Update March 16 2007:

Just wanted to post a graph of my measured velocities ... or put another way, how well my PD loop is controlling my motors. The motors have been commanded to go 14. 14 = 14 ticks per 20 ms. I have 1000ppr encoders on 3" wheels so that's .1357"/20ms at that speed. Expanding that the bot is traveling 6.7 inches per second or 407.12 inches per minute or 33.9 feet per minute or just for grins .382 miles per hour :D

Anyway, notice the error is only +-1 tick. I may play with adding in an integral component. The graph shows the output of the bot being commanded to drive in a 10" square. The first step drives both motors forward, then stop (it even reverse the motors to effect a quicker stop) then left reverse, right forward to turn to the left 90 degrees, the forward ...

One other neat side affect is that the motors resist any change from the commanded speed. Put another way, if the robot is told to stop (left and right = 0) then if you try to push it, it will resist (actively turn on the motors in the reverse direction. Cool, but is a big battery drain as the current will shoot to 1.2 amps.

Finally, at this PD rate (50Hz) the fastest encoder speed is 18ticks/20 ms which equals 8.7 in/s or 43.6 ft/min or .49 mph :)

Onward,

Jay

Update March 13, 2007:

The BlueSMiRF is paying huge dividends in my ability to code and test. My PID function is working great and I have set it for 50Hz. I have expanded my interactive menu to allow me to command distances and angles to the bot. Last night I finally added a separate switch for the motors, and mounted the motor controller circuit. I’ve been using a 3S Lithium Polymer battery for my power source, and am thinking of getting a 4S to see how fast I can go.

My next task will be to add the SoundGin circuit and play with announcing the current command or some phrase. Then I want to add odometry calculations and command waypoints. Then add in the sonar and some prox sensors. I’m still having fun with the blue tooth though.

On the CNC front, I lucked out (or maybe not, time will tell) in winning a CNC kit for my mill off Ebay. I’ve ordered the last missing components from McMaster Carr (great prices and fair shipping) and plan to install it this weekend. In the mean time, I need to disassemble the ball nuts to make sure they are not missing any and to clean them. It’s be a waste of time to install it all only to have to take it apart due to an issue regarding the ball nuts … at least that’s the way I see it.

Onward,
Jay