This is right on the edge of the topic, but I've decided it's worth posting on this topic, because it is a "belt + roller conveyor for balls". For our latest off season project, we've broken our team into three project teams to add some systems to our 2015 robot. Our final 2015 robot had a 4-wheel omni tank drive, and a 6'4" tall lift (including signal light height) on the "front". For this exercise, we gave the students autonomy, with the mentors available as "knowledge resources"; we'll base our build season balance of mentor vs student design decisions on the results of this challenge.
The floor of the classroom shall have a great many tennis balls (courtesy of our head coach from his house, so I personally expect a wide variety of "dead" balls with a fair number of "live" balls).
- Team 1 has to pick up tennis balls in the "right half space" outside of the original robot's frame perimeter and pass it to team 2.
- Team 2 has to accept balls from team 1, pass them behind the lift, and deliver them to team 3.
- Team 3 has to accept balls from team 2, and place them into a standard FRC tote in the "left half space" of the 2015 robot.
The tote begins and must end in a fairly small taped box. (If the team decides to carry it around, that's cool, but there are zero points if the tote does not end up back within the taped box.)
I've been working with all three sub-teams on their mechanisms, but it's team 2 I'm going to address here. It was pretty obvious that "passing the ball around the back" was a much simpler task than the other two, so the teams figured out that team 1 would hand off to team 2 fairly low, and team 2 would hand off to team 3 fairly high. "Passing around the back" is currently planned through a length of 3" diameter aluminum dryer hose, driven by gravity. This means that it is up to team #2 to additionally lift the tennis balls up from where they receive them from team 1 to somewhere quite a few inches above where they will deliver them to team 3. So far, I'm digging the teamwork - team 2 accepted additional tasking because they had been potentially under-tasked by the constraints.
So the question is, how do you lift a tennis ball by four or five feet? I would have probably pursued a polycord-and-plexiglas solution similar to our first year's basketball lift, but given the lack of another robot beating them up, team 2 decided to use a velcro loop. We are using a couple of 3" PVC drain covers glued together and covered in "Cro" (the hooks of velcro) to drive a 3" wide "belt" constructed of dual-sided velcro with the "Vel" (loops) inside and "Cro" outside. The opposite pulley may simply be a fixed axle that "loops" rub around, or may be another spool turned by the velcro loop.
*** - for anyone who does not already know, VelCro is brand name constructed as a contraction of two French words (both of which have English cognates). I do not speak French, but I've grown up in Southeast Louisiana, where French is ubiquitous in place names, food, and other random things, only a bit ahead of Spanish and German. When I went to France a couple of decades ago, I was able to puzzle out most of the road signs. Anyway, Vel is the first syllable of Velour, which means loops, and in English means a rather soft fabric which has a bunch of loops sticking up from a substrate layer, similar to but much softer than carpet. Cro is the first syllable of "crochet", which means hooks. There is a style of yarn work called crochet which uses hooks to pull yarn into intricate shapes. My mother was a serious practitioner of crochet in the late 70's and early '80s, and I did a bit of practice in it.