Gearing down continious rotation servo
metron9
Posts: 1,100
I am designing a new more powerful light for the lighthouse customer.
My plan is to use a servo with a mirror at a 45 degree angle to rotate at 2 RPM
The continiuos rotation servos I bought from parallax can go 2 RPM but there is not much wiggle room. A tiny twist of the centering set screw and it may be stopped at the current pulse or be moving too fast.
My initial plan to solve the problem of knowing how fast the servo is going is to use a sensor and timing disc to bring up the pulse to the servo where it just starts to rotate as the voltage will vary from 4.2V down to 3.75V.
Before I delve into that, is there perhaps a different gear ratio available to modify those servos or does anyone have any ideas on a 2 RPM motor or other MFG servo. It Needs to be about the size of a standard servo or smaller·and use low power.
The other Idea I thought of doing was to run a small stepper at 30 or more RPM and use a light pulse to rotate the light similar to the rotating clocks using POV.
I am using a 3 watt Luxeon as the light source placed above the rotating mirror.
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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
My plan is to use a servo with a mirror at a 45 degree angle to rotate at 2 RPM
The continiuos rotation servos I bought from parallax can go 2 RPM but there is not much wiggle room. A tiny twist of the centering set screw and it may be stopped at the current pulse or be moving too fast.
My initial plan to solve the problem of knowing how fast the servo is going is to use a sensor and timing disc to bring up the pulse to the servo where it just starts to rotate as the voltage will vary from 4.2V down to 3.75V.
Before I delve into that, is there perhaps a different gear ratio available to modify those servos or does anyone have any ideas on a 2 RPM motor or other MFG servo. It Needs to be about the size of a standard servo or smaller·and use low power.
The other Idea I thought of doing was to run a small stepper at 30 or more RPM and use a light pulse to rotate the light similar to the rotating clocks using POV.
I am using a 3 watt Luxeon as the light source placed above the rotating mirror.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
Comments
http://www.solarbotics.com/products/k_smd/
Looking at the servo wheels with the rubber bands around them. If I could find a 3 to 1 ratio I could use them to make a friction reduction and run the servo at 6 RPM to drive the bigger wheel at 2 RPM.
I am thinking of diecutting (I have die cutters in my business) to make 1/8 inch plastic discs the correct sizes and then make up a gig with a small grinder wheel to notch the edge of the disc and put an O ring on them for friction wheels. I can even die cut a rectangle part to fit a servo to attach the wheels too like the servocity gear reduction parts. We have some very light weight plastics that are thick enough to do the job. If I end up making some I will perhaps offer them to others to try as well.
Trying to keep the cost down and the gears are pretty expensive when you have to buy a hundred of them.
I have a servo running at 6RPM and it is using about 40mA I want to try one of the mini servos but not sure if I can mak them continious rotation yet. Perhaps they would use less power for this task. My other led light uses about 35ma total but runs for 2 weeks when very low solar power conditions. This light will have the capacity to be 40 times brighter as well as low medium and high light power switch.
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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
Can your die cutter read DXF files ? I could make the gear layout for you.
Bean.
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www.iElectronicDesigns.com
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Price and power requirements from the one 2 rpm one I have found.
I just found this one http://merchinv.com/catalog/display-motor-2-rpm-1-battery.html
Perhaps I can find a better price but it looks like it will work great.
Another possibility http://www.usaturntable.com/misptusmtuwe.html
Continuing to search....
Actually Bean the die cutters are steel rule die cutters so the gear teeth would have to be in the 1/8 inch or bigger.
I am also thinking about a quartz clock with a smooth second have movment hack. Suppose I could get at the crystal and replace it with a crystal that runs at 1/2 the speed? They are pretty cheap and I think would have plenty of power for my needs.
http://cart.clockparts.com/font-colorrednewfont-continuous-sweep-miniquartz-movements-p-816.html
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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
The center is at 0,0 so you can just add a circle for whatever hub size you need.
Note that the larger gear is 8" across.
Bean.
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www.iElectronicDesigns.com
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Beau, I have a sample motor on the way that runs at 4rpm on 1.5V and I am thinking I can use PWM to slow it down and get 2rpm. I am also thinking the voltage spike I get can be used as part of the power for the LED. I found a motor mfg that will make custom motors with a minimum order of $250.00 and the motors would be about $8.00 each. Their off the shelf one is the 4rpm model so I hope I can make it go 2rpm. Actually it is a 3V motor that runs 8rpm and they spec it at 1.5V for 4rpm. I don't know if PWM vs just lowering the voltage will make any difference till I can try it on the bench. I will let you know next week when I get it.
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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
Shoot, I broke it now so I can't test to see if that will work. My fingers are to big anyway for this tiny stuff.
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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
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- Stephen
Looks to be a pretty solid little bugger. I think my price will be in the 10.00 range but I have to order at least 25 to start with. If anyone would like a few i can add them to the order and charge you shipping cost plus my cost on the motors if interested.
It only takes 8ma at 1.5V running at 4RPM
I have not yet tested PWM but I am thinking of driving it directly from a pin on an atmel chip. Instead of sinking current I would drive it running the chip at 4 Volts.
Question, will I get any voltage spikes if I drive the motor from the positive side? I think I will start with a 3300uf 10V capacitor to smooth the voltage.
I will just go ahead and do it and see if I get any spikes with my scope.
<<<EDIT>>>
Just tried the PWM directly from a pin, no need for a capacitor. Just a 25% duty cycle at 2khz at 4V and I get a nice 2RPM. Still about 7ma. I can also PWM the luxeon III at just 30ma and the unit will use the same power as the old model. I plan to have a little tactile button to allow the customer to set the light intensity, off, low, medium and high.
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Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
Post Edited (metron9) : 4/13/2008 4:57:28 AM GMT