Linear Puncher Design Improvement Discussion

#1

INTRO
The Linear Puncher is going to be a great option for launching balls this year, since it is precise, doesn’t need to warm up to start shooting, and requires less power to shoot per ball, given the low possesion limit. However, the most popular design, the slipgear puncher, can only shoot at one power. Plus, there are many other optimizations that are to be discovered, and I wanted everyone to discuss their ideas here. The goal is to engineer new, different, and useful designs that can be classified in the puncher category. New and exotic ideas are welcome: we are brainstorming here.

I’ll start off with some of my ideas:

Improvement #1: Release the power after desired windup power
The reason why the slipgear puncher is such a good design is that it allows the mechanism to release all of the potential energy that was built up over a long period of time in a short period of time. This is why it is necessary to suddenly isolate (specifically, unmesh the gear teeth) the power delivery from the puncher so it is free to release the energy all at once. However, you can’t change the amount that the mechanism winds up before releasing from shot to shot. A solution is to make a mechanism unmesh the teeth in a user or code controlled fashion, instead of a built in, periodic, and unchanging fashion with the slipgear.
You can accomplish this the same way a transmission does ( example ), by shifting the axle so the teeth don’t mesh anymore. You can activate it with a motor, pneumatics, or even a passive mechanism influenced by another part of the robot, like the lift. Paired with sensors and code, you can make a puncher mechanism that can shoot at any power in a continuous range.

Improvement #2: Make the mechanism more compact
A typical slipgear puncher can get long and bulky easily. I wanted to find ways to make it more compact, due to the nature of this years game. One idea is to scrap the gear racks and wind it back with a rope and winch system. This way, the puncher arm doesn’t stick out the back when the mechanism is being wound. A slipgear can then be used to wind up the winch and release it to shoot (you could use another release mechanism, like the one I suggested above).

I suggested a few improvements to certain problems with the puncher above. But, I know that they aren’t the only ones. So I think it would be really great if we all found awesome ways to overhaul the puncher design.

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#2

I was thinking maybe having a wheel that would be wound up in a certain direction using elastics, that has a c-channel or something attached to it, that would spin back really quickly when released, resulting in the c-channel almost kicking the ball out. would this be an effective puncher? although it isn’t exactly a linear puncher, more of a rotary puncher or something.

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#3

Someone would have to test it but it sounds pretty good because you don’t need a lot of room horizontally, you just need enough room for the arm to swing around. But until someone builds it, we don’t know any other quirks.

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#4

How about having two slip gears on two racks attached to the same slide? Use ratchets so running a motor one way does one potential energy and another way does a different potential energy.

I’d also thought of unmeshing of teeth ideas like what you said, which allow for continuously variable potential energy.

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#5

I was thinking that you could adjust the height of the shot by changing the angle of a ramp in front of the puncher, probably using a worm gear. Since the turning point balls are plastic they should change trajectory fairly consistently when they hit the ramp. I’ll have to do further testing with this idea once I get my hands on the game elements.

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#6

Yes, I think that’s a much easier solution. My original ideas headed in that direction, too. But I do like that people are trying to think of other ways to adjust slip gear punchers.

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#7

I am not sure if I follow that well. Can you explain it a bit differently?

That is such a great idea! That would make designing the intake easier, and you won’t have to tilt the whole entire mechanism to aim.

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#8

Puncher

I don’t have many photos of the puncher design we used on the 400 series in NBN, but I’m happy to share what we have and what we learned. We had three different puncher robots throughout the season, X was a Flywheel-Puncher Hybrid robot for about a month before the Winter rebuild, 400Z (My little brother) adapted the original design to his middle school robot and added a variable shot distance capability as it was a puncher-only bot, and then 400S took the original X puncher and built their robot around hoarding and long-distance shooting.

In terms of variable distance, you really need to decide first what you are willing to dedicate to the shooter. If you are okay to have two separate systems, 400Z was very successful by putting their elastic mount on a linear slider with a rack and pinion, which allowed the elastic to be stretched to different lengths to change shot distance without involving any of the slip gear mechanism. If you are dedicating a motor to that, you could also just add an angle adjuster as has been previously mentioned. If you are set on some type of passive distance change or having it tied into the shooter motor, I’d have to put some more thought into it.

The one thing I can probably contribute to the most would be our custom slider, which was present on all of the 400 punchers that year. It is somewhat visible in the photos and I believe its already been reproduced somewhere on VF from when i posted it in discord last week. The actual plunger/punchy-thing (whatever you want to call it lmao) is just a 1x3x1 c channel with a larger strip of lexan on the casing below it to slide on. Spacers were added on either side and on top to contain it. The slider mechanism is really quite simple. We also might have had lexan strips on top of the plunger that the rollers slid on, but those were less important. When working with Punchers and custom sliders, I think its more helpful to think of it as a contained projectile rather than a tight slider mechanism you might find on an elevator lift or something of the sort. The slider only needs to keep the plunger inside the mechanism and lined up with the gears, nothing more. It doesn’t need to be tight or heavy duty, we took a very minimalist approach.

Punchers are a solid approach to Turning Point imo, flywheels were very dominant in NBN but having worked with the Discobots, that was mostly because of the skills challenge. In match play, Linear Punchers were just as capable at long-range as 99% of flywheels and were much easier to make reliable.

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#9

An idea that was discussed by our teams was to have 1 motor run the linear puncher as well as adjusting the angle. This could be done using 2 different slip gears and two different one way ratcheting gears. When the motor is turning one direction it runs the puncher. When the motor turns the opposite direction it operates the gear that adjusts the angle of the puncher. With the use of a potentiometer or some sort of shaft encoder, you could even have multiple pre-set angles for the the puncher while the puncher has just one very fast speed at which it hits the balls.

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#10

If the motor can only rotate in one direction when changing the angle of the puncher, my first thought was something like this , but a second slip gear would also accomplish that. Its a very valid strategy and it wouldn’t be all that hard, just complex. With the vision sensor coming out and the green markings on all the flags, I think a turret and auto-aiming might be a lot more common this year, so I’d be interested to see if all this could be produced compactly enough to work with that strategy as well. Then again, I’m thinking in VexU terms, so maybe there aren’t motors to spare for my turret dreams in high school ;p .

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#11

Yes, this would be much easier to do with unlimited motors (VexU). The slider crank mechanism would be a valid approach, but I do think the second slip gear would be easier and possibly more compact. The bottom line is that with only 8 motors, you will want to get all you can out of each on. If you can have one motor that both shoots and aims, that would mean a lot.

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#12

Would you require 2 ratchets in order to perform one function but not the other? If not neccesary and you are able to use just 1 ratchet, how would you make it possible to perform one action but not the other and vise versa?

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#13

You could swap between two different slip gears on the same rack with a single motor direction. Probably more a pain than it’s worth, though. Each time the rack shoots forward, you have it trigger something to throw the gears back and forth. If you can make sure they’re stopped on a slip section (which is most easily done if you set up appropriate ratios and have them both rotating at the same time so you never have to disengage one from the motor) they’ll slide easily.

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#14

Well, there is a very simple way how to make a single motor, single slip-gear puncher with variable enery output. Try designing one, it might hit you (sorry, I am bad with puns) now that you know it is possible (I don’t want to spoil the fun for those that like puzzles by revealing the full design).

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#15

Our team tried to use a rack and pinion to move the gear from the puncher, but we could not get it to shoot the ball that far. Plus the gear teeth could get stripped if the gear is not moved away from the puncher fast enough.

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