neamerjell
Pebble Pounder
It always makes much more sense when you figure it out for yourself!
Wheely King Stock Specifications:
Pinion: 21 Tooth, 48 Pitch
Spur: 90 Tooth, 48 Pitch
Transmission Internal Gears:
15 Tooth on same axle as Spur*
22 Tooth Idler
28 Tooth Output with drive shaft attached
Differential Gears:
13 Tooth attached to drive shaft*
38 Tooth attached to axle
*Separate sets of meshed gears that share a common axle have their individual ratios multiplied together
The Math:
Spur/Pinion Ratio = 90/21 = (roughly) 4.29:1
Differential Ratio = 38/13 =(roughly) 2.92:1
This is the part that initially confused me. I was sure that the idler actually mattered in the ratio, but it really just disappears in the math. It's size does matter in terms of torque and durability though.
Transmission Internal Ratio:
(I'm using traditional fractions to illustrate the point of the idler disappearing)
3 meshed gears consist of two separate ratios that are multiplied together
_22_ x _28_ = _28_
..15.......22.......15........... (roughly) 1.87:1
The idler's size doesn't matter in the ratio calculations because it ends up canceling itself out in the math!!! (Where's the smiley that looks like Einstein??)
So to calculate the final drive ratio, multiply the three ratios together:
(90/21) x (28/15) x (38/13) = 23.38
(You're getting a whole 1/3 of a turn for free! the official documentation says 23 even!:mrgreen
Note: I have rounded all values to 2 decimal places except for the final drive ratio. If you multiply just the ratios I have here you come up with 23.425116, which is slightly bigger, but inaccurate.
The differential is multiplied with the other two ratios because the drive shaft is the shared axle between the transmission and the differential. The differential gears that matter in the ratio are just like regular gears, but only change the angle of the mesh, due to the beveling of the gears.
Sources:
Stock Spur and Pinion Gears:
Wheely King Owner's manual, page 30 "Parts List", part numbers 6921 and 6990
Transmission Internal Gears:
http://www.rccrawler.com/forum/showthread.php?t=67764
Differential Gears:
Wheely King Owner's Manual, page 30 "Parts List" part number A855
I was unsure of the description's accuracy, so I went here
http://www.hpiracing.com/products/en/A855/
and I downloaded the image of the gears, opened it in Paint, colored one of the teeth to keep track of my starting point and started counting. "A picture is worth 1000 words..."
I hope someone finds this information and the explanation helpful.
Because they're on a shared axle, the two different sets of meshed gears would have their ratios multiplied together. However, mathematically, the idler cancels itself out as shown above in the math. So, now you know not only how it works, but WHY it works.
Wheely King Stock Specifications:
Pinion: 21 Tooth, 48 Pitch
Spur: 90 Tooth, 48 Pitch
Transmission Internal Gears:
15 Tooth on same axle as Spur*
22 Tooth Idler
28 Tooth Output with drive shaft attached
Differential Gears:
13 Tooth attached to drive shaft*
38 Tooth attached to axle
*Separate sets of meshed gears that share a common axle have their individual ratios multiplied together
The Math:
Spur/Pinion Ratio = 90/21 = (roughly) 4.29:1
Differential Ratio = 38/13 =(roughly) 2.92:1
This is the part that initially confused me. I was sure that the idler actually mattered in the ratio, but it really just disappears in the math. It's size does matter in terms of torque and durability though.
Transmission Internal Ratio:
(I'm using traditional fractions to illustrate the point of the idler disappearing)
3 meshed gears consist of two separate ratios that are multiplied together
_22_ x _28_ = _28_
..15.......22.......15........... (roughly) 1.87:1
The idler's size doesn't matter in the ratio calculations because it ends up canceling itself out in the math!!! (Where's the smiley that looks like Einstein??)
So to calculate the final drive ratio, multiply the three ratios together:
(90/21) x (28/15) x (38/13) = 23.38
(You're getting a whole 1/3 of a turn for free! the official documentation says 23 even!:mrgreen
Note: I have rounded all values to 2 decimal places except for the final drive ratio. If you multiply just the ratios I have here you come up with 23.425116, which is slightly bigger, but inaccurate.
The differential is multiplied with the other two ratios because the drive shaft is the shared axle between the transmission and the differential. The differential gears that matter in the ratio are just like regular gears, but only change the angle of the mesh, due to the beveling of the gears.
Sources:
Stock Spur and Pinion Gears:
Wheely King Owner's manual, page 30 "Parts List", part numbers 6921 and 6990
Transmission Internal Gears:
http://www.rccrawler.com/forum/showthread.php?t=67764
Differential Gears:
Wheely King Owner's Manual, page 30 "Parts List" part number A855
I was unsure of the description's accuracy, so I went here
http://www.hpiracing.com/products/en/A855/
and I downloaded the image of the gears, opened it in Paint, colored one of the teeth to keep track of my starting point and started counting. "A picture is worth 1000 words..."
I hope someone finds this information and the explanation helpful.
Because they're on a shared axle, the two different sets of meshed gears would have their ratios multiplied together. However, mathematically, the idler cancels itself out as shown above in the math. So, now you know not only how it works, but WHY it works.
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