Servos for lumia and grating wheels...

[Stuka]

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!! :

[mophead]

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

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

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

[Stuka]

That works, too!

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

[dave]

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

[mikkojay]

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

[ImageLight]

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

[mikkojay]

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

[Stuka]

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!! ) 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 !

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!

Randy

[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
-Mike

[Stuka]

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
-Mike

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., ....