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Nitro direct drive

Old 06-28-2013, 08:18 AM
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Default RE: Nitro direct drive

Nice looking brake caliper there...I presume you are not a machinist by trade?...neither am I...I have a minimill that I have toyed with so I can see the effort involved there...nice...keep it up.
Old 06-28-2013, 08:20 AM
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Default RE: Nitro direct drive

Double post..delete me please Foxy/ibtweety.
Old 06-28-2013, 08:30 PM
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...I presume you are not a machinist by trade?
Nope. Mechanic. I'm using a little hobby mill, Harbor Freight job. It works, but it can be aggravating. Chuck walks, table wobbles-these things have to be accounted for when doing final precision cuts. Always swipe one direction, preload the table with my hand and gently turn the dials, etc. Quality bits help, but the mill is just not great. I'll get a bigger, nicer one when I have room, but as of now, this little bench top is about all I have space for.

Got the other caliper done tonight. Still need to build a brace to go across the top, though, since each one is only held to the diff with one 8-32 screw. Not going anywhere, but not as solid as I'd like them to be for the speeds I expect to run. We'll see if the 180 oz servos can pull the cables hard enough to stop this car, too. I expect curb weight to be about 6 lbs. The way I profiled the brake cams, they don't need to travel far, so I should be able to attach them on the innermost servo arm hole and get max leverage.
Old 07-02-2013, 11:04 PM
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The Tamiya clutch bell came today-now I can get things moving! Still have a few parts to build, and we have to cut and TIG the little Tamiya dog bone to the larger OFNA shaft, but I have everything I need now, save for special clutch shims.

My only real concern is that the clutch bell won't be able to take the heat. With a 6.24:1 ratio on my other GT, I cooked standard bearings and shoes in minutes trying to get the power of that OFNA .32 to the ground through such tall gearing. This chassis is lighter, but the ratio is half. Only one way to find out, though.

I have decided that I want to try to break the current nitro speed record as well. I'm sure it'll take awhile, with many revisions, possibly even completely redoing it. But 120 MPH just doesn't seem like such a high bar. I'm not afraid to throw money at this, and I firmly believe that it's a good platform.

Probably going to run OFNA belted street tires, but I'm waiting for a response from them as to whether or not these tires can handle 11,000 RPM. That is the speed a 4" tire needs to rotate at to hit 130 MPH. With the 3:1 gear ratio, that is 33,000 engine RPM-attainable in theory. I do not know how much downforce the spoiler will apply, though, so the drag and friction coefficient may require more power than the stock motor makes to reach that RPM.

Even if I can't get there, I'm sure I'll have built the fastest RC10GT around [8D]

I hope to have the dog bone welded, engine & servo mounts made & installed, and brakes hooked up by Sunday. My goal is a first run by the following weekend. I will keep this updated
Old 07-03-2013, 07:08 AM
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Default RE: Nitro direct drive

Your going to have to get a rolling start at that ratio or the engine will just die, plus I doubt you will get anywhere near 33,000k rpm's. If that is even accurate, they got that with no load on the engine. Keep it up though! lol


Old 07-03-2013, 08:33 AM
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Default RE: Nitro direct drive

Your going to have to get a rolling start at that ratio or the engine will just die
It won't stall-the concern is toasting the clutch. That's why I opted for aluminum shoes, powerful springs and ceramic bearings.

The OFNA .32 had absolutely no trouble spinning tires on my other GT with the 6.24:1 ratio; despite the taller gearing, this is a lighter chassis and a more powerful engine.

I doubt you will get anywhere near 33,000k rpm's. If that is even accurate, they got that with no load on the engine.
Maybe, maybe not. There is only one way to find out. I'm quite certain it won't have the power to rap out with the current tires, but they ballon to nearly 7" diameter at just 50 MPH, which is nearly double the engine RPM versus inches of travel that I'll have with the 4" belted tires. I also know that those tires will probably come apart before I hit 100 MPH. Remember, this engine is meant to be a major upgrade for 1/8 scale vehicles weighing 2 times as much (or more), and with the added resistance of multi-gear transmissions and 4WD. I have very low parasitic loss with only a single differential.

