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Mon, 04 Feb 2008
driving servos and speed controllers from the SRV-1 Blackfin
We have several interesting projects in the works involving motorized drives other than the SRV-1 robot base. One of these project is a unique unmanned aerial vehicle (UAV) that uses a pair of counter-rotating fixed-blade props for lift and a couple of servos that shift the battery weight around to effect steering, similar in principle to the old Hiller Flying Platform.
This is called a coaxial rotor because we have a motor assembly with two brushless DC motors that are aligned with the shaft of one motor passing through the hollow shaft of another motor - see http://www.maxxprod.com/pdf/CR2805.pdf. The motors are driven with R/C airplane electronic speed controllers that take servo-style PPM (pulse position modulation) signals, we are able to modify the Blackfin processor's timer functions to a waveform that can drive PPM circuits. We are using the two timer channels that otherwise were driving the SRV-1 robot H-bridge with PWM waveforms to drive to two prop motor speed controllers. Another two servo signals come from the two pins that can alternatively be used as a second UART on the Blackfin, and the using a 5VDC regulator off the battery to power the servos and speed controllers. Note that the 3.3V logic of the Blackfin has no trouble driving the 5V logic of the servos.
The SRV-1 Blackfin is used here with our WiFi radio board that carries the Matchport 802.11g radio module. For remote control and monitoring, we modified some button definitions of SRV1Console to generate the flight controls, but didn't have to change any of the java code ...
The servo controls from the Blackfin work quite well. Our steering is another matter, as you can see from the following video clip ...
click here if you can't access the YouTube clip
In any case, this is a good start on a really interesting project, and the next step will be to add sensors for attitude (pitch/roll) and rotation (yaw) However, You can read more about this and other related projects, plus find links to download test firmware from this thread on the Surveyor Robotics Forum
Posted Mon, 04 Feb 2008 14:25 | HTML Link | see additional stories ...