Making a cheap launcher

Technical Technical Discussion
1

Our team doesn’t have a lot of money and are trying to build a cheap, but effective, launcher. The current plan is to attach the mini-CIM motor connected to a BaneBots P80 gearbox. The end of the gearbox will have a leftover Gates belt gear that came with the Andy Mark drive base kit, and this will connect to one large belt that will power two of the drive base wheels.

The reason for the gearbox is because the kids think that the mini-CIM on it’s own will not be able to produce the torque to launch frisbees. We’re all also unsure what would be a good way to have the mini-CIM directly drive two wheels.

Any help would be appreciated. I’m not sure what to tell them here. I think the mini-CIM alone will be enough, but setting up a direct drive system is just difficult.

2

Do you have any sort of budget amount you can allocate towards this?

There isn’t much torque necessary (in our tests) to launch frisbees. We have 1:1 CIM and a 1:1 Mini-CIM, both of which drive the wheels and launch frisbees extremely well.

So you don’t need to gear it down, if that’s what you’re saying you’ll do - if anything it’ll hurt performance - the torque is good enough, you want adequate speed now.

As far as direct drive is concerned, there’s a multitude of ways you can do it, and since I don’t know what parts you have (a lot more information about what you have is necessary to help you about how to do it) I would really suggest getting some kind of gearbox-esque thing going.

The modulox channel (http://www.andymark.com/product-p/am-2071.htm) is a great, cost-effective choice for simple 1:1 gearing like I suggest you use.

3

We only really have access to the Kit of Parts. Our budget on top of that is just a few hundred dollars. Knowing that direct drive should be enough, what I’m thinking right now is attaching drive shaft of the mini-CIM to a larger drive shaft. This drive shaft will direct drive one of the stock wheels, and a belt connected to this wheel will drive the other wheel. What I’m concerned about is what we will use for the larger drive shaft, and how the wheel will be direct driven by this shaft.

4

Are you constrained to using the mini-cim?
Many teams are successfully using one direct drive cim motor with nothing more than a kit wheel attached to it. This seems like the cheapest option, you could use a sheet of plywood to create a housing for the Frisbee and mount for the cim.
If your stuck using the mini cim i would not recommend direct driving, because of some failures mentioned in another thread, (that I can’t seem to find at the moment).
I would also not recommend gearing down the motor, even the mini cim provides enough torque, to shoot a Frisbee
Instead you could use that gates belt to connect the mini-cim to a wheel axle in a 1:1 set up. This would help with removing a lot of stress off that motor shaft.

5

The 8mm key hub is out of stock on Andymark, so I suggest you get this pairing:

$20 is doable, and this will let your 1 mini-CIM directly drive a KOP wheel. From thereon, just mount one of the KOP belt sprockets to the other end of the wheel and use that to drive the other wheel, as I believe you said.

6

There is no reason that a mini CIM won’r work for a launcher: we have a GIGANTIC wheel that weighs about 1.5 lbs (bad guess) and it spins up fully in about 6 seconds. I completely understand the tight budget part; we have a bit of an issue there too. In relation to this, we like to give an award to the team who we think that the students actually helped design and build the robot instead of having NASA engineers build it for them. What I mean is this: For me, FRC is about the learning, inspiration, and excitement of the last-minute innovative quick-fixes. I do not think that it is in the FRC spirit to have a perfect robot. While this is great and everyone wishes they could have a perfect robot, how does this prepare for the realistic world where not everyone has such an amazing gift?
So I do not mean harm, I just hope that you know that other people have felt the pressure of not having amazing resources.
Good Luck!

7

Excuse me while I rant on your comment here a bit.

Yes, some teams might have more resources than you, but it does not mean at all in the slightest that professional engineers are designing the work. Now I am not saying your comment is aimed at any one team in particular, but I find it kind of unnerving. I see you are from Florida, so I can assume you are talking about one team, but we won’t name them here. The fact of the matter is NASA actually sponsors hundreds (not sure on actual number) of teams every year through grants that you can apply for. If you want to be sponsored by NASA I suggest applying for it.

Now there are a number of teams who have engineers help or even design the robot. But I think you are missing the point of FIRST. Its not necessarily to build the best robot, yes it is a competition in a sports based format, but that doesn’t excuse to the fact that the core purpose of this program is to **INSPIRE YOU. ** There are the elite teams that have massive budgets, ultra precise CNCed robots and tend to do very very well. But these teams only got to that point after a lot of hard work. If you set a high goal to reach you can eventually reach it. These elite teams want to win, but they also aim to inspire through excellence. Karthik from Team 1114 just recently did a great TED talk on something similar to this and is quite good. I’ll link to that later. Personally as a mentor I took this year off, but I find it very satisfying in both aspects to watch students design their own things, and also to teach students more complex things as I have learned throughout the years in build season/offseason. My goal is to inspire by striving for excellence and teams like the one you just called out have been one of my main sources of inspiration ever since I joined FIRST, they have clearly figured something out.

Oh and finally, If you want to call out a specific team on a public forum please be ready to receive flack. I Honestly think its unacceptable to do something along these lines as they could always see it.

Here is the link for Karthiks TED Talk, his part comes in around 6:44:00. Sit back. Relax. And prepare to be inspired.

http://new.livestream.com/tedx/TEDxUTSC/videos/10683961

As for the OP. A MiniCIM is more than enough, if you need inspiration a source I shall provide.

http://www.youtube.com/user/robotin3days

If you haven’t seen it, it was powered by two separate CIM motors each geared up at a slightly different ratio, the final wheel being faster than the first. In fact, I’m pretty sure you could get away with directly driving a wheel from the MiniCIM and be shooting fairly decently.

