Band Brakes

This is part of my Brief Guide To Brakes series – a result of my research for Edinsolar, the University of Edinburgh’s solar vehicle team.

HOW IT WORKS

• a band is wrapped part round a rotating drum
• Pulling or pushing a lever creates tension in the band
• the difference in tension between the two ends of the belt results in a restraining torque
• it can be used dynamically to just slow down or statically to stop the drum entirely

Used for winch drums, chainsaws and sometimes bicycle brakes.

VARIATIONS

There are 2 types
• simple band brake – has one lever and only pulls on one end of the band
• differential band brake – has a lever either end of the brake to adjust independently

The effectiveness of the brake, , can be changed by altering:
• the coefficient of friction, μ, between band and drum
• the angle of wrap, θ

DISADVANTAGES

When hot,
suffer a loss of brake force
lots of grabbing and chatter

With a large coefficient of friction and angle of wrap,
It is very sensitive to changes in μ, the coefficient of friction
e.g. light rust on the drum may cause the brake to “grab” or chatter,
water may cause the brake to slip,
rising temperatures in braking may cause the coefficient of friction to drop slightly but in turn cause brake force to drop greatly.

Using a band material with low coefficient of friction increases the input force required to achieve a given brake force.

ADVANTAGES

With a large coefficient of friction and angle of wrap,
the brake is very effective
requires low input force to achieve high brake force

Some materials with a low coefficient of friction have more consistent coefficient across the range of working temperatures.