Preparing for Carbon Fiber top of our robot

Carbon Fiber preparation

We began preparation this past week for our carbon fiber top of our robot. Lead mentor,  Scott McMahon, is leading the charge of the process. It is a process that will take a little over a week for completion but it is very exciting for the students to be involved with such a cutting edge technology.  

We began with pink insulation in 4'x8' sheets purchased at Lowe's.  The protective barrier plastic was removed from both sides of each sheet.  It was cut into 3'x1' strips by the students.  This process was done a number of different ways but the most effective was to score the material about 1/4' deep along a utility knife.  The material then was snapped along the score line.  This created a very straight and clean line.  The strips were then adhesived together with Loctite High Performance Adhesive.  After the sheets were adhesived together, we used an electric hotwire to trim the block to into a rectangular block.  The form was cut into the shape of the form using a pattern that was cut out of MDF.  The block was then coated with a light all purpose joint compound.  The block was allowed to dry out over night.  The surface was sanded to attempt to create a smooth surface on each side.  A second application of the joint compound was applied but this time it was thinned with some water. Fibertape was used were cracks had developed in the surface due to the foam sheets beginning to come apart slightly.  The compound was allowed to dry again and resanded with sheetrock hand sanding blocks and 220 grit sandpaper. The final step was to use a repair joint compound for holes and cracks.  This material sets in less than 10 minutes.  It allowed us to create a very smooth surface with as few as possible dents, holes and hollows in the surface. The foam mold was sealed to the table using modeling clay.  

A temporary painting booth was created in the shop using two tarps suspended from the ceiling with binder clips.  The tarps were joined at the ends using the binder clips as well. A paint table was made using a large lazy susan with a piece of plywood on top of it. Four 1"x1" square pieced of tubing were placed under the mold on top of the plywood.  This created a work surface that could rotate rather the painter having to move around the mold. 

 Epoxy resin was prepared by mentors Joe Hershberger and Scott McMahon.  A air compressor was used with a spray gun to apply the material to the mold.  Respirators were worn to prevent from inhalation of the fumes.  A makeshift ventilation system was created using the shop vac.  The shop vac hose was placed in the painting booth while the shop vac was located outside the back door of the shop.  It was turned in this created a ventilation system to remove the fumes from the temporary painting booth.  

The finished product is a mold that now has a very smooth sealed surface.  This will be allowed to dry for 24 hours before continuation of the process occurs.  

The carbon fiber to should be completed over the next five days.  The steps will be detailed as they occur here. 

The following shapshots give a small glimpse into the process from a sheet of foam insulation into a nice looking mold.  

See and download the full gallery on posterous

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Two and half weeks left

Super Sunday night and we have two weeks and two days left until ship date.  I have not posted for a while in regards to the progress of the robot. 

Drivetrain

We have decided on a robot that drives wide instead of narrow.  The drivetrain will be 6" mecanum wheels on individual suspension.  The suspension for each pod consists of two metal plates joined on the interior edge by a hinge. The outer edge will have two springs between the two plates.  The top plate will be mounted directly to the robot chassis.  The bottom plate will have the wheel mount and the AndyMark Toughbox mounted on it.  This will provide suspension on each corner of the robot. 

Chassis/Bumpers

The chassis is the kit of parts chassis provided by AndyMark but we made modifications to the T Brackets to allow for the Toughboxes to be located below the chassis.  We have two set of bumpers: one red and one blue. Both sets are identical with front/back and left/right sides interchangeable.  This will make it easy to change bumpers and not be concerned which one goes on a specific side.  The bumpers are designed with a 1/4" stud for inserting into the chassis frame.  Two 1"x1" angle pieces are mounted to each bumper.  A 1/4" Cleco is used to hold the bumper in place thru a 1/4" hole in the top of the 1"x1" angle.  Numbers will be stenciled on each of the bumpers.  

Kicker

The kicker mechanism will mounted on a hinge on the front of the chassis.  The kicker frame is made of 80/20 (see below) purchased from McMaster Carr.  The arm consists of 1/4" aluminum plate (see below) with a powered roller for contacting the soccer ball.  The roller is powered by a FisherPrice motor with a Banebots transmission connected by #35 chain to the roller.  The roller has an AndyMark #35 aluminum sprocket with 4 Banebots wheels mounted on the shaft.  The shaft can be ran forward, backwards or with no spin at all depending on the desired kick of the ball.  The kicker will be powered by surgical tubing attached to the kicker arm and the chassis and loaded by an AndyMark Supershifter with the high speed gear removed.

Bot Top

The bot top will be made of a carbon fiber top covered with slow recovery foam.  The top is angled with a 3" drop from back to front.  It is also angle from each side to the middle to create a pathway for the ball to exit off the front of the robot near the middle of the robot. The top also encloses the Axis M1011 camera for locating the vision target. The carbon fiber top was chosen as the top for two reasons:  light and can be custom shaped.  The carbon fiber provides a light weight top that is custom shaped to our robot thus providing the ability to direct and control the ball path as well as have little effect on the robots center of gravity.  The bot top also leaves room at the back of the robot for the lift mechanism. The top was made by cutting insulation foam into 1' x 3' segments.  The segments were then glued together with Loctite Spray Adhesive  The block was cut into a smooth rectangle slightly smaller than the original size of 1'x3' with a hot wire cutter.  Foam was glued on the top to build up the back to the height of 17".  Cutouts of MDF were made to use for cutting the foam with the wire cutter  The MDF cutouts were adhesived to the front and back to guide the hot wire cutter(See the big pink foam cutout below).  It shows the form that was cut using the MDF form. The foam was covered in sheet rock mud and allowed to dry. The next step will be to sand the form smooth to prepare it for the seal that will be smooth.  The carbon fiber will be laid on the sealed form and then vacuum sealed.  

Bot Tub

The tub will be made in a similar way to the bot top but pieces of foam will be individual cut and glued.  The shape of the tub is dependent upon the kicker, motors and transmissions located below the chassis.  Carbon fiber was chosen for a different reason that the top: strength of material.  The carbon fiber will provide a strong mount for location of the battery at the lowest point possible and as close to the center of the chassis as possible thus helping with the center of gravity of the robot.  Our center of gravity is important in regards to attempting to traverse the bumps on the course.  The electronics will be mounted on the carbon fiber tub as well.

Lift Mechanism

The lift mechanism will be powered by a FisherPrice motor. A fiberglass pole will be mounted in one corner of the robot and be bent with a cable that is attached to the FisherPrice winch. The motor will release a cable used to bend the pole. The fiberglass rod will flex upright with a hook at the top of the pole attached to the cable.  Once the hook is placed on the tower, the winch will be reversed to lift the robot off the ground.  

Vision

The vision system will consists of three different cameras. One camera will be mounted on the top of the robot for vision acquisition.  Two cameras will be mounted below the chassis for ball location.  An onboard microprocessor will be used to process the images from the three cameras.  

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