FIRST Global Building Guide Created by REV Robotics 2019, Licensed Under CC BY-SA
40
Figure 69: Single Stage Reduction (15:20) with Idler
Idlers can be used to tension chain or increase the amount of chain wrap around a sprocket. From Figure 70, all power
transmission sprockets should have chain wrapped approximately 180° around the circumference of the sprocket. This
amount of wrap is necessary so that there are sufficient teeth engaged with the chain to transmit the torque. Too little
wrap (<120°) and the chain will skip under heavy load, while excessive wrap (>200°) can decrease system efficiency. In
Figure 70 the sprocket outside of the chain is noted with a warning because it has a chain wrap of <90°. If this sprocket is
an idler, then it is unpowered and minimal chain wrap is acceptable, however if this sprocket will be driving a shaft then
this amount of wrap would be insufficient.
Figure 70: Chain Wrap Illustration