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[DPRG] Maximum hobby servo voltage revisited

Subject: [DPRG] Maximum hobby servo voltage revisited
From: Jeffrey T. Birt ditto at ipa.net
Date: Wed Jun 14 21:16:54 CDT 2000

While sitting in traffic tonight, thinking of the battery configuration of my new 'bot.  I was still thinking over the possible problems of trying to run hobby servos at higher than recommended voltage.

As some might remember my latest bot is being built on  an RC truck chassis because I had this new RC truck chassis laying around and I wanted a 'bot that could be used in the great out-doors.  Being an RC chassis it was naturally designed to house a standard 7.2V RC nicad battery pack.  I was then concerned that the servos would not last long at this voltage.

We had a good round on the list about maximum voltage supplied to hobby servos and someone even had a link to a good site with an article on the subject.  All sources seem to indicate that one could get by with 7.2v.  It's been bugging me ever since.  I just wanted to drop about 1.2v and not waste a bunch of power in the process.  Any type of (linear) voltage regulator seemed overly complex, serovs don't need regulated power, and might waste a bunch of power (as heat) in the process.

....any how....tonight it hit me....duh!   How about a couple diodes in series with the servos?  It would drop about 1.2-1.4 volts and not waste much power.  When testing a Futaba S-148 (I think that's the model) servo I found that it had a nominal 50ma draw (idle) with a max peak of 300ma (trying to force it out of position).  This works out to 60 to 70 mw (idle)  and 360 to 420 mw max wasted as heat from the diodes.  Yeah, neah?

Jeff Birt
Halfway, Missouri

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