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encoder in smart motor 
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Joined: Mon Jun 30, 2014 8:03 am
Posts: 4
Post encoder in smart motor
I am hoping to set up a class activity connecting circumference of the wheel with the software.
The idea is to have kids take the distance for the robot to travel and calculate wheel circumference.
Then they would know how many rotations to put into the program.

However, it looks like the smart motor 'rotation' is actually the inner motor shaft turn. So a rotation is
360 ticks?
So, similar to kids using time to program distance, they would set their program for one rotation, download to the physical robot, run it and measure distance. Then set up a quick table- ie 1 rotation goes 14" so 3 rotations = 42" and so on?

Thanks for any help. I am in day 2 today of teaching a summer camp to kids! I am trying to stay one step ahead!

Tue Jul 15, 2014 6:31 am

Joined: Mon Oct 04, 2010 2:18 pm
Posts: 196
Post Re: encoder in smart motor
You could set it up like that. Or, you could have the students measure the wheel's diameter first, in order determine the circumference. Then determine that the Distance the robot needs to travel is equal to the Circumference * Rotations. With this, the students will know the Distance and the Circumference, they will just need to then solve for the rotations. Finally, you could leave it totally open-ended and see what the students come up with on their own.

Tue Jul 15, 2014 7:31 am

Joined: Thu Mar 13, 2014 8:22 am
Posts: 10
Post Re: encoder in smart motor
A couple other things to keep in mind:
Programming the robot to travel forward one rotation can work, but it's possible the robot's inertia will carry it a little bit farther. A handy strategy is to mark a wheel with a piece of tape so you can easily follow its rotation. You might not even want students to write a program for this, but just roll the robot by hand.
Also, the distance the wheel travels in one rotation is the wheel circumference, so if you want this activity to involve some more math, you may want to go with the diameter measurement approach :)

Tue Jul 15, 2014 11:27 am

Joined: Mon Jun 30, 2014 8:03 am
Posts: 4
Post Re: encoder in smart motor
ok. Today went well.
So i was thinking that the 'rotations' was an internal motor rotation number that didn't relate to
the outside shaft turn. Thanks for the correction.

I did one rotation. It went 8"
The wheel circumference is published as 2.75"
but i measured 2.5" 2.5 x 3.14 = 7.85

This matches up with many sites and your reply that there is a bit of momentum.

OK. This is a great activity for real world reasoning skills.
Thanks. And i am getting a lot of beneficial info from the summer of learning/Jason McKenna and crew!

Tue Jul 15, 2014 2:58 pm
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