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October 2015

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From:
Jeff Schoolcraft <[log in to unmask]>
Reply To:
Jeff Schoolcraft <[log in to unmask]>
Date:
Tue, 20 Oct 2015 15:43:32 -0400
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Lots of things go wrong with these robots, they’re only toys after all.

You can google for matching motors and wheels, as that’s been a known issue with NXT.  Not sure how good the EV3 production tolerances were.  There could be balance issues with the robot, e.g. more weight over the left wheels giving them more traction than the right wheels and causing a steer.

I’m not sure what code you’re referring to but with motor encoders you’re trying to zero out errors between the two motors to drive straight.  The gyro could drift or be subject to other input (vibrations?  I’m just guessing).

You can also try to “true up” your navigation as you go “squaring” to lines or walls.

Just thoughts…

-- 
Jeff Schoolcraft

On October 20, 2015 at 3:34:48 PM, Cedric D'Costa ([log in to unmask]) wrote:

Our kids have experienced that going in a straight line is a challenge. The Robot works differently
based on battery power or some unknown variables. Even the code found online using the
Gyro sensor does not always work. The EV3 will gradually steer to the right or left.
Sometime just the basic Move tank or Move steering works. This has led to a level of uncertainty
during programming.

Has anyone managed to make the EV3 go in a straight line consistently? Our success rate has been
3 out of 5 on an average using the Gyro so we're not sure how it will perform on Competition day.

Thanks,
Cedric

On Tue, Oct 20, 2015 at 1:48 PM, Frank Levine <[log in to unmask]> wrote:
PID is good when you have non-straight lines, because it will react to the 'D' term as the line starts to turn away.  In practice, PID is not easy to program (correctly) in EV3.  I have tried.  It also requires a level of math that my team has not learned yet.  They're in 5th grade now... maybe next year.  I do think that PID would be good for straight line driving using the gyro.  For almost all normal FLL tasks, just doing 'P' will get you where you need to go.

On Tue, Oct 20, 2015 at 1:44 PM, Thomas (Tweeks) Weeks <[log in to unmask]> wrote:
Thanks.. Great resource. :)



Still didn't see any pure PID straight line tutorials though.. although I DID like the "straight line" tutorial and how it used degrees.

:)



Tweeks

From: Todd J Lennox <[log in to unmask]>
Sent: Tuesday, October 20, 2015 1:04 PM
To: Thomas (Tweeks) Weeks
Cc: [log in to unmask]
Subject: Re: [VADCFLL-L] Any good EV3 Code Examples for a Straight Line PID program?
 
Try EV3 lessons. They have some really good stuff. 

Sent from my iPhone

On Oct 20, 2015, at 12:35 PM, Thomas (Tweeks) Weeks <[log in to unmask]> wrote:

I've seen a few videos and sites talking about PID based line following and balance bot applications.. but our kids just want to see a good example of straight line PID code (without trying to teach them calculus).



I can do this in C, but I'm not savvy enough with the mindstorms GUI tools to show them how to do it in Lego.



Tweeks

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