Author Topic: PC Controlled Jib Arm  (Read 1520 times)

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Offline davidhere40Topic starter

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PC Controlled Jib Arm
« on: February 15, 2012, 11:43:29 AM »
I'm making a computer controlled jib arm, the basic idea of a jib arm is this: Hague Camera Supports K8 Boom Jib
I'm trying to figure out how to motorize it. I want durability, because it's for an industrial application and will be in constant motion/use. It's not for photography or video. It's basically a really long robotic arm.
I could really use some help making the right mechanical and motor/controller choices.
Here is what I have so far:

I want to motorize three dimensions:
1) Telescoping in/out movement: I have added a slider to the jib. It is going to be driven by a v-belt. This allows it to extend like a telescoping arm. It will be able to extend 6 feet. The slider will only weigh about 4 pounds max (about 2 pounds for the telescoping square aluminum tubing and less than one pound for the payload). I'm also considering to use a counter weight on the other side of the v-belt that moves in the opposite direction. It would balance the arm at the fulcrum as well as would prevent gravity from creating any net force on the v-belt.
For the v-belt, I was planning to use a sheave and pulley with a radius of about 1 to 1.5 inches. I just guestimated though when I purchased it, because I have no experience here. V-belt was chosen for low cost at long lengths, simple maintenance, mechanical simplicity and durability, but I have no experience with them.
2) Left/Right of the entire jib. The jib has a bearing for smooth lef/right roation at the fulcrum (the point it balances on).
I'm not sure what actuator type to use here. I'm considering either a stepper motor or a linear actuator.
3) Up/Down: Plan to use linear actuator for this. but might consider using the steppers also, if it's more durable.

I've been working for a few days on the in/out (telescoping) actuator. I thought about using a 640 oz-in nema 34 stepper.
I calculate the real torque (68% of what they claim based on torque charts in the specs manual) to be:
17.4 pounds of torque at 1.5 inches (the radius of my v-belt sheave)
But, my load inertia to rotor inertia is 36 times with an 8 pound load and 1.5 inch radius sheave. I could possibly get it down to a multiple of 6 if I make the load 6 pounds and the sheave 1 inch in radius. I'm not sure the v-belt will even do that though.

Speed is important. I want to able to move something like 9 inches a second at top speed.

Is this design totally off?! What would you do to improve it or make the idea work? Any help would be much appreciated.

« Last Edit: February 15, 2012, 05:11:13 PM by davidhere40 »


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