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12mpghwy
Posted on Tuesday, September 05, 2017 - 12:31 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I made a belt tensioner. I am a little worried about it bending under deceleration.

People who have used similar tensioners any comments or advice on belt adjustment?

Thanks

here is a picture:


tensioner
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12mpghwy
Posted on Tuesday, September 05, 2017 - 01:26 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

installed
pic
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S1owner
Posted on Tuesday, September 05, 2017 - 02:19 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Well let me be clear these are my thoughts please dont be insulted just throwing them out to help you fine tune your design. first thing I see is that you greatly reduced the mass and the main function is a frame brace between the pivot block and motor I would be worried about that area.
Second your belt pivot point Were the tensioner pulley would be sould be directly or as close as possible to the swingarm pivot point. That way you get the most consistent tension during suspension travel.
One other thing I would do is make your pulley bolt hole a slot so you can move the pulley up or down to fine tune tension

Here is mine but I use a duramax idler pulley its smaller and needed for my situation











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Hootowl
Posted on Tuesday, September 05, 2017 - 09:26 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Would it be possible to put some flat stock aluminum or steel on the other end of the idler bolt, and run it to the large bolt at the front? You'd have to cut down the bolt spacer by the thickness of the stock. Seems like it would keep it from flexing, which is your concern.
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12mpghwy
Posted on Tuesday, September 05, 2017 - 10:35 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Criticism is welcome.

As to the idler pulley location, I copied that from the free spirit brace. My thought process was that bringing it close to the drive pulley would get the belt wrapping around the drive pulley as much as possible and reduce the forces experienced by the entire setup.

In comparison with the stock brace there is actually more material between the engine and swing arm than the stock brace. II'm not sure if it looks thin in the picture but its 1/2" think.

I think the weakest point of mounting a pulley like this is going to be twisting away down away from the frame at the bolt going into the engine (there is ~9" of leverage there) followed by bending the bolt going through the spacer. I was thinking of remaking it so that the area between the bolt going into the engine and pulley was 1" thick that way no spacer would be needed at the belt.
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S1owner
Posted on Tuesday, September 05, 2017 - 11:10 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I am not even sure how much stress the brace would normally get if any. I am just going off what it appears to do.
I get your thought on making the belt wrap tighter by bringing it closer - but the swingarm is an imperfect arc and the belt gets tighter as the suspension compresses. So with the pulley where I suggested it is effectively lessoning the tension on the belt as the suspension compresses but the arc is taking up that slack keeping the brlt pressure consistant. On yours it wont be releasing as much tension actually very little so the belts still have to be run scary loose and negates ehy you have the tensioner.
The free spirit one would have done that also as my original design copied their location too. Thats why we extended it backwards.
hope that helps

(Message edited by S1owner on September 05, 2017)
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12mpghwy
Posted on Tuesday, September 05, 2017 - 04:02 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Thanks that is helpful.

I think maybe the best design would be one that could use a spring and pivot to take up the slack in the belt.

Of course it gets more complicated. Maybe a timing belt or supercharger idler pulley with a builtin spring tensioner.
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Cyclone8u
Posted on Tuesday, September 05, 2017 - 05:16 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Just throwing this out there. I'm pretty sure it's been discussed thoroughly elsewhere, but the belts on the original tubers were never designed to bend backwards. The method of lining up the three axis of the output shaft, swing arm pivot and rear axle, then taking up the slack in the belt at it's tightest spot (not tight, just remove slack), then locking that adjustment down and never touching it gets the proper scary loose setting for the belt and prevents unnecessary wear in the entire drive train. This also yields your best belt and pulley life. The belt will touch the swing arm at full extension, but this seams to have no effect. Unless your doing something out of the ordinary with your rear end like swapping an XB system, it looks like your engineering a solution to a non existent problem. What is the ultimate goal you're shooting for?
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Hootowl
Posted on Tuesday, September 05, 2017 - 06:26 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I've broken three belts going over bumps under low or no throttle. Some of us believe that the swingarm movement, and the resulting rapid uptake of belt slack results in premature belt failure. Getting rid of the slack gets rid of the belt snatch. Could we be wrong? Absolutely. But three belts under the same conditions creates a bit of a pattern. I don't have one of these yet, but it's on my list. And yes, you do need to use an XB belt.
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12mpghwy
Posted on Tuesday, September 05, 2017 - 09:57 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I am going to swap to a different swingarm, that's a future project what I am trying to solve now is my XB belt skips unless its already binding at the tightest point.
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Scott_in_nh
Posted on Thursday, September 07, 2017 - 09:25 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I have the materials to build and idler pulley setup, but haven't gotten to it yet.

S1Owner and I have been on other threads on this subject.

I have no idea if it will help to stop breaking stock belts, but is needed to use a much stronger XB belt on a tuber with an otherwise stock tuber suspension, because the belt jumps on the front pulley when loose.

Mine has broken in a bit and with careful adjustment and testing I have found a sweet spot, but still have concerns over the tension.

Because I want to keep the belt loose, but not have it jump on the front pulley, I am going to place mine closer to it than S1owner did.
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12mpghwy
Posted on Friday, September 08, 2017 - 01:06 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I put on the Xb belt and suspended the rear end from a hoist. The belt is now tightest when in the slack position ( tire hanging as if doing a stopie) and loosens as it moves through the range of travel.

I would say that this position of the idler is just fine but s1owners positioning might keep the tension more consistent through the range of travel.
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S1owner
Posted on Friday, September 08, 2017 - 01:58 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Exactly!!
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Upthemaiden
Posted on Friday, September 08, 2017 - 02:24 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Have you gotten to try it yet? Ken's design would be the most effective at keeping consistent tension and has kept his belt from skipping. As far as the belt skipping, I would think even with looser overall tension on the belt, as long as your idler pulley helps lift the belt up to keep it curved around the pulley more, it might still accomplish it's job.

The issue with less tension and with the stiffer XB belts specifically would be that the loose tension lets the belt curve wider than the diameter of the pulley, so the teeth aren't all fully engaged. I would think if your idler/tensioner can correct that large front curve and pull it tighter by pulling the belt further along the shape of the pulley, I'd think you could keep the belt from skipping without necessarily correcting the tension over the full belt.

I'm not an engineer, so hopefully I worded that all well enough to make sense. Even if your belt is still loose, as long as the piece you made helps correct the shape of the front bend of the belt, it should help.

Only one way to find out, go take it for a ride and let us know how it works!
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Hootowl
Posted on Friday, September 08, 2017 - 02:37 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Ken, do you think yours would work with a stock 99+ swingarm, or is there not enough clearance? What about a steel 98- swingarm?
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S1owner
Posted on Friday, September 08, 2017 - 03:28 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Hoot
I have no idea. But here is what one can do
Contact Purpony and see how much he would chatge to 3d print one for you then you can put it on and see.
You could make any changes off that model and have marc mill you one.
Only change I did thats not in his program is change the pulley bolt hole to a slot and add a set screw in the bottom of the slot
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12mpghwy
Posted on Friday, September 08, 2017 - 05:33 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I did go for a short ride and had no issues with belt skip. I have about 1/4" on the inside of the idler. That would disappear if it were further back

You could actually figure out the best possible position for a tensioner by modeling the belt pulleys and pivot points in solid works or fusion 360.

I think the more foreword location is probably the best location for the stock swingarm.

After getting it all bolted up and tensioning the belt I am no longer concerned about the strength of the arrangement. The belt has a pretty significant leverage disadvantage against the pulley and the aluminum is plenty substantial. I will run fea against it when I get a chance.
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