15.3 Prototyping and Implementation
Physical Prototype
By duplicating this linkage and using central driven shaft it is possible to operate all the legs in sync with each other. This current protype has one side that is incomplete, but that component is a mirror of the completed side.
Iteration Documentation
Most of the iteration work done for this prototype was digital.
This was the first prototype for the linkage and it remains relatively unchanged across the rest of the iterations with the exception of the drive linkage (marked with green) changing as different methods to transmit power where considered. Initially the hope was to just use a single main shaft, but obviously since one of the linkages must pass over this point that would not work to connect all the linkages. In the end after multiple other designs where the best design found was to use a central shaft with gears that could power each pair.
Another system that underwent significant changes throughout the iterations was the design of the joints. The first design used off the shelf delrin bushings and shafts with circlips. However this was quickly abandoned due to the large amount of machined parts that would be required. From there the next iteration used laser-cut bushings, PTFE washers, and an M4 bolt.
This was still too complicated and the difference between Acrylic on metal and Delrin on metal did not justify the extra complexity the bushings added so the final iteration completely removed bushing relying on just PTFE washers and and the M4 Bolt and Nylock Nut.
BOM
Bill of Materials | Cost | Link |
|---|---|---|
DC motor | $ 26.99 | |
Arduino | $ 14.99 | |
Motor Controller | $ 6.99 | |
3 mm Plywood (28x16) | $ 10.00 | TIW |
3D printed Frame | $ - | TIW |
M4x15 Bolt (100 Pack) | $ 8.76 | 92095A125 |
M4xY Bolts (100 Pack) | $ 10.00 | ------ |
M4 PTFE Washer (50 Pack) x 2 | $ 19.40 | 95630A630 |
M4 Nylocks (100 Pack) | $ 5.82 | 90576A103 |
8 mm Keyed Shaft (300 mm) | $ 22.35 | 1439K211 |
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Estimated Cost | $ 125.30 |
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Final Design Process
In order to take the single set of legs that we had created for the prototype and turn them into a full robot we started by making the design of each set of legs repeatable. This meant shrinking down the supporting plate (now called the main spar) and ensuring that it was just big enough to capture the necessary holes for mounting the Klann linkages. At the same time, we added 4 holes that cleared the gears and linkages that could be used to connect the assembly in a row. Finally, as many connections as possible were changed from being bolted to being on shafts that ran through the entire assembly. These can be seen marked in red on the photo below. The spacing for all the components was determined by the necessary amount of clearance to clear the bolted connections on the linkages and the bolts that held the two large gears in place. Once this spacing was known 3D printed spacers and connectors could be designed in order to hold everything in place. These spacers went through multiple iterations, with the first attempt to bolt through each piece and the top bracket holes on the main spar, before that was scraped due to space constraints. The final design still utilized bolted connections but instead placed the bolted connections into 3D printed flanges on the connectors that were able to be offset at mirrored in order to guarantee space for the bolts to fit in.
The rotational power for the entire system was provided by the central small gear, which was placed on a large, keyed shaft that was driven by the output of the osculation mechanism.
Changes While Building
As the mechanism was built up there were a few changes that had to be made to ensure that everything worked nicely. The most major concern was removing the shaft from one of the top ground links and replacing it with a bolted connection. This was required because the link would interfere with the spacer, a result of the connections not maintaining perfect concentricity like they did in the model. The bolted connection fixed this issue, providing just enough clearance for the link to slip past. The other change was adding washers to the connector plates that held the main wooden plates in place. These were necessary to add a little extra clearance, due to very slight interferences from the bolts.
Final CAD with Oscillation Mechanism
Final BOM
Bill of Materials | Cost | Needed |
| Link |
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|---|---|---|---|---|---|
DC motor | $ 36.04 | 1 | $ 36.04 |
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Arduino | $ 12.90 | 1 | $ 12.90 | Unused | |
Motor Controller | $ 5.17 | 0.5 | $ 2.59 | Unused | |
3 mm Plywood (28x16) | $ 5.00 | 3 | $ 15.00 | TIW |
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6 mm Plywood (28x16) | $ 10.00 | 1 | $ 10.00 | TIW |
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3mm Acrylic (10x12) | $ 6.00 | 1 | $ 6.00 | TIW |
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6mm Acrylic (10x12) | $ 8.00 | 1 | $ 8.00 | TIW |
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3D printed Frame | $ - | 0 | $ - | TIW |
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M4x15 Bolt (100 Pack) | $ 8.76 | 1 | $ 8.76 |
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M4x18Y Bolts (100 Pack) | $ 13.24 | 1 | $ 13.24 |
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M4 PTFE Washer (50 Pack) | $ 9.70 | 2 | $ 19.40 |
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M4 Nylocks (100 Pack) | $ 5.82 | 1 | $ 5.82 |
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8 mm Keyed Shaft (300 mm) | $ 22.35 | 1 | $ 22.35 |
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Battery | $ 21.99 | 1 | $ 21.99 |
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4mm Rods | $ 7.49 | 1 | $ 7.49 | Unused | |
20 Tooth Pulley 6mm Bore | $ 7.89 | 1 | $ 7.89 | Unused | |
20 Tooth Pulley 8mm Bore | $ 6.99 | 1 | $ 6.99 | Unused | |
Belts | $ 9.99 | 1 | $ 9.99 | Unused | |
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Estimated Cost |
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| $ 214.45 |
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