Good morning,
I have a mbot2, I tried to program it with children and I had a problem.
When I ask it to 'move forward for 1000cm until don’e and then turn right, it stops and turn before the 1000cm. Is the robot has an issue ?
Thank you for your answer.
mBot 2 'Move forward 1000cm' moves less than 1000cm
P3C
#1
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#2
@P3C The block is not 100% precise — there is no way for the mBot to know exactly how far it has traveled. How far forward do you think the mBot is moving?
P3C
#3
First, thank you for your answer.
I understand your message but there is a big difference.
In fact we wanted to move about 18 meters but the robot only moved for 3-4 meters.
Nevertheless, when I try to move it for a determined time (2 min for example) it works correctly.
Best_codes
#4
@P3C Time is a lot easier to measure than distance, especially for a robot. 
Also, make sure that you have not modified the setup of the robot any (added tracks, changed wheel position, etc.) as the robot determines how far it has moved based upon how many times the motor shaft revolves.
Good luck!
P3C
#5
Thank you !
I didn’t change the setup (the robot is new).
I thought the robot was able to measure a distance, but it seems it is able to do it for a small one.
Best_codes
#6
@P3C Yes, the robot is usually precise at small distances (or seems to be). A difference of 10% at 10 cm is only 1 cm inaccurate, at 100 cm it is 10 cm inaccurate, and so on.
Since you did not change the setup, also note that the accuracy is affected by uphill / downhill slopes do to increased friction in the gearbox.
Would any of that affect your robot as well?
P3C
#7
No it’s not my case. I will do it differently so, using length for small distances and time for longer ones.