Accurate measurement of rotation

Captain Blammo

I'm putting together a project that needs to precisely measure (say to within 0.33 degrees) rotation of a tripod head in 2 axes. I've had a poke around this site and the web trying to find an approriate sensor, but haven't turned anything up yet. I'm going to assume that pots may be a bit too shaky for precise use, although I suppose it depends on who makes them.

Any recommendations for something appropriate would be greatly appreciated.

Jon Williams

I think you're going to want to use a hi-res rotary encoder. You'll have to "home" the head and then measure from there.

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Jon Williams
Applications Engineer, Parallax

Larry

a rotary encoder will do it Download NV8 on the Parallax website to get you started.

Be aware that a 128 or 256 count encoder will have to be turned slowly or you will lose counts,
I was only able to get about 100 counts per second with a quadrature encoder and a BS2.

If you need to count faster than that, you'll have to add some hardware to do the counting for you.
I think there's something in the Stampworks manual, but if you can't find it,
here's a site that will get you started with that.


abrobotics.tripod.com/Ebot/hardware.htm

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Jon Williams

One of our Tech Support guys, Chris, used a BS2px and and encoder with the input consolidated onto a single line and got really good performance out of it. Another choice is, of course, the SX.

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Jon Williams
Applications Engineer, Parallax

Bean

If you are controlling the movement with a motor, you could use a stepper motor.
Bean.

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"SX-Video·Module" Now available from Parallax for only $28.95

http://www.parallax.com/detail.asp?product_id=30012

"SX-Video OSD module" Now available from Parallax for only·$49.95
http://www.parallax.com/detail.asp?product_id=30015

Product web site: www.sxvm.com

"Never under estimate the importance of being nice when you don't have to be."
·

steve_b

You might look at a synchro to digital converter.
It's more hardware than you might've wanted....we use them on our radars

Here's some info on them:
http://www.evaluationengineering.com/pctest/articles/0399daq.htm
http://www.pentlandsys.com/download/synchro/ch1_2.pdf
http://www.pentlandsys.com/download/synchro/ch3.pdf
http://www.pentlandsys.com/download/synchro/ch4.pdf

Analog devices sells some converter IC's in 12, 14 and 16bit flavours.
http://www.analog.com/en/prod/0,,760_791_AD2S83%2C00.html

These are all a bit pricey...but I'm sure you can find some lower end ones that might work for you.

For instance, you could get the hold of an old synchro setup (we used to use them in our old wind equipment) and you could easily attach a 10-turn pot to the end of one of the rotor shafts and just do an RCtime input to your stamp.
Here's a quick look on ebay for ' synchro resolver '
http://cgi.ebay.com/Evershead-Vignoles-Synchro-Resolver-Type-FC34-0_W0QQitemZ7594260290QQcategoryZ42899QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
That address probably won't work unless you copy/paste.
http://cgi.ebay.com/Bendix-HSI-SYNCHRO-Synchronous-Resolver-Receiver-8Pcs_W0QQitemZ7593733146QQcategoryZ71395QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

wrt ebay...buyer beware!

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Steve

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Chris Savage

Jon Williams (Parallax) said...
One of our Tech Support guys, Chris, used a BS2px and and encoder with the input consolidated onto a single line and got really good performance out of it. Another choice is, of course, the SX.

The one I used was a Grayhill 16 position, which is good even on a BS2 at slower speeds (not whipping it around).· If you need more accuracy you could use an SX Chip and a higher resolution encoder without the detents.· Jon has an example of this in the SX/B help file that could be modified to your application.


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Chris Savage
Parallax Tech Support
csavage@parallax.com