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LINKED PROFILES University of Missour... Solar Miner IV	ARTICLE Solar Miner IV Body OCID cn00000349	LINKED CATEGORIES Shell/Array Support

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Solar Miner IV Body
by Eric Pieper
created 8/4/2003
submitted 9/15/2003 06:37:09 PM

This is a short paper about some of the processes used to manufacture the body of Solar Miner IV.

SMIV BODY

Design-

I have only a basic knowledge of aerodynamics so I wasn’t involved much in the aerodynamic design of the body for Solar Miner IV. I was, however, involved in the fine tuning of the shape to allow for optimum array power and also to allow the chassis and suspensions to not hit.
For the array optimization the UniGraphics model of the body, sans the nose, was divided into the same number of points as we had solar cells. The three dimensional coordinates of the points were then given to the EE’s. From the points it was determined what angle the cells would be pointed while driving down the road. This information was then plugged into a program that would give the optimum sub-array configuration. From this data, and the efficiency of the solar cells, we were able to get a rough estimate of how much power we would receive from the sun. Several iterations of this were done until the body shape was changed as much as we dared.

Now we tried to fit the chassis and the suspensions under the body only to find that the front suspensions would go through the body at maximum bump. To remedy this situation the suspension mounting points were adjusted as well as the body shape being changed slightly. After many heated discussions it was finally determined exactly how much each of the two would be tweaked.

With the shape of the body now determined a nose of a pre-determined length was added to the drawings. When it appeared that all of the components mated together smoothly we finally called a halt to the designing and sent the designs to the production team.
Once the finalized design was received, Casey Schultz and I determined the spacing we would use for the mold ribs, as well as the internal ribs. For the mold rib spacing we chose 20” (I think) and for the internal ribs we used the same configuration as on Solar Miner III. Looking back we should have reworked them to space the wheels in the middle of the wheel wells.

With the spacing of the ribs decided, we divided the drawing at the places the mold ribs would be. We transferred the outputs of the points to splines in AutoCAD. The splines were then transferred onto a mold rib template with a fixed origin. The rib drawings were then transferred to the waterjet software.

Mold Manufacturing-

With the drawings complete we cut the ribs from ¼” plywood. Because of the size of the ribs, each one had to be divided in half for the waterjet to be able to handle it. These halves were then attached together with scraps of plywood. A 2 X 4 frame for the mold was built and the diagonals measured to ensure it was square. The form was then braced at all four corners with large triangles of plywood. Next, small pieces of 2 X 4 were screwed to each end of all the ribs. These pieces of 2 X 4 were ten screwed to the form. We made sure the ribs stayed aligned by running ½” conduit piping through guide holes in each rib.

Now we had to make the mold ready to build the body. The top of each mold rib was felt for any imperfections. If anything was found it was then fixed with glass bubbles and/or sandpaper. Originally a small “shelf” was made on both sides of the body, marking the point where the side rib would go. For the good body these were removed because they proved to be a pain. One suggestion I have is to make an apparatus that will attach to the mold ribs and hold the internal ribs of the body in place while they are drying.

Body Manufacturing-

With the mold ready, we went about the task of laying down the top of the body. For this a very thick mixture of glass bubbles was made. It was about the consistency of peanut butter. The glass bubbles was dabbed onto the mold rib at various spots. Full sheets of ½” blue Styrofoam were pressed into the mold and glued together in the middle with a thinner glass bubble mixture. I have still not found a really good method for getting the edges of all four sheets to match up wonderfully in the middle. One method that had mild success was to overlap the sheets and then cut through both of them at once. The big problem with this method was cutting a straight line. When we made the good body for SMIV we attached the rear two sheets of the body first, weighted them down, and allowed them to dry. We then repeated this with the front two sheets. We kept the sandbags on the foam to ensure that it wouldn’t try to pull away from the mold even after the glass bubble was dry.

