Robo-blog

Yerobot 4WD Arduino Mobile Platform

After my earlier post in search of a base unit, this alternative appeared on LMR. It’s from DFRobot but available in the UK through Yerobot, and although designed for Arduino-based projects seemed big enough to accommodate the relatively huge Terk board. There weren’t many details on what’s included, but given the very low price it seemed worth a shot anyway, so I put in an order.

The base arrived fully assembled, which was a pleasant surprise. The four motors are wired up in left and right pairs so you only need two motor controller ports (although the terk has four, so it would have been interesting to try true 4WD control); there’s also a switch and a socket I don’t recognise attached, which I assume are for hooking up a power supply. As shown on the Yerobot page, the kit also includes an add-on deck for two tiers of mounting points, and another to extend the size of the base. The motors seem to be from the solarbotics GM-series, based on the double-flat output shaft, and the wheels are Tamiya.

After testing the platform’s motors worked on ports 3 and 4, I carefully swapped them for the existing motor cables (getting left/right and forwards/backwards correct based on observed behaviour causes me far more confusion than it should!), then was able to simply balance the qwerbot on the platform and take it for a test drive.

Sadly, this turned out rather disappointing. I don’t know if it’s a lack of grip on the tyres, or due to having four rather than two motors, but attempts to turn on the spot by running one side forwards and the other backwards simply produce wheel spin or slight, stuttering turns. This makes the standard Teleop interface unusable, and my custom controller didn’t fare much better- running just a single side of motors produces far more forward motion than turning. Probably fine for outdoors applications like R/C car racing, but for the uses I’m after (roaming, tracking or mapping indoors) I guess it’s back to the drawing board.

If I can find a suitable axle/hubs then I could try stripping out two of the motors to see if that helps with the steering; if I go that route I could also switch from wheels to tracks. Or with arduino boards being so cheap it’s probably worth picking up one of those just to try them out, since I now have both a ready-made platform and some spare servos.