Two-Speed Chassis

[Madison]

This was designed for SWAT Robotics (824) here in Seattle, WA. While they haven't definitely decided against this drivetrain and chassis, they've indicated a strong preference for the use of 80/20 and the ease of construction it provides. So, to be sure that this design doesn't go to waste, I'm sharing it here.

Premise

This design exists as an alternative method of achieving two-speed capability without employing a shifting transmission. Instead, it will rotate two sets of differing diameter wheels into and out of place along the carpet. It is equipped with two, two-motor, single-speed gearboxes and shifts via two, 1.5" bore, 7" stroke pneumatic pistons.

Low-Speed Configuration
To meet size constraints, the chassis begins each match in the low-speed configuration. This also ensures that the robot will be formidable in pushing matches should the shifting mechanism fail to operate. Top speed is approximately 4 ft/s.

High-Speed Configuration
The high-speed configuration offers a longer wheelbase for increased stability when rapidly accelerating and decelerating. Four omniwheels allow for zero-radius turning capability and low friction in all turns. Larger wheel diameter and additional gearing allow for a top speed of approximately 10 ft/s.

Advantages

• Increased control over design considerations -- By switching wheels and changing ratios through differing wheel diameters rather than by simply changing ratios in a transmission, this design offers more control over the chassis' high- and low-speed capabilities. Varied wheels types, sizes, widths and tread materials can be used on the high- and low-speed wheels to achieve precisely desired operating characteristics that best suit the game.
• Offers increased stability for high-speed translation and decreased resistance to turning in low-speed -- this allows for it to rapidly change direction at high-speed with reduced chances of instability or tipping over. It also allows for more torque to be exerted onto other objects during turning.
• Less high-precision machining -- Though, as shown, good machining capabilities are helpful, it is possible to employ this solution's concepts with less machining ability than that traditionally associated with most shifting transmissions. This isn't absolutely true, however.
• Stair climbing -- By switching from low- to high-speed configuration, chassis can climb ledge approximately 5" in height.

Disadvantages

• Weight -- heavier than traditional shifting transmissions.
• Size -- takes up more space than traditional shifting transmissions.
• Complexity -- more moving parts.

This was created with Solidworks 2003. The project files, in whole or in part, are available to anyone who asks. Feedback, constructive criticism and questions are encouraged.