B9 TreadsectionSam's B9 Homepage
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The first part I tackled on the B9 project was the treadsection. I purchased the Waist-to-Treadsection plans from Bermuda Triangle Engineering and they are well worth the price. Here is the build along with tips I've learned, some of them the hard way.

Here are the eight sides of the treadsection cut out of 1/4" and 1/2" medium density fiberboard (MDF) and temporarily screwed together for sanding. First mistake--I put the short sides and long sides together for ease of sanding rather than putting them in the proper order. Since I can't sand straight when I reordered the side they didn't match up and I had to resand making the entire treadsection slightly smaller than called for. The plans I've purchased call for using plywood for the treads and covering it with polystyrene plastic. I've chosen MDF as I believe I can sand it smooth enough that I won't need to cover it with anything. Treadsection - the eight sides ganged together for sanding
While the sides were ganged together I drilled the holes for the axles. Here is the first stack-up of the sides which gave me a feel for how big this robot is actually going to be--huge. Before continuing I cut out the center section of the outer three pieces on each side and a groove into the bottom of the six center pieces to fit the underplate. Treadsection - first stack-up of the treadsection
The soil sampler door was simply cut out of the right foot section using a jeweler's jigsaw blade to leave as small a kerf as possible. The hinges are #6-32 bolts with the heads cut off after they were screwed in. Slots were cut for these hinge pins and a cover plate was fashioned so that the door doesn't swing inward past the rest of the foot section. Treadsection - Soil sampler parts
Here is the soil sampler door assembled into the foot panel which is ready to attach to the sides. Treadsection - Soil sampler assembled
The soil sampler panel is ready to attach using screws and glue. Treadsection - Soil sampler panel in place
Even though the panels were predrilled for the screws, the MDF still cracked near each edge of each panel. I was able to glue the cracks back closed using these wooden clamps. Treadsection - Fixing the screw-split MDF
One reason you might want to buy tools at some place other than Harbor Freight. I broke this screw clamp while gluing one of the MDF splits. Treadsection - Broken Harbor Freight wood clamp
By using the screw clamps to put pressure on the panels before putting the screws in I was able to avoid the cracking. Second big mistake is shown here in the form of the white spots on this edge. On the left foot section I glued the end panels between the correct side panels but had them backwards. Since this side does not have any distinguishing characteristics (like a soil sampler door) I should have been able to simply flip the left foot around and use it. But, I had not drilled the axle holes exactly in place and turning this section around made the holes mismatched. The white spots on the panel you see are wood putty used to fix the panel after I tore the left foot apart and glued it back together in the proper orientation. Treadsection - Clamping the panels before screwing
The plans call for the rounded section at the bottom of each foot to be simply the polystyrene plastic covering. Since I won't be covering the treads with plastic I needed to fashion the rounded parts out of wood. Here you see an assortment of "slats" I've cut at different angles that I'll use to make a blank that can be sanded round. Treadsection - Slats to make the rounds in the foot sections
Each round was created by fitting four or five slats through trial and error. The slats were made to stick out over the side panels and sanded to the proper curve. Treadsection - Test fitting slats for the foot rounds
I used different types of clamps to make the round sections. Treadsection - Gluing one of the round sections
Here are two rounded sections, one freshly glued and the other with an initial sanding. Treadsection - Two round sections in progress
The round sections were installed using glue and brads which were countersunk and their resulting holes filled in. Lots and lots of sanding, filling, priming of the feet came next. Treadsection - Installing a round section
Now that the feet have been filled, sanded and primed I notched the side of the foot and the outer panel to accept the top part that covers the wheels. The 1/8" deep dado in the foot section and the 1/16" rabbet in the outer panel will give more gluing surfaces. These top panels were not glued at this step but much later. Treadsection - Notched the panels to accept the top
Some builders leave the feet separate, I chose to bolt mine together. I chose to put a half inch gap between the feet, much larger than called for in the plans but correct from what I can see in the robot publicity stills. Treadsection - Bolting the treadsections together
I don't know how many times I'll be installing and removing the bottom plate of my treadsections and screw holes in MDF are notorious for loosing grip if screws are installed too often. I decided to use screw in inserts and machine bolts so this wouldn't be a problem. Treadsection - Treaded inserts for the bottom plate
You can see my bottom plate here, with three tabs on each side instead of one (as called for in the plans). These tabs have screw in inserts in them as well so the outer panels can be attached securely. I also used pound-in plastic feet on the bottom plate to keep the treadsection slight elevated until the wheels/treads are installed. Treadsection - Bottom plate installed
Now that the bottom plate tabs will hold the outer panel the correct distance from the foot it is time to glue the wheel-top plate. I'm only gluing one side right now so I can reinforce the joint. Treadsection - Gluing the wheel-top panels
I added this angled cleat to strengthen the wheel-top plate to outer panel joint. I plan to round the outer side of this joint and hope this cleat will keep my glued edges from cracking. Treadsection - Reinforcement cleat for the wheel-top panel
I used wood filler, body filler (Bondo), and spot putty to make the treadsection smooth and uniform. Note that I created the fillets on the top of the wheel openings to mimic the welds in the original robot. I spent weeks sanding, filling, sanding, priming to get the treads smooth. Treadsection - Making the treadsection smooth
I put Fleckstone texturing on the treadsection and attempted to sand it flat into a more "orange peel" look. As I did many time before on this project, I over-sanded and had to re-coat. Treadsection - Texturing and oversanding
The treadsection is now textured and sanded, ready for final paint. Treadsection - Textured and sanded
Here is the treadsection completed. I am mostly happy with the results. It took me just about three months to complete this part of the project though I let the Teardrop trailer projects interrupt quite a bit. Treadsection - Finished
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Last Modified: September 24, 2005

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