8 Nov 2004 NateW   » (Master)

Another year has gone by so it's time for my annual robots.net journal entry. :-)

Still no new developments with the simulator, it stabilized back in '02 with the features I set out to create so I haven't had much inspiration or motivation to enhance it. There may be an extension before long to allow other applications to control simulated robots... but I'm not promising. Lots of other irons in the fire right now.

Moments ago I beheaded a Hitec 645MG and 5645MG (essentially the same servo, but the former is analog and the latter digital) and a Futaba 9252 (digital), and hooked them up to some RC gear to see how they would behave in continuous-rotation applications. I have long theorized that digital servos use PID feedback to get their improved holding power, and furthermore the "I" term in the PID equation would render them useless for continuous rotation. I was wrong.

If there were an I term in the feedback equation, I would expect the servo motor to accelerate to full speed if the desired position and actual position were held just slightly apart for a length of time. However, I was able to make the motor run at a low speed indefinitely. The Hitec 5645 seems to have slightly higher proportional feedback than the 645; the Futaba 9252 has substantially higher proportional gain (the 'window' that creates variable speed output is quite narrow by comparison to the others), but there's no evidence of integral feedback.

I surgicially reattached the heads of the aforementined servos and I am happy to report that all three patients recovered fully.

Warning, shamelessly off-topic self-promotion follows:
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Now, back to robot stuff...

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