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I like the following posts in First Forum re some lurch steering problem we have. (quoted from  http://forums.usfirst.org/showthread.php?t=12856&page=3)   LOL Comets, BTW, is an all-girls team that won THE Championship Award. http://www.youtube.com/watch?v=_1xqRx45Bws&playnext=1&list=PLD6FB6D5DFB96B47C&index=1     09-19-2009, 11:26 AM

LOLComets Member   Join Date: Apr 2009 Location: Southern California Posts: 47

Re: NXT move vs motor block help needed Looking at how this topic has changed, and if I am not mistaken, you have two issues: 1. Robot veers in a certain direction when it starts (we have the same problem) 2. Turns using the move or motor block are not consistent (everyone has that problem) For the first item, our team decided to run the robot for the first 50 degrees at different powers supplied to each motor. For example, if your robot veers left (towards the B motor), then your B motor block would run at 45% power and the right (C motor block) would use 50% power. Both blocks would use unlimited and the rotation sensor would be used to change the power and remaining degrees you want your robot to move. For the second item, I would suggest you accept that slippage, surface, and of course the robot is made out of plastic is not precise. You can minimize the turns using a different method to arrive at the desired destination, and design attachments to allow for the variability, i.e., your robot will end at a specific spot in a + or - 2 inches, so my attachments have to be wider. Getting your kids involved in learning and understanding PID is really a function of their age and interest. However, PID is something they cannot control. So the challenge is to solve the symptom of the problem, which is perhaps the approach that would be appropriate.

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#25   09-19-2009, 12:34 PM

GotRobot? Senior Member   Join Date: Sep 2008 Location: Elgin, Illinois Posts: 197

Re: NXT move vs motor block help needed Quote: Originally Posted by durant7 Got them again on Sunday. Any suggestions for the rookie coach accepted? Hope to move on to touch sensor which brings in the switch logic next but I feel as though we have not exhausted the move/motor/bot engineering yet. Alas Nov 14th is around the corner. A PID algorithm is already built into the MOVE block. The MOTOR block has it too but it's implemented differently. Each has their strength depending on how you use them. I wasn't sure from your post if you are measuring the accuracy of distance or turning but either way I have a few suggestions for you to consider. 1. Your wheel diameters are likely different enough to cause the robot to drift to one side. Try changing sides and see if it drifts the other direction. BTW- drift isn't bad so long as it's consistent. If it's consistent then you can predictably compensate for it. But eliminate as many variables as you can first. 2. Check and see if the wheels are placed the same way on each axle. 3. Smaller wheels take more revolutions (motor degrees) to travel the same distance as larger wheels. More degrees = higher resolution. Smaller wheels should be more accurate than larger ones. 4. Have the team explore using a skid or roller vs. a swivel castor. 5. Have the team explore the differences between point turns and swing turns using MOVE and MOTOR blocks. 6. Explore the differences in accuracy with a wide wheel base vs. a narrow wheel base. 7. Explore accuracy in distance and turning where the center of gravity is shifted closer or farther away from the drive wheels. ========== You're doing a great job coach. Keep it up. Stay thirsty my friend. __________________ Cheers! got robot? -- FLL Team 280 Cat herding since 2008