20 May 2009 RobotsAustralia   » (Journeyer)

Every mobile robot needs a battery...

"PEDRO" the quadruped robot got a lithium polymer battery last week courtesy of eBay. I had been putting off buying a heavy and expensive large capacity LiPo battery until I had got the walking algorithms working a bit better and I could truly test the ability of the robot to take the 500g or so of a heavy battery, but now batteries are available on eBay for not as much money, I just took the plunge and bought a 3000mAh 3 cell battery pack and charger for the robot.


The battery weighs just 215g, and cost approx AU$50 delivered. The charger can charge up to 5A and will do a balance charge, monitoring individual cell voltages.

Next I had to fit it to the robot, as the original design called for a larger pack slung underneath the body and neatly held in by the spacers between the side plates. The new smaller pack needed some extra holes and some plastic brackets to hold it in;



Once the battery was on and tested ok, I had to return to the firmware for the AVR micro and write some code to support turning the unit on and off via the onboard mosfet and soft on/off button. Also needed was some code to talk to the ADC chip on board which has the battery cell voltages on it, so I could implement low battery automatic cut out and (hopefully soon) viewing of the battery level remotely over the wifi link. Of course it didn't go smoothly...



Once again the usb logic analyser came in very handy in debugging the SPI comms between the micro and the AD7490 chip (16 channel, 12 bit converter). You can also see the JTAG MkII from Atmel connected (expensive gadget, but very handy for debugging AVR code).

I've also been working on the walking algorithms, and various other software and hardware bits and pieces such as improving the communications (the WiPort wifi module doesn't seem to work as well as I'd hoped - it needs really good signal strength or every now and again it will drop out for up to a second or so). Once I've got some of these wrinkles smoothed out and the walking nice and smooth I'll post some more video.

Syndicated 2009-05-20 03:09:00 from Robots Australia

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