Team 16, Baxter Bomb Squad, 2012

[tzjin]

Expect nothing less from an original team!

Good job pulling off a swerve robust enough to go over the bump! Since we're consider swerve next year, I'd love to get a closer look at that thing.

Aren't you scared of using surgical tubing to power your catapult though? If either end ever snapped, calibration sounds pretty painful. Unless your load sensor somehow can adjust to compensate?

[Meredith Novak]

Originally Posted by tzjin

Aren't you scared of using surgical tubing to power your catapult though? If either end ever snapped, calibration sounds pretty painful. Unless your load sensor somehow can adjust to compensate?

It is powered by a winch and belting. There are several discreet loops of surgical tubing on each side, so one break doesn't unwind the whole bunch. And, yes, the load cell is there to make up for discrepancies in tubing, belt stretch, etc.

And surgical tubing has been very good to us. We are sponsored by a medical plastics manufacturer...

Awesome robot! I've been waiting for this one all year!

Only question I have is: What is your reasoning behind the catapult? I know earlier you said wheeled shooters were getting "boring", but what was the tactical advantage you thought it gave you?

Just curious. Thanks a bunch for sharing this! I can't wait to watch the webcast!

[WarehouseCrew]

What is a "load cell" and how does it compensate for tubing and belt stretch?

[Jefferson]

Originally Posted by WarehouseCrew

What is a "load cell" and how does it compensate for tubing and belt stretch?

A load cell measures force. In this case the force the catapult is applying to the winch. Surgical tubing will relax when it is stretched for an amount of time. We use the load cell to quantify that relaxation and account for it to make our catapult more consistent.

[WarehouseCrew]

Would you be willing to share your design for the winch, belt and release mechanism for your catapult?

Our mechanism (cam that grabs a bar attached to catapult) is not as effective as we thought it would be. Our original linear catapult was scrapped because of weight and consistency problems, so we are scrambling to get a traditional one working.

[JDNovak]

Our original design was based on the Andymark dog shifter design. We bought all the parts individually and built the winch around that. We machined a pulley which rides on bearings and fastened the gear with the dog to it. this is driven by the dog which in turn is driven by a 26:50 gear drive from two window motors. In 2010 we used a fisher price driven dewalt transmission with locking pins. This year the window motor gearboxes are preventing backdriving.

Since the shifter was not designed to work with the load of surgical tubing we have, We had to use a much larger cylinder than the original design called for. This put a lot of stress on the pin holding the dog and it broke often. We fixed that by limiting the stroke so it never put full pressure on the pin.

The belt we use is standard Gates 9mm GT2. It has held up better than the cable we first used.

I don't have the inventor drawings but they exist. I can give you the part numbers for the shifter parts too if you need them. Our current design is totally fabricated here and includes some EDM work. It may be too difficult to pull off fast.

[WarehouseCrew]

Thanks for the information. We could not pull that off quickly. If you have the drawings, it might be nice to have that for a future robot.

I think we will stay with current mechanism and settle for the middle basket (not as much stress on existing mechanism).