[Eric Strebel] uses a small homemade vehicle with his camera mounted on it to get great tracking shots for the intros to his videos. If the movement is slow enough then the effect is quite professional looking. But he wanted it eight times slower. We not only like the simple way he did it, along with how he machined parts for it, but the result makes it look like a hot rod, hence his name for it, the dolly hot rod. He also has an elegant mechanism for disengaging the motor while he repositions the dolly.
The are many ways to slow down a rotation. We’re assuming he was already at the minimum speed for the vehicle’s 8 RPM motor transmission and electronic speed controller. Gears or pulleys would probably be the next options. But [Eric] went even simpler, switching from roller blade wheels to larger diameter scooter wheels.
As simple as that sounds though, it led to that age-old conundrum, how to attach the wheels to the vehicle. The axle is made up of PVC tubes. So he machined square the ends of some PVC plugs and bolted the plugs to the wheel bearings. That left only to push the PVC plugs into the axle’s tubes. There are a number of ways he could have machined the PVC plugs, and the full explanation of the one he chose is best left to his video below. But basically, it involved first machining a Bondo body filler cylinder with a bolt embedded in it and then using the cylinder to hold onto the PVC plug while he machined that.
His solution for disengaging the motor is clever for its simplicity, made possible by the way the motor drives the wheel. The motor shaft simply applies pressure to the outer circumference of one of the wheels. Instead of fixing the motor permanently in place, he put it on a pivot so that it could be levered up, disengaging the shaft from contacting the wheel. At that point it’s easy to roll the dolly along by hand. Lowering the motor back down again reengages the shaft with the wheel. He uses a spring to keep the shaft pressing firmly on the wheel.
The result is smooth moving, professional looking footage.
We’ve seen a few variations of camera dollies here on Hackaday. That includes a sleek looking 3D printed one, and a programmable one great for doing time-lapse photography.