I'm not counting on success the first time out. Or the second, the third. I'm counting on learning the capabilities of the engine and chassis by field testing, and then making the necessary adjustments and modifications to reach the goal. I don't know yet if my downforce will be to little or too much, if my alignment will allow handling at very high speeds when the suspension geometry starts changing, if the brakes will be able to slow it down in time or if they'll be too powerful and put it into a spin, etc. I have to learn these things and then apply the new knowledge.
Old 07-03-2013, 09:04 AM
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Default RE: Nitro direct drive


ORIGINAL: Sixtysixdeuce

Your going to have to get a rolling start at that ratio or the engine will just die
It won't stall-the concern is toasting the clutch. That's why I opted for aluminum shoes, powerful springs and ceramic bearings.

The OFNA .32 had absolutely no trouble spinning tires on my other GT with the 6.24:1 ratio; despite the taller gearing, this is a lighter chassis and a more powerful engine.

I doubt you will get anywhere near 33,000k rpm's. If that is even accurate, they got that with no load on the engine.
Maybe, maybe not. There is only one way to find out. I'm quite certain it won't have the power to rap out with the current tires, but they ballon to nearly 7'' diameter at just 50 MPH, which is nearly double the engine RPM versus inches of travel that I'll have with the 4'' belted tires. I also know that those tires will probably come apart before I hit 100 MPH. Remember, this engine is meant to be a major upgrade for 1/8 scale vehicles weighing 2 times as much (or more), and with the added resistance of multi-gear transmissions and 4WD. I have very low parasitic loss with only a single differential.

I'm not counting on success the first time out. Or the second, the third. I'm counting on learning the capabilities of the engine and chassis by field testing, and then making the necessary adjustments and modifications to reach the goal. I don't know yet if my downforce will be to little or too much, if my alignment will allow handling at very high speeds when the suspension geometry starts changing, if the brakes will be able to slow it down in time or if they'll be too powerful and put it into a spin, etc. I have to learn these things and then apply the new knowledge.
Only way to find out is to try!
Old 07-03-2013, 09:05 AM
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Default RE: Nitro direct drive

120 is the record for nitro....as in anything....there are different classes....from memory the record is not even from the "open" class....not too sure if your car would fit into the "open-wheel" class or it would go into "open"(because of the my bad memory of the specific class rules). If you are interested in comparing/making a record then all the info. is in the links I gave earlier and if you want help with wheel/suspension setup info. and generally any info. concerning speed running then there are other forums where the people making/recording the records will help....again should all be in the links.

Above all...good luck and have fun.
Old 07-03-2013, 04:00 PM
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Default RE: Nitro direct drive

Made a lot of progress today; it's pretty much assembled, most of it final. The rear chassis extension is done (6061-T651), brake cable bracket made and installed, servos, linkage, RX, fuel tank all in. All that's really left before it's ready for a test run is the dog bone hybrid welding, which a friend of mine will be helping me with tonight. It came out a tad heavier than I wanted at 6.42 lbs with a full tank and body sitting on it, so I'm going to see where I can shed some weight.




May have to revisit the brakes, though. The cable sheaths might not be strong enough, as they want to wrinkle under full braking force. The bracket came out fairly clean, though, despite a broken tap





Do still have to put body posts on, but this is how she'll look going down the road:



Will update after first run!
Old 07-04-2013, 10:45 PM
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Well, as anticipated, clutch problems. The engine actually moves the car pretty well off the line, but I never had a chance to dial it in and get it on radar. The aluminum clutch shoes started depositing material on the inside of the bell, and with the slightly smaller ID of the Tamiya bell, the end of the shoes where the pins go through ended up seized to the hub. Once it cooled, I was able to break it free, remove everything and laboriously remove the aluminum from the inside of the clutch bell. Funny thing is, it didn't really get all that hot; bearings weren't discolored, even the bell itself was only slightly tinged. I guess the aluminum shoes weren't as good an idea as I thought. We will give it another go with the carbon shoes, and running lighter springs to hopefully make the solid mechanical connection sooner. My thought process had been that the gear ratio would necessitate higher revving before engagement, but I don't really need to build that much RPM to get it moving, and this only served to increase temperatures as the clutch slipped more easily.