Since the internal ribs were already designed, all we had left to do was draw triangular shaped holes in them and send the drawings to the waterjet. For the inner lengthwise ribs and the front crosswise ribs we laminated Kevlar to a couple of sheets of Styrofoam. MAKE SURE YOU REMOVE THE PLASTIC FROM THE FOAM!!

While the ribs were being cut we laid up the inside of the body with Kevlar. The Kevlar was laid at a 45 degree bias for extra strength. The epoxy was spread onto the Kevlar from the center out. This method helps to minimize the amount of wrinkling that occurs. If there are any wrinkles in the fabric they must be worked out before it dries. Even a small wrinkle can cause delamination down the road. The pieces of Kevlar should overlap approximately 2 inches. The Kevlar should be sufficiently wetted, but should not have any pools of epoxy on it.

When the ribs arrived from the waterjet we had to do some assembly on them. Since the cutting area of the waterjet could only handle a small amount of the large ribs we had to break them into four sections. Each section had a unique pattern at the end of it so that it would only fit where it was supposed to. First we glued the pieces together with glass bubbles. Then we laid scraps of Kevlar over the seams for extra support. With the ribs all attached together we added them to the inside of the body. Pushpins were used to hold the ribs in place and sandbags were used to weight them down. A specially designed jig here would have helped greatly in keeping the ribs from being wavy. After the glue holding the ribs was dry we went back and ran a small radius of glass bubbles along the seam between the body and the ribs.

With the ribs all in their proper places we began attaching the bottom of the body. We used one sheet of foam across the back, one up either side, and one across the front. This ended up being wrong and we had to add more to the back later. It would have been easier to do it all at once. Before we glued down the foam we made sure that all of the proper wires had been ran in the body. We realized that after attaching the bottom it would be almost impossible to run them. When it was time to start, glass bubbles were added to all of the ribs and along the back of the body. The sheets of foam were then laid down and weighted down with sandbags on top of all the glued points.

Nose-

For the nose of the body we determined a distance over which we would like to try and perfect surface smoothness. I think we chose somewhere around 18 inches. The thing that made the nose different from the rest of the body was that when looking down from the top the edges were rounded. To make the shape of the nose we fit a curve around the front of the car to as far as we were willing to go without sacrificing too much array area. Once completed, we divided the drawing into sections, each ½” thick. When the drawings were all worked out we had the pieces water jetted out of ½” foam. ¼” guidance holes were made along the middle so the pieces would align properly after being cut.

After we got the pieces back from the waterjet, we glued them together and placed ¼” dowels through the guide holes. It is important to remember that even if you have several dowels holding the pieces in place, it is still possible for them to shift. Something needs to be done to hold the dowels at right angles to the bottom piece. When the nose was dry we began to sand the outer shape. A mistake we made was to begin sanding before we had glued the right and left halves of the nose together. This made for uneven curvature of the nose. After the outer shape was complete we hollowed out the inside of the nose. We left around 3/8” of foam around the entire piece except for what would be the very front of the car. We left a little more at this point because we would have to attach the turn signals here. Next we put a rib into each half of the nose.

Before we could attach the nose to the body the exact position of the turn signals had to be determined so the wires could be run. To run the wires we drilled holes through the nose. To attach the LEDs we hollowed out a little hole just big enough for the light. We then glued the light into place with glass bubbles.

To attach the nose to the body we sharpened two of the ¼” dowel rods and made a couple of alignment holes in the front rib of the body. We then aligned the nose with these holes and used glass bubbles around the edges to secure it to the body. We used ratchet straps along the length of the body to hold the nose in place while it dried.

Tail-

For the tail of the car we used a sheet of ½” foam and cut it to the proper dimensions to fit the rear of the car. Next we cut holes for the taillights and attached them in. Now the entire tail was glued to the car using glass bubbles. Once the tail was dried on the car we sanded it until it was curved sufficiently. Between Formula Sun 2003 and American Solar Challenge 2003 more of the tail had to be sanded off to meet length requirements. This made the taillights stick out a little.

