[MovieM8ker]

Hi everyone I am a filmmaker building a motorized dolly platform and I am trying to learn many things all at once, but in the process I need a little help with what I hope is basic physics.

My current idea is to build a 20-40 ft conveyor belt type loop of a chain type material (as in chain and sprocket). Above which will travel a Camera dolly ridding on a train track type rail system. They Chain will loop around a free rotating sprocket on one end and a motorized sprocket on the other. The top of the chain will be attached to the dolly platform and I will run a motor with an appropriately sized sprocket to move the dolly platform forward and backwards along the distance.

What I know:
The current camera system and (dollying) material will weigh approximately 29.4lbs or 470.4 oz. - in the future I will want it to be able to carry 75-100 lbs.

At its slowest speed I want it to move at about 22 in/sec and at its fastest about 86 in/sec

Ideally the rig will be smooth enough that I can accelerate the move from stand still to targeted velocity and not appear jerky, as well as slow it down to a stop at any point along the move. I'm not sure how to determine what the acceleration should be, but I recorded a dolly move on camera and timed how long it took to get to speed, with my best guess it took 1.567 seconds to get up to 25.87 in/sec.

I am under the impression that I will attach a sprocket directly to the motor, to drive the chain using a computer controlled Pulse Width Modulated DC gear motor. I have not ruled out additionally gearing down the DC gear motor to turn a larger gear if that is what is needed to achieve the proper power/speed balance. I am anticipating that the sprocket that turns the chain would be 2-3 inches in effective diameter.

Hub Mount Sprockets (.250)

I am looking at a gear motor that has a rating of Maximum Torque 624* oz-in. (Stall) with an RPM of 10

10 RPM Gear Motor

As there are so many choices out there, I was hoping to gain an understanding of what range of motor strength I will need to answer future questions I might come up with. As well as the formulas so I could figure this out on my own as I change and update the design.

And with all of this, if anyone has a better drive train type suggestion for moving this rig, I would welcome recommendations.

For big picture this is just one part of what will hopefully be a computer controlled rig that can perform a camera move live with the parameters of (dolly, pan, tilt, rotate, zoom, focus) and then be replayed numerous times for different purposes.

From its initial start point, all the motor signals will be recorded in time to when they were sent and then be played back to control the rig performing the move in subsequent passes. Ideally the whole rig could be moved, reassembled and the move could be replayed correctly at a future time, in effect creating a poor man’s DIY motion control system.

Thanks you so much for your future help answering these questions, I look forward to your responses.
A link to my first test with a rotating rig can be seen here:
YouTube - Many Jons

[ebaines]

One thing to consider is that the motor you are considering is way under-powered. If it provides 624 oz-in of torque at 10 RPM, that's equivalent to 3.25 ft-lb of torque, which at 10 RPM means it puts out about 0.00165 HP. That's an itty bitty motor! By way of comparison - a typical motor for a garage door opener, which moves a similar amount of weight as your dolly at similar speeds, is typically 1/3 HP or more. For your dolly to operate smoothy you probably want even more power than that.