30 Nov 08 The Robot - Progress and a Video

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Well finally, here is the promised video…

The majority of the previous hardware issues have also now been solved which is good. The degrading CF cards was caused by a bad Alix board (I’d probably blown a resistor somewhere at some point). A replacement Alix board has arrived while I sell the other on eBay as faulty for any enthusiast who may wish to try and repair it. I am also using a SanDisk genuine SD card in an SD to CF adapter rather than some unbranded CF card. No filesystem errors and the disk now behaves as it should.

The motor controllers sometimes dropping/misinterpreting commands during heavy load was solved by a number of different fixes. Firstly, I believe with the USB to TTL converters the data lines are pulled up to 5v with a 4.7K resistor. I added a second 4.7K resistor in parallel to Tx to give the controller more of a chance against interference. I also added various smoothing capacitors, and edited my serial port byte transmit tool to restore the serial port settings graceefully on exit. Oh - I also cut the cables from their default 1m to the 12cm that I needed.. No more dropped commands.

The wheels are better reinforced under the base to cope with the added weight and I have also balanced it out more by adding a 0.5kg metal cage to the opposite side to the battery. The metal cage houses a proper DC to DC adapter which takes about 7.5v-15v DC and converts to a clean 12V output.

So far so good… I think there’s about a week’s work to do on the hardware before I can put it aside as ‘complete’. I’m actually quite looking forward to finishing the hardware now so I can put the project aside for a while before I start on the software intelligence. Still to do on the hardware:

1. Tidy up big time. Cables, excess glue and excess tape. Maybe sand edges if time permits.
2. Fix that back head distance sensor. Question damaged cable.
3. Check custom circuits, check resistors - some are lower than they should be.
4. Make the device somewhat safe - tidy up all cable joins and insulate appropriately.
5. Work out voltage sensor analog output for voltages 9v to 15v, program appropriately and display current voltage [charge] on picoLCD. All picoLCD drivers and software compiled.
6. Add charging pads, device should be capable of being manually driven on to charge which currently it isn’t.

Here is my motor server - written in C which controls the Sabertooth motor controllers, and my motor client which is a shell script and requires ‘nc’ from the netcat package. The code is by no means perfect but works well.

Next update will hopefully be more pictures of finished hardware. After that I’ll have to take a break for a while before I start on the software. The device is IP networked over WiFi and if anyone would like to arrange to take a drive remotely, let me know and I’ll see what I can do! You might be better to wait until I have written some software. I plan for a simple ncurses map based on sensor input because driving it remotely without is would be fraught with crashes - the IP camera angle just isn’t wide enough.

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Tags: 4.7K resistor, alix, Alix board, DC to DC adapter, degrading CF, Linux robot, motor client, motor server, nc, netcat, parallel, sabertooth motor controllers, SD to CF adapter, smoothing capacitors, usb to ttl

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