Building a fast moving camera dolly (not for timelapse)

Community General Discussions
1

HI there!
We are in the process of building a RC motorized dolly which will be use this summer. I found this video while I was searching the web which shows exactly what we want to build. vimeo.com/32925345

We have no problem building the frame and tracks but when it comes to motorized it, it’s another story… :rolleyes:

I tried to use the tools on the website to find the right motor but it doesn’t seems to work on my computer.

Our dolly will need to run back and forth on the track (straight and flat) at max speed of 20mph but for an average speed of about 10mph. The total weight of the dolly including the frame, camera, batteries, wheels, etc. will be max 20 pounds. I did not chose the wheels yet but they will have a radius of about 1 inch.

Also, we will need an other motor to add panning (no tilt) for the camera. We need to pan the camera both ways for unlimited rotation.

Both dolly and pan needs to be control by the same remote

One other thing we are wondering is battery life. I we can achieve this speed with that amount of weight, how long can it runs (approximately)? I was thinking of using separate batteries; one set of batteries for the wheels and one set for the pan.

Hope this all make sense… :stuck_out_tongue:

Thanks guys for your help

Francis

2

Thanks for the quick reply! :slight_smile:

That look great and it would be even cheaper than I thought :wink: But like you said, I’ll do more research before combining these items.

Few more questions though:
For the GHM-12 Spur gear motor, it says in the description that it is specially designed to operate at low speed. Will I be able to reach 20mph with this motor? Will I need more than 1 wheel with a motor or should I use more? And I guess the wheels will be connect directly to the motor without any gear?

Also the Power gearbox combine with the 785 servo seems to have a maximum rotation of 1260º. Is there something else I could use since the camera need to rotate more than this?

Again, thanks for the help! This site is awesome! :slight_smile:

Francis

EDIT: Something else I thought over night (I guess when you start building stuff like that, you’re thinking about it 24/7 :stuck_out_tongue:). Is the GHM-12 constant speed? I would need a motor that I can control the speed to easily follow the subject when filming.

3

This is great infos! Thanks! It do help a lot. I think we have enough information to start making a plan :slight_smile:

thanks again and I will certainly ask more questions as the project progress and start ordering the gear in the beginning of 2013… if the end of the world don’t happen on friday! :wink: lol

Francis

4

Makes a lot of sense.

It looks like you really only need the following:

]main drive motor (DC gear motor)/:m]
]hub and wheel,/:m]
]servo motor (for panning)/:m]
]R/C DC motor controller/:m]
]R/C transmitter / receiver/:m]
]Battery pack and charger/:m]

Some ideas:

]GHM-12 Spur gear motor/:m]
]1 3/8" rubber wheel with corresponding hub/:m]
]Spare wheels (we can special order the same wheel with a round bore)/:m]
]5:1 Power gearbox with 785 servo (for heavier cameras)/:m]
]Sabertooth motor controller/:m]
]Spektrum DX5/:m]
]6V battery, charger, cable (WH-04 soldered to BATC-01)/:m]

We have never tried these combination of products, so it’s important to do some research before purchasing. Small items like servo extension cables, mounting hardware etc have not been included.

5

The motor can rotate at a maximum of 253rpm. Perhaps I should have emphasized that this was just an example - not necessarily your best option.

The motor was just an example of a DC gear motor. It all depends on the wheel and the load you choose. If you select a 1 3/8" wheel, use the formula V=w*r, where w= rotational velocity in rad/s and r = radius of the wheel.

253rpm = 26.5 rad/s
V = 26.5 rad/ s x 0.0573 feet = 1.5’ / s = 1 mile per hour
Choose a larger wheel, and the robot will move faster.

If you are set on a 1 3/8" wheel, work backwards to determine the rpm of the motor:
20 miles / hr = 29 feet per second
506 rad/s = 4832 rpm

If you really think about it - 20 miles per hour is quite fast, and for such a small wheel to travel so fast, it needs to be spinning incredibly quickly. Most DC motors turn at 10,000 rpm, so you would only need a 2:1 gear ratio. In order to get enough torque though (what’s the point of a fast turning motor if it can’t move anything?). Not many manufacturers make 2:1 gear boxes, so you can achieve that with a belt / pulley system or something else. You would need a much larger motor.

If you consider using a 4 7-8" wheel, you’d need a 1400rpm gear motor (~6:1 to 8:1 gear ratio), which is far more reasonable and will likely be able to provide enough torque to move the system. Consider RB-Rbo-74 for example. If you don’t get enough torque, use two. If you need even more, use four.

Note that you should ideally use a DC motor at the rated voltage, but if there is an operating range (for example a motor can operate from 6-12V, then running it at 12V will make the motor rotates much faster than if it was run at 6V.

The corresponding R/C motor controller might need to be more powerful as well. Once you choose the gear motor, we can help you select the hub and wheel.

Hopefully the reply above answered that.

The power gearbox with the 785 servo would rotate at 1260 / 5 = 252 degrees max. If you need to be able to rotate the camera and don’t care about position, then you can use another gear motor. The type of gear motor depends on the weight of the camera. If it’s a small Nikon, you can use a heavily geared DC motor and mount the camera directly to the shaft. If it’s a larger camera, consider something like the Super Duty Belt Drive Pan System (DC gear motor sold separately). You would need another DC motor controller for this.

If you apply voltage directly to any DC gear motor, it will rotate at a fixed (maximum) speed. When you use a DC motor controller, you have complete control over the motor’s speed (from stopped to maximum) and direction.