3d Watch Mechanism D&D Plot Device.

[Robbie]

Here's a larger render of all the action bits...now all I have to do is streamline the action and make it artsy.

[Robbie]

I'm stuck...anyone know anything about gear ratios???

I have a method in 3d studio to "wire" the rotation of one gear to the rotation of another gear to make a gear train...I can apply an expression to that wiring...for example, a gear that is "half" the size of its driver the ratio SHOULD be -1.5*Z_Rotation...but its not quite doing it right. (Negative to make it rotate the opposite direction)

Is gear ration related primarily to the number of teeth, circumference, or diameter of the gear...a website says that a 13 tooth gear linked to a 21 tooth gear should be a ratio of 1:1.62...which means the formula is -1.62*Z_Rotation, and it works sorta...but after a few rotations it starts getting off and the teeth no longer match up

[RPMiller]

Are the gears fully meshed? In other words the teeth the same size as the space they go into. I believe that affects the ratio as well. I used to know the full formula and I believe circumference was part of it as well... Man that was like 2 decades ago...

EDIT: Correction. It is diameter. http://en.wikipedia.org/wiki/Gear_ratio

[RobA]

Yep. With teeth, it is a straight ratio of the teeth. A 13 tooth gear would cause a 21 tooth gear to rotate at 13/21 or 1:1.615384615 which is probably why your 1.62*z sstarts getting off. That extra bit per clock cycle. Best to express it as a fraction in 3d studio if possible to get the max accuracy of the system.

-Rob A>

[RobA]

Are the gears fully meshed? In other words the teeth the same size as the space they go into. I believe that affects the ratio as well. I used to know the full formula and I believe circumference was part of it as well... Man that was like 2 decades ago...

Doesn't mater if they are meshed fully or not. The circumference and tooth engagement don't affect speed, they only affect play, or slop in the geartrain (unless there is so much play you can skip teeth, of course...)

-Rob A>

[RPMiller]

Apparently diameter factors in as well. Note edit above.

[Robbie]

Well...its still not making sense...I did a formula: (-1*(1+(13/21)))*Z_Rotation for a 13 tooth gear and a 21 tooth gear...no dice.

Here's an example:

Gear1
ToothMin Radius: 5"
ToothMax Radius: 8"
Teeth: 21

Gear2
ToothMin Radius: 2"
ToothMax Radius: 5"
Teeth: 13

Am i dumb or something?

[RPMiller]

Your math looks sound to me. I suspect that you are dealing with the accuracy of the modeling software though. Have you tried going out to more decimal places? If push comes to shove you could always change the number of teeth to something that gave you a clean whole number?

EDIT: Makes me think that this is where the watchmakers get their job security. They know some secret that insures they are 100% accurate, but the rest of us don't have that secret so couldn't achieve the result. Maybe they put in some sort of friction devices that slows one of the gears just enough to make it accurate or something. I don't know.

[Robbie]

Even numbers don't even work...except 1 to 1...its weird.

[RPMiller]

Ok, now that is weird. I wonder if the frame ratio has something to do with it? That is just weird. How about 1:2?