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Valen
Experienced Roboteer
Joined: 07 Jul 2004
Posts: 4436
Location: Sydney
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nick i had the same thaught lol.
angus PWM is really sucky for transfering information digitally. (PWM is what the radios use.
If you want your own controll system you really should look at digital radio, even the ones from jaycar for like $10.
The big problem with sensors is basically they suck ;->
a "cheap" pezo rate gyro will drift about 1deg/s (so after 90 seconds where you think you are pointing and where you actually are pointing can be off by 90 degrees)
ok so thats bad.
what you need is a full 6dof (6 degrees of freedom) IMU (inertal measurement unit)
Basically it works thusly. you assume that on average gravity points down.
(over a period of say 20 seconds) so if you average the acceleration vector from the acceleromiters you work out which way is the direction of down.
In the short term however (assuming you want to roll the ball in a different direction) you need the rate gyros to tell you whats going on.
Its not rocket science but its pretty dern close lol.
Re controll chips.
I'd suggest PIC's rather than PIC axes.
the 16F877A runs at 5Mhz, has 40 I/O pins, 8x A/D inputs, 2x hardware PWM outputs, Hardware serial I/O, Hardware SPI, Timer interrupts and a bunch of other stuff.
Theres a little more setup to program them ( a $25 programmer) but the capabilites are so far infront of a PICaxe that on a large project it's really worth it.
JAL 2.0 is coming out soon which will make a big difference too, you'll be able to use the full capabilities of the PIC in a basic like language.
360 bytes of ram, 16kb worth of program storage and 256 bytes of eeprom.
You may want some external ram though to do your acceleration vector calculations but perhaps not. _________________ Mechanical engineers build weapons, civil engineers build targets
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Sat May 06, 2006 11:57 am |
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