Why do you use the white "motorcycle" wheels & tires? PDF Print E-mail
Tuesday, 05 October 2010 21:21

Question 

Hi, Jamie,

I have another question. Many youtube videos including yours had large tires/wheels. I didn't see a lot of people using the original thick/small mindstorm NXT tires.

Are there any particular reasons for using the large tires/wheels?

It seems there is a large error and it may be more difficult to be precise, and since the tires are small, it would have to rotate the motors more to move which could consume more battery. Are these the main reasons for not using the small tires/wheels?

We haven't played with any large wheels yet, and we were just wondering if there were any reasons.

I am sure you have played with many different kinds of tires/wheels. Any info would be appreciated.

 

Answer 

Masaru,


It's actually a bit simpler than that.  We have played with a variety of tires.  Our first year we used what I'll call the small balloon tires that came with the NXT.  The numbers on the sidewalls read "56 x 26".  Then the next 2 years we ended up using the white "motorcycle tires".

Our main decision point the first year we used the large white motorcycle tires was that they seem to provide the best traction.  Both some reading we did and our own testing seemed to indicate that they had the best traction of what I'll call the common tires.

Last year, the second year we used the white tires, we just used them because we had the year before and they had worked well for us.

There is also one side effect which is kind of nice for the programmers.  The large white motorcycle tires are roughly 10 inches in circumference.   That means one rotation takes you 10 inches and .1 rotations takes you an inch.  So if you need to travel 37 inches across the field, you start by programming the robot to go 3.7 rotations.  It all works towards that thing from the workshop where everybody on the team should be able to take a tape measure, measure the distance you want to go, and program a move block that will get you very close on the first try.

Oh yeah, to answer your other question.  From a motor perspective I would expect both more precision and more repeatability from smaller tires.  But the critical factor in odometry as a way to measure location seems to be wheel slip.  So in the end better traction gives you the most accuracy, or at least limits your accuracy the least.  You still need some good programming to be accurate.

Jamie 

 
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