I have a couple of questions and thought that someone here could point me in the right direction. We are trying to build a stewart platform robot and currently have 6 L12 RC linear servos. As a proof of concept these servos work great but the lack of feedback (perhaps also low resolution) is making the system behave slightly erratically. Problems observed:
The servos tend to overshoot slightly for small angle changes and more significantly for larger angle changes.
The servos will not move for very small angles (fractions of degrees) making the movement of the platform jerky once they move.
The servos do not appear to move in synchrony but slightly delayed (this is more visible under slow motion filming). I am not sure if this is because the controller is not sending the positions at once or if it is because the resolution of the servos is slightly offset from one to the other. This ends up making the movement of the platform again jerky.
About the controller:We am currently using an Arduino mega controlling the servos with PWM (49.9Hz) over I2C using this board. We imagine the L12 P or L12I would yield better results since I could control the position and speed, preventing overshoot. The question remains if they would also help with the low resolution and jerkiness of the system, the same goes for moving the servos in synch. After reading the specs of the Firgelli Linear Actuator Control Board I don’t think it would do much for us but am I wrong?
Let me know if you have any ideas!Thank you,
Hi,
Using L12 P Linear Actuators will most likely improve your Stewart Platform. As you said, L12 P actuators will let you have position feedback which will prevent overshooting and increase positioning precision.
The LAC controller is specifically designed for Firgelli actuators to be controlled in a closed-loop configuration, therefore, it would probably be better if you use this controller in your design.
Regards,
Hi bdaouas,
Thanks for getting back to me.
I have some of the P series in storage so I’ll give them a try. The problem is I don’t the resolution of the potentiometer will be as high as I need. Do you know of any servos that size with other types of encoders?
Sebastian
Hi,
The Firgelli P series potentiometer values depends on the stroke option of the actuator.
From the datasheet of the Firgelli actuators, the feedback linearity should be less than 2% (Please search for “potentiometer linearity error”).
The resolution of the feedback will also depend on how much the low and high reference voltage are stable.
From Firgelli actuators datasheet :
Regards,