Servo - November 2015

worked (the ESCs were programmed with settings 0,0, 4, 2, 3, 5,1,1, 4 as per the previous tests).

My son, Andrew is designing a new 30 lber and we wanted to see if the same motors and gearboxes could be used in both Isotelus and his new heavier bot. We weighted down the chassis to 26 lb, hooked up a couple of 2S 2,100 mAh Zippy LiFe packs to give 4S, and tried it out. Ughhh! The bot wouldn’t move at all!

Must be uncharged batteries, we thought, but even after getting them freshly charged there was still no performance. This was bizarre after the excellent performance during previous tests. We were about to try another battery pack when I noticed I must have had a “senior moment” and had wired the batteries up in parallel not in series, so we had only been running it on 2S!

Correcting that issue, we headed out to try again. This time, the bot accelerated away briskly for about 10 feet and stopped dead! It looked like the speed controllers might be thermally shutting down, but again that would be strange as they had worked well with a bot of about the same weight and performance.

We stripped all the excess weight off and still the bot would only run for a few seconds before stopping. We had taken the top panel off for the last run, and just as it stopped I noticed the LED on the RX started flashing as it stopped. This suggested the problem was with the RX and not the ESCs.

First thought was that the RX was “browning out” due to a voltage drop, but then we noticed the LED would go solid when we approached the bot and start blinking again if we moved away! It seemed to be a radio range issue.

We tried driving the bot in close circles around us and it performed well. Then, I remembered this was the

RX that I had used in Trilobite at Clash of the Bots last year and had swapped it out along with the batteries after the bot kept glitching during a fight. The swap had fixed the problem, but I had never got around to tracking down the root cause. I swapped that RX for a known good one out of one of my hockey bots and all the problems disappeared. The bot performed well — even with all the weights added. The bot accelerates well, is fast, and is very drivable. One slight problem with all the weights added was a little less braking effect on neutral than would be ideal, but all in all, it was pretty impressive. The faulty RX joined the damaged motors in my trash can. The new brushless solution is 12 oz lighter than the old Speed 750 drive, and as a bonus the two 2S LiFe batteries are no heavier than the old 6S LiPo packs I used to use. That means I can use that extra weight to give me more choices in wedge attachments. Since we can now use these same motors, gearboxes, and ESCs in both our 12 and 30 lb bots, this means we can cannibalize one bot to keep the other going if the drive gets damaged in either.