DEWBOT V gearbox
A direct-drive gearbox for the middle wheels provides the benefits of:
- Improved reliability
- Lower mounting height for gearboxes and motors, contributing to lower center-of-mass
- Fewer, simpler and lighter chain runs
- Concentrate motor/gearbox volume low & central, leaving upper deck free for scoring mechanisms
Team 1640 designed a direct-drive gearbox for the 2009 Lunacy game. The design is based on AndyMark Shiftbox, but is modified by: 1) using custom front & back plates; 2) adding an additional axle and reduction gear for direct drive in lieu of sprocket output; and 3) allowing for just a single CIM motor (a 2nd CIM is unnecessary for Lunacy). Low gear reduction is 24:1, providing a maximum speed of 5.9 ft/s and more than adequate torque for turning.
High gear was disabled for Lunacy, but may be employed if desired.
Encoder mounting capability is retained.
Mass of Gearbox with CIM motor is 6.2 lb. A significant weight savings.
Gearbox Development
Based on prototype testing and the team’s improved understanding of drive-train mechanics, a provisional drive-train / chassis design was developed during the 2nd half of 2008 which, the team believed, would offer excellent drive-train performance under a wide range of potential game conditions. This hypothetical design included custom gearboxes directly driving the middle wheels, with slave chain drive for the front and rear wheels.
In adding the 3rd axle, first the two 12-tooth sprockets (S35-12H or am-0012) were replaced with one 20-tooth gear (am-0186). ½” nylon washers were added to fill the gap. A modified 45-tooth gear (am-0185) was used on the 3rd axle to provide the necessary reduction from the 20-tooth gear. The 45-tooth gear was modified to mate with an AndyMark 500 Key Hub (am-0077).
2009’s Lunacy game allowed some simplification of the hypothetical design. Only (1) CIM motor was needed. Shifting, while still implementable, was not needed and therefore disabled. These changes allowed a much more compact gearbox which could also be mounted horizontally, thereby lowering center of mass.
Mounting holes for the shifter and the encoder were retained.
Left and right gearboxes are identical.
The lower (2) spacer bolts engage the 80/20 rail used for mounting the front and rear wheel bearing blocks.
The two bearings for the 3rd axle in the gearbox allow this axle to be cantilevered. A terminal bearing & bearing block is not necessary. A cantilever approach was used in practice.
Specifications
- Gearbox type: Direct-drive Shiftbox (shift disabled)
- Motors: (1) CIM
- Gearbox: 9.4:1 reduction High Gear (disabled); 24:1 reduction Low Gear (enabled)
- Output: ½” shaft with 1/8” keyway
- Mass: 6.2 lb w/ CIM
