Gas station without pumps

2017 October 26


Filed under: Robotics — gasstationwithoutpumps @ 22:32
Tags: , , ,

I can’t share most of what I’m doing for the Mechatronics course, because I don’t want to put up things that students will blindly copy in future years, but I feel that I can safely put up pictures of MockRobot, the prototype we build in Lab 2 for learning SolidWorks, laser cutting, and foamcore prototyping.  The MockRobot is not very different from many other pictures students have access to, and pictures of other prototypes is not going to save them much (if any) effort.

A perspective view showing the overall shape.

The foamcore tower is properly bent with smooth paper on the outside. The lap joint was too weak with the glue I had available, so I used painter’s blue tape to hold the cylinder together. The box also has smooth bends on the bottom edge and mitered lap joints at the corners. The crushed foam was too springy, and one of the lap joints tore the paper, so again I used painter’s tape to hope things together.

The front view, showing the motor mounts on the edges of the platform, the foamcore tower, and the front skeg.

The top view with the tower in place does not show much.

Without the tower, the mounting holes for the tower and for a perfboard are visible. The tops of the two skegs are visible front and back.

The slots for the tower were a little too thin—fitted perfectly for aligned foamcore, but with slight misalignment of the tower, it was impossible for me to get the tabs in without crushing or buckling the tabs. More clearance is needed for foamcore.

The side view should show the screw holes for mounting the motors, but they are hidden behind the 3″ diameter wheels.

A detail of the motor mounting, showing the problems I had with having to reglue the parts several times—the glue kept the pieces from fitting properly after a while.

The motor mount was constructed with tab-and-slot construction on the very edge of the board, so that the wheels did not have to pass through wells. This turned out to be a poor choice, as the hot glue joints were not very strong, and repeated regluing ended up with thick layers of glue that spoiled the alignment.

In future designs, any parts that need to support weight (especially cantilevered weight like the motors here) will have slots that surround their tabs on all 4 sides (a full mortise and tenon, rather than a finger joint) and have bracing on both sides, probably using a crosslap joint. I might also have the tenon go all the way through so that it can be secured by a pin on the other side. I won’t count on hot glue to withstand any tensile forces, and only small shear forces.

I might also design wheel wells, so that when the robot bumps into things, it won’t be with the wheels. I already had trouble with the roach robots rubbing off their wheels if they had too much side force (while sliding along a wall at an angle), so I should have been more more protective of the wheels in this design.

I spent way too much time on this lab fighting the steep learning curve for SolidWorks.  It has a very arcane interface, where buttons do very different things depending where on the screen you are and what mode you are in.  Undoing things is difficult, and I frequently had to scrap several hours work and start over, because I could not figure out how to  reverse some poor early choice I  had made.  I’ve used a lot of software with bad interfaces, but SolidWorks has one of the hardest-to-learn interfaces I’ve ever been stuck with.  Despite the numerous features that SolidWorks has, I would never pay money for it—it is an experts-only tool, and I don’t want to spend the years it would take for me to become expert enough for it to be of value to me.


  1. I particularly like the burn marks from the laser cutting process. Gives it a certain edginess.

    Comment by CCPhysicist — 2017 October 31 @ 19:29 | Reply

  2. […] probably brighter than the robot will ever have to deal with.  I used one of the wheels from the MockRobot to be the target, since I could put a screw through the axle hole to get a more-or-less consistent […]

    Pingback by Tape sensors | Gas station without pumps — 2017 November 17 @ 15:06 | Reply

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