Adding Power Zoom to a Manual Zoom projector.

byancey

I've been researching the possibility of adding power zoom to my manual zoom projector.· I'm hoping to get some suggestions from some of the experts here. [noparse]:)[/noparse]

The projector is a Panasonic AX100U.· I've verified that I can rotate the zoom wheel very·easily by wrapping a small rubber strap around the wheel.· It doesn't take a lot of tension to get the zoom wheel to turn, so I figure a small motor or servo should do the job.· The trick now is figuring out what parts I need and how to hook them all together and control zoom.

All of the automation in my home theater is controlled via an HTPC running Girder, and writing a little software to get things working shouldn't be a problem.· I'm thinking something along the lines of controlling the zoom via the USB port on the HTPC.· The ability to bounce between two pre-defined zoom locations would be ideal (assuming no slippage on the belt), but just being able to move the zoom wheel one direction or the other would be sufficent.· If I can get it to the point where I can send commands to the motor from my PC, I·should be able to·handle the details of integrating·the control·into Girder.

Based on what I've stumbled on so far, I thought perhaps one of the following solutions would work:

1. Using BS1USB Board to control a stepper motor·such as this one: http://www.parallax.com/detail.asp?product_id=27964.·
2. Using a Parallax Servo Controller (USB) to control a·Standard Servo such as this:·http://www.parallax.com/detail.asp?product_id=900-00005

Not sure yet what all I would need to "glue" everything together (gears, belts, etc, etc).

Any suggestions for the best way to accomplish what I'm after?· Is there a simpler way to do this than the one's I've identified above?· Thanks in advance for any suggestions and recommendations.

Thanks!

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Bryce
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byancey

I've been doing a little more digging, and it appears to me that approch #2 (using a Parallax Servo Controller and a Servo) is probably the best approach.· It appears that the USB version of the PSC installs itself as a serial port on your PC and allows individual servos to be controlled via RS-232 serial commands.· This would make automating and control of a servo almost trivial, as I'm already using Girder to control two other devices via RS-232 serial commands in a similar manner.· Programming the servo to go to a pre-defined location when I hit a button on my remote should not take much effort at all.· Now I just need to solve the mechanical side of the problem. [noparse]:)[/noparse]

A couple more quick questions:

• Can someone who has used the USB version of the PSC please confirm that it can be controlled directly·via RS-232·Serial Commands?· The blurb on the website seems to indicate that it can use the same commands as the serial version, however, the pdf documentation for the USB version only talks about the graphical interface.
• I'm still open for any suggestions on the mechanical side.· I'm thinking a rubber belt drive might be the easist approach, but I haven't seen any·online suppliers·that provide rubber belts or wheels that would drive them (found sprockets and chains,·but I doubt those would·sufficently grip the zoom wheel on the projector).

Thanks!

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Bryce

Phil Pilgrim (PhiPi)

Bryce,

If you use a standard servo (as opposed to the continuous rotation type), you need to make sure that your mechanical drive won't slip. This usually entails some sort of toothed belt or sprocket. But that also means some sort of toothed attachment to the zoom ring on the lens. Whatt you could do is take a section of toothed belt and glue it to the lens ring with the toothed side facing outward. Then you'd have something positive for a mating toothed belt to grip.

-Phil

byancey

Phil,

Thanks for the reply.· If I'm following you, you are basically suggesting that I turn the zoom wheel into an improvised sprocket.· That would then allow me to us a standard sprocket and chain drive approach and eliminate any issues with slippage, correct?

I presume that would involve using parts similiar to those found at this link:

http://www.servocity.com/html/plain_bore_sprockets___1227_.html

I have been having·trouble locating parts for a pully and belt type drive, so I might be better off going the sprocket route.· The trick will be finding a material with appropriate size teeth and getting them attached to the zoom lense.· I haven't seen any toothed belts, only sprockets which I assume are made of hard plastic and may not attach well to the zoom lense.··The link below is·a closeup of the lense assembly to give you an idea of what I'd be attaching it to.

http://www.audioholics.com/productreviews/avhardware/images/PT-AX100U-angle2.jpg

Do you have any suggestions as to where I might find a toothed belt?· I've seen belts or treads that will accept a toothed sprocket, but not the other way around.

