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Topic: Braccio robotic arm - initial movement (Read 133 times) previous topic - next topic

ztyl

Hi there..

I've purchased a Braccio Tinker Kit and i'm having loads of fun with it. I only have one issue..

When i upload a new skecth to the arduino the arm stops moving (which is expected) but it then moves very fast and violently to a initial position before doing the movement steps i have programmed.

Is there any way one could get rid of that movement phase or if not, can the speed be slowed down so it isn't so violently??

Hope my question makes sense :)

/Jesper

vinceherman

#1
Sep 08, 2017, 09:14 pm Last Edit: Sep 08, 2017, 09:18 pm by vinceherman
Hi Jesper,
Are those RC hobby servos?  If so, usually on power up they move to a 'home' position.  If the servo is not already in that position, it will move there as fast as it can.
The usual fix for this is to have a structured power down process where you 'park' the arm in a known park position.  Then, before you attach the servos, servo.write to each servo with the values that put the arm in that park position.

Edit: Oh, I should probably mention, there is a mod you can make to the servo to expose the internal position potentiometer.  A bit of delicate soldering.  People open up the servo, solder a wire to the middle of the position pot, and run it to one of the analog pins.  You can then read that value of that pot before you attach, servo.write a value that tell the servo to move to the position that it is already at, and then attach.  You will still likely get a twitch but not the violent jerk when it tries to move the whole arm a long distance suddenly.


ztyl

Hi Vince

Thanks for that explanation. Is there any servos that doesn't move to home position on startup? Because yes - my servos are the RC hobby ones.
I have already found the home position and added that to the end of my program - i just thought there was a workaround for that..

I'm not good at soldering so i'll probably just destroy my servos when trying to solder :)

/Jesper

vinceherman

For hobby level servos, no I do not know of any that do anything other than move to where you tree it.
There *are* some robotic servos with more functionality.  Many times more expensive. I have never used them in my projects so I cannot describe that extended functionality.

Go to servocity.com and browse through their servos.

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