Canopy-

For the canopy shape we filled in the roll bar of Solar Miner III with chunks of foam. Since the roll bars of SMIII and SMIV were very similar the size would be very close. The foam was then sanded to a shape that would fit closely around the roll bar and still be not un-aerodynamic. On this shape we sprayed a covering that would sand very smooth and could be sealed. We then applied about 14 coats of wax to this. Each coat of wax was allowed to dry before the next coat was added. Now we sprayed a layer of gelcoat to this. Once the gelcoat was dry enough we laid up scraps of fiberglass to it. We kept laying up fiberglass until we had between an eighth and a quarter inch of glass built up. When this was dry we took the mold off of the plug. The next step was to put about 14 coats of wax onto the gelcoat finish of the mold. The wax was applied in the same manner as the previous time. Once the waxing was finished the carbon fiber for the part was cut. For the final time we used two layers of carbon with the fibers running in opposite diagonals from how the part would be. When pulled out of the mold the part had a smooth outer finish.

After the canopy was made we attached it to the body. We did this by setting the body onto the chassis, with the roll bar sticking through a hole in the body. We then cut the canopy to the proper size through several iterations. Once the size was definite, we placed it on the body and used glass bubbles to glue it down.

Next the windshield was made from plexiglass. The glass was cut to approximately the shape that would be needed. It was then put into an over to allow it to become soft. Once the glass was soft enough it was pulled out of the over and formed using the mold. Felt was placed between the mold and the plexiglass so nothing would get damaged. This process took us way too many tries for this car, but once you can get it right it will make an excellent windshield.

With the windshield and the canopy now done we went about attaching the two of them together. First the windshield was cut to the size we wanted it. Next a hole was cut into the canopy that the windshield would fit into. The windshield was then placed into the canopy from the inside and glued around the edges. After the glue was dry we went back and worked on the outside seam using aeropoxy light. Aeropoxy light was then used around the perimeter of the canopy as well. For the vent, a small hole was cut at the front of the canopy at the point where it meets the body.

Bellypan-

The shape of the bellypan was taken from the bottom of the body drawing. The bellypans for the previous cars were flat and this one was going to be curved. We decided that we were going to make the front of the bellypan from carbon fiber and use a sheet of foam for the back portion. We would accomplish this by having a solid mold in the front and only ribs toward the back of the mold. To make the bellypan mold we once again divided the drawing into sections. For the front we used about 21 pieces of 2” foam. For the back we spaced out ribs made from 2” foam. After the pieces were cut using the waterjet, we glued them together and sanded them smooth. A coat of thin glass bubbles was applied to try and seal all of the pores and cracks.

Now we were ready to begin the manufacturing of the part. For the front we were using two layers of carbon and a layer of Kevlar. For the rear it was a sheet of foam with Kevlar on both sides of it. We laid the first layer of carbon for the front and then we put the foam into it. With this done we proceeded to lay down the layer of Kevlar and the other layer of carbon. The initial plan was to vacuum bag all of this down. This didn’t work though because we couldn’t get a good vacuum on the whole surface due to the foam mold and the sheet of foam hanging out the back. In the end we piled everything we could on top of the solid mold to try and help the layers bond better. First we covered the surface with a couple layers of sandbags. Then we stacked on everything we could find that had weight to it. When the epoxy was dry we pulled everything off and got our first look at it. Although it wasn’t near as nice as vacuum bagging would have made it, it wasn’t too bad. With a little Aeropoxy light and some sanding it would be in good shape. We now laid up the Kevlar onto the sheet of foam, while it was on the mold still. With the Kevlar still wet we used wax paper to place sandbags onto the foam/Kevlar, so it would conform to the mold. After it was pulled from the mold the front of the bellypan needed extra support so a couple of cross ribs were added.

2827 words | pieper

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