FRC1899 Shooter Prototype

[penguinfrk]

As with 488, we reached similar conclusions that using wheels to launch the ball would create too much wobble due to the compression of the ball. Our solution was also similar, using some sort of container or cup to launch the ball with a quick release of energy.

The angle of the rail is at 45 degrees. Due to the limitations of our workspace (ceiling height), we're only using about 50-70% available power/length of the rail, and of course it can be further adjusted by manually changing the tension. The video shows shots fired at 21'.

We were making about 3 in every 4 shots. We made all of our shots when the ball was placed at a certain orientation (FIRST logo face up), but it veered slightly when it wasn't placed face up.

http://youtu.be/3Y3a4f30xXY

Any questions/critiques/suggestions? We'd love to hear some possible improvements to the design.

[GilaMonsterAlex]

Very cool!!! Are you worried about fatigue in the surgical tubing? Also, what about your release mechanism? But still that's awesome!! Great Work!

[JamesCH95]

Cool.

Any mechanism ideas for pulling/releasing? Or adjusting range?

[Chris is me]

I'm kind of wondering if we should just put three catapults on our robot instead of our existing manipulator now...

[Nuttyman54]

Originally Posted by GilaMonsterAlex

Very cool!!! Are you worried about fatigue in the surgical tubing? Also, what about your release mechanism? But still that's awesome!! Great Work!

An clever way to solve this is not to measure distance, but force. 190 utilized this on the 2010 robot, which had a surgical-tubing powered kicker. We mounted strain gauges on the struts which anchored the surgical tubing, which allowed us to monitor the strain (due to the deflection force provided by the surgical tubing), and correct for surgical tubing deterioration. It also meant that if the tubing ever got too worn out or broke, we could just replace the bands and not worry about getting exactly the same length/tension.

The 2010 application was much less sensitive, and I don't remember if we ever actually used it in our competition code, but we had the capability and proved that it worked. In an application like this where the accuracy is incredibly important, the ability to not have to re-tune your launcher if you have to replace the tubing could be very critical.

[Madison]

Originally Posted by Chris is me

I'm kind of wondering if we should just put three catapults on our robot instead of our existing manipulator now...

I can't speak for what 1899 is doing, but I will add that we are semi-seriously considering this. We just need a simple way of making sure they all point at the same place downrange -- and that it's adjustable.

[JamesCH95]

Originally Posted by Nuttyman54

An clever way to solve this is not to measure distance, but force. 190 utilized this on the 2010 robot, which had a surgical-tubing powered kicker. We mounted strain gauges on the struts which anchored the surgical tubing, which allowed us to monitor the strain (due to the deflection force provided by the surgical tubing), and correct for surgical tubing deterioration. It also meant that if the tubing ever got too worn out or broke, we could just replace the bands and not worry about getting exactly the same length/tension.

The 2010 application was much less sensitive, and I don't remember if we ever actually used it in our competition code, but we had the capability and proved that it worked. In an application like this where the accuracy is incredibly important, the ability to not have to re-tune your launcher if you have to replace the tubing could be very critical.

That's not a bad way to do it, and it certainly is better than doing nothing, but force != stored energy when the spring rate is changing.

[jason701802]

In our experience bungee cords, like the ones you use to tie things down, although not as stretchy as surgical tubing, are much stronger and more durable than surgical tubing, and usually much cheaper.

[Nuttyman54]

Originally Posted by JamesCH95

That's not a bad way to do it, and it certainly is better than doing nothing, but force != stored energy when the spring rate is changing.

You are correct, and I should have been more clear. There was a potentiometer on the system in addition to the strain gauges, which gives enough information to calculate the spring rate at any given time. We found that the surgical tubing was fairly consistent enough in the spring rate that it would have to deteriorate very far before the assumption stopped being accurate enough to make a difference, so I don't think we actually had this particular feature coded. We were using the black thick-walled stuff available from McMaster, very hardy.

As mentioned before, our measure of accuracy wasn't anywhere close to the degree necessary for this year's challenge, so your mileage may vary. I do believe you will be able to be more accurate with a measurement of force/spring rate, but it still might not be enough to have the kind of "drop in replacement" capability we envisioned for 2010.

[roystur44]

Why not just use a spring instead of the surgical cord. On one end you could add an adjustable buckle to change the tension. Set it and forget it or monitor it and change it for differrent distances.


Roy

[penguinfrk]

Sorry about the confusion. Point of clarification:

The surgical tubing was just for prototype's sake. We too were worried about the wear on anything with elasticity. Right now, we're considering adding a blade underneath the carriage, and using flywheels with encoders for energy.

My main concern for this design is the complexity. It's a good 3 or 4 stages, form intake, to lifting the ball, to depositing it in the ball cup on the carriage, to the mechanical trigger for the flywheels to make contact.

[Johnny_5]

All I can really say for 3484 right now is that we are using a similar design in the fact we are launching with a propulsion system instead of the friction launcher due to lack of repeatability. However our design is more incorporating a crossbow using extension springs

[nitneylion452]

3167 was testing a catapult design, but we decided to go with the pitching machine style shooter for 2 reasons: recovery time and space constraints. The way we saw it, there were too many thing that could go wrong with a catapult (ball misses when loaded; it doesn't get pulled back enough, if at all; etc).

But this design seems very nice and consistent. I like it a lot! Keep up the good work!

[Ether]

Originally Posted by Nuttyman54

An clever way to solve this is not to measure distance, but force.

For students interested in the math take a shot at this.

[rcmolloy]

I really like the conceptual idea of using the liner slides plus the surgical tubing. Very simplistic in only having to find the force to propel the ball without having to really account for ball compression and deformation with using a roller type set up. I am very interested to see the final design of the shooting mechanism in the coming weeks.