Smooth pan-tilt system question

Dave M

Hello! New member here and this entire subject is new to me. I,ve been trying to work out how to come up with a very smooth and slow pan-tilt head for a camcorder crane. I settled on DC gear motors that would be further reduced in RPM ratio to about .5 RPM.·I want to control the 2 motors speed and direction with a dual axis joystick.· After doing some research on this website and others I realized I would need an H bridge and microcontroller.· If I used the HB-25 motor controller would I need one for each motor? And would one Basic Stamp module handle the work? I know very little about this subject but what I've picked up is that code would have to be written to convert the analogue joystick output into digital pulses the HB- 25 could read. Is that correct?·· Thanks for any advice you might have.··· Dave M.

LSB

The specs should indicate you will need two (to my cursory perusal) HB-25s and one BS2.

The HB-25 is, by all accounts, an excellent driver, but big and expensive (relatively) if you your motor doesn’t require so much power.

May I offer a different approach? For small motors single chips are available that will do the job; one, the SN754410 for example is less than $2, requires no peripheral components, and will control two small (500mA) motors or one larger (~1 amp); chips may be piggybacked for even greater output. If this seems adequate then purchase the PWMPAL for $30 (will output 4 PWM channels), wire one (or two) additional chips, and pocket the difference.

Another possibility is the Motor-Mind B, but I haven’t used it—perhaps others will recommend it.

Also, look at the ADC0834, it's an easy to use 8 bit, 4 channel A/D converter

stamptrol

Dave,

The HB-25 modules are an excellent product and work really well. Note, however, that any required postion feedback will have to come from some other sensor on the crane.
I just finished a little test setup with a joystick, BS2, and one HB-25. If you're interested in the code, just let me know.

Cheers,

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tom Sisk

http://www.siskconsult.com
·

Dave M

Thank you for your quick replys. I will check out what LSB suggested and I will certainly keep Tom in mind when I need the code. I haven,t worked out the physics of this system to know exactly what I'll need yet. It may never work the way I want it to but it will be a lot of fun and educational building it.

Dave M.

CCraig

One other thing. In addition to being slightly big for your project, you should try to get by with a controller that can operate without the use of fans. i.e. heat sinks. QUIET ON THE SET.

May or may not apply, Chris

DiablodeMorte

A little off topic: stamptrol I would love to see your test setup w/ a joystick and BS2.

Dave M

That's a good point Chris about the fans. And I too would like to see the test set up. Tom, I would greatly appreciate the code you used for the HB- 25 and joystick in case I go that way.· Thanks, Dave M.

Dave M

I'm thinking of using this motor http://www.servocity.com/html/4_5_rpm_gear_motor.html·· One for the pan and one for tilt. With a no load RPM of 4.5 and using a joystick to control direction and speed thru the HB-25 can someone give me an idea what the RPM range would be. Basically, how slow would the motor turn moving the joystick slightly. I realize there are other factors like what will be the load on the motor. The camcorder is about 6 lbs. And the design would be well balanced.

Thanks,· Dave M.

Duffer

Dave,
It looks like you're pretty well committed to using DC gear motors for you project, but you might want to take a look at the slick pan/tilt mount that "T0m" has turned out for a bot mounted camera.
http://forums.parallax.com/forums/default.aspx?f=10&m=181523
He's quite the fabricator and if your camera is being suspended rather than the mount supporting the weight of the camera, some beefier servos on a mount like T0m's might do the trick (he says he's working on an upgraded model with ball bearings!). Also, using the Parallax Servo Controller with a setup like that would give you very precise control of position, position feedback and the ability to ramp down the movements of the servos for very smooth quiet operation and you wouldn't have to worry about component cooling like you do with the HB-25.
Just a thought, Steve

Post Edited (Duffer) : 4/4/2007 4:46:40 AM GMT

Dave M

I know that most people go the servo route for pan-tilt. The camera I'm using is a 6 lb. 3 chip camcorder. On another forum dealing with film making it's common to see people use servos to quickly set up their crane camera for another or different shot. But you wouldn't use it while filming. It's far too jerky. The studios use a huge crane with the camera man on the end panning and tilting while being elevated by the crane. I had this idea that maybe with very slow and controlable motors one could get a film worthy pan-tilt shot while on a crane. My only problem is I know very little about Basic Stamp, microcontrollers, PBasic, etc.· I should purchase one of the educational kits on this web site and learn something new.

Dave M.

I wanted to add that I've seen several DIY cranes where they attempt to get a smooth pan by using fluid heads and cables or rods set up in some fashion but I've never seen this attempted except by professional set-ups with computer controlled crane heads in studios.


Post Edited (Dave M) : 4/4/2007 5:18:29 AM GMT

Duffer

Dave,
I had many of the same feelings regarding the use of servos for camera work until I started using the Servo Controller. My favorite things about its use are that it provides 64 "ramp" speeds for servo movement. I.E. a ramp value in the 60s causes the servo to take up to 8 seconds to make a full 180 degree rotation very smoothly. It can control up to 16 servos (32 by daisy-chaining a second Servo Controller) and its all controlled by a simple 3-wire serial connection to the micro controller using only 3 or 4 simple commands. For setting up and shooting on a repeatable path, it's a simple matter of storing the coordinated movements of your shot and just "playing them back" to repeat a shot as many times as needed. Also, with the USB version (same price as the serial model), Parallax provides a free, downloadable PC application that you can use to test and calibrate your setup before you commit to the coding.
Sorry, I don't mean to sound like I get a kick-back on every unit that's sold, but that simple little $39 board has saved me a lot of time and headaches on several projects.
Cheers, Steve

stamptrol

Hi folks,

Got a little distracted with a couple other projects. Will get the joystick code up later today!

Regards,

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tom Sisk

http://www.siskconsult.com
·

Dave M

Steve, thanks for the input and looking forward to Tom's code.

As far as servos are concerned my only experience with them is in R/C flight. I understand your point about using a controller and an 8 second 180 deg. arc.· My concern is servos, from my experience, kind of jerk to the next step. In videography smooth is good, jerky is bad. It seems that continuous running motors would move the camera more smoothly. Also I'm thinking more like 24 to 30 seconds for a 180 degree arc.

Dave M

Dave M

By the way, I've been searching for joysticks and without hacking into an R/C transmitter the only stand alone one I've found is this http://www.p3america.com/pp/812.htm·I don't know how much it is. Looks expensive. Anyone know where I can get a decent but inexpensive joystick?

Dave M.

stamptrol

Dave and all,

I posted some code and pics over on the Sandbox.

Tom

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tom Sisk

http://www.siskconsult.com
·

skylight

Dave M said...

·The studios use a huge crane with the camera man on the end panning and tilting while being elevated by the crane.

Would that be either a Nike, Heron or Mole Crane? Which Studios are you describing? I'm interested as i have worked in television now for nearly 25 years.

Dave M

I wouldn't know. Just pointing out they use a person to direct the camera movements.···· Dave M.