Twelve Tips & Tricks To Get Your FLL® Robot Driving Straight

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The Joy of Getting Back to Base!
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Is your team having trouble getting their FLL robot to drive straight?  Read my 12 tips & tricks...

Here are some tips and tricks to help your team get their robot to drive straight that I've accumulated over the years:  
  1. For NXT based robots, use motor ports B and C for closer matched motor power between drive wheel pairs. Motor port A comes off a different/separate single-channel bidirectional motor driver IC (LM1930M), whereas, Motors B and C come of the same two-channel bidirectional motor driver IC (LM1836M).  This is not well documented unless you look at the NXT schematic diagram.
  2. Use a single MOVE block controlling both motors B and C instead of two independent MOTOR blocks controlling the motors independently (unless you really want to code your own motor synchronization or PID controller My Block, see FLL forum post Custom block to drive straight for some help with this).
  3. If you want your robot to move more precisely, set the Move block to brake, not coast, to enable the automatic error correction firmware do its thing.
  4. Does the robot always turn in the same direction? If so, switch motors and see if it turns in the opposite direction.
  5. Test your motors and try to find the best two for a matching pair.
  6. Motors are likely to perform more consistently at 70% power than at 100% power ( nxtmotor/nxtmotor.htm).
  7. Ramp up power to avoid jerky jump starts common at higher power settings depending on how well balanced your robot is.  Try and have most weight of robot centered over the drive wheel axels.
  8. It's important that the weight of the robot be balanced between the two drive wheels. If one wheel has slightly less weight on it than the other, it may spin just a bit and cause the robot to tend towards one side. Symmetry in robot design is important for going straight.
  9. Is any part of a drive wheel potentially rubbing against the robot chassis?  
  10. Are you using friction pins (blue or black in most NXT kits), when you should be using a non-friction pin (yellow/biege or grey) for any idler wheels or gears?
  11. Try different tires configurations - depending on the surface and the weight of the robot, different tires may have better  traction
  12. Check out the FLL forums for post like this one Keep-Robot-Going-Straight
Posted by David McQuiggan on Sep 9, 2014 4:58 PM Europe/London

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FIRST LEGO League 2014 "World Class" Challenge Coaches

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Blog for coaches and mentors of FIRST® LEGO® League (FLL®) robotics teams competing in the 2014/2015 "World Class: Learning Unleashed" global challenge.

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