OpenServo.com

[pbreed]

I'm using tonegawa PS-050 servos for my rocket valves.
these are more than 91.50 Kg/cm starting torque.

They are much larger than the open servos.
(I burned up more than 8 of the HSR-5995TG's in this application)

My Tonegowa in use can be seen in use here:
http://www.youtube.com/watch?v=KLhY5KU9ddA

I've found the tonegawa servos to be reasonable when ordered directly from Japan. I paid $140 each for 8 of them including shipping from tokyo hobbies.(info@tokyo-hobbies.com)

The downside to these servos is that they are analog, so there is no position feedback and no adjustments to deadband etc.....

In looking for a digital version of this servo I ran across the following article:http://www.informatik.uni-freiburg.de/hr/papers/HSR06_Control.pdf
any comments from the people who have been working on servos here as to the correctness of this approach?

The tonegawa has more than enough room to add a small add-on board
inside the case to do the digital parts. Add a Hall sensor for current and
change the time constant on the analog servo to take 10msec updates
and I see this as every bit as good as a purely digital approach.
Would anyone like pictures of a disassembled tonegawa?
I can send some.
They have a cutaway view showing the empty space here:
http://www.tokyo-hobbies.com/PS-050.PDF

Paul

[ginge]

Hi Paul,

Those servos are huge! I don't see why you can't use portions of OpenServo software and hardware to make something to control the servo.

Do you know how much current those motors draw? I would imagine a stock OpenServo would catch fire in one of these servos going full speed.

BTW nice video.

Barry
_________________
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[jamma]

You'd probably be fine with a custom version of the OpenServo with beefier MOSFETs in the H bridge. Of course, once you've gone that far, you could then use virtually any gearhead motor + pot to actuate the valves in your application (although the servo package looks nice and tidy). Ginge has made modified boards for larger servos used in robot arms, so his advice will be particularly relevant.

PS: Very impressive app. Do you use servos for gimballing too, or only fuel mixing? Any URLs describing your work?

[pbreed]

>PS: Very impressive app. Do you use servos for gimballing too,
>or only fuel mixing? Any URLs describing your work?

I'm working on a vehicle to compete at the xprize Cup Lunar Lander Challenge.
It will have 4 throttle able motors, no gimbals.

You can follow along at my blog...
http://unreasonablerocket.blogspot.com/

For a description of the overall vehicle...
http://unreasonablerocket.blogspot.com/2006/11/virtual-vehicle.html

I started with the HSR-5995TG servos...
Here: http://www.rasdoc.com/paul/rockets/ballvalve.html

[jamma]

Very cool! Rapidly going off-topic, so I'll be short. I have dreamt of using the OpenServo in a gimballed rocket. Inspiration found here:
http://www.ukrocketman.com/rocketry/gimbal.shtml#gimbal17

Ultimately, I've decided to stick to bi-peds for now (just never enough time...)

Best of luck on your project! I'll be following your progress with interest.

[robotjay]

Paul,

I asked Tokyo-Hobbies what the maximum current for the Tonegawa servo is, and they replied: