Larger Hands + Electromagnets = 7 Ball Juggling!!

A project log for Juggling Robot

This robot can juggle 7 balls and various juggling patterns by rolling balls on an inclined surface.

Nathan PetersonNathan Peterson 10/06/2015 at 00:560 Comments

The previous hands were working great for 3 balls and sort of ok for 4 balls, but going beyond that required some upgrades. The main problem was still balls not settling properly even with butyl tape. I figured it was time to revive the electromagnets. One of my friends pointed out, that the last time I tried using electromagnets, I was manually disconnecting them from the power supply, which left them in an open circuit state. If drove them with an h-bridge instead, they may turn off more effectively. Also, I redesigned the hand again. This time to be much larger (deeper).

Here is the result:

Top view:

The connector was printed inside of the bearing because there is not much room in the 8mm bearing. Especially when needing an addition hole for the electromagnet wire.

I wasn't so sure about stuffing everything in that small 8mm bearing, so I additional ordered some larger bearings online (17mm). Here is the size comparison:

Here is the printed arm with large bearing:

As it turns out, this large bearing is very heavy. I weighs more than the combined parts of the previous arm:

I decided to try both the small and large bearings at the same time. Here they are being setup:

Neither of them are ideal. The small bearing was wobbling a bit and making a bunch of noise. The large bearing was much more stable, but forced me to lower the angle of the ramp because of the extra load on the motor prevented it from accelerating as much.

The deep profile of the hands ended up causing me to have to do reverse throws because otherwise the ball would hit the inside edge of the hand as it was being thrown. I need to fix that problem at some point, but for now it is doing reverse throws (from outside to inside) just fine, and it worked so well that I easily blew throw 4 and 5 balls and skipped straight to 7!