Friday, May 23, 2008

Part I - I started this diary in September of '07 and just began this blog so I just pasted the whole thing here. As soon as I'm able to figure out how, I'll post some photos as well.
I picked up my first R/C magazine in a couple years for a flight to Seattle and was settled back in my luxurious coach seat when I saw an article on the World’s Fastest R/C Car Challenge. Just like a crack addict, I was instantly hooked. The present nitro record is 88mph....heck, I could beat that easy! By the time we landed I had my car designed.....a four-engined, nitro TC3. That center shaft was just begging to have more engines attached to it. Did I really need four engines? Probably not but what’s yer point? Remember, some’s good (.12 engine), more’s better (.21 engine), too much is just enough (two .21engines), and if in doubt, double it! (four .21 engines!). See? It was simple math.

I was completely possessed by this project. I had a hard time sleeping, thinking about what parts needed to be made, what parts could be bought. I have been building R/C chassis and parts for 20 years and it was as if this was to be my destiny. As soon as I got home I was on eBay and bought three junker TC3's. When they arrived they were disassembled and it was quickly obvious that the ring and pinion in the diffs were the weak point as the gears in four of the six were toast. I weeded my way through piles of parts, tossing some that were bad, cleaning the remainder.

Then came the real design work. The official nitro record is 88mph......what was I shooting for? The official electric record is presently 127mph although the holder, Nic Case, has run an unofficial 141!! I don’t think a nitro car is going to beat that simply because of the weight and the necessity for air to the engine(s), causing drag so my goal was somewhere between 88 and 127. So I set my goal at 100mph but my gearing has the potential for 117 at top rpm. I found large steel gears for the two-speed pinions (36 and 48 teeth!) which would require me to drill and tap them for the Associated clutch bells.

The chassis was laid out using two aluminum TC3 pans. I pulled the .12's out of my regular racers and put them in place. The four engines were going to be set up as pairs, front and rear, each pair driving a common spur gear. I was initially going to just put a second spur gear on the drive shaft but it was quickly obvious that wasn’t going to work. Instead, the front portion of one chassis pan was trimmed off at about the centerline of the rear axle. The two speed was left in its original position (but with no differential) and then the rear portion of a second pan was cut and welded to the tail of the first with the second two-speed assembly and differential. This stretched the wheelbase considerably for stability and a mish-mash of Associated parts cobbled from the three junkers finished up the drivetrain.

My plan was to use the aluminum pans for an initial test and then duplicate the mounting points onto a sheet of carbon fiber for the final stage. I mounted all the chassis parts and things were really looking good. I brought it down to Jake’s for his comments and while looking at it he very easily gave the now very long chassis quite a twist.............dang! That’s not good at all. Back to the drawing board.

Although the aluminum chassis was short lived, it was crucial for the location of parts and working out the very concept of the project so it was worth trying that way first. I had a piece of G-10 fiberglass onto which I transferred all of the mounting points, then drilled the holes and installed the parts. A thin top plate between the diffs worked wonders in stiffening the whole works. Wheel cutouts were removed, suspension bolted on and all of a sudden, it was a roller!

What engines to run was quite a quandary. I did internet research looking for the best power to weight ratio. In chatting with the present nitro record holder (Tony Lovering in the UK) .21 engines were recommended as the best candidates. There are a LOT of engines available, some with good power but a lot of weight, others with claims of great horse power debunked by independent dyno tests. I settled on Picco P9, Evo 2 engines. Picco claims 2.5 hp, and even thought a dyno test came up with 1.5 hp, it still had the best power of the .21 engines tested and was considerably lighter than the others. I could only afford one at a time over a couple months and Jake had to scour the country for the last one! I’m hoping that somewhere between six and ten horsepower is enough!

As things continued to come together other problems reared their ugly heads like, how do you start four engines at the same time? I scored a starter box on eBay for $6.50 and have set up pegs on it that match holes at each engine station so I’ll start them individually. Then, what if it flips? A full roll cage needed to be fabricated from thick music wire around the engine heads so if it does get on its lid those very expensive heads will be somewhat safe. I have had to accept that ANY crash approaching 100mph is going to be costly.

Another safety feature being developed is a drag chute. Now, besides looking too cool for words, if something goes completely awry merely letting off the throttle will release it, dissipating energy. Its set up so that once wide open throttle is achieved, a cog on the brake’s servo releases the chute when the throttle returns to idle. Any throttle setting less than WOT won’t release it. I’m anxious to see this work!

Although much of the car is low tech like the basic fitting of parts and pieces, there is some high tech on it..... a gyroscope. This is R/C helicopter technology used to keep these high speed cars straight. They take thousands of samplings per second and, with a high speed servo, constantly make adjustments to the steering so it stays on the course you choose.

