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Old 11-20-2010, 10:16 PM   #1
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Smile Ball diff pulley, different teeth on front vs rear theory.

Hi everyone at R/C Tech forums, this is my first post on here so hello everyone! thank you everyone who has contributed so far to this excellent site(saved me a heap of heartache already!).

Sorry if this has been mentioned before, I didn't see this anywhere.

Anywho, to the point, i have this theory which seems great (in theory :P). Let me know what you think.

Basically with a belt-driven 4WD setup like my Ta05v2, you get a center one-way and change the rear ball diff pulley from the 37T to one just a little bit smaller, say a 35T? The idea being that when the wheels are off the ground the rear ones travel just that little bit faster than the front, so, that when its on the ground they all travel the same speed but the front ones free-wheel until the rear tires lose traction. My thinking is that with all the power going to the rear wheels you don't lose all the power of having a 4WD, and when you need it, it puts power to the front wheels.

Same with cornering, there would be a little bit of slip when the rear tires spin and then the front starts putting power down to counteract the oversteer. The power would go to the ground on all four wheels at that point until the rear gains traction as you pull out of the corner and provides maximum acceleration.

Therefore; it should act like a real 4WD car with a true central diff and the central diff set to put most of the power to the rear.

I have very little doubt that this won't work, but, i do have doubts over whether the speed increase would make any difference.

Any thoughts?

Thanks for any input.




oh, and heres my car! ^_^
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Ball diff pulley, different teeth on front vs rear theory.-stang1.jpg  
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Old 11-20-2010, 11:50 PM   #2
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Only thing I could think is that once you have lost traction it is very hard to get it back without backing off the power.

Saying this I have no experience with the TA05v2, will be interesting to see what the gurus say.

Rhys
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Old 11-21-2010, 12:46 AM   #3
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a post from the 1/8 on road guys, who always use some overdrive....

"There is a certain amount of overdrive to the front that is perfect for the way you drive. I run a 1/8 car.

What I have found is that the more you overdrive the front the more power on push you get. Too much front overdrive also makes it difficult (for me) to control the turn-in because when you go from power on to power off you will suddenly get a lot of steering. Then as you accelerate out of the turn it will push because the front tires are spinning.

Too little overdrive to the front or overdrive to the rear causes the car to be very loose in the back coming off of the turn. However, you will have a TON of steering in a power on sweeper.

I usually run between 1 and 3% overdrive to the front (front tires are going 1 to 3% faster than the rear). This gives my car the stability I want without sacrificing power on steering or having a car that makes a radical change in turn-in when going from power on to power off."
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Old 11-21-2010, 02:36 AM   #4
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I have looked on a tamiya stockists website and they have a 36T pulley for the rear, to replace the 37T, and a center one way. The 36 and 37 seem to be the only teeth available. I should have the parts in the next week or so. I'll post my experiences on here.

So that guy has pretty much done what I'm thinking of but putting the power to the front and without a center one-way and altho he gets the same effect coming out of the corner as I'm expecting it seems that he would go through a lot of front tires with them spinning every time he corners. So would putting the power to the rear and using a center one-way give a similar effect without burning tires? Altho I assume that his would have a tendency to understeer whereas mine would oversteer(which I much prefer anyways), but should I also assume that the front tires would kick in and keep it inline?
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Old 11-21-2010, 03:24 AM   #5
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And also does anywhat know what effect a front one-way would have on the aforementioned setup?
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Old 11-21-2010, 03:47 AM   #6
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what the f^&&!!! i came up with that setup 3 weeks ago!!! do you by any chance read minds? i thought about this deeply and i dont think it would work.
it would only work if the one way effect was at the diff cup or axel, but its not. the one way effect applies on the belt. if someone desigined a one way front axel, it would work.
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Old 11-21-2010, 04:01 AM   #7
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Ha ha. Well I claimed it! Early bird gets the worm!!

This has been on mind for ages, started thinking about converting to a central diff but scrapped that with the complete loss of braking... Then then idea of a dynamic split of power, like a real car, putting the power to where it's needed and most effective. Better than the 50/50 power split on stock belt driven rc cars. It spawned from that since I bought my first rc(the ta05v2) just over a month ago. Burnt the rear diff pulley out when the diff slipped lose and that gave me the final inspiration for this idea. ^_^

Well I'm gonna try it as soon as the parts arrive, a week or two hopefully. Isn't a front one-way diff the same effect as your thinking? I'm 99.9% sure on this setup working but not sure on how great the effects will be. I guess it's just one of those things that has to be done to know it I guess...
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Old 11-21-2010, 04:23 AM   #8
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i guess its a race to be first to patent the desigin
it wouldnt be hard to get that desigin going. it would make the axel cups longer. this would make the dogbones too long, but with used of shorter dogbones it would be perfectly fine.
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Old 11-21-2010, 04:29 AM   #9
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Quote:
Originally Posted by unsane_chimera View Post
Ha ha. Well I claimed it! Early bird gets the worm!!

