Trim robot to move straight

My development robot uses two CR servos; one moves CW for forward & one moves CCW for forward motion. I have found that something seems to change (I don't know why, maybe due to the battery voltage or the surface they are running on). In order to make them move in a straight line, I've added a "trim" routine at the beginning of my code to adjust the right wheel and make it move faster or slower as needed to run straight (could have been the left wheel). This works well and seems to take care of the problem. Do others have this problem?? and how do you handle it? Thank you, JimS

interesting!

Hi, welcome to the forum!
Jim, I too had same problem with both continuous servo and plain motors with small gearbox. The trim tric works for a bit, but prolonged time running it will eventually start to jitter, at least in my case.

Best scenario would be some sort of speed controller for each independent motor.

Usually No servo or motor is build the same.some would move faster and some slower! That's why I would suggest 1 motor for motion and servo for steering!

jims said:

Do others have this problem?? and how do you handle it?

Click to expand...

This guy will explain it for you. Brian Douglas

Thank you...JimS

Very typical and frustrating with analog CR servos, welcome to my world! I think battery voltage is a contributing factor. Try a very stable battery, LiPo or Li-Ion instead of alkaline, or use a voltage regulator. A PITA, but it helps. I think temperature is also a factor affecting the null point of a CR servo.

I usually gauge my bot's accuracy on powerup by seeing if the nulled wheels are drifting. A temp workaround is to simply turn the servos off to stop instead of sending a specified value.

And old fashioned testing is required to find matching servo values to drive straight at various speeds, as demonstrated more or less here: http://youtu.be/aBgAEAjk0po

You were wise to post here in Active, it's dead in the Robotics forum. Nearly a full month with zero activity.

erco...I start the robot's mission using a "clicker". One of the options at the beginning is to run a trim program to get it moving straight before the mission actually begins. Seems to help. Also; I believe there would be more activity in the robot section if it wasn't in the "finished projects" area.