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[DPRG] hacked servos responding differently

Subject: [DPRG] hacked servos responding differently
From: Sluggy! slugmusk at linuxlegend.com
Date: Thu Jun 14 00:50:46 CDT 2001


montgomery f. tidwell wrote:

> i've hacked two Hitec HS-303 servos the exact same way.


> however, they don't respond the same way. 

Because the servo circuitry is analog, there will be minor tolerance 
issues even when the modifications are mostly identical. Even if the 
circuitry in the servos was absolutely identical, the added resistors 
could be off a few ohms and result in the symptoms you describe.

Probably the easiest way around it is to find the value that stops the 
errant motor and add or subtract from the ideal number in your software. 
This will allow for the software to be adjusted later when the 
electronics again drifts out of calibration.

Another way is to replace one of the resistors added to your hacked 
servo with a 5K or so potentiometer to allow you to trim the response of 
the servo itself. Technically, you would only have to do this to one of 
them, but it'd probably be better to do it to both. Being largely 
mechanical in nature, trimmer pots are notoriously unstable, especially 
if exposed to physical shocks, so the software method might be more 
reliable. Having them reachable through a hole without having to 
disassemble the servos to adjust will help, too.

In reality, both would probably be good. You could adjust the trimmer to 
make the servos respond alike, then fine tune in the software.


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