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November 2014

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From:
Greg Trafton <[log in to unmask]>
Reply To:
Greg Trafton <[log in to unmask]>
Date:
Fri, 7 Nov 2014 11:46:54 -0500
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The team is not running the motor into a hard stop.  The timer is a good idea (they've used it in other situations, but not this one).  But what actually happens is that the motor is supposed to move at 50% power for 180 degrees and instead it moves very fast, just spinning (motor gone crazy! ;-).  The motor could be malfunctioning but we don't have a spare.  One suggestion I got offline was to stop the motor with a coast rather than a hard stop -- this  may not lock the rotation sensor into thinking that it is in a specific location when it is moved later.  This hasn't been tried yet, but it is a sporadic bug.  

Our tournament is tomorrow, so we will see how it turns out!

thanks!
greg

On Nov 7, 2014, at 11:39 AM, Frank Levine <[log in to unmask]> wrote:

> Are they running the motor into a hard-stop?  Our team does this too, but we use a timer to exit the loop after we know that it has reset to the correct position.  It sounds like your motor is malfunctioning... do you have a spare?
> 
> -Frank
> 
> 
> On Fri, Nov 7, 2014 at 9:59 AM, Greg Trafton <[log in to unmask]> wrote:
> Hi, all.  Our team has been having a great time with the missions this year.  They have been using the medium (rotary) motor for a couple of missions, but it has been mis-behaving and I'm looking for suggestions.  Here is the behavior:
> 
> 1) The kids put an arm on it and move it to the correct position (backdriving the motor).
> 
> 2) They reset the motor in code before it is used.
> 
> 3) Sometimes (20%?) the rotary motor spins like crazy over and over causing a failed mission and stop mission penalty.
> 
> The only fix the kids have found for this has been to unplug and then plug in the motor from the EV3 controller before the mission, but that takes time and sometimes doesn't work either.
> 
> My guess is that backdriving the motor at the beginning is the source of the problem, but there is no way NOT to do that at least a little.
> 
> Earlier in the season the kids tried changing ports (no luck) and wires (no luck).  We haven't changed motors because we don't have a spare.
> 
> Has anyone else had this same problem?  Any possible fixes?  Bad motor or something else?
> 
> Thanks for any suggestions!
> greg
> 
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