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Mon, 10 Aug 2009
New 4WD motor controller in the works -
As discussed earlier, we have been experimenting with various motor configurations for larger payload versions of an SRV-1 4WD motorized robot base. One of the first prototypes, which hosts an SVS camera head, was briefly described here a few weeks ago -
In the process of testing this configuration, we found that the pan head added significant instability to the camera mounting, and that by reducing the camera mounting to a tilt-only servo with bearing pivots and using on-axis rotation of the robot body, we had the functionality of pan/tilt with greatly reduced camera flop. However, in order to achieve the need position accuracy of the robot rotation, we needed more precise motion control.
The result of this exercise has been the design of a new motor controller, currently designated "srv-4wd-v1". The controller has separate 5A Infineon TLE5205-2G h-bridges for each motor, and should be able to support doubled output by stacking additional h-bridge devices. The motors we have been testing have bearing-supported planetary gearheads and integrated quadrature shaft encoders, and while only rated at 3A stall current, seem to provide adequate power to the 10-lb prototypes. To integrate the encoder data with the PWM motor output, we have added an ARM7TDMI processor (NXP LPC2101) with UART and I2C host interfaces. Using the LPC2101 analog inputs, we have added a battery monitor circuit and headers for 4 Sharp IR ranging sensors. And finally, we have added 2 headers to interface to either 3.3V or 5.0V yaw gyro. Between the encoder and gyro feedback, we should be able to develop a fairly complete dead-reckoning position solution, freeing the host Blackfin processor for higher level navigation tasks.
Board size is 1.5"x2.5" with 1"x2" centered mounting holes. We have started the prototype fabrication and firmware development process, and hope to have first production boards in 4-6 weeks. No idea yet of pricing, but we will post that information once we have working prototypes.
Posted Mon, 10 Aug 2009 11:25 | HTML Link | see additional stories ...