Old 03-29-2009, 09:26 AM
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Default Spool vs Oneway

I've tried all three diff: Spool, One-way, and Ball diff.

So here's a question for some one with first hand knowledge..

Besides having to drive the car different with a one-way in comparison to a ball diff or spool:
Have you also had to adjust the setup of the car to 'control' it easier?

If so, what did you do?

What tires were you using and on what surface?

Did you notice a difference in how hot the motor was and how much MAH were used?

Spdjunky is offline  
Old 03-29-2009, 02:02 PM
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Originally Posted by niznai View Post
Nope. On power in a straight line a oneway is basically a spool so it pulls at full power with all four wheels. No freewheeling happens here.

Here's why.

A one way is exactly that. A device that transmits power when driven one way but not the other. For example from the motor to the wheels but not from the wheels to the motor. Or the other way around (if you put it the wrong way). But not both. For comparison, a gear will transmit power either way. Another application of the one way is in automatic gearboxes on real cars. This is why you can not start an automatic car by pushing it. The motion chain is broken by the one way bearing which doesn't transmit motion from the wheels to the engine, but only the other way. Another application is the pullstart on a chainsaw (or fuel car). You can spin the engine with the chord wrapped around a drum attached with a oneway on the crankshaft, but the engine can not spin the cord drum (it would be quite funny if it did).

This is why the wheels driven with a one way diff are going to do the pulling under acceleration at all times. They freewheel whenever they need to spin faster than the oneway drives them to. These situations are three.

1 Offpower. The drivetrain spins turned by the inertia of various parts and because the rear wheels still turn the drivetrain as long as the car is coasting. The front wheels are just spinning because the car pushes them along the ground so the only thing that will determine how fast they spin is the distance they have to travel.

2 Braking. The drivetrain is slowed down by drag in the motor, the rear wheels have no choice but to slow down as the drivetrain slows down, but the front wheels are still pushed by the car, so they'll spin at whatever speed they need, being efectively disconnected from the drivetrain.

3 On power but only around corners. This is interesting. Now the outside wheel needs to travel around a larger circle, therefore a longer distance, but in the same time as the rest of the car (hence the other wheels) because it is attached to the car! It needs then to spin faster than the drive applied by the one way, and the one way can't stop it. It will therefore spin faster but not pull the car. On the contrary, the car will be pushing it. This is freewheeling. The inside wheel on the other hand will just spin as fast as the oneway is spinning because it has no other choice. The car will therefore pull with three wheels, the outer front coming along for the ride. The difference to a car with balldiffs is that there will be no slippage in the front diff so the entire power delivered by the motor will go to the front inside wheel and the rear wheels, so the rear diff won't be tempted to slip because the front wheel is doing the hard work of pulling the car at the speed imposed by the motor. I will admit is a bit more complicated than this but for now I'll leave it here.

On power in a straight line, a oneway basically becomes a spool (off power is a different story). A balldiff will always allow some slip (unless it's done up tight enough to actually become a spool but in this case your car will have serious handling problems) so under heavy acceleration and good grip conditions (wheelspin not possible), something has to give and it's the balldiff that will give. This means it will slip some. The one way won't. Wheelspin not being possible, the oneway driven wheels will pull like beelzebub it's hot on your trail.

A side effect is that the diff outdrives will have to put up with tremendous pressure on the driving side of the slots where the driveshaft pin goes. Normally one ways come with hard steel outdrives.

Also, keep an eye on how the outdrives wear where the oneway grips them. If you have uneven wear there, you will have uneven drive and possibly uneven freewheeling left to right which in a straight line will cause the car to pull sideways. Every now and then, I swap outdrives left to right. This also extends the life of the outdrive because they will push now with the other side of the slot so the wear evens out a bit more.

Center oneways need constant attention too and here you will need to inspect the shaft they grip on because this will wear and at some point it will slip or remain engaged permanently. You need then to replace it and possibly the one way too.

The rule of thumb is then to keep the oneway (wherever it is) very well oiled and very clean.

About braking, try not to use it, or just brake very very quickly (like a short burst of brake) and always in a straight line. Adjust you brake control (the amount of braking delivered by the speedo) according to track conditions. You can do this by taking the car out on the track and brake at top speed on the straight line as hard as you can and see if the car swaps ends. Turn down your brake setting on the speedo so you can fully brake (push the trigger all the way) but without the car swapping ends. My GM speedo allows the maximum brake applied to be fine tuned in 10% increments from 0 to 100 (and I think this is what most speedos do these days). Using the exponential function on your controller works too, so you can brake 100% at full travel, but very little at smaller trigger movements. This is what I do because sometimes you have to brake hard to avoid a serious crash, no matter if your car spins out.

Hope this helps.
That is so well put, I tried one in my 18r car on the carpet, put the spool out front and the accel out of the corner is ridicilous. The car is almost at take off speed.
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