How to Select, Capture, and Support VEX Plastic Shafts

Shafts

The VEX plastic construction system uses square shafts to allow assemblies to spin or rotate. This square shape allows the shafts to fit into a square socket in the motors and provides a physical connection to drive them. The square shape of the shafts also fits into the square hubs of motion components such as Wheels, Gears, Pulleys, and Sprockets which provides a physical drive connection to spin the components. These shafts are available in a number of selections, each with different features and options:

Metal Shafts

These shafts are intended for high torque situations, such as supporting a large arm assembly. These shafts are also found in the longest lengths of all the shafts.

Plastic Shafts, Capped Shafts, and Motor Shafts

These lightweight shafts are for low-torque applications. They are available in 2x, 3x, 4x, and 5x pitch sizes in the Super Kit, Foundation Add-on Pack, or the Plastic Shaft Base Pack.

Straight shafts require a shaft collar or bushing to secure components in place.  

Capped Shafts eliminate the need for a shaft collar on the capped side. The cap can secure a wheel, gear, or other motion components.

Motor Shafts include a flange that will capture the shaft when a Smart Motor is mounted directly to a 2X Beam or 4X Plate.

Idler Pins

Idler pins are not shafts and can not be used to drive a component. However, these pins can be used to attach wheels, gears, sprockets, and pulleys so they will be free spinning. 

These pins are available in 0x2 and 1x1 sizes in the Super Kit, Foundation Add-on Pack, and the Plastic Shaft Base Pack.

Capturing Shafts

Capturing a shaft refers to fixing a component to a shaft so it will spin with the shaft, keeping a shaft from sliding back and forth within its supporting holes, or keeping a part/assembly from sliding back and forth on a shaft.

Fixing a Component to a Shaft so it spins with the shaft is accomplished when a square hub slides onto the square shaft. The VEX Plastic Wheels, Gears, Sprockets, and Pulleys all have square hubs so they are fixed to the shaft as soon as they slide onto a shaft. When an assembly uses beams and/or plates and it needs to be fixed to a shaft a Shaft Lock Plate needs to be used because beams and plates have round holes. A Shaft Lock Plate has a center square hub and attachment holes to allow pins to attach it to a structural component. The square hub of the Lock Plate fixes the component to the shaft when it is slid onto the shaft. The 1x2 Shaft Lock Plate works well with 1X Beams and Specialty Beams. The 2x2 Shaft Lock plate works well with 2X Beams and Plates.

Keeping a shaft from sliding back and forth Is accomplished by using a Rubber Shaft Collar or a Shaft Bushing. A Rubber Shaft Collar can be slid onto a shaft and be placed against a supporting structural component so it is oriented opposite to the direction the shaft needs to be kept from sliding. A Shaft Bushing works in a similar manner. The end of a shaft is placed into the square hub on one side of the bushing and the pin side of the bushing is inserted into a hole of the opposing structure component. While there are many instances where a shaft needs to be kept from sliding back and forth, capturing a shaft which is inserted into a Smart Motor drive socket is essential or the shaft may slide out of the socket and it will no longer be driven. As mentioned previously, the Plastic Capped Shafts and the Plastic Motor Shafts have features by which they are already captured in one direction because of their design.

Keeping a part/assembly from sliding back and forth on a shaft can be accomplished in two different ways. One way is to place Rubber Shaft Collars on the shaft so there is a collar on each side of the part/assembly. Another way is to place a Shaft Washer or 0.25x Pitch Spacer on the shaft and between a supporting structural component and the part/assembly. Then slide a Rubber Shaft Collar onto the shaft on the opposite side of the part to capture it from sliding in either direction.

Capture with Rubber Shaft Collars Capture with Shaft Spacer and Rubber Shaft Collar

Components for capturing shafts can be found in the Super Kit and the Foundation Add-On kit.

Supporting Shafts

For many assemblies utilizing a shaft, it is important to provide at least two parallel points of support. This can be accomplished by passing the shaft through the holes of parallel beams/plates. Another method is to use a Shaft Bushing on the shaft and inserting the pin side into a hole of a parallel supporting beam or plate. If two supports are not provided, the shaft may pivot slightly up or down on the single point of support and this will make the shaft harder to spin. The heavier the robot assembly the shaft is supporting, the more important it is to provide these two points of support. For example, a decorative hand might be assembled out of beams and specialty beams then fixed to a Shaft and Smart Motor assemble. This light assembly may only need one point of support as the motor waves it back and forth, whereas a heavy arm and claw assembly will need two points of support.

Two Points of Support One Point of Support