DEWBOT XI Internal Stacker

Our main scoring system allows us to build stacks of up to six Totes under a Recycle Container and to score these. This stack is built inside the robot chassis and we score by simply dropping the stack and backing up. This required a U-chassis, the scariest design element of DEWBOT XI.

Stacking Strategies

Analysis of this game makes it clear that in competitive matches, RCs will constrain scoring potential and maximizing the score per RC is therefore essential. The only sensible stacking strategy is therefore to:

1. Pick up an RC
2. Build an stack of six totes under the RC
3. At some point in the process, put litter in the RC
4. Score the stack and repeat the process

The resulting stack scores 42 points per RC, the maximum possible. The robot should produce as many of these stacks as possible.

Human Player Station versus Landfill loading: Ideally, be able to do both. We focused on Human Player station loading due to the perception that it would be faster. The 30 human player totes provide materials for 5 stacks.

U-Chassis

Chassis weldment - before and after "diet"

To minimize the stack's impact on robot center-of-mass, we decided to build the stack within the chassis. To score by simply dropping the stack and backing up to disengage, we determined to have no floor under the stack carried by the robot. These decisions led to a decision for a U-chassis, Sab-BOT-age's first. Form must follow function.

This was our scariest design decision. From 2009, we have designed rugged welded chassis frames. How to do this for a U-chassis? Is this even possible?

To help overcome the intrinsic weaknesses of a U-chassis, we designed the chassis around a sturdy "backbone": a 41.5" long 2" x 2" x 0.125" wall 6061 Al square tube. This backbone was not cut for light-weighting, except at the very terminal ends.

Structural connections across the robot's back at different heights were also included to provide structural integrity. 1" x 1" x 0.125" wall 6061 Al square tube members were employed for this purpose.

Extensive diagonal bracing and gusseting was originally designed and planned. The need to rationalize weight led to a significant reduction in this bracing (with considerable trepidation).

Stacker

Lift evolution from dual-purpose original design to simplified stacker

The stacker mechanism went through some evolution.

1. The original stacker concept provided 2-dimensional actuation: vertical for stacking totes & RC; and a horizontal fork to enable scoring of co-op stack points. Since the stacks were built inside the robot chassis, a separate mechanism was required to deposit coop totes on the step. As originally designed and built, this weighed 15.8 lb (excluding chain drive). An AndyMark 9012 motor with BaneBot 64:1 gearbox drove the coop fork.
2. This stacker mechanism was aggressively weight reduced. Aluminum slides replaced the steel originals and lightweighting holes were cut. The steel spring clips to support the totes proved to be too springy and easily damaged by picking up the RC and were replaced by polycarbonate hinged support plates.
3. The coop mechanism was never actually used. The decision to abandon this arrangement was driven by weight concerns and the understanding that if we were to be a stacker robot, we needed to do this well and without compromise. Prior to Hatboro-Horsham, the coop fork system was disabled and its drive motor removed.
4. Between Hatboro-Horsham and Seneca, the entire original stacker assembly was replaced by a new, simpler and lighter assembly weighing 4.6 lb. Hinged supports were retained, but the forward section (bearing most of the tote weight) is 7075 Al. Spring steel tote aligners were included. This new stacker has a designed-in 2^o back tilt for improved stack stability.

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