So we’re in quite the dilemma. We have a shooting mechanism, but it doesn’t shoot high enough. We attended a scrimmage and the ball would barely make it into the goal, and that was with the robot pressed up against the tower, it actually missed plenty of times by not even clearing the bottom of the hole.
During this scrimmage we consulted other teams that suggested many great suggestions such as replacing the CIM motor with a NEO motor and attaching a flywheel. We ordered the NEO motor because we were told it was twice as strong as the CIM. When it came in and we installed it, but it was only slightly better, shooting about a foot higher than the CIM.
We have one idea that has shown promise. We ran a quick test by having another Motorized set of wheels behind the ball to give the ball an extra push and reduce rotational energy (we realized the rotation of the ball when being shot is pretty significant). It was significantly more powerful and faster, even with the slow, rigged setup. However, this’ll be wire an undertaking to add the new bar and motor and would like to keep this as a last resort. As for speed, we have a 4:1 gearbox, and a 2:1 gear ratio for the sprockets resulting in a net ratio of 2:1. We considered getting even larger sprockets to reduce this ratio further, but I’m pretty sure that’s not the underlying problem here
What are some other ways that we can increase shooting distance? What has your team done to shoot the ball? Any ideas are welcome, regardless of how hard they would be to implement.
The ball needs compression and also needs longer contact path, getting rid of the gearbox would also help if you can drive it 1:1. A cim is more than enough to get it there.
Yeah, the compression is required in order to create the momentum needed to propel the ball. so some kind of hood, even slight, can increase the force needed to have it shoot. Also if you do keep the gearing, get rid of the gear box. Cims are way strong enough to shoot a ball.
Although not shown in the picture, we had a piece of polycarbonate along the back for compression. As for the 1:1 ratio, we don’t have a connection from the CIM motor shaft to a 1/2 inch hex shaft.
Although not shown in the picture, we had a piece of polycarbonate along the back for compression. As for the 1:1 ratio, we don’t have a connection from the CIM motor shaft to a 1/2 inch hex shaft. You say that the Cims are strong enough but we’re not having my luck with them.
It looks like the wheel is only in contact with the ball for a few inches, which means that the ball doesn’t have much time to accelerate. There isn’t a good way to increase the amount of time the wheel contact the ball in this design though, so the pre-accelerator wheel is the way to go.
The accelerator wheel behind the shooter is a good idea! I would make the surface speed of that wheel about half the surface speed of the shooter wheel.
Those wheels are really compliant, which isn’t necessary because the ball is already plenty compliant on its own. You’re probably losing a lot of energy to friction. Try a harder wheel.
Assuming I understand correctly, you’re gearing the CIMs/NEOs down 4:1 and then up 2:1, for a total reduction of 2:1? Most CIM/NEO shooters I’ve seen have been geared either 1:1 or up 1:1.5. It sounds obvious, buy try spinning the wheel faster? Plenty of teams are shooting 35+ feet using 2 CIMs, NEOs, or 775s, so motor power isn’t your problem. The problem is that you’re gearing the motor down, giving you lots of torque, but not enough speed.
If you can get your hands on some Teflon (or HDPE for a cheaper alternative) you can use it to line the back of your polycarb sheet to lower the friction and increase your shot velocity.
Edit: Use these parts to directly connect a CIM to a 1/2" hex shaft. Total cost is $60.
Are those 2" compliant wheels? That’s a bad choice. You should use rigid wheels with a larger diameter. That will dramatically increase the amount of energy stored in your spinning shooter wheels and ensure that the ball, and not your wheels, are deforming during the shot.
If you can’t put larger wheels, at least put rigid smaller wheels and spin at a 1:1 ratio. Your shaft is pretty long, so you can add extra mass to the shaft. (If you have any steel gears with a 1/2 inch hex bore, that can help).
I attached a picture above as a response. We were able to adjust the curvature by bending the top of the polycarbonate as needed, for the scrimmage we had a slight curve that angled it a little forward, enough to just teach the goal when the robot was right up against the tower
You definitely need to curve it to keep the compression you have, much longer on the ball prior to exit. Plus it will definitely give it more of the trajectory needed to go into the goal.
That should be easy enough with the back horizontal bar you have already in place.
Do you have more of those 6" wheels? you can also swap for those, bigger wheels will give you more speed, and they are rigid. Not ideal but at least may get you closer
We do, but the problem then becomes clearance with the conveyor belt wheels. The compliant wheels have around a 1” clearance with the ones directly below it. If I am to put in the larger wheels I’d have to remachine the side bars that hold it in place to allow for more clearance, and at that point I think it would just be better to add the wheels in the back.
These are a lot of great suggestions, and the parts you linked are extremely useful, I didn’t know there were such things. If it comes to it we’ll definitely order some.
About the compliant wheels, these are the stiffest wheels Andymark sells, it feels like solid rubber, it does not comply with ball at all. Also, why do you suggest the accelerator wheels be half the surface speed of the shooting wheels?
You suggested using Teflon to reduce friction while moving up the conveyor belt. Something we ran into is that the balls rotate while being pulled up by the conveyor belt because one side is stationary (see the earlier picture above for reference). This caused jamming if the balls weren’t spaced about a full ball length in between. We talked to another team who solved the same problem on their robot by adding a moving conveyor belt on the other side to prevent rotation and reduce jamming. The mechanism can be seen loosely implemented in the pictures in the original post, it still hasn’t been motorized. If we add Teflon, won’t that make the ball more likely to rotate?
Thank you for your suggestions, they’re greatly appreciated
