We’re a brand new team, and have figured out using a programming language, but have been encountering problems with mechanically executing our ideas. So far, we have tried using two wheels rotating in opposite directions to propel the balls. However, even with gearing, we could not achieve the distance we were hoping and expecting. Our second idea was to pull back the balls like a slingshot, using surgical tubing. The problem we encountered here was that there was too much tension, and caused our metal to bend. When we lowered the tension, there was not enough power. We have another possible idea which uses a motor to pull back like a battering ram to release the ball. We are still thinking about our loading mechanism and have not tried any ideas for loading the balls.
These seem like to of the first ideas that come to everyone’s mind when they thought of this competition personally, from experiences in last years FRC Lunacy, the two opposing wheels work the best. One thing you need to remember with this design is compression, if your using the regular wheels as your rollers you don’t have a lot of contact and you may in some cases only contact one wheel. So I suggest wrapping the wheels in a rubber material such as the allowed surgical tubing you could slice it down the middle to increase surface area then lay it on the wheel with a zip tie going through one of the outer holes on the wheel and then attach it that way. also if you have it so the wheels are positioned like the machines that throw footballs so that are horizontal to one another you will receive less distance and power than you would if the wheels were vertical and you stagger them so that you throw the ball up at an angle, preferably 45 degrees.
Another design I’ve seen is to have a long rod spinning as fast as you can get it then once it is up to speed then move the ball in front of it’s path and you can whack the ball with decent forces. Hope this helps
You should at least in theory receive the same power, distance being determined by angle of trajectory. Staggered wheels have a little more contact time and are easier to set an angle with (since you’re shooting upwards it’s a good thing), though with paired wheels you could again theoretically curve / spin the ball into a goal. Never tried it though.
Test a bunch of different flywheel combinations out and see what works best. Maybe more than one wheel per axle could get you better grip.
I believe the simplest solution is to spin two 4-inch wheels on the same shaft, and shoot the ball “over the top” with a guide plate or rails. “Hot Shot” is a derivation of the 2006 FRC game “Aim High” and that was a popular, simple design. You are going to spend on extra gears, though, as you will need to gear up the motor speed quite a lot. Our FTC robot is using a pair of 12-volt motors driving a 27:1 ratio gear train spinning the wheels. This system is too “hot” – shooting a ball both higher and farther than legal, so the students will be slowing it down either in software or different gearing. Comments here on the forum have indicated that 18:1 can work.
One of the keys to shooting a ball with a single wheel launcher is to provide some kind of pressure plate or rails to hold the ball against the wheel at the moment of release. You can achieve this by having two wheels aligned vertically and spinning in opposite directions, but this adds weight and complexity and takes up a lot of room on what is a pretty small robot. I’m sure teams will make it work, but a single wheel (or dual wheels like on a big Ford or Chevy pickup) is easier to engineer and will work just about as well.
I shall give you something we found works amazingly take a tetrix wheel and cut some Kydex sheeting into 1in wide and 4 inches long little paddles ziptie them to a wheel cut a space at one end for the plastic to fit on the wheel. Build a housing for it and it shoots perfectly.
FTC 35’s test of our shooter concept. two DC motors geared up 1:27. One Word: Overkill. 21 ft range. we reduced the ratio to 1:9 and it’s more manageable. Will post more this week
If you want even more length-wise compactness, one of our kids came up with putting the motor mount on standoffs closer to the wheel. It works out very nicely for them. Maybe I’ll get a pic up Tuesday night.
These high gear ratio spinners take a while to get up to speed. So wait till they are at full speed before shooting.
Note: In MD, some teams spun up their motors at the start of the match before Autonomous was actually enabled.
I posted a question on the FTC Q&A regarding the legality of this. As I suspected it’s not legal for a couple of reasons. Only the servos are permitted to be powered before autonomous is run…
