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Thunderhorse
05-28-2008, 11:39 PM
Word,

Here is my project: I am essentially building a robot, or series of robots rather, that can move a video/film camera for special effects that call for smoothness and repeatability in camera movements.

As an Electrical Engineering undergrad, I have the background to build the structure, and anything that I don't design myself, I'll probably buy off McMaster-Carr or other third parties (as the motors will need to have higher torque than most of the ones on this site). However, for the brains I have investigated FPGAs and microcontrollers, but both of these lack the same thing: a sleek software application interface. I want to be able to control my motors and sensors directly from my laptop.

That is exactly what you guys have been doing at Trossen (or so it seems), but I don't believe I would be able to use the types of bridgeware you have demonstrated considering that my motors will need to be bigger and such.

Anyway I'm not much of a software guy, which is only to say I am no where near close to what you guys know. Also, I'm on a Mac and would like to utilize OSXs GUI for my project.

If no one has any ideas on this, then even just some information on how computers communicate through the USB and serial ports would be great. Also, I want to get under the hood of my iMac to directly access my computers ports.

Thanks for reading

Ian

Adrenalynn
05-29-2008, 01:38 AM
>> but I don't believe I would be able to use the types of bridgeware you have demonstrated considering that my motors will need to be bigger and such.

Welcome to TRC!

I don't think that's necessarily the case. Motor controllers (aka speed controllers aka ESCs, or Electronic Speed Controllers) sit another layer back in hardware from the PC. The PC generally talks to a different class of device. Low voltage, very low current. At the simplest, relays would go from an analog out on the PC to the motor controller. More likely, you'd have a servo controller at the PC that talked to the motor controller utilizing PWM.

I'm running four 160A @ 36V motors (at stall, 64A nominal/free) from a serial port... They're generating almost 5HP (about 7HP at stall), and can trivially propel 400lbs + to 35MPH without yet optimizing gearing. Here again, I use a serial controlled servo controller that talks PWM to multiple high-amp motor controllers that control power from the batteries into the motors.

In that case, what we've begun working on here would be directly applicable.

Does that help you to reconsider your architecture?

Again welcome to the Community, we hope to see you here regularly, and will contribute thoughts and notions however we can! Sounds like a fun project!

Thunderhorse
05-29-2008, 11:40 PM
I now realize you are entirely correct. Motor controllers are a must. Particularly for power supply reasons, which you seem to be using much more power than I will need!

How exactly do you control the motor controllers through your serial port? Do the controllers communicate back to your computer at all? What brand are you using?

Ideally, I would like my project to have an application in the gui where I could move digital knobs and levers to control the motors. Thoughts?

Ian

ps thanks for the welcome, I'll certainly be around!

Adrenalynn
05-30-2008, 10:24 AM
Hi Ian,

Some motor controllers do communicate directly back. Some would require a servo controller that interfaces to the motor controller.

In my case, the motor controller only understands PWM - Pulse Width Modulation - just like an R/C car's receiver (which it's designed for). So in that case, I use a servo controller which can talk over RS232 Serial and spit-out PWM.

How large of motors are you thinking about employing? Or how much weight at what kinda speed? I was a certified steadicam operator a few years back, and I know I'd be expecting to drag around 85 lbs on my body just for video, let alone film... If you're looking to build like automated dollies and/or cranes for film, you may be looking at weights similar to my project, especially if you want to look at IMAX.

ooops
05-30-2008, 12:35 PM
I'm running four 160A @ 36V motors (at stall, 64A nominal/free) from a serial port... They're generating almost 5HP (about 7HP at stall), and can trivially propel 400lbs + to 35MPH without yet optimizing gearing. Here again, I use a serial controlled servo controller that talks PWM to multiple high-amp motor controllers that control power from the batteries into the motors.


