LISTSERV - VADCJRFLL-L Archives

Mandy,

Take a minute and read about the DARPA challenge from about 5 years ago. Whole teams of university faculty, industry teams and scientists worked to have a “car” drive around a desert track. It took at least two years for the first team to finish the task. The robots went off course, stalled for no good reason, got stuck, broke down, etc. Google is just now figuring out how to drive a car on a real road (Google!). How many of NASA’s missions have gone screwy after launch? It’s hard work to make a reliable robot – even with LEGOs. But boy does it feel great when it works!

I’ve never seen a program like this (FIRST) that would cause kids to spend so much time working together and solving problems, working through the frustrations and failures and doggedly figuring it out. As a team they’ll get better every year.

I hope that each of them pursue a tough, technically challenging degree in college and go on to solve big problems – and when they hit the wall in calculus, computer science, engineering or physics – and just can’t figure out why something isn’t working…they’ll have the skills they need to work through it because of what they’re doing right now.

From: First Lego League in Virginia and DC [mailto:[log in to unmask]] On Behalf Of Mandy Wilson
Sent: Thursday, November 04, 2010 3:29 PM
To: [log in to unmask]
Subject: Re: [VADCFLL-L] NXT merry go round effect

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 5^th 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 6-9^th 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