We currently have 2 methods in mind, one is to have a adjustable hood with a single flywheel, to obtain different angles at different ranges, other are 2 flywheels with different rpms as per different distances, so would you suggest any one of them or any other methods?
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Speaking in a lot of generalities, depending on what you are shooting and how far, and into what kind of goal, you will probably get a larger variety of shots using a hood. If there are just a few similar places you are shooting from, you can get away with flywheels. There will be some variation in your shots, but with only one launch angle you are limiting yourself.
With a hood, you can change the release angle, and if necessary the speed of the flywheel to get a much more varied shot. All depends on what your goals are.
Something else to consider, two flywheels is probably mechanically simpler than a hood. Just pointing that out. Good luck!
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Casual survey of teams I’ve seen in the past few years, the adjustable hood seems to be preferred over a speed differential in two flywheels. I’m not 100% sure why to be honest, though I assume it is at least slightly tied to the specifics of the gamepiece and the goal.
Both will involve similar controls challenges:
- Creating the mapping of mechanism setpoints (speed/angle) based on pose relative to the goal
- Setting up closed-loop controllers to achieve the setpoint in a timely manner.
- Coordinating the injection of the ball into the launcher - this needs to wait until the closed loop controllers have actually achieved the correct setpoint.
- Managing unique challenges related to shooting from arbitrary locations, or arbitrary robot velocity.
Take a look at the FRC 20212 game Rebound Rumble
There are a bunch of considerations though.
How squishy are your balls - are we talking about a foam ball or an inflated basketball?
How high is the shot / how far away are you from the basket. In general, a single flywheel will make the ball roll along the hood so your ejection speed is lower than if you had two flywheels going in opposite directions (where the upper wheel imparts some translational velocity.
How high can your mechanism be? If you’re trying to fit under a color wheel like in 2020, then a hood can have a lower profile than a second flywheel. If you make your flywheels smaller in diameter to reduce the height, you’re reducing the moment of inertia of the system - the whole reason to use a flywheel
I guess I’m saying the horrible saying of “it depends”. There are trade-offs with either path and the one you chose is based on the requirements and restrictions you have. There isn’t one “better” way to do it
Edit: I forgot one other method - the catapult arm. The flywheel methods rely on compressing the ball between surfaces (the wheel and the hood or between two wheels). If your game pieces vary in stiffness (like old, used balls compared to new ones or balls from different vendors) then one way to mitigate this is to shoot without having to compress the ball. You push on it from the back like a catapult. As above, there are trade-offs made for different design choices, in some cases one is optimal and in others it is not
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If you take a look at the specifics in implementation, hooded shooters are just easier to do well and more reliable at achieving the ability to shoot exactly how you want it do. Usually, we see flywheel adjustment when teams don’t want to add the complexity of making an adjustable hood, but then they run back into the same complexity because differential speeds are just harder to work with.
- Extremely large range of adjustment
- Easy to adjust, a hooded shooter is easy to model, vs differential flywheel where the change in spin adds another variable that’s extremely hard to model
- Extremely long contact distances are easy with hooded shooter
- Reliable adjustment, the nature of a hood gear reduction reduced the effects of backlash, while making it hard to backdrive the hood under power.
- Easy to control, you can just tune a PI controller in a few minutes and have near-perfect control because the system has a lot of natural damping and control authority
- Lower shot velocity without extra gearing, high exit velocity is not nessesarily better
These advantages outweight the benefits of not having to build a hood, as you just lose a lot of control and the ability to model the system easily when running double flywheel.
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Less consistency in dual wheel designs as the gamepices wear, the hooded variants are less prone to slippage completely changing the shot.
The acceleration is a little less violent /more forgiving in hooded designs. This matters a lot when compression isn’t turned up to 11.
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Perhaps less power draw too?
Its negligible. A vast majority of the power draw from shooters that care about power draw comes from spinning them up to speed in a the first place, which is primarily a function of how much inertia you have. By not putting on extra flywheel mass, the power draw of either configuration is negligibly because the system spins up in milliseconds, so then the power draw comes down to which setup has more bearings that are misaligned, which doesn’t really matter.
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If the current draw of your shooter is too high, it means something is probably not running right.
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just to add to this:
vibration is a loss as well: (high melt) hot glue can be one heck of convenient way to balance stuff (looking at you highgrip wheels as a flywheels… nice easy to access hub to balance primary and secondary vibrations)
Having a flywheel you can spin up to 6krpm and it’s barely noticeable is a fun experience.
e.g.
Not hard to make one of these if you really wanted to with the little low friction bearings for fidget spinners, just need to be careful to keep things axially aligned
The key really is the type of game object and the goal. The last few years offer a great set of examples.
In 2020/21, the Infinite Recharge game was ideal for hood shooters. The balls were relatively soft, the goal mouth was horizontal, and the back of the goal presented surfaces to bounce off of. All good for a hood shooter and the backspin that tends to produce. Rapid React in 2022 was very different. With a larger and less compressible game piece and a cone-shaped vertical goal, the last thing you wanted was backspin, as too many if us discovered the hard way. Some stuck with hood shooters and used methods to reduce the backspin, but that complicates the shooter’s construction. Most teams came around to dual flywheel shooters, which have very little or no backspin. Most teams that did this had no real problems with hitting the goal from anywhere on the field. This year, Crescendo had an odd game piece and an horizontal/overhanging goal. While the goal shape might suggest that backspin would be good if the game piece were a ball, that just wasn’t possible with the Notes. Instead, you saw a lot of two or four flywheel shooters, the second essentially a split dual flywheel. That did give a chance to introduce spin (as we did with our shooter) by having a slight rpm difference between the left and right sets of flywheels and getting a flat spin to increase flight stability.
Honestly, having had our team build both kinds, I’ll say there really isn’t much practical difference between them just as shooters. The real differences you need to pay attention to are the goal and game piece. That’s what will tell you what kind of shooter you want.
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We have a basketball going into a basket, pretty simple format, we want to shoot into it once, then we will have a break, and we want to shoot while moving, I just have these two methods in mind, any other possibilities are also welcomed.
how can we use hot glue for alignment?
It was more of a tangetial comment on flywheel balance than relevant to your particular situation I guess…
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Is this for Robocon 2025, by any chance?
I am absolutely new in mechanical field, like in robotics aspects, so just trying to get my head around things, like everything, from sensors, controllers, drives, algos, all in all, so nothing specific. But would a specific event change your responses?
Almost every team I saw in CA ran single flywheel hooded shooters. I think maybe some teams had a reversed or passive, smaller wheel on the top of their hoods, but I think that could hardly be considered a flywheel. I believe what the OP was saying about dual flywheels could be considered something like a football shooter, with two sideways flywheels to impart spin on the balls.
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Most teams ran a top roller of some form, but the top roller was still usually on an adjustable hood for teams that had distance adjustment. Sometimes they were full sizes, sometimes they were smaller and geared up,
FRC Rapid React was essentially shooting balls into a large basket. The key to shooting from anywhere is to utilize both an adjustable hood and a flywheel with adjustable speed. If you have enough flywheel speed to give the ball the velocity to make a long shot at an appropriate launch angle, keeping that same speed with a short shot would mean shooting a shot with a VERY high arc. To produce optimal arcs for a range of distances to the basket you need control of both angle and velocity. Having two flywheels to impart a controlled amount of backspin is also important. Very high rates of backspin from one flywheel impart a Magnus effect on the flight trajectory that makes the ball sail more that you might like. A limited amount of backspin helps stabilize flight without much or any negative impact on trajectory.
so is 2 flywheel better than a flywheel and a hood? for shooting a standard ball into a standard basket, while moving