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Problems with Hitec HS-5745MG Servos on TETRIX 
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Joined: Sun Jun 23, 2013 4:44 pm
Posts: 1
Post Problems with Hitec HS-5745MG Servos on TETRIX
I'm new to this NXT and RobotC stuff (but an old hand at c and embedded programming). I've got a semi-custom arm built using Hitec servos. Two HS-5745MG servos are used - one for the shoulder and one for the elbow - and three smaller servos - one each for the base, wrist and pincher.

Generally speaking, the arm works fine with the simple RobotC code that tests the arm. However, at seemingly random times, the two large servos seem to reset and the arm folds up and unfolds repeatedly (i.e. the two large digital servos seems to go to the zero position for no reason at all and the arm starts to spaz out).

I'm thinking this is some driver or timing issue in the TETRIX... can anyone shed some details?

Is there any way to force a reset of the TETRIX at the start of each run?

RobotC version 3.54 (can't use the latest for compatibility reasons)


Sun Jun 23, 2013 5:01 pm
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Joined: Thu May 24, 2012 12:15 pm
Posts: 722
Post Re: Problems with Hitec HS-5745MG Servos on TETRIX

Would you be able to post the code using the [code] tags? From what you are describing it sounds like the code is correct but we would want to check just in case.

The servos themselves should use the standard PWM servo communications, so the issue may be more hardware related than software related. The current draw of the servos may be an issue, depending on the setup and load of the arm itself; I would check each servo individually by unplugging the other servos, running your code for a while, and seeing if the error continues without the other servos drawing power. If the problem persists, I would suggest trying other ports, another servo controller, etc until you are able to narrow down where the issue lies. We'll take a look at the code first though to make sure that there aren't any programming issues.

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Thu Jun 27, 2013 3:47 pm
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Joined: Wed Jan 24, 2007 10:42 am
Posts: 620
Post Re: Problems with Hitec HS-5745MG Servos on TETRIX
Quick question: Are the servos going "nuts" when a program is not running on the NXT brick (and the ROBOTC debugger isn't active either)?

The servo controller will time out after no communication for 10 seconds, putting all of the servos in a "neutral" position.

Timothy Friez
ROBOTC Developer - SW Engineer

Tue Jul 16, 2013 12:55 pm
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