Adrenalynn , wow that is some project, have you detailed it somewhere else on here?
The “how to” mechanics of what you are doing sounds like it would be very handy info for a number of us! If you haven’t shared already … please do tell.
If I did the math right (in my head, real quick, after being on the road for 48 hours) that’s over 5,000 watts of power per motor (at peak)? Coooooool stuff:veryhappy:

metaform3d
05-30-2008, 12:56 PM
What sort of camera rig did you have in mind? Something like an animation/effects stand (http://www.pictures-and-words.com/images/gallery/large/early_film/AnimationStandShoot.jpg) could be as simple as a 2 or 3-axis table. I think you could make a pretty serviceable one using full extension drawer slides and stepper motors from an old printer. Motion-controlled cameras (http://www.mrmoco.com/images/MR0025.jpg), on the other hand, tend to be much larger and would be a much more complex build. Which you want will depend on your subject matter.

I guess you know what you want to build -- I'm just being nosey.

Adrenalynn
05-30-2008, 01:03 PM
I haven't detailed it until I get a bit further down the road here and figure out if I'm keeping these motors or not.

The motors are golf-cart motors. They're realistically looking like about 2100 watts operating, so I suspect they're a bit over-rated. But yes, stall current is a bad thing. They're not exactly easy to stall, though. I've had them rip their way out of a couple 8" bench vices and decimate 3/8 lags in 2x4's trying to stall them and measure current.

Each side (two motors each side, four total) will get 3x60Ah gel-cell batteries in series. At the moment I'm testing with spillable lead-acids that I had here, lawn tractor batteries that each deliver 275Ah peak (cranking). Nail down my power delivery before I start spending serious dollars on batteries...

But hey, this isn't my thread and I'm hijaacking the heck out of it. I'll blog a quick list of my outstanding projects this evening...

Back to Thunderhorse's project!

Adrenalynn
05-30-2008, 01:04 PM
What sort of camera rig did you have in mind? Something like an animation/effects stand (http://www.pictures-and-words.com/images/gallery/large/early_film/AnimationStandShoot.jpg) could be as simple as a 2 or 3-axis table. I think you could make a pretty serviceable one using full extension drawer slides and stepper motors from an old printer. Motion-controlled cameras (http://www.mrmoco.com/images/MR0025.jpg), on the other hand, tend to be much larger and would be a much more complex build. Which you want will depend on your subject matter.

I guess you know what you want to build -- I'm just being nosey.

Excellent points and questions, Meta! I was assuming motion-controlled cameras or dolly/crane effects. Not a good assumption my my part!

Thunderhorse
05-31-2008, 12:14 PM
Thanks for taking interest everyone!


How large of motors are you thinking about employing? Or how much weight at what kinda speed?


Adrenalynn,
I'm thinking I might be going larger actually. I'm not looking to move any dollies or cranes yet, but I would like to get to that level. As for metaform3d's inquiry as to the kind of rig, I'm looking to do both.

My first project will be to build my own pan and tilt camera mount system. This should be able to support 10-50 lb loads moving them up to about a 180 degrees a sec. This camera mount would then be universal to say simple 2 axes table systems up to a crane system.

As for the system I would like to start out with: a simple, small (1x1 ft) platform on a small rail track to do 1 axis movement (moving forward and backward). So I imagine this will be a pulley and belt system moving up to 70 lb at speeds up to 4 ft a second.

However, the loads will change when different cameras are put on them. Right now I only have some small to mid size digital camera, but would certainly like to be compatible with a Panavision or something. Also, for all the high speeds that I would like to accomplish, I also want to be able to move extremely slow, too (like a ft/hour). You know that beautiful opening first shot of the Godfather? Haha I need to be able to go that slow as well, so I imagine I'll be looking at microstepping and such.

Anyway there's some more info on the project. I hope it gives you a better idea of what I am doing!

Ian

Adrenalynn
05-31-2008, 12:35 PM
Moving 180 deg/sec with those kinds of loads is not going to be accurate by any stretch. What are you thinking about doing to compensate backlash?

For telescopes, we move them fast until we get close, then slow way the heck down. The last few degrees may take ten seconds...