  • Andrew
8

What criteria are you going to use to decide whether you “think” the students helped?

9

[rant]
To truly achieve excellence, compete by bringing yourself up and surpass the competition instead of dragging your competition down (From Karthik’s TED talk).

Take this into consideration when you speak. On CD you are not hiding behind a wall of anonymity. We may not know you personally, but your profile tells us what team you are on. When you drag somebody down, you drag your team down. Keep stuff GP because everything, good and bad, reflects on your team.

[/rant]

Back to OP:
Sorry to hijack your thread. I echo the direct drive CIM. We have not spent much manpower on our shooter (we are 30 point hanging) but an average skilled member of ours was able to get something going in about an hour using minimal tools and material. We spent $25 dollars on the hub and used plywood and a wheel that we had laying around.

If you are especially frugal, you could probably spend about 30-50 dollars getting it to work using the items and spitballed prices.
CIM (KOP)
Small Piston (Bimba Voucher)
Pneumatics (KOP)
Hub (25 on AM)
Plywood (depends, probably 5-10 dollars depending on what you get)
Spraypaint, team color (sexy, but not necessary at 8 bucks a can)
Wheel (KOP)

I’m not posting any pics on this first post on purpose because I don’t want to ruin the fun in the chase. However, I am willing to email you a full CAD of our current prototype if you want me to. Just send me a PM and let me know.

Good luck :slight_smile:

10

Here’s a easy way to direct drive a 1/2" hexed wheel.

Buy some 1/2 hex rod from Vex Pro. Also buy 4 each 1/2 Hex collars. Buy some hexed banebot wheels. cut the hex shaft into 2 each 3.5" pieces. Using a lathe drill a .312" hole 1.25 deep. Make two shafts. After drilling take a hack saw and cut a .3/4 cut down the middle of the shaft… The hex will go over the cim shaft, then put a collar on and tighten. Slip two banebot wheels on the shaft and use a second collar to hold the wheels on.

11

Eight bucks?! The good stuff at Lowe’s is five; the cheap cans (black/white/gray and good enough to mount to wood) is 99 cents!

That quibble aside, I think Garrett is on point here. I think attempting a $0 solution will cause you to spend $20-30 on heartburn and blood pressure meds, so spend that on a couple of AndyMark parts and get rolling. :slight_smile:

12

It depends on the materials you already have. I’ve seen both 1 and 2 wheeled shooters that work pretty well. Here’s what my team did:
Essentially, a flat surface (sheet metal, plywood, etc) with two cim’s on the left side (one in the midpoint and one at the end) and pneumatic wheels attached to the cim’s. Then at the bottom of the surface, we put a window motor and bent some angle aluminum to serve as an arm to push frisbees into the wheels.
As for HOLDING the frisbees, we went to home depot and got a 5gallon bucket and mutilated (read: cut) it to fit our design needs. So if you already have the motors, this could be a cheap option for you, and it’s been VERY effective for us. If you’re interested, check out my signature

13

Our launcher is simple, robust and works. We use the smaller CIM with an 8mm hub coupled to a FIRST plastic rimmed wheel. On the wheel, we attached non-skid material (the stuff one uses for stairs for we old folks not to slip). we fabricated our launcher system with angled aluminum and some lexan. The most expensive stuff was the super slick Teflon tape we applied to the channels in which the Frisbee rides. Got that from McMaster Carr.

We use a cam (hand crafted from wood) system attached to a PG71 to push the Frisbees into the shooter. Our loader is made from Lexan as well. We don’t have a large budget so it was hand crafted. Nothing like a heat gun to make the bends.

Please drop me a line off list (pm). I bought several more 8mm hubs than we needed this year. In fact I didn’t pass the stupid test and double ordered. You’re welcome to 1-2 if your team needs them. We don’t have any more of the mini CIMS but I think we’ve got a regular sized one if you’re in need as well. We hand fabricated the motor mounts for the CIMS. I could send you the CADs for the shooter and motor mounts if you’re so inclined. It works and works consistently out to about 40’.

Again, drop me a pm and let’s see if Team 3355 can help y’all out. We’re willin’ if you’re willin’ to accept the parts. That’s how we roll…gracious professionalism!!!:]

Steve Miller
Coach-Team 3355
The Purple Vipers
Summit International Prep HS
Arlington, Texas

14

^^This. If it wasn’t for experienced teams willing to help we wouldn’t have made it last year (our rookie year). This year I think we’ll make it on our own, and hopefully next year we can be one of those teams that can help rookies. I encourage your team to take advantage of offers like this, and don;t feel bad about doing it, just look forward to the day when you can do the same.

15

If you’ll be at Orlando I would like to extend an invite to you to not only take a peek at 79’s robot but their code base as well. Let me know if, based on your criteria, our students did it or our NASA engineers did*. Bonus points if you can point out the parts in our code that students did compared to what the software mentors did.

*Well, we don’t have NASA engineers but we have Honeywell and MITRE engineers and I assume for the sake of this discussion those will suffice.

16

I haven’t heard anything back from this team. I guess they got everything handled. I’ll extend the offer to any other teams that need to get their bots done. If you need these parts, drop me a PM. Again, we’ve got way more than we need this year and are willing and able to share our good fortune. :smiley:

Steve Miller
Coach-Team 3355
The Purple Vipers
Summit Prep HS
Arlington, Texas