What Shooter Design was Most Consistent

[pfreivald]

Originally Posted by CalTran

Next question would be what you think would be the best approach to analytical testing? Some of our programmers are getting overwhelmed with exactly what to test. Ideally, we would like to pin it down to one independent variable (Whether it be the top rpm and change the bottom rpm to the accuracy, or set both rpms and find the corresponding distance, or something of that sort) and test from there.

For non-fender shooting, we found that top rpm = bottom/2 was nearly close to perfect every time. I hope that helps when you tune things.

Originally Posted by CalTran

When we attempted to create an entrance chute to reduce the feeding variability, it simply resulted in a drastic reduction of range (Down to less than 5 feet)

We squeeze the heck out of the ball just before we feed it to the shooter, using some bent polycarbonate and rivets (that is, not much weight). I can't say whether or not it works for you, but it seems to work for us. Consistency in feeding to the shooter is critical for accurate shooting as far as we can tell.

Originally Posted by CalTran

Finally, would it be worth it to scrap the quadwheel shooter all together and design a compression hood shooter in time for Oklahoma Regional (March 29th-31st)

I don't know that this is answerable by anyone on this forum... It depends on what your team can get to work well between now and then!

[CalTran]

Originally Posted by pfreivald

I don't know that this is answerable by anyone on this forum... It depends on what your team can get to work well between now and then!

I suppose the question would be how easily did other teams find dialing in a compression hood shooter? And if they happen to have experience from previous years, is it easier to dial in a compression hood rather than a quad wheel shooter? How much time and testing did it take other teams to map out the rpms?

[V_Chip]

I'd suggest using a catapult!

[Wayne TenBrink]

1918 uses two aluminum drums, 4.5" long x 3.5" dia, weighing about 2.5 lb each. Each drum is directly driven by an RS775-18 via a BB 4:1 gearbox. Wheel speed is monitored, but control is open loop for now. Balls exit at around 65 degrees (fixed angle). Azimuth is controlled with the chassis - no turret. Camera assist for aiming. The bottom wheel runs wide open, and the top is throttled to maximize backspin and control distance. Drivers have preset speeds, but can scale and/or adjust the speed with the classmate if needed. The current drums have a smooth OD and are coated with belt dressing (which increased distance significantly, but wears over time). We compress the balls about 2". Balls enter the shooter head while travelling in a straight line through a feeder chute set at a 50 degree angle (moving belt below, parallel moving trigger "shoe" above, close fitting guides on either side). The system is very rigid. It worked well enough to achieve a Teleop OPR over 10.5 (and win at Gull Lake with the help of 85, 1677, and 4327) despite an early string of 4 or 5 matches where we didn't score any.

We plan to replace the smooth OD drums with "toothed" OD profile shortly in an attempt to minimize the effects of unpredictable surface friction coefficients and ball compression modulus. Reducing variation (or being able to score despite it) was and remains a high priority.

[Ether]

Originally Posted by Wayne TenBrink

1918 uses two aluminum drums, 4.5" long x 3.5" dia, weighing about 2.5 lb each. Each drum is directly driven by an RS775-18 via a BB 4:1 gearbox. Wheel speed is monitored, but control is open loop for now. Balls exit at around 65 degrees (fixed angle). Azimuth is controlled with the chassis - no turret. Camera assist for aiming. The bottom wheel runs wide open, and the top is throttled to maximize backspin and control distance.

No pictures on your web page. Bummer

[TeamSpyder1622]

We have 4 6-inch 2008 kit wheels (two on top two on bottom) and it has been extremely consistent. While on the practice field we were able to make 20-30 in a row without missing. As long as you let the wheels get back up to the same speed (takes a little longer with two sets of wheels) then it has seemed to be just as accurate as the one-sided shooters

[GRT808]

During the six week build season we had a double axle shooter nearly identical to the one you described. However, although it could shoot balls across the field it also was very inaccurate. We slapped together a hood in about three hours from the KOP and some polycarbonate, no fancy or precise measurements, an installed it in our robot at SD regional. It worked beautifully and launched us into the position of highest scoring robot (not including the bonus) at the competition. We used a bit of PID for a preset speed but other than that our driver used dead reckoning which worked because the shooter was so consistent. I also noticed that us and Code Orange (another stationary shooter that scored high) scored much faster than the turreted shooters (probably won't stay like this in the coming weeks).

If you can go with a hood I'd highly suggest it.

[Wayne TenBrink]

Originally Posted by Ether

No pictures on your web page. Bummer

We're not going to win any website awards this year. We posted some pre-bag video http://www.youtube.com/watch?v=D-q-Db6RMIQ. I haven't seen any pictures or video from Gull Lake. We're trying to get something posted.

[MrRiedemanJACC]

Wayne 2" of compression? That is good to know what you are doing. I second the week 10 Farming....


RB73, how much compression are you putting to the ball?

[CalTran]

So, our team is looking into rapidly designing a shooter under the pretense "CAD it twice, cut once". If any team would be willing to post up some high detail CADs of just their hood shooter then it would be much appreciated. I've already started going through the CD Media, but if someone could direct me to specific ones they feel are good to emulate, that would eb much appreciated. My email is calvintran01@yahoo.com

[DavidGitz]

Originally Posted by CalTran

So, our team is looking into rapidly designing a shooter under the pretense "CAD it twice, cut once". If any team would be willing to post up some high detail CADs of just their hood shooter then it would be much appreciated. I've already started going through the CD Media, but if someone could direct me to specific ones they feel are good to emulate, that would eb much appreciated. My email is calvintran01@yahoo.com

Check out FRC-Designs http://www.frc-designs.com/index.html
We posted our CAD of our complete robot. Our shooter is a single 6" KOP wheel powered by a BB-550 w/ a CIM-U-LATOR and a fixed polycarbonate hood with open-loop control. We shoot around 85-90% power from the key. I couldn't tell you an exact number for compression but probably around 1". We found it very consistent. I had seen many teams that were using 2 wheels and thought we would need to install a second one to help with left/right alignment but we never had a problem with that. Our shooter is a little less consistent than what we had found at our lab due to the new balls, but we were able to dial it in Thursday morning and we had a great OPR (~18).

If you watch/saw the elimination rounds at GKC you will see that we missed most (all?) of our hybrid shots. This was due to our alliance partners determining that their machine was more consistent with shooting from the center and we hadn't spent any time adjusting the power values for shooting from the left/right corners due to the new ball issue.

[aldowyn]

Our shooter (3507) was one of the most consistent at the OK Regional. It has two wheels right next to each other, both above the ball when it shoots. What's different about ours than most is that the ball is in contact with the wheels for about half a rotation. Our feeder is also quite consistent, having guides to put it into the shooter just right, and then the two wheels pull it into place if it's out. Finally, we have a shield on the back end to propel it forwards properly.