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krudeboy51
29-04-2011, 09:16
sorry for the weird thread name but, is there any way to program a robot to stop on a dime instead of rolling like an inch away from designated stopping area?
Mike Betts
29-04-2011, 09:34
sorry for the weird thread name but, is there any way to program a robot to stop on a dime instead of rolling like an inch away from designated stopping area?

Kory,

Can you stop your car on a dime?

If you are talking dynamic reaction (ex: teleop), no. Acceleration is defined as the change in velocity divided by the change in time. In this case, "immediately" implies that the change in time is zero hence the accereration is infinite. F=ma requires that the force also becomes infinite. Yada, yada, yada...

If you allow for a trajectory plan (ex: autonomous) then you have to plan the deceleration of the robot to stop exactly where you wish.

Read about PID controls and the response of a PID to a step change input. There are several excellent CD white papers on the subject.

Regards,

Mike
Mark McLeod
29-04-2011, 09:34
That would be a finely-tuned PID loop with encoder feedback.
Here is a student paper (http://www.team358.org/files/programming/PIDControlTheory_rev3.pdf) on the topic.
virtuald
29-04-2011, 13:36
It's not an instantaneous stop, but if you set all of your Jaguars to 'brake' mode instead of 'coast', that will stop you reasonably quickly too. If you want something more exact, then PID is definitely the way to go.
krudeboy51
29-04-2011, 14:25
It's not an instantaneous stop, but if you set all of your Jaguars to 'brake' mode instead of 'coast', that will stop you reasonably quickly too. If you want something more exact, then PID is definitely the way to go.

how do you do break mode?
virtuald
29-04-2011, 20:37
how do you do break mode?

There's a jumper on the Jaguar... refer to the user's manual for the Jaguar (http://www.luminarymicro.com/index.php?option=com_remository&func=download&id=1358&chk=1a35dfde4340a21e1ca7329ad6a96fd9&Itemid=591) on page 11.
WizenedEE
01-05-2011, 13:51
The jumper is generally set to brake, and it's unlikely it's on coast unless someone on your team changed it.

If you're braking the jaguars, the only other option is spinning the wheels backwards, or slowing down before you stop.
slijin
01-05-2011, 18:09
Alternatively, Victors are by default set to coast. To change this, move the jumper on the Victor to a pair of pins including the one labeled "B".
krudeboy51
09-05-2011, 15:50
Ok i got it now thanks for your assistance!