torsion differentials
07-01-2009, 07:42 AM
#2
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RE: torsion differentials
The word torsen is a description in itself, of what they do... 'Tor'que-'Sen'sing differentials. In 1:1 applications, they work exactly the opposite way to a standard spider gear diff. The 'open' gear diff, sends the power to whichever wheel has the least traction (causing the ballooning you see in truggies as one wheel spins wildly faster than the others when it lifts off the dirt)...This actually makes cars easy to handle, as over-power is bled off as the diff unloads, keeping the wheels that HAVE traction from spinning. The torsen on the other hand, senses which wheel has the MOST traction, and sends power to that wheel. This makes the car put it's power onto the ground VERY efficiently, but makes the car much twitchier and more difficult to handle. In the hands of an outstanding driver, the torsen would be the best way, in the hands of an amateur, the open diff would be better. In reality, that's why we use viscous diffs, to limit the slip from the open diff. Hence the definition 'limited slip diff'. A standard viscous gear diff in an RC gives you a good mix of both of these 'abilities'.
My Honda S2000 has a torsen diff on the rear as standard, it's one of the reasons the car is very difficult to drive on the limit, but very fast round the corners.
That's how it works in real cars. I have to assume that it's the same in RC, but I must confess, I've never run an RC car with a torsen diff, and I suppose its possible (wouldn't be the first time), that an RC applicatoin works a bit differently to real life. Hope that helps.
My Honda S2000 has a torsen diff on the rear as standard, it's one of the reasons the car is very difficult to drive on the limit, but very fast round the corners.
That's how it works in real cars. I have to assume that it's the same in RC, but I must confess, I've never run an RC car with a torsen diff, and I suppose its possible (wouldn't be the first time), that an RC applicatoin works a bit differently to real life. Hope that helps.
07-01-2009, 08:22 AM
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RE: torsion differentials
ORIGINAL: rcpowerhorse
so they are kind of like traction control in a full size car??
so they are kind of like traction control in a full size car??
Imagine this situation... I'm going round a corner in my rear wheel drive car. I have a regular gear diff at the back. As I'm going round the corner, the inside tire is much lighter as the car leans toward the outside of the bend. I (foolishly) try to feed in more power. The gear diff sends the power through the path of least resistance, to the lightest driving wheel, the inside one. It spins and smokes, but the outside wheel keeps it's traction and I make it round the corner safely. This is how the Mazda Miata (or mx5 depending on your region) diff works.
Same situation with a torsen... I try to feed in more power, the diff senses that the inside wheel is light as it begins to spin, and corrects by locking the differential, sending equal power to both rear driving wheels. They both start spinning (provided my engine can generate sufficient power to break traction of both rear tires), and the back end o the car tries to come round. I correct by applying opposite lock to the steering, or I crash into the wall. In actual fact, this locking effect is desirable on a racetrack. It teaches the important lesson that if you go into a corner too fast and are understeering, you need to APPLY power to pull through it, and push the back round. It's a very hard technique to do because it goes against every instinct telling you to slow down. This is how the Honda S2000 diff works.
07-01-2009, 03:32 PM
#7
RE: torsion differentials
Some people like them for their center diff in truggies/buggies. A torsen center diff in a buggy/truggy can give you a much better launch, however there is 1 problem with them, as far as I know, they work the same off power, so if you are on a low grip track and your rear end steps out off power, you may get some ill-effects on the handling, and same thing if you have one in the front or rear of the buggy/truggy. In my opinion, the Losi Smart Diff is the way to go for a center diff. It locks up on power, you can change how soon or late it locks up, so one takeoff you have 100% of power going to the front and rear wheels, and off power it unlocks and works exactly the same as a viscous gear diff, as it has oil in it and thus you can still tune it. Torsen diff's also have oil, but no matter what they always send power to the side with the most traction, oil can never change that, but with the Losi Smart diff, it always locks on power, always unlocks off power and acts as a viscous gear diff, so its more tunable.
The reason I don't suggest a Torsen or Losi Smart Diff for either the front or rear is because if you have one in the rear the car can become too difficult to drive (like Foxy said), and with the Smart Diff in the rear, if you try to power out of a corner, the rear end is going to want to slide around alot because its locked on power. In the front, a Torsen diff can give you either under-steer, as the outside wheel is usually the one with the most traction, thus the Torsen diff sends power to that outside front wheel, and on pretty much all buggys/truggys you have Ackerman, so that outside wheel doesn't turn in as much, thus giving you understeer. With a Smart Diff in the front, you can get either over-steer or under-steer depending on your car setup and track conditions, but typically on a lower grip track you are going to get oversteer as you basically have a locked front end on power that is going to yank the rest of the car around when there is not much grip.
Now I noticed in you signature that you have a Hobao ST, which is OFNA so you can only get a Tosen diff (however Losi Smart diff could be modded to fit in the center but anyway), you should choose a Torsen diff based on your track conditions, your driving style, your driving ability (like are you new to racing, intermediate, or are you an advanced driver and you can control your RC very well), and on what your truggy is lacking in handling. If you have the money, I suggest get a front, center, and rear Torsen diff, and try out different combos, like center only, front only, rear only, front center, front rear, and rear center, and see which helps your handling the most. But if you don't have the money to get 3 Torsen diffs, then just try different oil weights in your diffs, which in my opinion is the best way to go as it seems to work great for most people.
The reason I don't suggest a Torsen or Losi Smart Diff for either the front or rear is because if you have one in the rear the car can become too difficult to drive (like Foxy said), and with the Smart Diff in the rear, if you try to power out of a corner, the rear end is going to want to slide around alot because its locked on power. In the front, a Torsen diff can give you either under-steer, as the outside wheel is usually the one with the most traction, thus the Torsen diff sends power to that outside front wheel, and on pretty much all buggys/truggys you have Ackerman, so that outside wheel doesn't turn in as much, thus giving you understeer. With a Smart Diff in the front, you can get either over-steer or under-steer depending on your car setup and track conditions, but typically on a lower grip track you are going to get oversteer as you basically have a locked front end on power that is going to yank the rest of the car around when there is not much grip.
Now I noticed in you signature that you have a Hobao ST, which is OFNA so you can only get a Tosen diff (however Losi Smart diff could be modded to fit in the center but anyway), you should choose a Torsen diff based on your track conditions, your driving style, your driving ability (like are you new to racing, intermediate, or are you an advanced driver and you can control your RC very well), and on what your truggy is lacking in handling. If you have the money, I suggest get a front, center, and rear Torsen diff, and try out different combos, like center only, front only, rear only, front center, front rear, and rear center, and see which helps your handling the most. But if you don't have the money to get 3 Torsen diffs, then just try different oil weights in your diffs, which in my opinion is the best way to go as it seems to work great for most people.
