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Ask Tony: Hey, I Got Your Answer!

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This article was originally published in RC Driver’s October 2016 issue.

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BRUSHLESS JUMPHOT MT
Hi Tony. My 7 year old son and I are new to hobby grade RC; each owning the HPI Jump- shot MT. They have proven to be a ton of fun and bash worthy, but inevitably the 540 15T brushed motors need replacing. I’m interested in upgrading to a brushless system, not because we desire more speed, but because I’d like a more efficient and longer lasting motor. I would like to mention that we’re running on 6cell NiMH and I’m not quite ready to make the jump to LiPo for safety reasons. Does it make sense to go brushless in order to achieve a more efficient setup, yet keep running on NiMH? I’ve been researching for a reputable brushless system for MT’s and my head is spinning. All I know is that I want a sensored motor I think, lol. The trouble I’m having is that none are advertised specifically for 1/10 Monster Trucks. I have no problem identifying systems recommended for SCTs, Sport, Racing, Drifting, and Crawlers, but I don’t know if these translate well to MT’s. Please steer me in the right direction. Thank you!
Edgar, Chicago, IL

Hi Edgar, First off let me commend you and your research prior to purchasing. I don’t know how many times I’ve come across someone that has dropped a brushless system in their car that is so overly-powered they don’t enjoy driving it anymore. The HPI Jumpshot MT is a great car for beginners. It is very durable and has just the right amount of speed to keep things fun. However, that stock brushed motor is pretty anemic and, as you stated, is a prime candidate for a brushless replacement. I would recommend, however, a very mild brushless system for the simple fact that the gearbox isn’t designed to handle a huge increase in power. Stick with something in the 2100Kv-2700Kv range and you should be fine. I would also suggest keeping your NiMh cells in play and they won’t produce as much power as a LiPo upgrade, further reducing the power output. This should keep you going and going and going for quite some time. Enjoy!
—Tony

COG COG COG GOES THE 50” DEEP VEE
Hey Tony. You’re probably going to tell me to take my boat questions elsewhere and if so that’s ok. I just converted a drop dead gorgeous 50” Exceed Deep Vee gas to brushless electric. The motor is a Leopard 5692 1340Kv and the ESC is a Swordfish 220 Amp Pro. The boat has indiscriminate gremlins. It will run fine, then start jerking, cutting in and out, run fine for a while, etc. I checked all the connections and none of them appear to be loose. The radio is a Dimension GT3X. I am thinking bad receiver. However, I plugged the steering servo into the ESC port in the receiver and it worked ok. Any ideas?
Mike San Diego, CA

Hey Mike-Gas (or Nitro) to electric conversions can be quite tricky. What you might be experiencing is what’s called ‘cogging’ and this is somewhat common in non-sensored motors like the Leopard 5692. The whole cogging thing is best for another article, but basically what’s happening is the motor and ESC are out of ‘phase’ the ESC thinks the motor is in one position when it’s actually in another. Since you didn’t tell me what batteries you’re using, I’m going to blame it on that for now. When your electronic system is under high load (a full throttle launch, for example), the electronics try to pull maximum power from the batteries; if there’s not enough juice there (ie, underpowered packs), you’ll get cogging. Once you’re moving it doesn’t need the initial spike, so it probably runs fine. My guess is that your drop dead gorgeous 50-incher is just a bit too big and heavy for the batteries you’re using. The Swordfish 220 Amp Pro is capable of running from 2S-6S of LiPo power I’d give it a shot at the full 6S and see if that cures your problem. Good luck!
—Tony

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