273LikesSerpent Project 4-X
12-06-2018 | 02:35 PM
#661
We only count teeth on pulleys as a convenient way to determine ratio, we assume that both pulleys have the same tooth profile (in our case 3HTD) which will give us a certain circumference for each tooth and hence a diameter for each pulley.
Seeing as how the serpent centre pulley OD seems to be slightly larger than it ought to be if the tooth profile was correct it leads me to believe the tooth profile isn't correct.
Small drawing attached,
For or a 20tooth pulley (I just happened to have drawn) at 3HTD profile (red line) the arc length between teeth is 2.907mm, which gives a circumference of 58.11946mm
Now I increase the OD of the pulley by 0.2mm (yellow line), arc length between teeth is 2.939mm, so circumference of 59.90389mm
Circumference of a 40 tooth 3HTD pulley is 117.80972mm
Ratio for the correct 3HTD tooth profile is 117.80972/58.11946 = 2.027027
Ratio for pulley increased by 0.2mm is 117.80972/59.90389 = 1.9666
With a slightly bigger pulley, and since the belt isnt skipping teeth, the belt must be stretching the 0.032mm difference, and seeing as how I saw people saying the belts were binding at high speed and slowing the car down, it would seem likely that the belt is stretching slightly over each tooth.
I hope that makes sense
*disclaimer* The pulley drawings I have are generated from a program which produces best fit polylines, so the pitch isn't exactly 3mm.
Seeing as how the serpent centre pulley OD seems to be slightly larger than it ought to be if the tooth profile was correct it leads me to believe the tooth profile isn't correct.
Small drawing attached,
For or a 20tooth pulley (I just happened to have drawn) at 3HTD profile (red line) the arc length between teeth is 2.907mm, which gives a circumference of 58.11946mm
Now I increase the OD of the pulley by 0.2mm (yellow line), arc length between teeth is 2.939mm, so circumference of 59.90389mm
Circumference of a 40 tooth 3HTD pulley is 117.80972mm
Ratio for the correct 3HTD tooth profile is 117.80972/58.11946 = 2.027027
Ratio for pulley increased by 0.2mm is 117.80972/59.90389 = 1.9666
With a slightly bigger pulley, and since the belt isnt skipping teeth, the belt must be stretching the 0.032mm difference, and seeing as how I saw people saying the belts were binding at high speed and slowing the car down, it would seem likely that the belt is stretching slightly over each tooth.
I hope that makes sense
*disclaimer* The pulley drawings I have are generated from a program which produces best fit polylines, so the pitch isn't exactly 3mm.
(Note: There's a small amount of play in the mesh so the belt might not actually need to stretch to account for the size difference)
12-06-2018 | 02:38 PM
#662
Tech Elite
Joined: Mar 2011
Posts: 2,057
From: Chatham Ontario Canada
12-06-2018 | 02:43 PM
#663
It is still extremely close. Not something that translates on lap times.
I tested the Xray pulley and rear belt + xray canam gearing and did not go faster. I am back with the Serpent pulley/belts and 99/32 for super stock. If anything else, we have options for motor placement since we now know that we can get same FDR with a wide array of different spur/pinion combinations.
I tested the Xray pulley and rear belt + xray canam gearing and did not go faster. I am back with the Serpent pulley/belts and 99/32 for super stock. If anything else, we have options for motor placement since we now know that we can get same FDR with a wide array of different spur/pinion combinations.
12-06-2018 | 02:46 PM
#664
We only count teeth on pulleys as a convenient way to determine ratio, we assume that both pulleys have the same tooth profile (in our case 3HTD) which will give us a certain circumference for each tooth and hence a diameter for each pulley.
Seeing as how the serpent centre pulley OD seems to be slightly larger than it ought to be if the tooth profile was correct it leads me to believe the tooth profile isn't correct.
Small drawing attached,
For or a 20tooth pulley (I just happened to have drawn) at 3HTD profile (red line) the arc length between teeth is 2.907mm, which gives a circumference of 58.11946mm
Now I increase the OD of the pulley by 0.2mm (yellow line), arc length between teeth is 2.939mm, so circumference of 59.90389mm
Circumference of a 40 tooth 3HTD pulley is 117.80972mm
Ratio for the correct 3HTD tooth profile is 117.80972/58.11946 = 2.027027
Ratio for pulley increased by 0.2mm is 117.80972/59.90389 = 1.9666
With a slightly bigger pulley, and since the belt isnt skipping teeth, the belt must be stretching the 0.032mm difference, and seeing as how I saw people saying the belts were binding at high speed and slowing the car down, it would seem likely that the belt is stretching slightly over each tooth.
I hope that makes sense
*disclaimer* The pulley drawings I have are generated from a program which produces best fit polylines, so the pitch isn't exactly 3mm.
Seeing as how the serpent centre pulley OD seems to be slightly larger than it ought to be if the tooth profile was correct it leads me to believe the tooth profile isn't correct.