Thanks again for your help.

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Bryce


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Phil Pilgrim (PhiPi)

Bryce,

That setscrew may be your key to success. If you can replace it with a longer, panhead screw, you'll have an attachment point for the chain. (It only takes one, assuming the zoom control doesn't need to turn more than a half revolution or so.) That would be better than gluing something on, if you're concerned about permanently altering the projector. You could also use a toothed belt, though, teeth facing inward. Just drill a hole through it, and run the panhead screw through it into the lens ring. Then use a toothed belt sprocket to drive it. BTW, you can get toothed belts and drive pulleys here: http://www.smallparts.com. One advantage of toothed belts over chain is that they're quieter.

-Phil

byancey

Phil,

That setscrew·you were looking at·is actually obstructed by the casing of the projector.· I could probably access it by removing the case, but even if I attached a belt/chain, it wouldn't have clearance to turn once the case was back in place.

That link to·smallparts.com is great.··Last night I actually managed to track down the timing belts and pulleys section at http://www.robotmarketplace.com/marketplace_timing.html.· I'll have to see what smallparts.com has to·offer as well.

Based on what I found over at Robot Marketplace, I think I have a plan that might work without modifying or gluing anything to the projector.· Here are the highlights of what I'm thinking.· Let me know if it sounds like a plausible approach.

• You may notice from the photo of the projector that the zoom·barrel is actually covered with tiny teeth.· These are much too small to directly mate with the teeth on any of the timing belts I've seen.· However, they do provide great texture for gripping.· The zoom also adjusts with minimal tension.· If I wrap a small strap around the barrel, I can easily·adjust the zoom with no apparent slippage just by gently·pulling the strap back and forth.· I would think the teeth on a 0.080 pitch timing belt would grip these little teeth quite well, even if it isn't a perfect match.
• The full range of the zoom adjust on the projector is actually only about 1/4 revolution of the zoom barrel and I'll generally only be zooming within a small fraction of the full range.· I think I should be able to size my timing gear such that I can accommodate the full zoom range of the projector well within the 180 degree movement range of the standard servo.··I can leave sufficient overhead in the·servo range vs. the·zoom range in order to·accommodate for some minor slippage without hitting the extreme range of the servo.·Assuming slippage occurs in both directions (both zoom in and zoom out), it should average out and generally keep the servo in the middle of it's range (if I have to re-center the belt occasionally, I can live with that).
• I'll basically be switching back and forth between two fixed·zoom settings.· In terms of controlling the zoom from my remote control, I·will have a single button that·roughly toggles between the two zoom settings (two locations on the servo).· If I find there is some slippage, I can have two other buttons on the remote·for zoom in/zoom out which I can use to·fine tune the servo settings for each zoom location each time I switch between them.

Assuming there are no issues with·attaching the timing gears·to the standard servo, I would think this approach should work.· Does this sound like it would do the trick?·· I'll also take a look and see what smallparts.com has to offer that might help.

Thanks again.

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Bryce

Phil Pilgrim (PhiPi)

Bryce,

I think you have a good plan!

-Phil

kelvin james

This may be a little on the ghetto side, but might be worth a look. Since you say the zoom ring moves with little resistance, and only has a 90 degree range, this might save you a ton of trouble. You may have to use an extended horn on the servo to get the range of rotation desired. Diagram is pretty crude, but shows the concept.

kelvin

byancey

Yes, that might also do the trick, but assuming I can find all the correct parts to use the timing belt, I think I'll give that a try first.

Thanks for all the assistance. If I get this up and running, I'll be sure to post the results back here.

Thanks!

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Bryce

byancey

I just completed this little project, and it works great!· I can now use my remote control to automatically switch between the zoom setting I use for 16:9 content, and the zoom setting I use for 2.35:1 scope·content.· I also have buttons on the remote to fine tune the settings to account for slippage, however, so far slippage doesn't seem to be a problem.

Thought I'd post a few pictures of the results.







And one quick picture of the other side of the wall...




Thanks again for all the assistance!

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Bryce
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