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Stephen, the editor of RC Car Magazine, and Traxxas both put a lot of trust in me on this massive and expensive 80 hour project which took a fresh from the box 3.3R Revo and did both a direct conversion using the stock Revo tranny and a more typical but tweaked E-maxx tranny conversion - the results were amazing. Lots of custom hand made parts...and fun in the snow with a little winterizing.
Since the release of this article I have received
tons of questions for more detail on the builds. Though this
article was never intended as a how-to, but rather and overview of this
advanced modification. Individuals attempting these NTB conversion do
need to have a basic RC modification understanding. Click on any
of the images for a very high-resolution photo. Additional
notes are embedded in RED
A revolution is defined as a significant change that usually occurs in a relatively short period of time. Our editor previously described how brushless motor/ESC and lithium-based battery systems are rapidly changing R/C'ing. The annual iHobby event was a sobering reminder of the significant influence these technologies have delivered in only the last year. Are the days of nitro numbered? I think not. However, for those like myself that want Nitro speed and power without its headaches, this brushless and lithium-based revolution now offers a convenient plug-and-play upgrade for electric cars and an alternative power source for completing NTB (Nitro to Brushless) conversions on nitro powered R/C cars.
As with any NTB conversion, the basic idea is to remove all gas related apparatuses, mount a brushless motor and ESC, fashion battery holders, and assure everything is hooked together. Just to prove how good brushless and LiPo technology really has become, I created two NTB conversions using one of the top 1/10th scale four wheel drives trucks on the market, the Traxxas Revo 3.3. For Project Revo'Lution, I engineered both a direct NTB conversion that retains all stock Revo hardware and redesigned a more typical performance conversion, which relies on an E-Maxx tranny to run things and ditches the superfluous gadgetry of the stock Revo.
The accessory list for Project Revo'Lution reeks of gluttony and excess. At the heart of the conversion is a Novak HV High Voltage 4.5 brushless system powered by two A123 1" diameter 2S 2300 Lithium Ion battery packs. More powerful brushless systems can be pieced together, however the HV system is the only Maxx class plug and play option. The A123 packs also feature Turbo Voltage Controllers, which trade current output for incremental voltage boosting all the way to 10V per pack. After testing, I omitted the Turbo units to take advantage of the high current wheelie producing output from the A123 packs. To lighten and simplify these beasts, the dual steering servos were converted over to one HiTec HSC-5998TG coreless digital titanium gear servo. With 15.6lbs/inch of torque this single servo delivers almost twice the stock turning power. How did the Project Revo'Lution systems fair? I think you will be surprised.
Revo NTB Conversion
Direct Conversion – this conversion uses basically works and retains almost everything as your stock Revo sits – if you buy a Electric Motor Mount Adapter and RC-Monster Hardened Steel Mod1 15T Pinion this mode become very easy.
The ESC's, ESC to RX lead's power wire (center RED) is pulled from the lead as the RX pack will be powering everything. Plug in a Y adapter harness so the brake servo and ESC plugs share the same output. With the exception of making someplace to stick the battery packs, you are done.
To begin the NTB conversion, the motor and gas tank assemblies and mounts are removed. Hand made custom motor, ESC and Plasti-Dipped battery mounts were made from 1/8" aluminum to mount up to existing chassis holes. To keep things simple and easy from a gearing perspective, the stock spur gear was removed and replaced with a modified to fit Associated 69T 48P spur gear. After testing a range of pinions, 22T and 28T pinions were finally settled on as best bashing and speed gearings. With the Novak system delivering loads of torque right from the start, I also reduced the shift point to about half way on the transmission (about one half counterclockwise turn) to get the Revo into top gear a little quicker and maximize top speed.
Unfortunately the RX pack was retained because the ESC's BEC (battery eliminator circuit) just didn't supply enough juice for the Revo's OptiDrive ESM to operate reliably. The recycled dual servo splitter cord allowed the OptiDrive to feed both the ESC with "go" commands and the braking servo with "stop" commands all via the one output. This isn't the most electrically efficient setup, but it keeps things simple and allows the brakes to still function on the one-way transmission of the Revo. To avoid that freaky freewheeling sound when accidentally thrown in reverse, I set the Novak ESC to program #2 to disable reverse. The batteries and ESC were secured to their fabricated mounting plates and a system check was run to verify everything was connected together and ready for the next phase...testing.
I like this NTB conversion for the simple reason that you can flip back and forth from brushless for bashing to Nitro for racing in under an hour and required no chassis modifications whatsoever. This NTB conversion delivered impressive results with about the same balance as a stock 3.3 Revo with no more post run maintenance than a battery charge. The extra stock gadgetry still riding on the chassis along with Revo's somewhat unpredictable automatic shifting transmission softened the raw power of the brushless system, but still provided plenty of wheelies and a few full flips even in the 3.3's extended chassis. Runtimes in the seven minute range were pretty good considering we were running just 2300Mh packs. How fast? We hit a little over 40 MPH pretty consistently after final gear and transmission tuning with viscous Nitro beating acceleration. Now that we have matched Nitro speed and increased power, let's see what we can do with the E-Maxx Revo NTB conversion.
Revo NTB Conversion
[Showing the single steering servo conversion, the chassis modifications, and front drive shaft conversion]
Swapping the front drive shaft for a shortening beefier Revo secondary drive shaft to provide the extra reach to the E-Maxx transmission was expected, and once completed things got much easier. The Novak HV 4.5 motor was simply bolted to right side of the E-Maxx motor mount with a 22T pinion and the ESC was left in the previous conversion's location. With the BEC easily powering the steering and mini-shift servos the 4 oz. RX pack was omitted.
To save a little weight, the channel 3 controlled stock micro servo was secured to a custom mount above the rear shocks with T-Maxx carb linkage. The 60T 32P spur gear equipped slipper clutch received a more durable diff ball upgrade. Due to the power and speed of the brushless systems, many people simply lock the E-Maxx transmission in high gearing, but I like the ability to shift between a high and low ratios for speed or wheelie needs. . With A123's slim 2300mh batteries were Velcro strapped to a custom dual pack sized battery holder and the receiver and aluminum antenna mount secured to the vacant servo location, I was ready to program and start scaring my nitro buddies.
This conversion definitely was not in the plug-and-play category, but the performance and weight reductions were rewarded with a much higher performance NTB conversion. With more straightforward and tunable transmission, over 2/3 lb. of extra equipment removed, this NTB conversion delivered huge power and speed boosts over the previous conversion with RC flipping power just a trigger throw away. Not only are wheelies eminent going forward but also in reverse. Shifted into low this conversion delivered wheelies on demand and a very respectable 34 MPH, in high gear the nitro beating Project Revo'Lution hit 50 MPH. Weather and the deadline limited testing, but I am confident further tuning would increase those already outstanding speeds.
On the Other HandBoth conversions delivered lid-flipping power, but the lighter E-Maxx based conversion was the performance winner. It delivered more torque on demand and more agile handling than either the direct conversion or stock nitro. Sure the top speed is only a little faster than stock, but the acceleration and torque on either conversion will humiliate its nitro equivalent when under 40MPH.