I decided to build a cable cam. Not the type that you swing on, but a cheapy version that the camera just sits on.
Got some 3mm steel wire. 50m for £30

The went to the model shop and bought a radio control two servers and a speed controller and a motor for £60.

A couple of DMR chain device rollers.

Then scavenged some old aluminium from the skip for £0.00

I thought for the prototype I would just have a fixed camera position have a variable speed along the wire.
I tried it at the local trails, but the camera doesn’t travel fast enough to keep up with the bikes. I’ve got a bigger motor and some gearing on the way for Mark II.
Mark III may have some pan/tilt too.
I’ll post up a vid soon.