Brakes worked OK, not great. I'm going to make longer cam arms, as I don't think these tiny cables can take it if I increase leverage on the servo end. I did end up making aluminum cable sheaths; the plastic ones crumpled under the strain of a full size servo.

Hopefully I'll have another update after the weekend.

Happy Independence Day!
Old 07-05-2013, 04:56 AM
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Default RE: Nitro direct drive


ORIGINAL: Sixtysixdeuce

Well, as anticipated, clutch problems. The engine actually moves the car pretty well off the line, but I never had a chance to dial it in and get it on radar. The aluminum clutch shoes started depositing material on the inside of the bell, and with the slightly smaller ID of the Tamiya bell, the end of the shoes where the pins go through ended up seized to the hub. Once it cooled, I was able to break it free, remove everything and laboriously remove the aluminum from the inside of the clutch bell. Funny thing is, it didn't really get all that hot; bearings weren't discolored, even the bell itself was only slightly tinged. I guess the aluminum shoes weren't as good an idea as I thought. We will give it another go with the carbon shoes, and running lighter springs to hopefully make the solid mechanical connection sooner. My thought process had been that the gear ratio would necessitate higher revving before engagement, but I don't really need to build that much RPM to get it moving, and this only served to increase temperatures as the clutch slipped more easily.

Brakes worked OK, not great. I'm going to make longer cam arms, as I don't think these tiny cables can take it if I increase leverage on the servo end. I did end up making aluminum cable sheaths; the plastic ones crumpled under the strain of a full size servo.

Hopefully I'll have another update after the weekend.

Happy Independence Day!
what brand of clutch are you trying to use ?
Old 07-05-2013, 06:05 AM
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Default RE: Nitro direct drive

what brand of clutch are you trying to use ?
It's an Associated MGT 4.6 vented flywheel with OFNA purple racing shoes and the Tamiya bell.
Old 07-05-2013, 06:19 AM
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Default RE: Nitro direct drive


ORIGINAL: Sixtysixdeuce

what brand of clutch are you trying to use ?
It's an Associated MGT 4.6 vented flywheel with OFNA purple racing shoes and the Tamiya bell.

OFNA purples are heavy, but soft as hell............ did you seat the clutch.... ?
Old 07-05-2013, 07:34 AM
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Default RE: Nitro direct drive

Run the shoes backwards if you aren't already, should reduce slippage a bit.
Old 07-05-2013, 11:02 AM
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Default RE: Nitro direct drive

OFNA purples are heavy, but soft as hell............ did you seat the clutch.... ?
During the bench break in, yes. Just held the bell and started bringing the R's up until I could barely hold it, did that a few times and called it good.

The idea behind soft, heavy shoes and stiff springs was that the motor would rev up pretty decent before engagement and then grab hard with minimal slippage. It just didn't work out well.

Run the shoes backwards if you aren't already, should reduce slippage a bit.
Huh. I've never heard of doing that. Does it really work? The geometry seems all wrong.
Old 07-07-2013, 12:45 PM
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Default RE: Nitro direct drive

what is the front wing made of? i'm guessing 16 gauge steel sheet. if it is, i'd suggest replacing it with plastic or at very least aluminum. that should cut at least an ounce or 2. or if you want to get fancy, use carbon fiber.
Old 07-07-2013, 09:34 PM
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Default RE: Nitro direct drive

what is the front wing made of?
18 ga aluminum.

