Saturday, April 4, 2009

New Worm Gear Box





Diagram for input shaft quote.


Well I have finally purchased my first major part for my DIY Motion Control Rig. It's a worm gear box which will be part of the Pan Tilt Head System. The pictures I took with my phone make it look much larger the it actually is. The gearbox weighs about 1.2kg which seems fairly light compared to some of the rotary tables out there used for the same setup.

It was about $150 AUS and if it's works the way I hope, I will buy another one for a second axis. The gear box ratio is 60:1 (60 motor revs = 1 output shaft rev) to ensure I have enough resolution in my camera pans or tilts. There seems to be a bit of backlash but I will need to run some tests before I know if it's of any concern.

I still need to make an adapter shaft between the motor an the gearbox. I'm getting a quote from a local machine shop for that.

I'm thinking of going for a nema23 stepper with this setup, but still need to do a bit more research. Can't wait to try this out!

Here's a link to the transmission suppler: www.tea.net.au

9 comments:

Kevin Larson said...

Wow. That's a big unit. How my HP motor is that designed for? One thing I like about your worm gear is that they reduce the axial backlash to a minimal amount. One issue I'm fighting in my design is backlash! I can send you pictures of my model if you send me your email address.

I retrofitted an 80 lb industrial pan tilt assembly. I've done all the machining for motor mounts with my father on his CNC mill. Essentially a motion control rig is a CNC machine with different axis' layout. The reason we want to go down the path of using Maya for the visualization is that CNC's language called GCode doesn't really allow for timing in seconds and frames and you have to code every move. If you want to work together on this IC that caches a move from Maya let me know. My dad is an electrical engineer and he would be a great asset to get something working with Maya.

Kevin Larson said...

How many** HP not how my... ha

Dan Thompson said...

Hi Kevin,

You having access to a CNC mill! You lucky bugger! My mail is frankenegger at gmail dot com. I would be very interested in chatting further via mail and seeing some pictures. Being able to vary the playback speed of the move data is definitely on my to do list.

I do not know how much hp the gearbox is rated at. I will add the data sheet to the post, it may make more sense to you and your Dad. My model number is "30" for reference.

I had a quick look at some of the servos you mentioned. Sounds very interesting. I had not even considered them as a possibility until I saw this www.camblock.com
mmm, camblock...

Phil Warner said...

BACKLASH

Backlash is only a concern on the panning axis. Gravity takes care of any backlash on the tilt axis.

I've seen the mirror slap cause slight movement on my panohead when I have it set up perfectly level and the wind will move it too. It's not an issue in the day time unless I'm bracketing images. The longer exposures at night is where it becomes a problem.

The cheapest solution might be making a break that holds the pan axis when the shutter is open. I'm thinking about making a servo actuated break but I haven't made it yet.

Are you making this for 360° spherical panos, gigapans or both?

Phil Warner

Dan Thompson said...

Hi Phil,

Thanks for the tips on backlash. The kind of backlash I am getting is about 20 degrees of play when you rotate the input shaft. It happens before the output shaft engages and begins to move. But if you try to move the output shaft at any point, it's solid as a rock!?

Not sure if backlash is the correct term but it could be an issue when I want to repeat a complex move several times.

I should mention that this setup is for primarily for motion picture, although I'm sure that I will do timelapse and HDR Panos as well.

The camera I will be testing with is the Panasonic Lumix GH-1(mirrorless). it's not out yet but I can't wait to get one when it is.

I'm a big fan by the way. Love the work you did with the Panobot. Beautifully simple design.

Dan.

Phil Warner said...

Hi Dan,

Motion pictures! My neighbor wants to build the same thing so we'll have to keep an eye on your progress. I can't wait to see it when you get the camera moving on the pan and tilt. Is it going on the end of a jib arm?

I found your site by searching for stepper motors + backlash while trying to decide if I want to experiment with them using the Pappywizard software. The backlash bugs me because I like low light photography. It looks like everything has a little backlash unless it's locked down.

There is an anti backlash gear that I'll test out in a few weeks and we'll see how good it holds. I'm not sure why you have one loose shaft and the other is tight.

Phil

Kevin Larson said...

Dan you are correct the 20 degrees you are seeing is backlash. "Backlash, sometimes called lash or play, is clearance between mating components, sometimes described as the amount of lost motion due to clearance or slackness when movement is reversed and contact is re-established."
http://en.wikipedia.org/wiki/Backlash_(engineering)

For motion control purposes this should be a fraction of as degree or less. An anti-backlash gearbox coupled to as motor is often called a Harmonic drive.

Dan I would check if the worm gear has any adjustments. Usually you can tighten the mesh to minimize backlash. I think my unit has about 2 degrees of play on the tilt, but Phil is correct about one thing. You can correct most of the play on the tilt on a crane style design by weighing one side of the crane with a little more weight to keep the gears always engaged.

vipermesh said...

Hey guys.. This is a must read post. I will certainly keep an eye on this. I'm learning allot on this whole motion control rig setup system. I understand the comment stated from Kevin speaking about the more weight at the end to keep the gears always engaged. But, wouldn't it be possible to also set up some springs on the main pan axis to be constantly pulling (rotating) to the left or right as this will also keep the gears engaged on the pan direction? But would this effect the worm drive containtly fighting the stepper motor as power is drawn nonstop?

Awhile ago you mentioned about the pan and tilt system from servocity. I'm also looking at getting one (maybe) from them as well.. From what you've learn t so far through your investigation on motion control systems.. Would you suggest that i should go get one? hehe.. They say there's a new product that's uses digital electronic speed controllers and precision gearmotors to allow for super quiet, smooth, accurate and powerful movements.

Gears Manufacturers said...

Pretty cool information about new worm gear box, its looking very nice I would like to know more about it so now I am going to visit your website. Thanks for sharing this awesome information.

Worm Gears