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junkmunki

Chain drive

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I was just reading the discusion over in the re release area about the new Kysoho optima that is being released, and it got me to thinking.

When people such as Kyosho re release the kits, they obviously make improvements to parts that were known to break, or upgrade to better materials, but i remember that Kyosho produced some buggies that were chain drive for the 4WD, but having never seen one in life, much less run one, were they any good/reliable? and would they be worthy of a re release?

Has anyone got a chain drive? im curious to know if they were noisy at speed.

J

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Not noisy, exactly. They make a characteristic sound, sort of a "hiss" as the chain goes through the guides. Probably a lot more drag there than there needs to be. The Rocky was probably the worst offender for excess drag; the chain ran backwards and at layshaft speed, not axle speed, so it was really whizzing along when the car was running.

As for durability, they're fine. The chain stretches out a little over time, but there's usually a provision to tighten it. But loose works fine too. I used to have a Kawada chain-driven 1/12 scale on-road car that had a really loose and floppy chain, and it never skipped.

What's cool about the re-re Optima/Javelin is that they included both the chain drive and the belt drive, so you can try both. (And since the chain/belt is completely inaccessible without tearing apart the entire car, you get to build it twice!)

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I built my re-re Optima with the chain, much for the same reasons; I'd never had one, and was curious. I found it fun, the noise is different but not noisy I'd say.  I have a re-re Javelin that I built belt drive, and running them side by side you could identify the noise difference, but the belt drive car wasn't whisper quiet either. I've bashed, jumped, beached etc my Optima, and it's all been fine. I doubt I've run it enough to stretch the chain, but so far so good.

I'd recommend an Optima/Javelin, they're a great build, sturdy and handle really nicely. If you fancy the belt drive, the Optima and Javelin come with everything you need to do either. The Turbo Optima doesn't come with a chain (there's a sticker in the blister pack highlighting that it's now an Option part), but I think it has everything else.

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The drag from the chain is pretty minimal, even in the Rocky.  The chain guides are molded in very smooth and slippery plastic and are mostly in line with the the front and rear sprockets, so not much power is lost from guide friction or noise.  Chain will never be as efficient as belt or shaft drive, but it's not horrible.  But you will note that no 4WD cars today use a chain because it's not as good as the alternatives. 

If the chain tension is too tight it will have more drag.  For the Rocky, keeping the chain tensioned so that it lifts up about 10mm at the top center of the chain when you pull it up with a finger like the manual says is just about perfect.  Too tight and it also rubs the bottom of the battery pack and could wear right through the battery shrink wrap (in the case of NiCd or NiMH stick packs), which would be REALLY BAD (as in dead short bad).  I sometimes add a piece of tape to the bottom of the battery pack in order to stop the chain from wearing through.  It's an annoying Rocky chassis/drivetrain design quirk.

If there was a lot of friction, then there would be a lot of noise and/or a lot of heat.  The less noise, the less energy is being lost to creating sound.  The less friction, the less energy is being lost to creating heat.  Belt or shaft drive is a lot quieter and is more efficient for sure.

Prior to buying four vintage Rocky's last year and getting totally hooked on them (they are one of my favorite vintage 4WDs right now), I had no experience with chain drive.  Now I love chain drive and found it to be much better than I expected both in terms of noise and efficiency.  For example, I thought the chain guides would be a high-wear item, needing replacement often.  As it turns out, they don't wear much at all.  I also thought the chain would be really loud and annoying.  It's not.

The ends of the guides are the most prone to wear because that is where the chain first hits the guide at an angle from the sprocket.  In the Rocky, the most wear is the front of the top guide because the chain is being pulled from the rear sprocket and therefore has the most tension.  Using the 19 tooth sprockets instead of the 18 tooth helps because the sprockets are slightly larger in diameter so the chain has less of a height difference to hit the guide.   You can see what I mean in this picture:

image.png.c45d521957ada48637d172ede350b008.png

As @markbt73 mentions, the chain is rotating "backwards" (counter-clockwise) on the Rocky when looking at it from the right side (the "chain side" of the chassis).  The rotation direction has nothing to do with efficiency, though, since half the chain is moving towards the front of the chassis and half the chain is moving towards the back of the chassis no matter which direction (CW or CCW) the chain is rotating.

