Tuesday, January 08, 2008

What does it take...

My Son is currently working on an interesting business idea with some friends up in the bay area. So I'm currently working on the project solo. What does this mean?

I'll give you a brief rundown of just this evening. (A fairly typical evening.)

I got home from work about 5:45.
I usually sit down and have dinner with my wife and who ever is here.
My Wife is battling a cold (the one I had last week) so she was asleep so I heated up some soup in the microwave and watched the NH election returns while I ate dinner.

6:15 out to the garage.
I'm trying to get a handle on valves so I pull out all the sample valves and actuators I've collected to look at them. I think I want to concentrate on the brush less actuator and the Dynamixl actuators.

One of the possible valves is a cyro rated globe valve, but it takes multiple turns.
The torque of the brush less actuator is insane with the 256:1 gear box, but I need faster if I'm going to use a multi turn valve. So I remove the brushless motor from the 2656:1 and put it on the 36:1 gear box. This involves removing one very stubborn screw and machining two parts on the lathe. Elapsed time 2 hrs its now 8:15. On the 36:1 gearbox the brushless actuator is still stronger than I need. however the actuator speed is not symmetrical, the brush less controller still thinks its driving a car, not a servo. So go dig through the manuals files looking for the programming instructions for the Novak "goat" brush less controller. After decoding their programming scheme with 4 multicolor blinking lights and a single button I have the controller operating in servo mode. Still insanely strong and veryfast. It looks like a good possibility.

Next I move on to the next actuator, the Dynamixel RX-64.
I go to the computer and download and print the manual. I review the specs and discover that the claimed max torque is the same as the much bigger, beefier and heavier tonegowa, cool,
I knew it was good, but my mental model had it half that strong, My head stores data in a variety of units and I messed up the mental Kgcm to inoz conversion in making that assumption.
Now to make it work. Step one build a wiring harness, first problem the manual talks about 5 pins, the connectors and cables only have 4????

After some head scratching I see that the case and semi-hidden PCB have 5 pins, but the connector soldered in is only 4 pins. mystery solved. Get up from the computer go out to the garage and set up the soldering iron and heat shrink gun and make a nice cable.
Now what to connect the actuator to for testing? It needs RS-485 half duplex, so I dig through my NetBurner junk box and find a carrier board that supports RS-485 half duplex.
Next I dig up the schematic for the obsolete carrier board (The obsolete stuff comes home, the new stuff gets sold.) and wire up the RS-485. I haven't done any RS-485 programming in awhile, so I haul out the scope to make sure the enable disable timing is correct. It is,so
now I have to figure out what the default baud rate is. The dynamixel manual tries very hard to hide this important bit of information but I hunt it down. In a few more minutes I have the actuator exchanging packets with me and giving me its internal temperature and status.

I just can't seem to get it to move....
Alas I have to enable "torque" and realize that the internal position commands are of a different endian state than what I was passing. The actuator moves and I can command it back and forth. Its reasonably fast and seems very strong. Cool! that only took 2 additional hours.

So I spent in excess of 5 hours this evening and I accomplished:
Changed gearbox on a possible actuator.
Verified that the dynamixels do what they say they do.
Wrote up this blog entry.

I usually take one evening a week and go do something with my wife like go to a movie or play. I usually take one evening to just vegetate. Other than that I'm usually woring on the rocket project. Only 10 months til LLC 2008, not nearly enough time.


Anonymous said...

A very interesting read. It really gives some perspective to the vastness of the endeavour.

Try not to burn out, your schedule sure sounds a bit crowded (week after week).

And, thanks for sharing, these kind of posts are actually some of the most interesting ones to read!

Good luck and keep it up!

- K.Luojus

V said...

Mr.Unreasonable Rocket
Hope all is well.
I was wondering if you managed to get any additional information about the RX-64 servos, especially about the motors they have inside?
I know they use a maxon RE-max, but have been unable to figure out which model. I desperately need to know how much power the motors can generate.
Any information will be useful.