DEWBOT XVI Climber
- Needs to be easy for drive team
- Must be capable of hanging in switch center
- Must be capable of hanging on raised area of switch
- Robot must remain up when disabled
- Robot needs to be easily removed from switch after match by two students
- Robot must be removed from field and returned to pit without needing power
- One motor may be used
- Climber must remain entirely below 28" height prior to deployment
When the Shooter Arm was under consideration, it was intended that the Climber would be incorporated into this system. With the Arm abandoned, the Climber became a stand-alone mechanism.
The Climber makes up a rectangular frame with the longitudinal elements made of 1½" x 1/16" 6061 Al square tubing and the transverse elements connecting these made from 1¾" x 1/8" 6061 Al U-Channel. The longitudinal elements contain extendable hooks driven synchronously via leadscrews. The rear U-Channel is highly relieved and incorporates the leadscrew drive. This rear U-Channel also terminates in ½" shaft for bearing mount, allowing the entire structure to rotate. The Climber deploys via this rotation, driven by a pair of 1¼" x 12" stroke pneumatic cylinders.
Extensions are composed of 1" OD x 0.028" wall x 28-5/8" long 4130 steel tubes with printed square linear bearings outside and bronze leadscrew nuts inside at the rear and ¼" 6061 Al hooks at the front.
Leadscrews have the significant advantage of not backdriving under load without power. At the same time, they are easily driven by hand in order to facilitate easy and safe removal of the robot from the switch after a match.
Leadscrews are driven by a single NEO motor mounted on a custom shifting gearbox. Gear reduction ratios are 1:1 (for rapid extension under low load) and 4:1 (for lifting the robot). Gear shifting is pneumatically actuated (¾" x ½" stroke) utilizing a 4-tooth Andymark dog. The gearbox has an encoder mounted on the output shaft.
A 3/8" shaft extends from the gearbox between the two output shafts, rotating in the opposite direction. This shaft allows a hand drill to be used to drive the leadscrews without robot power.
Leadscrews are 3/8"-10 2-start 4140 steel leadscrews with right-hand thread (McMaster-Carr 98940A012), each 30.5" long. Travel is 0.2 in/rev. Leadscrews have 3/32" keyways milled to engage the HTD5 drive pulleys. Leadscrew Nuts are matching round 932 bronze nuts (McMaster-Carr 1343K121) which are turned down from the original 1.344" OD to fit into the extension tube; also drilled and tapped 4x each for 6/32 screws.
Mounting & Support
The pivot point for the climber is necessarily relatively high on the robot. The Climber is mounted into carbon fiber side panels ("Wings").
Team 1640 has utilized carbon fiber composites since 2011 (DEWBOT VII - Logomotion), primarily for electronics panels. This is really the first time that carbon fiber was used specifically for structural purposes and specifically for its excellent mechanical properties.
Extension distance: 25-7/8 in
Unloaded extension speed (1:1 Reduction): 17 in/s
Full Power Lifting speed (4:1 Reduction): 3.25 in/s (@ 33 A)
Maximum Hook Height: 76.5 in
Height of hanging robot: 55 in from centerline of Rung
- Encoder on gearbox output shaft (measuring actual leadscrew rotations)
- Limit switch for minimum extension
- Limit switch for maximum extension
Solidworks CAD files.
- We want a reduced hang-down distance from the Rung, so that we always score a hang
- A reduction in reach is not acceptable
- A single center hook is desired
- But without sacrificing the capability of climbing in the center of the switch
An easy solution is available which would reduce hang-down by 4.3 inches (55 to 50.7 inches) with a reduction in reach of 4.5 inches (76.5 to 72 inches). This was considered insufficient (in terms on hang-down) and unacceptable (in terms of reduced reach).
An alternative solution requires folding down the climber after hanging (so at least no more than 12 inches of climber extension extends beyond the frame perimeter). This raises the robot well off the floor under any switch position and conditions. Also, since this additional lift is pneumatic (and uses a double-acting solenoid), the lifting continues after the match end. Switching from two (2) 1.25" bore x 12" stroke to two (2) 2" bore x 12" stroke cylinders did not quite get there, but with two (2) additional 16 lbf Vulcan constant force spring, this works.
Sanjai Bashram pushed to replace the (2) 16 lbf CF springs with 24 lbf CF springs, and this works considerably better and faster.