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View Poll Results: What is your autonomous mode strategy?
Line-tracking 23 38.98%
Dead-reckoning 37 62.71%
Seek-Enemy-Stack-and-KILL!!! 14 23.73%
Other - please list. 15 25.42%
Multiple Choice Poll. Voters: 59. You may not vote on this poll

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Unread 21-01-2003, 13:37
Jeff McCune's Avatar
Jeff McCune Jeff McCune is offline
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We originally looked at the CSMP03, which runs about $40 and has a 20ms response time and is accurate to within a few degrees. Unfortunately, we couldn't buy it from a dealer authorized by First, so we had to build our own.

I forget which part number we ended up buying, but basically it's a $20 2-axis magnetic sensor from digikey. We've got an ECE guy who wired up a nice circuit with some op-amps to condition the output from the senor (I'm CIS, so that stuff is beyond me a bit.). It outputs 2 pulse trains corresponding to the x and y magnitude (if you think about it on a cartesian plane) We're using the PULSIN basic stamp instruction to sample the pulse width of the two PWM signals and convert them to BRAD's (Binary Radians: 0-255 rather than 1-360 degrees) After that, it's a simple arctangent to get your cardinal direction, which the stamp provides with the ATN function. Pretty straightforward really.

The compass senseor + support circuit only ran about $40. The stamp-2P we bought is the most expensive part, just under $100.

It all works wonderfully at this point. We've got the RC sending joystick values down a couple of PWM lines to the 2P, which doesn't always get through perfectly, but they're joystick values so they can be a little fuzzy. The 2P has 32 general purpose I/O pins, so we just set 16 to output and wired those directly to rc_sw_A and rc_sw_B. We've then got 16 lines still available on the 2P for any sensors we need. Plus, since we're not doing serial in or out on the 2P it's main loop cycles MUCH faster than the main loop of the stamp on the RC. This faster cycle time allows us to do interesting stuff like implement soft interrupts on some of the extra I/O pins. (This is how we're doing our shaft encoders.)

Yes, it's very, very cool right now. But talk to me in 4 weeks. <g> It's going to take an enormous amount of time to fine tune our robot. Not to mention the nightmare of the continuously variable transmission that the ME's want taken care of entirely in software... *sigh*
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