on 6 telescopic aluminium poles and tighten with 6 nylon strings and pegs plus 2 at each end of the whole track. The reason for this is to compensate irregularities on the ground. However, when the ground is very flat and smooth, the whole track can simply be put at ground level and fixed with mini pegs.

The dolly cart contains 2 Festo MTR-DC1 intelligent servo motors which are responsible for the linear and rotary movements. It is our intention to add a tilt movement in the near future.

The first motor drives a belt that turns the 2 axles. Dolly is now a 4x2 with only 2 driving wheels on the side of the belt. We found indeed that floating wheels on the other side were giving better result in term of linearity. The precision is 1 mm on the track.

We have recently added a mechanism to control the linearity of the movement along the track. It includes 2 mini bearings fixed on the side of the dolly cart and 2 other bearings mounted on a spring-loaded pivoting arm that slide along the outside of the rail.

The second motor gears the rotary plate which has a precision of 1/100 of a degre.

A Festo FC20 PLC controls the 2 movements as well as the triggering of the camera (focus and release), and can also trigger multiple exposures at each step (mirror-up & HDR).

A Nikon D2X or D700 digital camera is fixed on a video tripod head on top of the rotary plate.