This thing doesn't have much steel on it. Diff gears, out drives & dog bones, clutch bell, crankshaft, bearings, screws-that's about it.
Old 07-08-2013, 08:11 AM
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Default RE: Nitro direct drive

i see, steel where steel is needed and no where else. i wonder what would happen with 2 LRP's... tuned by supertib...
Old 07-08-2013, 09:30 AM
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ORIGINAL: cumquat

i see, steel where steel is needed and no where else. i wonder what would happen with 2 LRP's... tuned by supertib...
He would smoke two clutches instead of one.
Old 07-08-2013, 09:33 AM
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Default RE: Nitro direct drive

but it'd sound awesome! and in theory it would cut the load on each clutch in half, possibly saving them. wheelie bar would be mandatory though.
Old 07-09-2013, 07:01 AM
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Default RE: Nitro direct drive

i wonder what would happen with 2 LRP's
Believe me, the thought has crossed my mind. I'm pretty well out of real estate on this chassis, though.

The belted tires showed up yesterday, but I haven't had time to mount them or work out the front wheel bearings yet. I'm hoping the reduction in rolling circumference, as well as shedding a little bit of weight, will help. These are 4" tires, and they can't balloon. Those 5.5 inchers are getting up toward 7" at speed.
Old 07-10-2013, 08:17 PM
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Default RE: Nitro direct drive

LMAO!! I can't believe I stumbled on to this.
I had just found a crazy pic of your car (same pic as 1st post) on a random goodle image search of rc10gt + big wheels and talked about your stance on another forum!
Anyhow, I cant figure out how to get those size wheels on my gt. If you could tell me I would be so appreciative!! On that other thread we were all wondering (guessing) how that sucker would handle!
But, after skimming through your thread here, I really admire all your work. Quite talented. I wish you nothing but luck reaching your goal!
Old 07-11-2013, 03:37 AM
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Default RE: Nitro direct drive


ORIGINAL: Sixtysixdeuce

Your going to have to get a rolling start at that ratio or the engine will just die
It won't stall-the concern is toasting the clutch. That's why I opted for aluminum shoes, powerful springs and ceramic bearings.

The OFNA .32 had absolutely no trouble spinning tires on my other GT with the 6.24:1 ratio; despite the taller gearing, this is a lighter chassis and a more powerful engine.

I doubt you will get anywhere near 33,000k rpm's. If that is even accurate, they got that with no load on the engine.
Maybe, maybe not. There is only one way to find out. I'm quite certain it won't have the power to rap out with the current tires, but they ballon to nearly 7'' diameter at just 50 MPH, which is nearly double the engine RPM versus inches of travel that I'll have with the 4'' belted tires. I also know that those tires will probably come apart before I hit 100 MPH. Remember, this engine is meant to be a major upgrade for 1/8 scale vehicles weighing 2 times as much (or more), and with the added resistance of multi-gear transmissions and 4WD. I have very low parasitic loss with only a single differential.

I'm not counting on success the first time out. Or the second, the third. I'm counting on learning the capabilities of the engine and chassis by field testing, and then making the necessary adjustments and modifications to reach the goal. I don't know yet if my downforce will be to little or too much, if my alignment will allow handling at very high speeds when the suspension geometry starts changing, if the brakes will be able to slow it down in time or if they'll be too powerful and put it into a spin, etc. I have to learn these things and then apply the new knowledge.

which clutch springs are you using ? FYI you want the softest clutch springs possible for what you are doing ....the harder the clutch springs the easier the clutch shoes will burn out.......

Also seating the clutch needs to be done more aggressively then what you did....., PIn the car down to the ground and give the engine some bursts of throttle......2-3 second bursts.....
Old 07-12-2013, 08:01 AM
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Default RE: Nitro direct drive

I cant figure out how to get those size wheels on my gt. If you could tell me I would be so appreciative!!
It was actually quite easy. Just pick up a set of Traxxas Slash 17mm hex adapters, re-tap the retaining nut to #8-32, and drill the pin hole in your axle stubs to accept the slightly larger cross pins (not 100% necessary, but advisable).

Those adapters are no longer on my car, as it now has an OFNA Ultra complete rear diff & suspension assembly, but it did in the pics in the beginning of this thread.

Handling was actually quite good, excellent stability. The downside is reduced braking power and weight; those HPI Phaltlines wheels/tires weigh .59 lbs EACH.
Old 07-12-2013, 09:22 AM
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Default RE: Nitro direct drive

Here's how it will run on the next attempt:


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