Hardware > Bobcat DMX Servo Controller

Help with powering movement.

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typoagain:
I am really excited about where our hobby is headed. So many new things coming out and so many possibilities!

I am fairly new to this and last year was the first year for animated lighting. But I have never wanted a display with tens of thousands of lights. What I want is a display that is uniquely mine. I want a display that is made of elements that you can’t just run out to target and buy. Animation is the direction I have wanted to go in, so the new control board is exactly what I have been looking for.

I can handle the fabrication items. I can do the welding, wiring, software, design,…just about all of it. What I don’t know I can generally find online and learn fairly easily.

All but a couple of things. I don’t fully understand powering the actual movement. I need to learn a lot more about using servos, wiper motors and other small motors.  I can deal with 440v 3ph 40 hp blower motors. I have even assembled vacuum systems that stacked a dozen 12” impellers on 30 hp motors. But I am totally lost with small frame motors and servos.

 No matter where I look I can’t find information on choosing the right servo. How do I know how much torque it will take to move an object? How do I know which serve will supply the correct amount? I don’t want to spend a ton of time building something just to find that it burns out servos because the servos are too small. But at the same time I don’t want to run the cost of a display element through the roof by installing oversize servos.

 I understand how to use PWM for controlling the speed of a wiper motor. But how do I control exactly where it stops at? I know this can’t be that hard to do because every car on the road built in the last 50 years does it, I I’ll be damned if I can figure out how to do it!

Pneumatics are no problem for me, but I really don’t want to use them. They can be noisy and I don’t want my display tied to a big compressor.

So I am here asking for help.

I need guidance as to where I can find information on sizing servos for different designs. I go to the ServoCity website and find that it is more than a little overwhelming!

I can see how people are using wiper motors to supply movement. I really like the idea since wiper motors are tough, powerful, waterproof and cheap. But I need some way to control exactly where the motor stops. For example, I would like to build an animated snowman that dances. I just want to make his hips move back and forth. A wiper motor would be perfect for this. But when the motor comes to a stop I want the hips centered. Frosty would look a little weird standing there with his hips thrust off to one side.

So, anyone have any suggestions as to where I can find some info on these topics?

pokey:
I found this doc this morning:

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I too am excited about where this could all go, but I am going to need to borrow from the collective wisdom of the group to get through it.

dlhoppe:
You are not allowed to view links. Register or LoginI found this doc this morning:

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I too am excited about where this could all go, but I am going to need to borrow from the collective wisdom of the group to get through it.

--- End quote ---

Excellent paper at that link. One thing that it only touched on very briefly that should be mentioned in much more detail is "gear ratio". By that I mean the ratio of movement between the servo arm and the object being driven. 1:1 ratio means that the servo torque specs can be applied without any further math to determine the limits of what it can/will push and pull. If the object you're driving needs to travel less than the distance the servo arm travels, then you've got an advantage. You can drive heavier items. If the object needs to move further than the servo arm travels, then you're at a disadvantage. This ratio works exactly the same way the sprockets work on a 15-speed bicycle. Larger sprocket in front (servo) and smaller at the rear (driven object) means it's harder to pedal, but the bike travels further in one revolution of the pedal crank. Smaller sprocket in front (servo) and larger at the rear means it's easier to pedal, but the bike travels less distance in one revolution of the pedal crank. The latter requires less torque to move the weight of the bike and rider, but it doesn't travel as far. This concept is very important when you're considering the mechanical linkages in your display.

Food for thought...

jess_her:
If you want Santa's head bobbing to the beat of the music I would use servos. But if you just want say Santa doing swivel hips for a period of time then I would think about this.
You would have to manufacture a cam to attach to the output shaft of your motor assembly. a set of points like pinball leaf switches (cheep) and I'd use a bosh style relay with a spiking diode. But any relay that would fit the control voltage of the lynx hardware again a spicking diode installed. Another option is that most wiper motors have a park relay built in,  you would have to figure out  the circuit.

The lynx would pulse or turn on the relay for your set time.  Cam points then would close. When relay is de energised  cam points would be the current path and open at  the high point on the cam. Another type of points can work with a notch in the cam and might be easier to manufacture.


I would not directly drive the motor from lynx, you would burn up transistors and  would be electrically  noisy not a good thing.

This is getting a little off topic So I'll start a new thread if anyone is iinterested.

rimist:
I'm definitely interested!

-Rimist

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