Important puncher aspects

So, me and my team have made a slipgear puncher for launching balls at flags, but I am not greatly impressed by the range we were able to get on the puncher.

Note: Our slipgear is a 36 tooth gear with 6 to 7 teeth shaved off (I would be more specific, but I do not have the gear with me, nor the memory capacity) anyways it has at least less than a quarter of the teeth shaved off.

So I want to know what are the most important variables for changing puncher range (launching distance, if you prefer that kind of stuff)

These are the only important variables I was able to think of (this is for our puncher which already has the friction problem pretty solved.)

  1. Rubber band force
  2. draw back distance
  3. Angle (this will be heavily determined by the other variables)
  4. point at which the puncher impacts the ball
  5. Weight of the punching bar (momentum and such, I could be completely wrong on this, but from the small amount of testing we have done, rubber bands don’t care much about how much weight they are pulling unless it is out of x threshold, and as long as it is within x threshold the rubber band pulling speed is rather consistent.)

Any advice on this would be greatly appreciated :slight_smile:

(edited for grammar, I hate anguish class… OOPS I meant English class)


Mostly plagiarized from my own response in this thread:

An elastic collision is a collision where no energy is lost. This type of collision only exists in a physics textbook, but you can make your collision much more elastic by adding some sort of padding to the face of the puncher.

That video does a pretty good job of showing how effective 8044’s elastic friction matt paddle was. Below is a very rough prototype I slapped on my ITZ chassis in June (sorry about the build quality!) but it shows how I adapted the concept to this game.

Check it out here!

In an open area, it launched the ball just over 11 feet.

At the end of the day, you can use the green rubber from 4" tires, you can cut rubber links in half, you can build a rubber band paddle face, you can use friction matt, etc.

To summarize, your mechanism looks great, but your power transfer is probably the source of the issue. If you can fix this, you will see a dramatic improvement.

Good luck!

@Anomaly thanks for the reply, but I have actually already seen this post, and while understand that this might be able to help increase the distance on our puncher, I do not think we will be able to correctly apply this to our puncher with the amount of space we have. I could be wrong but this seems to be something to experiment with after you get the actual punching part down.

Oof, sorry about that!

You will want to put as many rubber bands as possible onto your puncher, angle it at around 45 degrees, try to give the puncher some “follow through” (don’t stop the puncher as soon as it makes contact with the ball), and not worry too much about the weight or pullback distance. A heavier puncher reaches a lower maximum speed but slows down less when it contacts the ball, so the weight shouldn’t matter much within a reasonable range. Also, again within reason, don’t worry much about the pullback distance. If your motors are exerting the same amount of force over the same amount of time, it doesn’t matter if they pull back the puncher a lot of distance with a little force per distance or a little distance with a lot of force per distance. The most important thing is to load up the puncher with as many rubber bands as possible to maximize distance.

Also, you don’t need a fancy rubber band paddle face for a more elastic energy transfer. You can make your collision more elastic by simply zip tying light green rubber from the smooth 4" wheels onto the face of the puncher.

Hope this helps!

@Anomaly thanks for the detailed reply!

This information with be very important to our further testing and designing, and all I really want now is some more input on this to be adequately satisfied with the responses.

Do here’s my opinion and experience:
1/ Add as many elastic bands as you can without overstrressing your motors.(assuming you want maximum power)
2/The draw back distance from the slip gear you described should be good, that’s about 4.5”
3/The most efficient angle will be 45 degrees but anything between 30 and 45 degrees should work well.
4/The point at which the puncher hits the ball is probably the most important part. The puncher should hit the ball about 0.5” before it stops. This might take some tuning though. You can significantly increase your power if you get it right.
5/ The weight of the puncher arm should be about the same weight as the ball. If it is lighter you will not get the maximum power out of your puncher and if it is heavier you will be putting more stress on your robot when you fire. Personally I would say a bit too heavy is fine.

This will depend on the height of the launcher and how far back they’re firing from. Since the question is about range and the puncher won’t be at the target level, 45 degrees won’t be the ideal angle. We’re talking about the range to the flags without specifying shooting from the expansion zone, the targets are probably higher than the puncher. Then you’ll get more range above 45 degrees. Of course, you want to hit the flags as horizontally as possible when the ball arrives, too, so just going for maximum range this way isn’t necessarily what you want.

Yup. I’m glad to see someone suggesting this now. I’ll note a nice way to tune is with a video camera. You look for when the puncher loses contact with the ball. You want to see how far it had to go after initial contact, and you want it to actually stop.

You’re personal preference is actually more correct here. Good instinct/feeling. While the ideal may be the same weight, the collision won’t be truly elastic. The question is just how close to elastic it is. With a little bit of loss, the ideal weight of the puncher is close to but a little heavier than the weight of the ball. Again, video can help a lot. You want the ball to fully stop the puncher.

While it’s true that slowing the puncher down due to weight won’t really matter because the same energy is being put into the puncher from the draw against the rubber bands, one should really worry about the puncher weight. The problem with the puncher not slowing down enough when it hits the ball is that you can end up with a big fraction of the energy left in the puncher after the collision instead of being transferred to the ball. Sure, “within a reasonable range,” qualifies things. But that’s a pretty small range. The puncher should be a little heavier but not a lot heavier than the ball. If it’s noticeably heavier than the ball, you’ll have to start adding a lot of rubber bands to make up for the energy you’re wasting; the motor and battery will have to do more than really necessary, and you’ll put more strain than required on your stopping mechanism.

I am glad to see that the responses are thorough and many of them have the same information which further qualifies the information as fact. This has been a big help.

Thanks for the info everyone.

I’m correcting what I wrote. I remembered the ratio incorrectly. Sorry. You actually want the puncher a bit lighter, not heavier. You want the puncher as much lighter as the fraction of energy you lose. So if you lose 10% of the energy, then you want the puncher to be about 10% lighter than the ball.

But aim for approximately the same weight, and you’ll be in the right ballpark. Once you’re in the right ballpark, small changes won’t matter so much.

Try to minimize friction as much as possible, when we made a puncher for this game we made it out of a c-channel resting on an axel with shaft collars on. This will put your puncher at the right hight and reduce alot of the friction, especially if you lube it up. Message me if you want pictures.