John from Wisconsin writes…

Feb 01, 2008 No Comments by

My Brushless 1/8 scale Sportwerks Mayhem By John

In the fall of 2005 some friends and I were talking, in between races at the local hobby store (RCPerformance) , about the new 1/8 scale brushless conversions being designed and built. One guy, Dave, said “I’ve never seen one done right. Bada Boom! That little seed he planted fired me up to meet this challenge. Even thoug I had never driven an 1/8 scale before, I decided I wanted to build an electric 1/8 scale that could compete with, if not be, faster than the nitros. So a year and a half later, five burned up ESCs, and one too-far-reaching failed experiment later, I reached my goal! Five key steps had to fall into place for this to work for me. 1. I needed to choose the best motor for this application. I took a lot of advice from the RC Car Action Forums. I wanted to race a 15-minute main on a 30-second lap outdoor track. I went with a brushless Neu 1512 1.5Y (1900kv). 2. For the battery I chose a 4S (4S means 4 LiPo cells in series which is 16.8 volts when charged) and 8000mAh. The 8000mAh is a bit overkill, but I wanted to make sure I could make a 15-minute main. 3. Now I needed to decide on a brushless ESC. The first year I burned up a few ESCs from various manufacturers. I almost gave up until I found people were over-volting Castle Creations Mamba Max ESC! So that was it: a Castle Creations Mamba Max. 4. Then I started designing it. I started by measuring the parts I would use from the original car. The nitro-based parts got tossed in a box. I used to be a mold maker, so I can run CNCs and other shop machines. I was able to take a class at the local tech college and made all the new parts for the car. 5. I needed good luck on race day. I was always very prepared, having done preparatory maintenance on the car before. Out of 10 or 12 races, I never finished worse than 4th. I often finished 2nd or 3rd plus few wins. Billy Easton came out to our track one weekend (the Rock Pile, Deforest, WI). He won and one of our local upcoming drivers, Josh Stough, came in a close second and I came in 3rd. That made my day. By May of 2007 I had the car basically done and it worked very well. December 2005: I bought a used Sportwerks Mayhem Pro. My initial design was very conventional (for a brushless 1/8 scale of the time). I selected a Feigao 540C 9T Motor to go on one side with the batteries on the other side. This was fairly cobbled together; you know, hacksaw, hand drill, duct tape, etc. It actually worked pretty well, but it burned up a few ESCs. The ESCs were rated to 4S and that’s what I ran it on. It didn’t take that for more than a few runs. I think the motor was a bit short on efficiency and a bit too high of a kv. December 2006: I wanted to try something really different. I designed and built a chassis that would take two direct drive motors. I thought it would be nice to be able to adjust front rear bias (drive or brake) on the fly from the radio (since each motor is on its own channel). I tested it before it was completely done and it had some promise, but I burned up two more ESCs trying to run 5S. Also the 600 kv outrunner motors I tried did not take the abuse of a ground vehicle. One of the stators came loose from its hub and this ended up damaging the winding wires. So I had to go back to the drawing board mid-semester. I really had to work this out quickly. I wanted to do something a bit different than the existing conversions. I did what I call a Full Conversion. This basically means throwing out all the gas stuff and the chassis–yes the chassis gets tossed too. The stock chassis had many holes in it and too many pockets that would compromise the design. The first thing I wanted to do was to have a central motor (above the diff) and saddle batteries. The diff needed to be moved forward for that. That meant a longer drive shaft in the rear and a shorter drive shaft in the front. I found a Losi LST drive shaft that worked for the rear. I shortened the front drive shaft and coupled it back together. I made two overbuilt motor/diff mounts to hold the motor and center diff. In addition to the two 3mm bolts that hold the motor in, I also designed and built a rear motor clamp that helps hold the mass of the motor to the motor mount A top plate holds everything in place and stiffens the chassis up. I mounted various items up on the top plate such as the Mamba Max ESC, power switch and the Castle Creations BEC. Initially I made this from aluminum, but it buckled a few times in hard crashes. I decided to outsource the top plate and have it made from carbon fiber sheet. The batteries are strapped to thin mounting plates that are bolted to the chassis. This keeps the battery mass low and close to center. I took care to seal the bottoms of the batteries to the plates to prevent sand or other small debris from getting under the LiPo battery pack which can damage the cells. I’ve raced and driven this car all summer outdoors and indoors and it has held up very well. In fact, there has not been a single failure on this design.

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