Making all of this stuff work together is half the fun. An unusual project like this requires more than just out of the box thinking, it takes ‘that’s just crazy enough to work’ thinking! The four carbs are connected by cranks and rods to the throttle servo and the three disc brakes have a separate servo at the back of the car. One small fuel tank at the front of the car should feed the engines for the two or three minutes each run will take and the receiver pack is at the very back. The front engines’ mufflers go to the back, the back engines’ to the front. There are lots of wires and hoses to run, connecting all of the carbs, servos, controllers and exhaust pipes.

Piece by piece, the Problem Child came together. There were very few ‘do-overs’ needed and everything went together pretty easy for a project this complicated. After a couple months work the front two engines were ready to fire. On the starter box it went and with my finger over the exhaust to prime the carb I pushed down on the car. The engine spun for a few seconds and then we had one running engine. I let it run for several minutes, allowing everything to get warmed up before stopping it. I repeated the procedure on the other engine, running it for several minutes but then instead of shutting it off, I restarted the first engine ............what a glorious sound!!!!!! A blip of the throttle brought loud and instant rev response. The only thing I can liken it to is a top fuel dragster warming up in the pits. I ran the engines up to 60 mph and everything was very smooth. My original plan was to have two engines ready for a test on December 9th. I had other commitments which postponed the test for a week so now I had time to mount the other two engines.

Because I had worked out all of the details on the first pair the second pair went in fairly easily. I mounted the gyro and high speed steering servo and had to work out the common fuel and exhaust pressure lines. I welded up a roll cage to protect those very expensive heads and then fired up all four engines. If there’s such a word, it was an even gloriouser sound!

The day before the official test the car was run on a short side street to work out any bugs...and there were a few. One was the plethora of batteries that have to be charged prior to running - transmitter, receiver, starter and glow plug starter. Nothing wants to work so load everything back up, head home and charge all the batteries.

I returned a couple hours later and easily got the engines fired up. It was cold outside so they didn’t want to get to operating temps but once they hit 160-70 I set on the pavement and it moved under its own power for the first time. It had decent acceleration and I ran it up and down the street at moderate speed to try and warm it up but a problem immediately became obvious. That little tank could not feed those engines for long, at all! I could only make one or two passes down the street before re-fueling and then I usually had to start a stalled engine.

My original intent was to have each engine independent so that if one went out it would not affect the others. I had no idea they were so susceptible to small changes in fuel pressure. During construction I wasn’t convinced that one fuel line could feed four engines and it appears I was right. Each time the car went out it came back with one or more engines out. Then, if that one engine died, because all of the exhaust pressure lines were connected, the fuel pressure dropped and killed another. Despite these recurring problems, it did tap into the 50+mph mark, not great, not what I was hoping for but it was running, steering straight and stopping well.

That night I hooked up a second tank and ran the right and left pairs separately. I also changed the transmitter and receiver packs to 2000mAh AA’s to be sure I’d always have power. The gyro seemed to drain the small standard receiver back pretty quickly. The next morning(12/15/07), I was at my ‘official’ test site with the second tank and again had cold temperatures and balky engines. Once they were all running and as warm as they were going to get, I set it down and drove off. Part of today’s test was the radio range and it was stellar. I could drive it several hundred feet away and still have instant control. The car did a couple slow 40mph runs and it came back into the pits with all four engines still running!!!!! Top up the tanks and off we went for a speed run. Because this strip was longer than last night’s course the front engines sucked up all the fuel and shut down the rear two. If it ran hard long enough it would come back to the pits with only one running.

Again, it was a problem filled day as "Problem Child" lived up to its name. It ran into the 60+ mph range, usually on two engines, so there was some improvement. The next plan was to install a tank for each engine which should solve the fuel starvation problem and help tune the engines. I also had to replace one of the nylon gears...something got caught between the pan and the gear, and squared off the teeth. The one-way bearing in that same two-speed wasn’t grabbing consistently so had to be changed too. I designed the car to be as easy to repair as I could but it’s still time consuming. All in all, these were very minor problems but still a bit frustrating. I want to go faster!!!!!!

In order to mount four NTC3 tanks up front I had to add a little plate to extend the pan but since I’m going to re-cut it out of CF it doesn’t matter if it doesn’t look that great, as long as it does the job. The tanks ended up being mounted with the pickups at the front and although this isn’t the best place, for testing purposes it would work. The eight hoses necessary to run the engines would seem to be cluttering, but actually they were neater and less problem prone than the two lines and a bunch of T’s that I started with. When it comes time to build the body for this beast these NTC3 tanks will be replaced by some ‘bullet’ tanks by Sullivan. They’re a bit long but their length will allow a more sloping nose than the present variety.

Test date, 12/31/07. I was ready to go fast!!!! A half hour before heading out I checked to make sure everything was in the GO! position. I started all four engines with hotter plugs and made sure all the batteries were charged up. I got to the site and set up. Hoping to make sure that the day would be successful I tried to start #3......the starter box wasn’t working! I had replaced one of the motors with an old race motor and apparently should have replaced both. (20-20 hind sight!) Some fiddling with the old motor got it running but not strongly. Try to start #3 again.....something was hanging up in the drive train. An inspection revealed the clutch was engaged. The engine was removed, the errant clutch spring re-installed and the engine remounted. Try to start #3 yet again.....everything is spinning, nothing’s happening. Move to the other engines.....finally one starts, another stops at TDC every time. The starter won’t get past it to start. Finally I get a second engine to start and set it down but they promptly stall. Put the car in the trunk before I run it over!!!!!!!!

