DEWBOT IV
Building DEWBOT IV in 2008 to play Overdrive was one of our toughest challenges.
- DEWBOT IV Build
- season is detailed here.
Our build process is divided into the following five stages:
- Brainstorming & Strategic Goal Setting
- Prototyping and Tactic (Game-Play) Development
- Designing
- Building
- Testing & Training
We prototyped the following features:
- Trackball capture using Forks
- Catapult from Forks
- Drive-train arrangements
- Fast Trackball removal from Overpass
This year, for the first time in our Team’s history, our Robot was by-in-large designed prior to building. We used AutoDesk Inventor during the design process. A sub-team has been trained in its use and developed experience during the design process.
Special Challenges we needed to Overcome
Team 1640 faced a number of daunting challenges during the 2008 build season.
The most severe of these was the temporary loss of the Team’s founder, leader and head-Mentor, Paul Sabatino, following essential back surgery early in the season. Mr. Sabatino is recuperating and we are all looking forward to his return next year.
The team also had to deal with a Teacher’s strike, which forced us from our home at Downingtown East High School for a full two weeks during the build season. The night before the strike, we all assembled at the school and loaded Robot, parts, supplies and essential tools (including a drill press, belt sander and a band saw) into parents’ mini-vans to relocate our operations. Fortunately, a local family, the McFaddins, became aware of our plight and very graciously loaned us the use of their stable as a workshop for the duration of the strike.
Design Details
DEWBOT IV is unique in combining a Fork-Lift with a Catapult mechanism. The combination provides the benefit of allowing the robot to remain entirely below the Overpass while hurdling the Trackball over it. We can therefore hurdle on the fly, without having to stop or slow down.
To pick up the Trackball, the Fork drops down to a few inches from the ground and level with it. We need to drive the robot so that the Trackball is between the Fork arms. When we do, an ultrasonic sonar sensor detects the Trackball and the Fork is automatically rotated up 20 degrees to capture the Trackball.
Dewbot’s lift also extends above the hurdling height, allowing us to place a Trackball on the Overpass at the end of a match for bonus points. This also allows us to knock off an opponent’s Trackball.
The fast method for us to remove a Trackball from the Overpass, however, is to set the Lift to “Hurdle” and drive under the Trackball. Flexible tabs on the top of the Lift will push the Trackball off the Overpass.
All of the Lift operations are controlled automatically. When planning our game-play, we were able to define eight discrete and unique logical states, or modes, for the Lift. Each of these eight modes combines a specific lift elevation together with the logical states of the three sets of air cylinders that control the Fork and Catapult operations. The operator selects between these eight modes via buttons on our Operator Interface.
While air cylinders actuate the Fork and Catapult, a motorized winch controls the Lift elevation. The winch has a double spool with opposing winding and so pulls the Lift both up and down via a cable and pulley arrangement. This arrangement allows us to enjoy the elevation range of a double extension Lift while using only a single drive source and control. Lift elevation is controlled via PID (Proportional, Integral & Derivative) control using an encoder on the Winch drive shaft. A limit switch at the bottom of the lift travel zeros the encoder count. There is also a limit switch at the top of travel for safety.
Five relays (spikes) are employed to operate the pneumatic system. One operates the compressor based on input from the pressure switch. The other four each operate one solenoid valve. Three of these solenoids actuate the Fork and Catapult system, while the last is used to shift the transmissions.
A restrictor valve in one exhaust port of the catapult solenoid provides asymmetric operating rates. As a result, we can “Arm” the catapult slowly (so that we don’t lose the Trackball) and fire it quickly.
The Process
Dewbot’s drive-train is 2-wheel drive (the rear wheels are driven) with a 2-speed transmissions powered by 2 CIM motors each to provide both speed for laps and fine control for catching and placing Trackballs. Driven rear wheels allow us to recover by reversing should we become hung up on the Overpass. We’ve put Omni wheels in the front for agility. Arcade steering (single joystick on the Operator Interface) is employed.
Each motor (4 drive & 1 winch) is driven by a speed controller.
People
See our other robots at FRC Team 1640
