Servos for lumia and grating wheels...

Having recently started experimenting with the idea of DMX-controlled servos for grating and lumia effects, I decided to check out a modifed hobby servo available from a company called Parallax here in the U.S., which specializes in microcontrollers and related components for robotics and other electronics applications. One of the items they sell is a modified standard Futaba hobby servo, that has been adapted for continuous rotation operation.

They work great, and inexpensive, too!!

http://www.parallax.com/Store/Access...%2cProductName

Since I already have a Northlight DMX servo controller currently in use on my "Jolly Green Poly Slab" experiment, I decided to give one of the Parallax servos a "spin".

http://photonlexicon.com/forums/show...53&postcount=1),

(Note - Having just read Dave's post about the DMX servo controller they're offering at LaserShow Parts, I suspect their board may offer finer low-speed control. I might have to check that out...)

http://photonlexicon.com/forums/show...79&postcount=1

Anyway, using my existing DMX servo controller, the Parallax servo, and DMX capabilities of my Pangolin QM2000.net and the QM_DMX console applet, here's my results:

DMX setting of 146 = servo stopped. Solid. No jitter, no nothing!! :)

DMX settings of 147 to 255 = counterclockwise rotation, with servo speed increasing as DMX value increases.

DMX settings of 145 to 0 = clockwise rotation, with servo speed increasing as the DMX value decreases.

Slowest possible rotation settings are at DMX values 145 and 147. At these settings, the servo rotates at a consistent 3 1/4 RPM (I can live with that!! :))

Fastest possible rotation settings are at DMX values of 0 and 255. At these settings, the servo rotates at a consistent 50 RPM.

So, there you go - cheap, reliable motors for lumia and grating effects wheels that require continuous, variable rotation! Adding a wheel to the servo is easy, too - a dab of silicon adhesive will easily attach just about any glass or plastic wheel or rod to the nylon output wheel of the servo! With a multi-channel DMX controller board, a couple of Parallax continuous rotation servos for the wheels, and a few standard servos to work the non-rotating optics, you could add quite an effects setup to the projector for very little investment!

I hope to test my "lumia wheel" with one of these later this evening.
In the interim, here's the required photo.

Look - it's a servo!! :p:

Quote:

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Originally Posted by Stuka

One of the items they sell is a modified standard Futaba hobby servo, that has been adapted for continuous rotation operation.

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There are several sites showing how to mod servos that y'all may already have too.

http://www.seattlerobotics.org/guide/servohack.html

That works, too!

Although I figure I personally have saved myself a lot of grief - and sliced fingertips :eek: - by just buying the ones that were already pre-modded!! :D

Interesting Randy,

Whilst i have read somewhere about people modding servos, it must have gone in one ear and out the other, as I didn't realize the mod gave speed control:)

Hey Randy,
Thanks for all the great info- I am definitely going to check some of this stuff out!
-Mike

Slowest possible rotation settings are at DMX values 145 and 147. At these settings, the servo rotates at a consistent 3 1/4 RPM (I can live with that!! :))


Hey Randy,

Can you decrease the supply voltage to the controller to reduce the speed any further?

Mark

Hey guys- on the topic of rotation speed, you could also try this (it worked for me). I used some spare RC car gears to mount my motor to the rest of my drive train. I used this arrangement to help solidify the mounting of the motor to the chains & sprockets, but a side effect was a reduction in speed by a factor of like 3x slower.
-Mike

Cool gear train you're using in your projector, Mike!! :)

Mark -

I haven't tinkered around with the board settings yet, but my gut feeling is servo supply voltage may not have a huge impact (could be wrong on that - certainly wouldn't be the first time!! :o) These boards actually use a separate supply voltage for the board itself (8 to 12 volts) and a 4-6 volt input for the servos

One thing that I might play with is the adjustable pulse width setting - mine is set at the max range to give me full travel for my Poly-20 wheel. Since it appears that travel range for a standard servo = travel speed for a continuous rotation servo, dropping the pulse width might slow down the rotation speed - but again, I might be smokin' crack with my untested assumptions ! :p

The only drawback is the pulse width setting is applied to each servo on a multi-channel board; so, if dropping the pulse width does slow the board down, you might be giving up range of motion on all the channels.

More experimenting to come! :D

Randy

Hey Randy,
The gears were leftovers from a swap I did on an RC car to change the drive ratio- probably 15 years ago or so. That is why I very rarely throw ANYTHING away! Just about every other drawer in my house is a "junk drawer"- and this is an example of how I justify it :D
-Mike

Quote:

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Originally Posted by mikkojay

Hey Randy,
The gears were leftovers from a swap I did on an RC car to change the drive ratio- probably 15 years ago or so. That is why I very rarely throw ANYTHING away! Just about every other drawer in my house is a "junk drawer"- and this is an example of how I justify it :D
-Mike

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I hear ya'!!

It's amazing the stuff I've wound up using over the last year or two, that previously just took up space and collected dust for the last 5 or 10 years! Of course, everything I used has been replaced several times over by spare optics, diodes, etc., etc., etc., .... :p

Servo supply voltage will have an effect on slowing down the servo (actually the cheap Chinese servos I have here work a lot better on lower voltage - damping is a lot better) , however I doubt pulse width will make much difference at all..

Guess I was right about me smokin' crack with my untested assumptions... :D

What servo voltage seems to work best for your applications, Dave?

Good question,

5v seems to be pretty good. I am just running them off a bench power supply... Maybe its a good idea to build up a variable lm317 supply so you can adjust the volts easily.. Something like this

http://www.ladyada.net/library/equipt/diypsupp.html

That adjustable power supply looks like a handy supply to add to the work bench - thanks, Dave!

Another thought on the multi-channel servo boards:

For the channels being used with standard servos and non-rotational optics (shutters, Poly-20 wheel, etc.), I would want to maintain full pulse-width (probably?) and servo speed. However, for the channels that will be driving continuous rotational effects (lumia wheels and gratings), it probably would be nice to be able to "dial back" the power to the servos and slow them down a bit.

Any thoughts on a simple circuit that could be added between the servo and driver board to accomplish this without causing issues on the board itself?

Thanks!

Randy

PS -

Just found this:

http://www.hobby-lobby.com/servo_slo..._2157_prd1.htm

I might have to give one a try and see how S L O W we can make those servos run under DMX!!