We installed a ball compression transducer on Thursday morning of the MN 10,000 Lakes Regional. It is a 10 lb. load cell made by Measurement Specialties Inc. (FC2231-0000-0010-L) purchased from DigiKey. Thanks to Team 2169 for the help. It is opposite one of the rollers in the ball handler. There is approximately 1 1/4" of ball compression where it contacts the load cell. There is a 4" X 4" 1/8" thick polycarbonate plate between the ball and the load cell to compress a large area of the ball and transfer the force to the load cell. The plate is held in place at one end with double stick tape. We made an aluminum cup with a flange around the upper rim to hold the load cell. We drilled a 1 1/4" hole to drop the cup/load cell assembly into the ball guide. Sorry but we got rushed and did not get pictures - you know how it is on Thursday morning…
We ran 5 balls through 5 times each to find out how much variation there is for a given ball. The variation for each ball ranged from 2.6 to 12.5% of the average value and the difference between balls is larger than that so we concluded we could differentiate between hard and soft balls as they passed through.
We saved the peak value for every ball that went through the robot. The data is in the attached Excel file. The data for about 120 of those balls is in the file. The remaining data from semi finals and finals is still in the cRIO. In the rush at the end of finals we failed to download the last 4 match files and now it is sealed in a bag in the crate on the way to St. Louis.
Initially we gathered data only. As you can see in the data, the new balls are easy to pick out. It appears we were maxing out the load cell at a 918 output value when the hardest balls went through. Over time, we started triggering a shooter speed reduction for hard balls and and hood angle change for soft balls. By Saturday afternoon were calibrated pretty well.
Our next task is to match up the force data and shooter speed data to each shot in our match videos to determine if we can improve our algorithm.
Thanks Bruce!! This is some great data, and I look forward to seeing the sensor in the robot in St. Louis.
Unfortunately I can attest to the fact that the data seemed to help their shooting improve on Saturday.
This is one of those ideas I never thought about, but it makes perfect sense. Keep up the good work!
You know guys, that’s really cool! I think it’s a great way to use a sensor that usually isn’t found on a FIRST robot.
Kudos
Mike
After struggling to hit many of our shots through Kansas City, we decided this would be the best way to address the issue of various ball consistencies. We would launch new balls several feet over the backboard and old balls would fall short of the hoop. As Bruce mentioned, after collecting data through Thursday and Friday, we were able to start implementing wheel speed drops and hood adjustments on a per ball basis. This resulted in us hitting 9/10 and 5/11 balls from the key our finals matches at 10,000 Lakes, allowing us to come away with a regional victory. While there is still room for improvement, we are very excited that Captain Pike is performing at a more competitive level and we’re excited to bring out game to champs in a few weeks.
On the topic of ball consistency, what are some other examples of ways teams have addressed this issue? I know of three teams that have compression load cells (2169, 1625, 525). Some shooters have built in ways of dealing with this issue whether it be using a catapult or having a longer contact time with the shooter wheel that the ball will have an extended period of acceleration resulting in a more consistent shot. I have also seen others that simply shoot each ball at the backboard with enough force and enough backspin that the ball will almost always drop in.
So what have other teams done to combat these issues or what are you planning to do?
Count us in the “smack the ball off the backboard with loads of backspin” camp.
Team 1218 is also using a transducer to measure ball compression and adjust the speed of their shots.
We are also in the as hard and as much backspin as possible camp. The backspin gives a pretty big margin of error for us.
Yes it did! Congrats 525, good luck in St. Louis 
2052 falls into the backspin + backboard = basket camp as well.
KING TeC developed this due to problems with their shooting mechanism in 2009. The lunacy balls were always broken causing completly different shots to result. My jar dropped the first time I saw them shoot in 2012. :ahh:
Nate
KING TeC - Alumni (2009-Present)
KING TeC -Coach/Forman/EE/ME (2007-2008)