Chain stretching is a thing, but once the initial stretching is done, it doesn't really keep stretching over time.  The metal in the chain is way too strong to bend like that and keep bending.  It takes a strong set of pliers to bend the chain wire to remove a link.  The original Rocky chain is actually made of slightly thinner wire than the re-re Optima chain.  I bought some of the re-re Optima chains to see if they would fit the Rocky (they do - the chain and sprocket pitch is the same - but the Optima chain is too long so you must shorten it).

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2 hours ago, Champ85 said:

The drag from the chain is pretty minimal, even in the Rocky.  The chain guides are molded in very smooth and slippery plastic and are mostly in line with the the front and rear sprockets, so not much power is lost from guide friction or noise.  Chain will never be as efficient as belt or shaft drive, but it's not horrible.  But you will note that no 4WD cars today use a chain because it's not as good as the alternatives. 

If the chain tension is too tight it will have more drag.  For the Rocky, keeping the chain tensioned so that it lifts up about 10mm at the top center of the chain when you pull it up with a finger like the manual says is just about perfect.  Too tight and it also rubs the bottom of the battery pack and could wear right through the battery shrink wrap (in the case of NiCd or NiMH stick packs), which would be REALLY BAD (as in dead short bad).  I sometimes add a piece of tape to the bottom of the battery pack in order to stop the chain from wearing through.  It's an annoying Rocky chassis/drivetrain design quirk.

If there was a lot of friction, then there would be a lot of noise and/or a lot of heat.  The less noise, the less energy is being lost to creating sound.  The less friction, the less energy is being lost to creating heat.  Belt or shaft drive is a lot quieter and is more efficient for sure.

Prior to buying four vintage Rocky's last year and getting totally hooked on them (they are one of my favorite vintage 4WDs right now), I had no experience with chain drive.  Now I love chain drive and found it to be much better than I expected both in terms of noise and efficiency.  For example, I thought the chain guides would be a high-wear item, needing replacement often.  As it turns out, they don't wear much at all.  I also thought the chain would be really loud and annoying.  It's not.

The ends of the guides are the most prone to wear because that is where the chain first hits the guide at an angle from the sprocket.  In the Rocky, the most wear is the front of the top guide because the chain is being pulled from the rear sprocket and therefore has the most tension.  Using the 19 tooth sprockets instead of the 18 tooth helps because the sprockets are slightly larger in diameter so the chain has less of a height difference to hit the guide.   You can see what I mean in this picture:

image.png.c45d521957ada48637d172ede350b008.png

As @markbt73 mentions, the chain is rotating "backwards" (counter-clockwise) on the Rocky when looking at it from the right side (the "chain side" of the chassis).  The rotation direction has nothing to do with efficiency, though, since half the chain is moving towards the front of the chassis and half the chain is moving towards the back of the chassis no matter which direction (CW or CCW) the chain is rotating.

Chain stretching is a thing, but once the initial stretching is done, it doesn't really keep stretching over time.  The metal in the chain is way too strong to bend like that and keep bending.  It takes a strong set of pliers to bend the chain wire to remove a link.  The original Rocky chain is actually made of slightly thinner wire than the re-re Optima chain.  I bought some of the re-re Optima chains to see if they would fit the Rocky (they do - the chain and sprocket pitch is the same - but the Optima chain is too long so you must shorten it).

Thanks for all the info guys, I'm quite fascinated by the whole concept. I can see me having to get one now.....

As Champ85 states, it's not as efficient as shaft or belt drive, so I wonder why the concept even made it to production? 

J

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8 hours ago, junkmunki said:

Thanks for all the info guys, I'm quite fascinated by the whole concept. I can see me having to get one now.....

As Champ85 states, it's not as efficient as shaft or belt drive, so I wonder why the concept even made it to production? 

J

Because it's tough as nails, I would imagine. Kyosho even used chain drive in 1/8 scale nitro-powered cars back then. I think it was also probably easier to manufacture a chain and a couple of sprockets than a set of bevel gears, or a teeny-tiny toothed belt, back in the days before CAD and CNC.