Small drawing attached,
For or a 20tooth pulley (I just happened to have drawn) at 3HTD profile (red line) the arc length between teeth is 2.907mm, which gives a circumference of 58.11946mm
Now I increase the OD of the pulley by 0.2mm (yellow line), arc length between teeth is 2.939mm, so circumference of 59.90389mm
Circumference of a 40 tooth 3HTD pulley is 117.80972mm
Ratio for the correct 3HTD tooth profile is 117.80972/58.11946 = 2.027027
Ratio for pulley increased by 0.2mm is 117.80972/59.90389 = 1.9666
With a slightly bigger pulley, and since the belt isnt skipping teeth, the belt must be stretching the 0.032mm difference, and seeing as how I saw people saying the belts were binding at high speed and slowing the car down, it would seem likely that the belt is stretching slightly over each tooth.
I hope that makes sense
*disclaimer* The pulley drawings I have are generated from a program which produces best fit polylines, so the pitch isn't exactly 3mm.
12-06-2018 | 05:22 PM
#665
They temporarily deform. The overall speed does not change though as the teeth on the belt cannot move faster than the teeth on the pulley without skipping.
12-06-2018 | 05:47 PM
#666
Tech Master
Joined: Nov 2007
Posts: 1,554
From: Edmonton Ab
The diameter of the pulleys will define the ratio. You can skim CA on the lay shaft pulley in mutiple thin layers to increase diameter. The teeth of the belt will still engage the holes but with the larger small pulley dia. The FDR is effected. Trick showed to me by some guys running ETS before the FDR checker.
12-06-2018 | 06:08 PM
#667
Joined: Feb 2011
Posts: 8,406
The diameter of the pulleys will define the ratio. You can skim CA on the lay shaft pulley in mutiple thin layers to increase diameter. The teeth of the belt will still engage the holes but with the larger small pulley dia. The FDR is effected. Trick showed to me by some guys running ETS before the FDR checker.
12-06-2018 | 08:20 PM
#668
Okay kids, this has gotten 100% out of hand. Having very slightly taller or shorter teeth on your pulleys will not affect the final drive ratio. If you have a 20 tooth main pulley, and 38 tooth diff pulleys, your ratio is 1.9. End of story. The ONLY possible advantage to having a slightly taller tooth of the same pitch would be to have it be a bit less likely to skip teeth. This is like how you could mix Mod 0.8 gears with 32 Pitch, where they were very slightly different one tooth on the spur moved one tooth on the pinion, same as how one tooth on the pulley moves the belt... one tooth! Which then moves the other pulley... ONE TOOTH!
This is getting too dumb for words. Stop measuring your pulleys with calipers and count the teeth.
This is getting too dumb for words. Stop measuring your pulleys with calipers and count the teeth.
12-06-2018 | 08:22 PM
#669
The diameter of the pulleys will define the ratio. You can skim CA on the lay shaft pulley in mutiple thin layers to increase diameter. The teeth of the belt will still engage the holes but with the larger small pulley dia. The FDR is effected. Trick showed to me by some guys running ETS before the FDR checker.
12-06-2018 | 10:57 PM
#670
12-06-2018 | 11:09 PM
#671
The belt stretches and then contracts locally. That doesn't affect the total belt movement as that's governed by the teeth. Counting teeth is not only convenient, there's a physical barrier preventing the teeth from getting out of alignment. If that barrier is violated, the teeth have just skipped.
(Note: There's a small amount of play in the mesh so the belt might not actually need to stretch to account for the size difference)
(Note: There's a small amount of play in the mesh so the belt might not actually need to stretch to account for the size difference)
this is correct, only way to change ratio is to change tooth count. I have found that you can go +/- one tooth with the same diameter and not skip teeth. I used to sell over and under drive pulleys for schumacher and the 224 and never had issues.
12-07-2018 | 06:28 AM
#673
Yeah this really did get out of hand! I actually find it hard to believe that people could actually believe some of the things that they are posting. Someone even attached a video of how a CVT operates😯, that only proves a complete lack of understanding of what is going on. Internal ratio is 2.000000000000000000000000000000000000000000...... ......0000000000 period.
12-07-2018 | 06:39 AM
#675
Tech Elite
Joined: Mar 2011
Posts: 2,057
From: Chatham Ontario Canada
So my setup would be this according to Can-Am rules:
NB: Serpent Project 4X was checked and due to the O.D. of the center pulley the internal is not exactly 2.000. Testing revealed it is closer to 2.005. For Serpent Cars ONLY, the drivers who wish to be as close as possible to the Minimum FDR can use the following spur/pinion combinations: SS TC => 99/32; Stock TC => 97/36; USGT => 101/46.
According to the special rules for the Serpent I can run a 5.389 FDR in Stock TC and all the other racers have to run 5.400 - the minimum FDR. If everybody is okay with this then we can move on.
NB: Serpent Project 4X was checked and due to the O.D. of the center pulley the internal is not exactly 2.000. Testing revealed it is closer to 2.005. For Serpent Cars ONLY, the drivers who wish to be as close as possible to the Minimum FDR can use the following spur/pinion combinations: SS TC => 99/32; Stock TC => 97/36; USGT => 101/46.
According to the special rules for the Serpent I can run a 5.389 FDR in Stock TC and all the other racers have to run 5.400 - the minimum FDR. If everybody is okay with this then we can move on.