I also wonder too- we all know the robots are often not 100%  
consistent- but the children do have a chance to show their  
programming- and "programming" will show during the robot design  
judging.....I have told my team that cause they did some very nice  
programming- battery power equally makes things erratic. Laura
On Nov 4, 2010, at 3:29 PM, Mandy Wilson wrote:

> Turns out that our problem was a faulty motor on the left side which  
> caused the merry go round effect when it turned right.  My son, who  
> is homeschooled, read all of the emails and helpful suggestions that  
> came in and ran upstairs to test.  Sure enough when the right turn  
> was changed to a left, the program worked perfectly.  (It didn’t  
> occur to me that was the only right turn the team had done in the  
> last few days).  When he replaced the motor the right turn in that  
> program worked perfectly.  Always nice to have a motor burn out 2  
> days before the competition!  Now apparently many things are just  
> slightly off as this motor is a little different than the last and  
> my son is not pleased that he and his friends now have to redo  
> almost everything!  Maybe this is why people drop out of events?  No  
> the team is not dropping out, but it will be nice if they can get  
> back to where they were.  Thanks to everyone who helped.  I don’t  
> know what this team would have done without all your help as today  
> the merry go round effect was occurring 50% of the time.  I’m sure  
> the motor would have been completely dead in 2 days.
>
> Mandy
>
> From: First Lego League in Virginia and DC [mailto:[log in to unmask] 
> ] On Behalf Of Eric Palmer
> Sent: Thursday, November 04, 2010 1:43 PM
> To: [log in to unmask]
> Subject: Re: [VADCFLL-L] NXT merry go round effect
>
> My team this year had a robot with a particular mission and  
> attachment set that had a "veer left bias" They changed the whole  
> robot to our backup and it "veered very slightly right" on further  
> inspection the first robot has an axle going through a beam that has  
> been damaged so there was more friction on the left side.
>
> For the right bias they moved a counter weight to the left and the  
> robot goes straight most of the time.  But even with that it varies,  
> sometimes badly.
>
> We are using disposable batteries this year and they monitor voltage  
> closely.  The front missions they use fully or nearly fully changed  
> batteries and the last mission they use batteries whose top voltage  
> has been lowered.
>
> They use a slight moist cloth to wipe the dust off the table before  
> practice and we occasionally wipe the dust off the wheels and let  
> the tires dry.  They store the robot upside down so the wheels don't  
> get flat spots.
>
> The team pays attention to many more factors for repeatability as  
> well.
>
> But that said we still have problems with erratic behavior.  Turing  
> for example seems to work best (for repeatability) one wheel at a  
> time.  That slows down the missions but makes the missions more  
> repeatable.
>
> All learning opportunities.
>
> Eric
>
> On Thu, Nov 4, 2010 at 1:24 PM, Nagesh Chintada <[log in to unmask] 
> > wrote:
> This is hard to figure out without seeing it, but couple of  
> questions come to mind:
> 1. Has your team tried to reduce the power, to say, 50 or below?
> 2. How is the robot balance and center of gravity? For example, does  
> it happen if the attachments are removed?
> 3. I noticed that sometimes loose wheels can cause strangest  
> behaviors in movement, so not a bad idea to check if the any part of  
> the attachments/ frame and wheels are not loose.
>
> Just a comment: The great fun of FLL is ruined especially to rookie  
> teams because of all the variability in the NXT Robots. These are no  
> doubt complex products, and it is not easy to get consistent  
> behavior. It requires some experience and lots of practice. This is  
> not my first year, but I am still learning.
>
> I wish Lego or FLL would make it easier for all the teams - and  
> improve the fun factor - by providing some basic information/  
> instructions/ best practices to reduce variability as part of the  
> NXT kit or FLL kit. Just a thought. I'd like to see more teams  
> having more fun than struggle so much.
>
> Nagesh
>
>
>
> On Thu, Nov 4, 2010 at 10:15 AM, Mandy Wilson <[log in to unmask]>  
> wrote:
> This turn does not involve sensors.  It’s just a plain point turn.
>
> From: First Lego League in Virginia and DC [mailto:[log in to unmask] 
> ] On Behalf Of Eric Palmer
> Sent: Thursday, November 04, 2010 10:09 AM
> To: [log in to unmask]
> Subject: Re: [VADCFLL-L] NXT merry go round effect
>
> I wish I knew what causes this. We see it occasionally. Something  
> lose wires. Sometimes changes in battery levels. Do check to make  
> sure that if you are using sensors that they are working reliably.
>
>
> On Thu, Nov 4, 2010 at 10:06 AM, Mandy Wilson <[log in to unmask]>  
> wrote:
>
>
> Our team has a part of its program where the robot is supposed to  
> turn some nominal amount (around 30 degrees) and for some reason  
> every 5th run or so, it spins about 120  degrees.  They have put a  
> reset motor block, a break block and even a 1 sec wait block in  
> front of the errant turn in order to stop the issue, but nothing  
> they have done works.  They’ve even tried deleting the block and  
> putting another one in.  They thought it was the gearing on the  
> wheels coming loose which also causes it to act up, but on the 6-9th  
> run it works fine and then at run 10 it does it again.  Well not  
> quite that predictable, but you get my point.  Has anyone else had  
> this problem and is there a way to fix it, or should the team just  
> be resigned to blow a round at the tournament?  Thanks for all the  
> help – this is our first year!
>
> Mandy
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>
> -- 
> Nagesh Chintada
> Phone: 703-829-0284
>
>
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