What always made me wonder about the Rocky's chain is not that it runs backwards, but that it runs 2 or 3 times (or whatever the final drive ratio is) faster than the Optima/Javelin (or Yokomo, or Marui Samurai) chain drives, which are direct to the axle. I figured the extra speed of the chain links would cause a bit more drag and wear. But apparently not? Admittedly, I had one Rocky, once, and I got to run it about five minutes before the steering bellcrank self-destructed...

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I never liked the look of the chain drive bitd (reminded me of Lego chain, which I was big into at the time) , i was tempted by the Optima Pro and the Rocky,  but didnt bother as i thought the chain drive would be weak, my first 4wd being the Optima Mid. 

It's sounding like my fear was unfounded. (Don't know if that's because the chain doesn't take much abuse in forward motion, front wheels are unloaded, but surely hitting the anchors hits the chain hard? Or that it's made of tough stuff!) 

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On 9/10/2019 at 11:19 AM, markbt73 said:

I figured the extra speed of the chain links would cause a bit more drag and wear.

You are definitely correct.  It certainly does increase drag and wear due to the higher speed of the chain on the Rocky.  I didn't mean to say or imply otherwise.  I was more focused on the direction in my post and ignored the high-speed aspect.  On the Rocky I can't really "feel" the drag from the chain, per se.  I mean, it's there, but the motor drag has such a high level of effect that I can't tell what is drag from the chain vs from the motor.  I'd have to remove the chain and test it as a rear-wheel drive car for a while to see if I can notice a difference.  I'm usually running on pavement, so open flat surfaces, rather than dirt track with jumps.

I created a 3D printed steering bellcrank for the Rocky last year just to see if it was possible to improve upon the original.  One of my 4 Rocky's is using it now for testing and it seems to work well.  I should finish it up and release it on Shapeways and then make a post about it on my blog (which I hardly touch these days) and here.  I just don't beat the crap out of stuff, though, so I'm not really sure how tough it really is on a hard-core dirt/carpet track with jumps.  I mean, these cars are over 30 years old, so I tend to take it easy on them.

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While it may not make any difference now with the high-capacity batteries available, the relative inefficiency of the chain vs the belt on the Optima was obvious BITD with 1200mah NiCads. A friend of mine used to race a chain-drive Optima, while me and most of my friends used belt-drive Mids, Cats and Dogfighters. The Optima, being heavier and having chain drive, used to really struggle for either speed or battery life, depending on gearing and surface. Don't get me wrong, we all used to struggle for battery life, but the extra drag from the chain, plus the fact that the Optima was seemingly machined out of one solid block of aluminium and therefore weighed about a quarter of a ton meant that it always struggled for competitiveness. After a while my friend bought a belt-drive upgrade and it immediately increased his battery duration and the responsiveness of the car by a noticeable amount (the chain has a lot of inherent slop, which introduces a lot of drivetrain shunt). It was still too heavy, but the belt conversion made it smoother, more efficient and took a lot of slop out of the drivetrain.

As to why it was introduced, previous answers have probably nailed it. Chains of the sort which the car used were probably an off-the-shelf commodity and were more or less modular, as they could be manufactured on an industrial scale to any length required. Belts would have had to have been specially designed and manufactured, however, which would have been a lengthy and expensive process in the mid 80s. Also, remember that when it was originally released in 1985, the Optima did not have any belt-drive rivals and its only real 4WD competition initially was the plastic-chassis, shaft-drive Tamiya Hotshot, with its weird suspension and compromised set-up.

Also, I would take issue with the poster above who suggested that shaft drive was inherently superior to chain drive. Chain drive does have a lot of inherent issues, but the issues which come with shaft drive (torsional flexing of the shaft, the fact the direction of the drivetrain has to go through a 90 degree change not once but twice to get the power from the rear to the front, the fact the tub chassis on most shaft-drive Tamiya cars flexed like badword, the increased driveline shunt caused by the shaft sockets) mean that it is no more efficient than a chain drive, and may in many cases be worse.

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Hi, im trying to find the part number for rocky 4wd RK8 deck plate. 
 

it’s the last part I need to finish my rocky build. 
 

I will then have turbo rocky and 2 rocky 4wd. 
 

all the best 

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My old diesel Nissan Patrol had a chain drive in the transfer case, and that was a 4X4 built for third world off-road conditions where ultimate reliability isn't just the best thing, it's the only thing.

So there's probably nothing fundamentally unsound in using a chain drive.

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