I too am new to this forum and robotics in general, but I figured I'd try to help. (Hopefully I'm not breaching forum etiquette by skipping a formal introduction.) If the robot is not tracking straight, you will have to first find out if the servos are centered. Send a PULSOUT command to the pins your servos are connected to, on my BOE it's pins 12 and 13.
you need to send a pulsewidth of 750 to center the servos. If you hear any humming or feel any "chatter" in the servos, one or both may need to be centered by adjusting the pot inside. This will require the servo be removed from the chassis.
If they are already centered, then it's probably a software problem. One quick way to check would be to swap the servo connectors. If the robot veers to the right, it could mean the right wheel is turning slower. By swapping the servo connectors, the robot will run in reverse, you can then observe to see which way it turns. If the opposite wheel runs slower with the servo connectors swapped and the robot running backwards, you know that you problem is likely not with the servos.
Even with a brand new bot, I found that I had to tweek the software and do a bit of trial and error experimentation to find the optimal pulsewidth to get mine to track straight. One servo just runs a little faster than the other at full speed, so I had to slow it down a little to get the bot to track straight. If you follow the course in the book "Robotics with the Boe-Bot" exactly as it is written, it explains in detail how to do this.
Unless you changed the program or the centering in the servos
you are seeing the effect of the battery voltage changing as the batteries run down. This is normal. The only way to avoid this is to run the servos from a regulated supply but why bother, its a toy, not the space shuttle. Some of the difference might also be the result of internal heating in the servo PC board... ·
It is normal for servos to have different speeds both before and after wearing/breaking in.· The BOE-Bot guide discusses how to correct this, which involves slowing down the faster servo by adjusting it's PULSOUT value closer to 750 from where it is.· No two servos are exactly alike, so some calibration is always going to be a factor once in awhile.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Chris Savage Parallax Tech Support csavage@parallax.com
Comments
you need to send a pulsewidth of 750 to center the servos. If you hear any humming or feel any "chatter" in the servos, one or both may need to be centered by adjusting the pot inside. This will require the servo be removed from the chassis.
If they are already centered, then it's probably a software problem. One quick way to check would be to swap the servo connectors. If the robot veers to the right, it could mean the right wheel is turning slower. By swapping the servo connectors, the robot will run in reverse, you can then observe to see which way it turns. If the opposite wheel runs slower with the servo connectors swapped and the robot running backwards, you know that you problem is likely not with the servos.
Even with a brand new bot, I found that I had to tweek the software and do a bit of trial and error experimentation to find the optimal pulsewidth to get mine to track straight. One servo just runs a little faster than the other at full speed, so I had to slow it down a little to get the bot to track straight. If you follow the course in the book "Robotics with the Boe-Bot" exactly as it is written, it explains in detail how to do this.
you are seeing the effect of the battery voltage changing as the batteries run down. This is normal. The only way to avoid this is to run the servos from a regulated supply but why bother, its a toy, not the space shuttle. Some of the difference might also be the result of internal heating in the servo PC board...
·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support
csavage@parallax.com