Brandy makes a key point about timing vs rotation:  This may be another “teachable moment”.  If you conclude that the robot behaves differently depending on the level of battery charge there may very well be software changes  you can make that solve or greatly alleviate the problem.  For example, if your team has decided to use time to pace the robot’s movement around the table (go forward for 2 seconds, then turn 90 degrees then go backwards for 3 seconds, etc.) then you’re setting yourself up for a problem – the distance the robot travels in a given number of seconds will vary greatly depending on battery charge.  BUT if instead you use the rotation sensor (for example – go forward for 480 degrees of rotation, turn right, go backward for 720 degrees of rotation) you’ll have much more repeatable behavior (the main source of variability being tire slippage).

 

This was an issue with the first generation of mind storms (RCX – before NXT and EV3 came along!).  The early kits didn’t have rotation sensing so many teams resorted to using time to pace the robots, with unpredictable and often unrepeatable results….

 

-          Glenn

-          (former FLL coach)

 

 

From: First Lego League in Virginia and DC [mailto:[log in to unmask]] On Behalf Of B Bergenstock
Sent: Tuesday, October 29, 2013 5:41 PM
To: [log in to unmask]
Subject: Re: [VADCFLL-L] Robot consistancy

 

For my team, it was a motor that decided to not break completely, but not work at "regular" speed. So the advice of the painters tape to check to see if a robot is running straight is a great tip!  For us, there was no way to correct for it because it seemed to not have a consistent slowing down in that motor.  After discovering it, the kids had to rebuild the robot to make the 3rd motor the right wheel motor and move that "broken" motor up to the 3rd motor position where it's slower speed didn't affect the driving of the robot.   I have since outlawed hand-spinning  motors- you know when the kids stand there with the robot and just rip away at the wheels to make them move? Yeah. Ask them not to do that.

  Our biggest problem by far was user error, but battery power really hurts you if you have programmed any timed missions, vs. degrees/rotations.  Not that you want to redo any of your missions this close so game time, but you might have time to update one section on the most critical missions if you used the timed distance option. 

Good luck! And have fun :)

Brandy

 

On Tue, Oct 29, 2013 at 3:48 PM, Scott Rakestraw <[log in to unmask]> wrote:

Mandy outlined all the consistency issues.  In my team’s experience, it has been battery assuming the robot is not changing.   The team would start with a fresh battery and as the practice went on, things that were working would stop working.  They would make adjustments.  Once the battery was charged, the stuff that was working stop working.  After experiencing this rinse and repeat cycle, we now limit programming practices to one hour.  

 

Scott Rakestraw

Coach

Capital Girls and Code Crackers

 

From: First Lego League in Virginia and DC [mailto:[log in to unmask]] On Behalf Of Tonya Lapham
Sent: Tuesday, October 29, 2013 12:34 PM
To: [log in to unmask]
Subject: [VADCFLL-L] Robot consistancy

 

Hello,

 

I seem to have this trouble each year.  The robot will be doing just fine.  Then suddenly the programs that were working fine now are not working the way they were programmed.  And it seem to happen about the same time during the tournament season, only it is with a different set of kids each time.  Any suggestions on how to trouble shoot these issues?

 

--
Thank you!!

Tonya Lapham

Coach

Seismic Wave

 


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