ROTARY MOTION

[High Seas]

Hey! We don't have a Forum for this topic!

Seems with a few exceptions - most of us get to Linear Motion, by first rotating something first!

Stepper, servo -- or my latest interest: Harmonic Drive.

Feel free to dump - or move this and my following post as appropriate.

Cheers - Jim

[High Seas]

The poll may be tounge-in-cheek - but maybe not. Likewise this may not be the right place for the question -- but it didn't fit elsewhere. Moderator -- do your thing if needed!

Well, I hope I've done due diligence with the search on site and GOOGLE ! Seems like most of the HARMONIC DRIVE discussions and builds are over a year old. Widgetmaster - has a nice build log putting together a 4th axis using one and several others adapted to 4th and 5 axis ideas too.

BUT -- here's my question:

HOW DO YOU DRIVE IT?
I've been to some of the supplier sites -- they reference drive software -- but don't post any. I don't see where MACH2 (haven't migrated to 3 yet) has any provision for a HARMONIC DRIVE.

To put in perspective -- Yes it would be cool touse a a 4th/5 axis. But for starters I'd like to:
1. Rotate 0 - 360 degrees in (chosen) increments
2. Rotate CW and CCW (by choice)
3. Speed control slow med fast (have no idea here)

I understand that some of the ROBOT folks may use these drives. Any good hints in that realm I can chase down? Of course, looking to any collective experience here first.

APPLICATION: A high resolution direct drive Turntable.

[neilw20]

CAMSHAFT: A machine for converting regular rotary motion into irregular linear motion regularly.

[neilw20]

High Seas.

You need to be able to read that old record without damaging it.
http://www.elpj.com/about/
found by:
Google 'laser turntable'

[High Seas]

Niel:
Actually - a direct drive turntable for LASER Scanning! The other features would be nice to have - speed control, etc -- Could be a high end audiophile deal.

BTW -- cool reference - laser turntable- Once to digital it could be de-noised as well.

[neilw20]

Denoising mostly not required. Laser reading still gives analogue signal.
Scratches are on the top surface and the laser looks below the top of the groove and pssibly where a stylus has not rubbed.
Maybe the odd click to get rid of clicks from deep scratches.
Quite often noise is caused by poor quality vynil which is grainy.
Most denoising can wreck the original recording if not used with great skill.
Old MONO records that have been put onto CD sometimes have been transcribed on a stereo pickup. This introduces new noises that weren't there. Put the stereo track into Goldwave. Subtract the 2 tracks from each other and listen to the newly created noises etc.
Listening to a single track on it's own has half half of this noise (or is it 71% ?). If you subtract this noise signal from the single track, you can get rid of the noise created by using a stereo pickup. The 71% may vary depending on the original stylus shape.
Just cos' it is digital does not mean it was done the right (read that as optimal) way. Quite a few commercially released CD's have been engineered poorly.

[High Seas]

Over 200 "lookers" and only 12 votes. Hope the turn-out is better in November! Maybe unregistered/non-voters

[CarbideBob]

High Seas,
Harmonic drives are rotary reduction devices. Think of them as high reduction gearboxes. You drive the input with a stepper or servo motor so there is no reason Mach can't drive one.
Yes, many robotic arms use these or ball reducers at each joint.
Bob

[High Seas]

AH HA! So the motors you can occasionally see on eBay as being described as, "motor for harmonic drive.." are stepper/servos? Thanks CarbideBob
Jim

[Steve Crum]

This has had me perplexed all day. Math isn't one of my strong points and favorite son is away at college now. I have a 4'x8' CNC plasma table and I'm adding a rotational axis. I made 2 tapered aluminum centers so I can chuck a piece of pipe in them. I intend to drive the centers with a Pacific Scientific 2 stack stepper motor which is identical to the motors on my table. When I do circumferal cutting I can set this rig on the plasma table and align the torch over the tube. I would then un-plug the X axis and plug it into the rotational axis stepper motor. The Y axis would remain operational for longitudal cutting in conjunction with the rotational cutting. I DO NOT want to alter the programming, so while I am building this axis, I want to gear it to operate on the same programming as the normal table X axis. The way my table is set up, the program runs the stepper 1.5 revolutions per 1.000" of travel as dictated and measured by the program. The current X axis motor has a .891" diameter 14 tooth 1/5" pitch timing belt pulley. I intend to order the same pulley for the rotational stepper motor. As such 1.5 revolutions equals 4.1985" of belt travel if my math is correct. My question is what size/number of teeth pulley do I need as the driven pulley to achieve 1.000" of shaft rotation on the center cones?
Somebody has to be better at math than me! Thanks

[RICHARD ZASTROW]

Don't forget the circumference of the workpiece will still effect the feedrate. A larger diameter workpiece will have a faster feedrate than a smaller diameter at the same RPM.

I know this is obvious but you'd be surprised how many fail to adjust.

Dick Z

[svenakela]

I could let this forum be renamed to both linear and rotary motion. Yes?..