Making a Lip for a Robot Contest Scoring Area

We’re part way through making a nest for a robotic egg hunt competition. The concept of a lip surrounding a scoring area is practical for any robot contest with spherical like objects, whether they are balls or eggs.

Depending on how flat your flooring is, or due to the reversing motion of an exiting robot, the eggs may roll out of the nest if there is not some sort of barrier to stop them. A raised strip at the front of the nest, consisting of a long flat piece of wood or plastic, should suffice.

Plastic egg on nest lip

Plastic egg on nest lip.

The taller the barrier, the more likely the eggs are to be contained. Unfortunately, the taller the barrier, the more likely it is that robot will become stranded on it. A balance needs to be struck.

I chose a 1/8 inch tall strip of PVC plastic. This seems to be enough to stop a slowly rolling egg, without being so high as to prevent removal by a robotic egg thief. But, even at a paltry 1/8 inch, the robot contestants still need to be purposefully designed with enough ground clearance, motor power, and traction to overcome this barrier.

Side shot of the front of the nest with a profile of the lip

Side shot of the front of the nest with a profile of the lip.

Depending on how fancy you want to make it, the lip can have a rounded front edge, can overlap the floorboard, and can be firmly screwed into the side panel.

Cutting The Leading Edge

By rounding the leading edge of the strip, it should be easier for robots and eggs to enter the nest, without affecting the ability for the strip to discourage eggs from leaving the nest. I suppose this kind of makes the strip like an egg diode.

The curved edge can be made with an appropriately curved bit on a router table. Since I don’t have a router table, I used a 1/8 inch radius corner-rounding end mill (05208418 from MSC Direct). Unlike standard flat-faced end mills, a corner-rounding end mill has curved flute tips.

Curved end mill verses flat

Curved end mill verses flat.

With the plastic strip inserted into a vise, roughly align the top of the corner-rounding mill. Then set the vertical stop at the back of the milling machine.

Setting mill position based on front of lip Setting mill position to correct height

Setting mill position based on front of lip (left) and height (right).

Then, roughly align the front of the corner mill.

The final position of the corner-rounding mill still requires some fine tuning. Begin on one end of the plastic strip. Power up the milling machine and lower the mill down to the previously determined height. As a test, mill a couple centimeters of the edge of the plastic strip. Stop the machine and check the edge.

Before and after bevelling edge of lip

Before and after bevelling edge of lip.

If there is a raised mark ① on the front of the plastic strip, then the mill needs to come forward slightly. If the rear of the plastic strip doesn’t seem to have been cut completely round, then the mill needs to move backward slightly.

If front has a raised line and the rear is not cut, then the mill needs to be lowered slightly (which may require you to adjust the vertical stop). At some point, both the front ② and the rear will be cut, with a nice smooth curve in between.

Cutting bevelled edge on lip

Cutting bevelled edge on lip.

The rounded-end mill quickly and easily cuts a smooth curve on the front of the plastic strip. Depending on the length of the milling machine table and vise, it will likely be necessary to stop the mill and slide the plastic strip over.

Stopping, repositioning the workpiece, and restarting can produce some minor transitional inconsistencies in the rounded edge. However, I found that the worst cut sections occurred where the workpiece sagged due to lack of underneath support because those sections were not held directly by the vise. For the best results, it is much better to stop milling and reposition each uncut portion in the vise.

A rounded edge is already a luxury for robot contestants. And, you’d be perfectly kind to stop there. However, with some extra effort on the next page, you can make a smooth transition between the lip and the floorboard.