Difference between revisions of "DEWBOT VI Mechanical"

Revision as of 20:31, 16 March 2010

Kicker at work

DEWBOT VI’s scoring strategy is focused on scoring soccer balls. Towards this, we should be able to:

• Herd up to 3 soccer balls and push these into the goal if playing in the alliance zone
• Herd balls with the robot side as well and also push into the goal using the side.
• Kick the ball towards the goal. We expect to be able to reliably score from Mid-field and to at least be able to reliably move balls from the opposing zone to the alliance zone with a single kick over both bumps. Bonus if we can reliably score from the opposing zone.
• Clear soccer balls from the tunnels

DEWBOT VI has no provisions to Elevate or Suspend.

Ball centering is passive. We really want to kick on the move.

Kicker

How do you move a soccer ball?

How do you get a soccer ball you can't pick up into a goal?

It's not a big surprise we ended up with a kicker on DEWBOT VI.

The Kicker is latex-tubing powered. Kicker is 15” wide and had a kicking face tangent to the ball at the contact point.

The Kicker will be cocked and fired pneumatically via the following sequence:

1. Disarmed - Kicker in untensioned condition, such as after being fired
2. Cock - a Main 2” bore, 4” stroke Cocking Cylinder with a 1.25" bore "helper" Cylinder extend to drive the Cocking Arm which in turn drives the Kicker into the fully-tensioned position. The Cocking Arm and Kicker pivot on the same axis.
3. Latch - a ¾” bore, ½” stroke Latch Cylinder extends to close the Kicker Latch, holding the Kicker in the tensioned position
4. Arm - The Cocking cylinders retract (only the "helper" cylinder is powered on the retraction, to conserve on air), retracting the Cocking Arm at the same time. The Kicker remains in the tensioned position due to the Latch.
5. Fire - the Latch Cylinder retracts, opening the Latch and releasing the energy stored in the latex springs.

This sequence is illustrated in the following four (4) images. In these images, the Kicker is color-coded Cyan, the Cocking Arm is color-coded Olive; and the Latch is color-coded Violet.

• 

  1 & 5) Kicker disarmed or fired

• 

  2) Kicker cocked

• 

  3) Kicker latched

• 

  4) Kicker armed

The Kicker power will not be adjustable during a match. It will be possible to adjust the latex tubing between matches to attenuate the Kicker’s power.

The Kicker is a robust, welded aluminum assembly supported by a substantive welded structure within the chassis. Firing the Kicker releases a great deal of stored energy.

The Kicker must be disarmed prior to crossing the bump.

Kicker Development

fire in the hole!

Kicker development proceeded in stages:

1. Conceptual testing of several different kicker concepts using relatively simple prototypes to demonstrate feasibility.
2. Refinement and testing of the selected concept - a latex-tube powered, swinging, wide kicker.
3. Design and construction of intended Kicker and the design and construction of a proxy chassis into which the Kicker was installed. Kicker performance was verified. Cocking and Latching systems developed and tested. A Possessor tested. When we were satisfied with the Kicker System's overall performance, the System was transferred to the Robot.

Concepts tested were:

• A motorized flywheel driven Kicker
• An air-spring Kicker based on a constrained, charged, 2" bore pneumatic cylinder. We really wanted this to work. It would have made our engineering jobs easier & happier.
• A latex-spring powered Kicker - the selected concept. It's just awesome, and awesome trumps easy any day. 'nuff said.

Kicking cross-field (over both bumps) required (5) pre-tensioned latex bands. The 2" bore Cocking Cylinder had some difficulty tensioning this, so we added a "helper" Cylinder. First a 3/4" bore; then 1.25". A bonus of the "helper" Cylinder is that it can do the retraction by itself, thereby conserving compressed air.

The Latch proved the most troublesome element to develop. High pressure on the latch contact surfaces either prevented release or resulted in unacceptably high wear rates. Steel was always used for these parts, but ultimately a piece of hardened tool steel was used for the catch plate. A couple of wire ties on the Latch provided a lubricous Latch surface which could be easily maintained.

Possessor

Possessor mounted on the proxy chassis

The finished robot has no possessor. One was developed, but found to be ineffective.

The developed Possessor consisted of a 15" x 1¼" PVC pipe covered with grippy 1/16 neoprene rubber sheet shore 40 hardness. The roller was rotated by a Fisher Price motor attached to a Banes Bot 256:1, and later a 64:1 transmission. This seemed to be effective on the static proxy chassis, but when mounted on the robot, it became clear that the possessor allowed the robot to ride up over the ball far too easily and was ineffective at possessing the ball.

The possessor was removed and replaced with a passive system.

UPDATE

After competing at the Finger Lakes Regional, we decided that we needed to revisit the idea of ball possession. It seemed that both ball possession and centering was key for accurate and rapid scoring. It will allow us to spend less time lining up the robot to the ball and to the goal, and make it so we just have to align the robot + the ball to the goal.

Since Breakaway is not a high scoring game the ability to score reliably is a desirable trait for robots to have.

With that in mind we have resumed prototyping the ball possessor.

This year the main diet of robots consists of eating #9 soccer balls, robots find these to be delicious. Ball possessors help give the robot the teeth needed to eat them which was part of the main issue. Possessors that hold the ball in front of the robot also push the ball into the robot. We observed many teams that had catches setup to stop the ball from being consumed.

The system that we have in place to stop the ball is a passive free rolling aluminum rod. When the ball is pushed back it will come in contact with the rod and spin on it, if the ball does begin to be pushed further back it will roll under the passive rod and lose contact with the possessor and will no longer have force applied to it. The only concern with the passive roller is that the kicker may contact it.

As for the possessor itself, we are currently still testing different materials for it. We have the correct height for possessing however as far as centering we are still testing gripping material vs. spacing.

Current Materials to test with

• Green Polycord
• Elastic tubing
• Closed Cell Foam Pool Noodles

The possessor is driven by a 4 stage gear box with 1 stage pinned out and 2 green polycords as drive belts.

Sideguards

A quick test revealed that DEWBOT VI easily drove over balls when driving towards then sideways. This would result in a penalty.

Eyebolts and bungee sideguards were added to the robot side to prevent incursion of the balls under the frame. These sideguards do not interfere with crossing the bump. They do enable the robot to herd balls into the goal using the long chassis side.

• 

  Crossing bump with sideguards in-place - no problem

• 

  Herding with robot side & sideguards. We can no longer drive over the balls from the sides.