Friday, January 9, 2009

was dumbbot, now nudgebot

Nudgebot engine base

After some push test with dumbbot I found a few issues. First was some 'crabbing' by dumbbot. This was where the chassis would go sideways rather than straight ahead. This was due to the pulleys being pulled back at different angles. That was countered slightly but it was always going to be an issue as the axle mounts are quite loose.

I also found the power transfer from the motors wasn't great. There was a degree of belt slippage, but that was expected. However on the higher end of the push tests (ie .5kg dumbbot pushing .5kg opponent) there was very little pushing going on and a lot of belt slipping. I added some heat shink wrap on the engine shafts to try and reduce this but it was still an issue.

All these things together made me think that although the pulley drive system was cool it wasn't the best design. A sumobot that went sideways instead of straight that could barely push the 500gm weight wasn't good enough. Even those dumbbot was going to be an opponent I still wanted it to be up to standard. Thus a redesign was considered.

I needed a drive system that was solid and had the torque needed. The gearhead motors available to me were too long to sit side by side so I would have to have the axles at a 90 degree angle to the engine shafts. Annoying and hard to engineer properly. So I went back to my good friends at Tamiya and decided to use the dual gear motor set that I used for Trackbot. It fits well on the base plate obviously and was under 10cm wide. I used the lowest gearing ratio that gave 2276gf/cm and only did 38rpm. With two motors I should be able to push anything.

I used the same wheels but I sanded down the wheel hubs to reduce their width. I also cut the axles from approx 5cm to 4.7cm. Again this was to reduce the width so the engines plus wheels were under 10cm. With this extra work they were. A lot of grinding, cutting and fiddling around but the end result was a much better engine base. No point having a working circuit which is going to be let down in the pushing department.

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