Oh, I love it when guys just agree to disagree! If we all agreed then what would be the fun in that? If we all ran the same 350 Chevy small block that would be no fun either.
I think it is great to have a some die-hard TRA fans in the hills, as it is important to be able to compare stuff. How would you know which clutch is better if every one had a Polar clutch on their Rotax power?
Besides someone has to keep BRP honest. If we all ran that TRA crap, BRP could just sit back and collect the money. Nobody would be any the wiser or able to know for sure that BRP is dooing you wrong. Aw it's obvious BRP doesn't care, just look at the number one top topic regarding the BRP sled in the mountains. The TRA! People cutting holes in their nice sleds, no stable rpms and blowing belts. That is just miserable.
OK, maybe I'm just making it worse because the TRA boys are always buying more crap to "tune" the Bouncing Betty. TRA parts sales means more money for BRP... Hmmm... It would sure make a lot of people mad if BRP tossed in the towel on the TRA, all that money and wasted time down the drain. Hmmm... All those after market shops, lots of vested interest in keeping that TRA around. Tough call.
But back to the TRA -
The TRA creating more force out of nothing is physically impossible. If you used a 5 ton press to squish the drive belt between the sheaves while it was rotating, what would happen? The belt would squirt out and move to the outside of the sheaves. Right?
But you could keep the belt between the primary sheaves by putting enough tension on the belt, until the belt busted. So the force is limited by what the secondary can contain in tension. Right?
What make the force that pushes the sheaves together? The weights, and only the weights, force the sheaves together. IF you make the work of the weights more difficult by using tight binding bushings, big coil springs, adding dirt and rust to the ramps, steeper ramps and so on, what happens? The force of the weights gets used up, and you need more weight. You add too much weight and the secondary gives up or the belt busts.
The TRA can't put anymore tension on the belt than any other clutch, so to say the TRA creates more force is physically impossible. It's just that the TRA is a bastard to run because the design of the clutch is to suck up lots of the good force produced by balancing the weights against the parasitic architecture of the TRA. The big main TRA spring that needs to be over come, and balanced against, is at the core of the problem. The ramps need a good curve to combat the springs compression curve, and that curve needs a constant power input and a set sled weight as a base line. It's becomes a real mess in the mountain environment when those things change all the time.
Anyway good luck, and keep trying to get that TRA to run. Don't let it drive you nuts. I'm counting on you!
"What make the force that pushes the sheaves together? The weights, and only the weights, force the sheaves together."
The weight of the arm are a part of the equation, yes, but they are only a part of the equation. Force = mass x acceleration right? Weight (or more correctly, mass) is only half the equation. The other half is accleration.
For constant circular motion: acceleration = velocity^2 / radius
Velocity can be found using the formula: v = 2pi * radius * frequency
1) frequency = 8,200 RPM * 1 min/60 seconds * 2pi = 858.27 radians/second
2) radius = the measurement (in metres) from the centerline to the point the roller touches the ramp.
Radius and ramp angle are the keys here. The greater the radius, the greater the force. (Think of a water skier behind a boat. When the boat makes a turn, the longer the rope, the faster and the greater the force the skier travels with.
The thinner the ramp the further the arm can swing out and therefore the greater the force it has to push.
(There is more to this as well, though I think it`s been argued to death in prior posts. Suffice it to say, not all of the centri***al force of the arm gets transmitted to pushing the sheave closed. Some of the force tries to pull the arm away from the centerline and tear the arm away from the clutch, though this is the same for anything that spins, including the Polar. The basics are, the flatter the ramp, the more of this force is transmitted to closing the moveable sheave.)
"The TRA creating more force out of nothing is physically impossible."
I'm not implying the TRA creates force out of nothing, I'm saying that IF (big IF) the TRA is tuned correctly, it wastes less energy than any other clutch simply because it has so many ways to adjust for different conditions.
YDPC, when your sled gains altitude and begins to make less power, how do you decrease the amount the Polar squeezes the belt? Or when your sled comes down from altitude and begins to make more power, how do you increase the clamping forces the clutch provides on the belt? If you can't adjust either of these things then you are losing power due to friction from too much or too little belt pinch, right?
You can argue that the TRA is tempermental, that it's difficult to tune properly, that it is rarely tuned correctly or that it is just too complicated. Argue that and I'll agree with you completely. I'll even agree with you that your Polar clutch is less fussy and easier to tune... no argument here. My contention is that any clutch design that doesn't have the same degree (or even greater) of adjustability as the TRA does leaves power (because of excess friction) on the table. A non-adjustable clutch either pinches the belt too hard when the engine is making less power (causing friction) or doesn't pinch the belt hard enough when the engine is making more power (again, causing friction through slippage).
"IF you make the work of the weights more difficult by using tight binding bushings, big coil springs, adding dirt and rust to the ramps, steeper ramps and so on, what happens? The force of the weights gets used up, and you need more weight. You add too much weight and the secondary gives up or the belt busts."
Clean the clutch!
"The big main TRA spring that needs to be over come, and balanced against, is at the core of the problem. The ramps need a good curve to combat the springs compression curve, and that curve needs a constant power input and a set sled weight as a base line. It's becomes a real mess in the mountain environment when those things change all the time."
I think we've established that most clutches use similar springs with similar spring forces. I'll leave that alone.
But more importantly I like the part of your quote that I've underlined. Conditions on the mountian change all the time. You need to be able to adjust your clutching to compensate for each and every change you find. The QRS is a great clutch design but IMO needs to have an adjustable ramp helix to take advantage of all it's capable of. The TRA has this adjustability and it's that adjustability that I that makes it best clutch on the hill.
I will say this, if Polar makes a clutch in the future that has this adjustability built in to it, I will be the first in line to check it out and see if it was an improvement. I have no loyalty to the TRA. Find me a better, more adjustable, clutch and I'm there.
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