sprocketRadius .... which measurement

[nellyt]

Which radius am I measuring for sprocketRadius ?

I pull on the handle attached to tape which spools around to top spool of radius A. Mounted direct to the tape spool and fractionally larger is a wheel of radius B around which a drive belt runs. The belt is tensioned with a small wheel whose size is irrelevant.
The belt then passes around a small wheel radius C on the axis of the main fan.

Which radius is sprocketRadius ? A B or C ?

What I don't understand is that we have made a gear with those 3 wheels and the overall effect is a function of all 3 yet only 1 radius is required? Maybe some of it just drops out in the maths ?
Thanks

[JaapvanEkris]

Radius is important for handle force calculation and drive distance calculation. The latter can be measured relatively easily, so that might provide an approach to empirically verify it.

Key is the radius of the wheel attached to the fan. If that belt is directly connected to the handle, that is the only thing you'll need. If there is some transmission where the belt is driven by another belt with some gearing in between, you need to take that into account. If you pull the handle, you move the flywheel x radians, that transmission needs to be known for handle speed etc.. to work.