When I got home I tore everything apart, finding the bad plugs and another chewed up gear. The scary thing was that if I had gotten all of the engines running and tried to get some speed, I would have surely damaged the car since the brake servo, although it appeared to be plugged in, wasn’t working. Maybe someone was trying to save me from myself. I can’t figure out what was wrong with the plugs although I did switch the polarity on the igniter....I’ll have to check that out before running again.

Well, the post mortem investigation was quite revealing. The gel cell in the starter was apparently dragging down the power available to the starter motors so I removed it and rewired the motors in 12 ga. wire and replaced the 16 ga. with 10 ga from the power supply. I also replaced the cheaper original motor with another old race motor so they spin much faster now and with more power.

The glow plugs fell victim to a wayward 12 volt supply which went from a the power supply to one of the starter motor’s cases to the bolts mounting the roll cage to the igniter. I heard a pop once when I attached the igniter, similar to my last foray into bad voltage. The new wiring will prevent that from happening again. Once the starter was rewired and new plugs installed the engines fired right up.

One problem I haven’t been able to solve is getting the engines all in tune. They came from the box very rich and I have slowly leaned them out but they’re not getting much leaner. Reading the instructions gave me a ‘5 turns from bottom’ starting point and I was still a long way from that. I believe that the only way to get them all in tune is to do each one separately so I’m going to remove all but one engine and get it running good, then switch in another, working my way through the bunch. I believe that the car will be light enough for a single engine to pull it with the cage and other engines removed. Then once they’re all running well, re-install them and the roll cage and try for a speed run. Other wise it’s a hit and miss sorta deal.

I’m also chewing up some gears. I think the power of the engines is allowing the gear lash to get too wide so I’ll have to close that up, maybe even a bit tighter than normal. If the weather clears I might try for some tuning runs this weekend but it’s supposed to rain.

A week later it continues to be rainy and cold.....While the weather was uncooperative I decided to make things easier to work on. I ran yellow fuel and exhaust lines but with four per side it was often difficult to trace which line went where so I changed the exhaust lines to blue. I was also running into trouble when removing or installing the engine plate bolts since the interior ones were very difficult to get to. I trimmed some T nuts down and put them in the interior plate slots and changed the exterior nuts to wing nuts so they can now all be tightened or loosened from the bottom of the car without a socket or wrench.

It’s still raining.....=-( I’m hoping that by Saturday (tomorrow) it’ll be clear enough to do some tuning.
The weather cleared and I was at my test site by 10 AM. The road was still pretty damp but I was anxious to get going. I set everything up and got the engine started and warmed up. I set the car down and began making some easy passes to get the engine to temperature. I had turned the needles all the way in and then 5 turns out to approximate the correct mixture. It was still a little cool on this engine (right rear) so turned it in a quarter at a time until the temp was at 220.
The engine ran good but wasn’t able to rev. I adjusted everything I could but it still seemed to be starving for fuel. I’ll put a larger diameter fuel line on it and try it again but it may be a carb problem and will switch it with another as a different test.

I changed over to the right front engine and tuned that one in. It ran great and had plenty of revs but the one way bearing was slipping and the engine would rev without pulling. The gyro was acting weird so I unplugged it (I thought) but instead unplugged the brake servo so when I went down the road and went to turn around the car was moving too fast to turn and smacked the curb, shattering the four fuel tanks!

I was unhappy about the crash but the car had hit 65 mph on one engine so the day wasn’t a total write off. I went home and removed the remains of the four tanks and fabbed up a mount for the bullet tanks I would ultimately be using. I also picked up a new one way bearing and installed it in the front two-speed.

Sunday was sunny so I headed back out with a bigger fuel line for the rear engine as an experiment. The car started right up and I took a couple easy passes and the one way worked great. I came in to refuel and set the car down pulling away at partial throttle. At about 20 feet away it was obvious to me that I had no control over the car and could only watch as it moved away to some surely tragic destiny. It slowly arced left and then rubbed along the curb at about 20 mph until it ran into the side of a storm drain inlet and was catapulted out into the street. I jumped into my car and drove down, sure everything was broken.

It was surprisingly intact, only the front tank extension plate broken. It appeared that the receiver wasn’t working but I had mounted all of the electronics on flexible plates to avoid damage in just those situations like the previous day’s crash. The culprit turned out to be the on/off switch which chose to fail in the ‘on’ position. When the switch is bypassed, everything comes to life. Whew! I was afraid that I’d get it home and everything would suddenly work fine, causing me to not be at all confident that the problem was solved.

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