585A Reveal: KRONOS
Here’s a short little video of the first iteration of our NBN robot, we went with the cam design and we’ve had a lot of success with it.
Nice!
Excellent robot guys! Are you planning on starting a 2nd iteration design?
I really like this, especially the accuracy. Where do you plan to go with this in the future? Any lift ideas?
Edit: 3921 just barely beat me to the question.
Nice robot guys! I like the X drive and how accurate it is
I like the concept with the nodulus gear, I have seen many good robots that use it. The only drawback i see is its firing rate. Any ideas on how to increase that?
More motors with a faster ratio to pull back the launcher? You could also increase the mass of the puncher so less rubberbands are needed to launch a certain distance.
We’re working on version two over christmas break. It’s going to look a lot different. We’re working on a half court shot and we’re going to try and drastically increase the fire rate. Im honestly not sure how we’re gonna get the half court, but we’ll find a way.
We were thinking about actually having two cams, and having one with half the rubber bands
Is there anyway that you could add a piston to change where the ball sits so that the puncher makes less contact with the ball? This would allow for you to make the half court shots with the same cam launcher.
The most effective effective way I’ve seen this done, is to have pneumatic pistons that change where the ball is when it is hit. I’ve seen it work very effectively on team 502’s robot.
Edit: This is the second time today that @3921 has beat me to an answer by 30 seconds.
Got some awesome robots going on so far, pal. Georgia’s game is really firing up this year. BTW, 585A, your team ID really tricked me into thinking that you guys just suddenly came out of absolutely nowhere and started dominating. lol. I know that your school FCHS’s number is really in fact 5854. Great way to establish a new team identity. You guys are awesome as always.
Talking about the very very first robot reveal of NBN ain’t ya. Ummm, that pneumatic vs. 2 motor choice is a thing…
Lol. It’s this sort of thing called passion that gets people to make iterations and make their robots stronger and stronger.
Great robot! I saw some YouTube videos of a competition you were in not long ago. The accuracy looked great, I’ve seems similar bots with a certain lack of accuracy.
Edit: looks like someone already commented on that.
Great robot! Just wondering, what are you using the IME’s for?
We had it set up so that it would rotate the cam one complete rotation before loading the next ball in during autonomous. The ime helped us to make sure that the cam was in the same spot every time. @LEER
Thanks for the reply!
I have a question about the mechanism.
What do you use to stop the linear muncher at the right position when it’s firing forward? Anything we try seems to bend over time. I have had one thing work, but I want to see if you had a better idea.
In my experience the opposite is true. IMO, you want the lightest puncher possible. More puncher mass means more mass to accelerate to the ball velocity. Lightening the puncher on my initial design allowed me to half the number of rubber bands for the same range. F=MA so if your mass is higher it takes more force (rubber bands) to accelerate the same amount. If your puncher is only in contact with the ball for a brief moment the opposite might be true but I’m not sure.
I’ve been using rubber links as impact dampeners on my LP. They get worn out pretty quickly but they do prevent things from bending. I would be interested to see what everyone else has been using.
What if you used rubber bands tightly wound around a medium-ish screw. It would do the same thing as the rubber links, only without destroying said rubber links and only damaging rubber bands instead, it might be more resilient as well.
I did some crude physics about your launcher and based on my derivation I agree with your intuition. It somehow goes like this:
Consider your launching process as three phases:
First, the cam releases the kicker, the rubber bands accelerate the kicker, which is to say give it kinetic energy.
Second, the kicker hits the ball, and in a very short moment, the kicker and the ball moves together. In this moment, complicated things are going on. To keep going with the topic, skip to next paragraph. To mention it, the speed of the kicker at the very moment of impact actually drops, because this is an inelastic collision and we have conservation of momentum, and technically some fixed amount of energy is lost because inelastic collision is always a loss of energy. Then, this tiny loss of velocity is immediately compensated by the rubber band’s acceleration or energy transfer from elastic potential energy to kinetic energy during this process. This process can be nasty to model. Not differential equation nasty, but because rubber band has an “elastic constant” that’s not so much of a constant like that of a spring but rather a function of stretch. But whatever, we don’t care. I’ll probably do some analysis about the short instance of collision later.
Back on track. Third stage is of course when your kicker is stopped by some mechanical point on the robot and the ball flies away to win you the match. To digress again (skip this one at will), technically the kicker being stopped by the hard stopper is also an inelastic collision between the kicker and the robot. Because the robot is so massive, the entire system barely moves after collision or never overcomes the static friction.
Notice that there are two inelastic collisions present in this process. We are interested in the one, right at the exact moment when the kicker touches the ball, between phase one and phase two – let’s define some values.
Kinetic energy of the kicker before collision: E // Supposed to be K but I typed it incorrectly in equations. Sorry
mass of kicker: m1
mass of ball: m2
initial velocity of kicker: vi
final velocity of kicker and ball: vf
The reason we wanna use kinetic energy here is that it is basically impossible to model elastic force or acceleration or kinematics, because of the reasons stated in the long paragraph, elastic constant being ugly. But, we do know that if the charging distance, the distance the kicker accelerates in phase one, is constant, then we know that the kinetic energy of the kicker right before collision with the ball must be converted from the elastic energy that’s released during this distance, which is basically constant given the rubber bands don’t decay. The reason I say converted from rather than equal to is that there’s friction on the rail, and the kinetic energy E is always a little smaller than the elastic energy that’s lost in conversion due to friction. So assuming that you don’t change anything about the rail and coefficient of friction, we can say that right before collision, the kinetic energy of the kicker E is somewhat constant as well.
So let’s do calculation. Finally.
By the calculation of kinetic energy, we can say that this constant E is equal to a half times the mass of the kicker times the square of the kicker’s velocity right before impact, which is:
[attachment:567b8e29c2963]
So we can derive the equation for initial velocity vi:
[attachment:567b8eae3e99a]
So by the great corollary of Newton’s third law we have conservation of momentum before and after this collision:
[attachment:567b8f4935595]
Deriving for the after velocity of the ball, which is really what matters, and substituting in vi, we have:
[attachment:567b8ffdbc561]
Looking at this equation, you see that m1, which is the mass of the kicker, is squared in the denominator and not much so in the numerator inside the square root. This means that as m1 gets bigger, your denominator gets bigger faster, and the entire thing, which is vf, decreases.
So to paraphrase it, the bigger the mass of the kicker, the slower the velocity of the kicker and the ball all together immediately after impact, given that immediately before impact, the kinetic energy of the kicker, regardless of mass, remains constant because rubber bands do not suddenly decay and the rail more or less remains the same friction force.
So in this collision, yes, you want the mass of the kicker to be small to make your system more energy efficient and make the ball fly further with less rubber band.
Further, we can simply look as the second phase, when the kicker and the ball are accelerating together, as a F=ma problem. As you said, in this phase, if there’s a greater overall mass of the ball and the kicker, and the rubber band forces over time are the same, there would be a smaller acceleration in this brief moment of impact.
So, if the mass of the kicker is big, the velocity directly after the impact is smaller, and so is the acceleration after impact. Both make the final velocity given to the ball to be smaller and the system more energy inefficient.
So your intuition and experiment results are proven correct, I think. If you’re fond of this, put it in your engineering notebook and I bet it will appear legit to judges lol.
Horray!