Sometimes the old tricks work the best. The Belt and Pulley solution for mechanical power transmission has been around for a couple of centuries, and despite all the ‘high tech’ motion control, it’s still alive and well. This seems strange at first glance, but it’s based on simple mechanical truth; belt and pulley are still the cheapest means of transmitting power.
The belt and pulley has been around since the second century BC but became refined and very widely adopted during the first industrial revolution. A key element of powering machinery in the first industrial revolution was to locate manufacturing facilities near waterways and create power using water wheels. The low-speed water wheel was generally a large diameter and used to create torque. By increasing the speed and powering a shaft that runs in along a large building, multiple pieces of machinery could be power without any steam or electricity. Each piece of equipment required it’s own power takeoff and pulleys were designed to create speed ratios.
Over time the V belt and pulley design became very widespread and persists today in a wide variety of machinery. The belt technology has become very sophisticated to include a variety of high strength fibers in the belting to increase the load capacity of the belt. From simple fan belts in cars to primary drive train in motorcycles at hundreds of horsepower of power transmission, belts are able to provide incredible power density. Large mining industry conveyors are really just big, often miles long belts that carry tons of rock.
There are toothed belts which provide considerably improved accuracy over ‘V’ belts. Fine pitched small belts are able to power wafer handling robots in the semiconductor industry. And toothed timing belts can be scaled up to high loads as well. Notably, the recent Harley Davidson switch to belt driven motorcycles was based on a toothed belt.
A belt and pulley solution can be very efficient, low inertia, lightweight, compact and last for a long time when properly designed. They are very scalable. Large-scale grinding machines in the feed industry at several hundred horsepowers use parallel belts with special pulleys.
As with any technology, there are trade-offs. They have speed limitations at higher speeds. Bend radius and tension are important considerations to ensure proper operation and life expectancy. Alignment of the pulleys is important for long-term operation and safety to ensure that the belts don’t jump off their pulleys. The biggest design consideration is the support bearing and adjustment for tensioning the belts. Belts put a lot of load on one side of the bearing which can cause accelerated wear and difficulty executing repairs.
But it is truly amazing to consider the success of the humble belt and pulley and the many great industry solutions that have been created around this basic technology.