This has been on mind for ages, started thinking about converting to a central diff but scrapped that with the complete loss of braking... Then then idea of a dynamic split of power, like a real car, putting the power to where it's needed and most effective. Better than the 50/50 power split on stock belt driven rc cars. It spawned from that since I bought my first rc(the ta05v2) just over a month ago. Burnt the rear diff pulley out when the diff slipped lose and that gave me the final inspiration for this idea. ^_^

Well I'm gonna try it as soon as the parts arrive, a week or two hopefully. Isn't a front one-way diff the same effect as your thinking? I'm 99.9% sure on this setup working but not sure on how great the effects will be. I guess it's just one of those things that has to be done to know it I guess...
whether or not it works depends on where the one-way effect applies itself.

i noticed we are both ausies. we should work togeher on this. wudaya say?
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Old 11-21-2010, 04:31 AM   #10
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I think your losing the point. All this setup needs is a center one-way and a diff pulley, both available from tamiya, if it required a front one-way(which I can't see why it would), is also available from tamiya and has nothing to do with the dogbones. Do you have much knowledge of real-life motor sport or even something like how to effectively tune on forza 3? I'm trying to do what is called torque splitting. It's about putting the power to the rear wheels and thereby increasing acceleration and top speeds. Google it.
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Old 11-21-2010, 04:41 AM   #11
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i know what your talking about, unfortunately your dont get what im talking about... and i came up with the idea of this setup well over 3 weeks ago, i just took a wild guess at how long ago i thought of it. i thought of it while thinking about drifting... led to realising the benifits of rear only while it has traction/4wd without traction like the 4wd systems on skylines and evos. in other words, active tourqe split.
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Old 11-21-2010, 04:49 AM   #12
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also, if you want it to smoothly engage/disengage the power without clunking in/out of gear like its bunny-hopping- you would need something like a slipper clutch built in to the set-up

ive thought about this very deeply and in vast detail about this. its all a very complex set up i have devised.
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Old 11-21-2010, 06:31 AM   #13
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Not to keep you from trying to make it work, but if it was the hot ticket for Touring Car set ups (wether it be in TC or VTA or whatever), it would be used by all the fast guys and team set ups. Check everywhere you can find references, as darn near every chassis out there has the parts you're talking about available. Check the set up sheets posted online, too. If it was the super secret uber set up, the secret would be out one way or another, as every major race where the factory teams show up have had pictures plastered all over the web for years and years of every car ever entered.

If it works for you, good deal, but I'm betting that it's a blind alley at this scale and with the power levels we have available.
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Old 11-21-2010, 07:14 AM   #14
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don't mean to burst anyone's bubble but overdrive or underdrive has been done and is being done already... check out the losi JRXS thread (as far back as 2005)...

http://www.rctech.net/forum/electric...-jrxs-338.html
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Old 11-21-2010, 08:07 AM   #15
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Front overdrive/underdrive is nothing new. It's one of the biggest adjustments to a 1/8th onroad car. Since we run foams, we mainly adjust it with tire size but different pulleys are available too. They have front one ways in them but that is not really the issue since we usually overdrive the front. It's not done for speed, it's all about putting all that power down off of the corner.

Bigger front tires or a pulley resulting in more front overdrive will reduce on power steering, better forward bite and stability.

Smaller front tires or a pulley resulting in less front overdrive will result in more on power steering and a SLIGHT improvement in straightaway speeds but is not noticeable and not really worth adjusting for.

The problem with doing this on your TC is that a 1 tooth pulley change may be too much. In 1/8th, the max adjustment range is really just 1.0 to 1.04 front overdrive. I suspect a pulley change will be more than that.

Also you are talking about spinning the rears quicker. What we in the 1/8th world would call underdrive. This will make the car quite lose on power off of the corners, one way or not. Also while this may SLIGHTLY improve straightaway speeds, the loss of front breaking and stability will slow you down FAR more.
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