2013 - Turnigy Nitro Buggy
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(originally posted on UltimateRC.com on 2014-03-18)
This one has been a long time coming, thanks partly to the Slow Boat From China (i.e. shipping delays), partly to a really bad crash around New Year's that left the vehicle totally inoperable, and partly to my own persnickosity. (yes, I made that word up; "persnicketiness" wasn't fun enough.) Nonetheless, with the final problem solved, I can finally say this one is finished -- and just in time too, because my girlfriend is moving in and I no longer have the luxury of leaving RC car parts scattered all over the floor of my study for months.
The list of upgrades to this vehicle is...long. I replaced the stock engine with a Picco P-0 with .085 cubic inches of bone-crushing power (if you're a moth, anyway), I rebuilt the clutch about ten times until I found springs that worked well and didn't break every third run, I replaced the stock exhaust with a mandrel-bent job from GotNitroOnline, I outfitted the exhaust with a custom-made silencer that I basically invented myself because nobody else knew how to make it work right, I added a tiny fuel filter made by Great Planes, all of the aluminum and carbon-fiber upgrades available from Turnigy were added to improve durability, aluminum wing supports and wheel hexes and titanium turnbuckles and swaybar parts were commandeered from AsiaTees' product listing for the Kyosho Mini Inferno, the servos were replaced with a pair of Hitec HS-5055MGs, a foam bumper was added from the Turnigy Rally Extreme in a (successful) attempt to fend off further catastrophic crashes, and finally, the wheels and tires were replaced with 1/10-scale rally-car wheels and tires from HPI.
And of course, that doesn't include homebrew fixes for problems that there were no pre-made parts for, such as the the brake linkage that I rebuilt from scratch using a proper coil-spring instead of a lame little piece of squishy rubber hose, or the soda can that I cut up to make a dirt shield for an inconveniently-placed hole directly under the gearbox.
This started out as an experiment, so I could honestly say I tried nitro, before going back to my electric vehicles, and it ended up being my very favorite RC. Once the noise level was brought under control, so I could run it in my apartment parking lot without my neighbors giving me dirty looks, and once the resulting changes in engine performance were compensated for, I discovered there was something very addictive about the "tiny F1 race car" sound made by a well-running nitro engine. I liked it so much I bought a spare nitro buggy, so I could still enjoy the sound when one of the buggies was out-of-commission for repairs.
I'm especially pleased with how the exhaust silencer turned out. Originally, it just consisted of a 90-degree rubber hose, stuffed with a 1-inch wad of bronze wool from an art-supply shop. (steel wool would rust from exposure to the caustic exhaust fumes, but bronze has lasted for months and is still going strong.) However, as anyone who runs nitro knows, backpressure in the exhaust pipe is used to pressurize the fuel tank, and normally stuffing the end of the exhaust pipe with something to muffle the sound causes serious tuning problems because it messes up the fuel pressure. Well, I figured out how to solve that problem -- I added a bleeder valve (actually a remote fuel-mixture needle valve for an airplane, repurposed to serve my needs) to allow some of the excess exhaust pressure to escape. As a side benefit, this setup also allows me to have full control over the fuel pressure going into the carburetor, an extra dimension of control which un-muffled nitro engines lack. It works perfectly and I plan to continue using it for the rest of the life of the buggy.
To be sure, I could've picked an easier introduction to nitro, but building this vehicle has been immensely satisfying nonetheless. The only question now is, what will my next nitro vehicle be?
I finally got the clutch and engine tuned just-right. I rebuilt the engine a while back and replaced the crankcase because I couldn't get the bearings out of the old crankcase, and ever since then there's been rather a lot of oil on the side of the engine after each run. For whatever reason, I only just now examined the engine carefully enough to notice there's a casting defect on the underside of the exhaust mount. So I rebuilt the engine *again*, using another crankcase that I know has no casting defects. While I was in there, I modified the clutch shoes again; I shaved the middle of the clutch shoes flat, to reduce contact area, so they engage more like a 3-shoe clutch. Here's what it looks like now:
I also ported the cylinder sleeve and rounded the edges on the conrod, to increase turbulence in the combustion chamber and reduce turbulence in the crankcase.
Between porting and polishing the engine internals, replacing the defective crankcase, lightening the clutch shoes to raise the engagement RPM, and retuning the carb to be a little richer now that I don't have to fight the clutch engaging too soon, the engine runs like a dream.
Finally! After a year of keeping a lookout, I finally found clamping hexes that fit this vehicle:
They're actually made for the MERV, but they work just as well on the Turnigy Nitro Buggy -- and presumably on any other vehicles based on the same platform.
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