Wednesday, May 17, 2006

A Test






intro goes here rest goes here

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The Brushless Stampede - 375 Watts Of Fury

Finally, some content!

I've found the Traxxas Stampede to be nearly bulletproof in its stock form, and it has to qualify as the best "1st RC" ever. But, after running a few packs through it, my not-quite-beginner self was getting a bit bored with it. So out went the stock electronics, and in went a custom 12-cell pack and Novak's HV-Maxx sensored brushless motor - a combination that produces a claimed 375W (or 0.5HP) with a claimed free-running maximum speed of nearly 60,000 RPM at 14.4V. Step inside for a closer look.


The installation of the speed control (ESC) and motor is very straightforward.


To mount the ESC, I used RPM's mounting plate for the Stampede, as the stock ESC has built-in mounting tabs. I could have fabricated something, but for $4 I don't think it was worth my time. The HV-Maxx ESC and its on-off switch are secured using 3M double-sided tape. I retained the stock Tamiya-type connectors; with the minimal amp draw due to the Stampede's lack of mass and traction, they presented a negligble voltage drop and didn't overheat.



The motor installs, well, just like the stock motor. It's a 550-size can, so the diameter and mounting holes are the same as a standard 540-sized brushed motor. It is a bit longer, which means that the motor is a bit more exposed than I'd prefer. I used a 12-tooth 48-pitch pinion and the stock 87-tooth spur gear.

The stock motor wiring and Hall-effect sensor harness was the perfect length, so I simply secured that wiring to the rear shock tower with a zip-tie. I did the same with the capacitor, as my original mounting of it to the ESC plate with double-sided tape only lasted a few runs.


The battery pack is straightforward - one 6-cell in a "side-by-side" configuration lays in the stock battery location. A second pack in a 3x2 configuration was glued to the bottom pack. I used some 1800mAh cells that I scavenged from a couple of cheap stick packs.

Each 6-cell pack has its own connection to the ESC; the controller is apparently wired this way as to draw the BEC current (which powers the receiver and steering servo) off only a single pack. Since the BEC is regulated at 6.0V or so, powering it from a 7.2V source requires significantly less voltage drop than the full 14.4V that's applied to the motors, and therefore makes for a simplifed and more robust design. For this reason, it's not possible to run the HV-Maxx off a single 7.2V and a Y-harness - I tried (without really thinking, I should add)! For those interested on running the HV-Maxx from 6 or 7 cells, the instructions show the necessary wiring modifications.

The result of dropping this bomb into the Stampede was a complete transformation. With the stock 20-turn Stinger brushed motor, runs were pretty much six or seven minutes (on the aforementioned cheap battery packs) of WOT throttle. I mean, as long as I didn't hit anything, I could hold the trigger down under the pack went dead.

With the HV-Maxx, the 'pede would end up on its lid within seconds of turning on the power switch. Anything over half-throttle from a standing start resulted in a half-backflip if the truck hooked up. With it rolling along at an estimated 25 MPH or so (significantly faster than the top speed of the stock motor), applying full power would cause a satifying rolling wheelie. The top speed with the 12T pinion was perhaps 35 MPH or so; I saw no reason to gear it up for anything faster, as the Stampede already felt a bit out of its element at those speeds. Run times were in the neighborhood of 10 minutes or so. I credit this partially to the efficiency of the brushless motor, but from a practical standpoint it probably had more to due with the necessary throttle disipline required to keep the truck shiny side up.

Alas, on the third or fourth run, the truck stopped moving. The motor spun up just fine when applying throttle, but something was missing between it and the rear wheels.

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Sunday, April 16, 2006

Image Testing, And Gratuitous 1/8 Buggy Pics



Here's a couple shots of my Kyosho MP7.5 Kanai 2 buggy. This is a test of image uploading.





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Monday, February 20, 2006

Projects

There will be a few big write-ups coming soon, but I can briefly report on two projects.

First, a Novak HV-Maxx brushless motor setup and 12-cell pack installed into a Traxxas Stampede produces some truly scary results. We're talking backflips when it hooks up, which isn't very often. With a couple inches of snow on the grass, it just floats over the top, making roostertails along the way.

Second, a Mamba 25 Competition X brushless motor setup in an Associated RC18B is insane. Due to the weather, I've only run it inside, where I discovered that going WOT from a standing start with the steering at full lock will result not in a spin, but rather with the buggy launching and landing on its back.

More to come on both, obviously.

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