Hi everyone, hoping for some ideas here.
We are running a launcher on our robot with the following setup, but we are not getting much power out of it. We are way short of being able to make it into the speaker from up close.
Top and bottom full length rollers, 1-5/8" diameter each
~1/2" compression on the note
Powered by 1, 775 pro at 1:3 reduction
Using electrical tape as a grip material on our plastic rollers
I think you need a whole lot more RPM.
Many teams are running larger shooter wheels and gearing up (not reducing ) the RPM.
May also need a bit more motor than just 1 775
Look to see what the open alliance and reveal teams are doing to get a baseline.
We were running the 775 pro at 1:1 but it actually performed significantly worse, assuming due to stalling out the motor.
That is likely evidence that you need more motor then.
Maybe a bit less compression too
(I am sure that there are others on here with more knowledge of shooter design than I who will hopefully help you out)
I assume you mean 3:1,or that for every 3 rotation of the motor you get 1 rotation of the output shaft.
So, do a little napkin math. If your system is 85% efficient, what is the roller rpm?
.85 x motor rpm / 3.
Now, you can’t go by the max rpm of the motor. Normally you want to do your calculations around 50% of max motor rpm. (go look at some motor curves to determine why).
So
. 85 *. 5 * max motor rpm / 3.
Now you’ve got a ballpark of where your roller rpm Will be. With that and your roller diameter you can calculate the surface speed of your roller. Import that surface speed into a trajectory calculator to see what your object will do.
Of course that all assumes no slip.
So you likely don’t have the wheel surface speed to fire the objects. In addition, with a small motor and small rollers, you also have little rotational energy in the system so even one lightweight note slows it down significantly.
Polycarbonate rollers have a small moment of inertia (small thin rods in general have next time none along the major axis). Adding a flywheel (large steel gear, 4" higrip wheel, etc) would likely help, especially since this year we only can shoot one at a time. Store some energy ahead of time.
This only works if you can get the flywheel roller up to speed and then feed it into it.
One thing that immediately stands out to me is that the only powered roller is the bottom one, which can only interact with the note for about 2 inches of travel before it loses contact. This is only about 0.4 rotations of the roller. There’s very little time for energy to be transferred from the roller into the note, and there’s no way for the motor to accelerate up to full speed before the note is already long gone
Looks like there is provisions for a belt… Not positive though.
(For side between the gussets)
Yeah, I see the pulley on the top roller but no matching pulley on the gearbox shaft. Could just be the angle of the picture. At the very least, get that top roller powered!
That is an old picture. We now have both top and bottom powered through belts
In my mind the key design feature is that your “staged” ring is NOT in contact with your shooting wheels. You spin up the shooting wheels to speed, then use another motor to feed the ring into the already spinning shooting wheels.
Hopefully this clears up some of the confusion. These are screenshots out of our CAD model.
The note does not touch the shooting wheels until we want it to.
One data point - we are running 3" wheels at about 3500rpm, with a design that allows spin up to target velocity before the note touches. It’s about as low a roller surface speed as I’d recommend, and without doing the math I think you might be below it?
We also have 2x falcon total power. If you can get a second motor you may be well served.
It does look hard to test reducing your compression to try to reduce power consumption requirements, a full 1/2" is kinda high.
Stick a 4" hi grip wheel on where the green is. Or a large steel gear (like 50 - 60Tooth) ideally both sides, but anything is better than nothing. You will likely need a different piece of hex shaft unfortunately. (These flywheels are also available from SDS, but not cheap, would only need one)
Let the flywheel speed up for 2-4 seconds before you feed in the note. Should help a fair bit.
I don’t think surface speed is your problem, a 775 pro is ~18k rpm so through a 3:1 on a 2 inch wheel it should be well over 100 fps surface free speed (aproximated) so slipping and or compression may be at play robbing a lot of energy the t could be accelerating the note.
There is not a lot of torque from a 775 on a 3:1 (relative to a pair of brushless that a lot of teams are running), which have lower free speeds) thus the flywheel recommendation.
Other than electrical tape which we are already using, are there any easy to obtain/easy to add materials we could use to increase our friction with the note?
We are using 2 Falcons on a 1:2 UpDuction shooting around 35% motor power or 4400Rpm with 4inch stealth wheels.
Works beautifully, takes about 1.5 seconds to get up to speed.
We’ve had good luck with this stuff, just keep it clean, and try to make sure that it doesn’t start unwrapping as it shoots the note:
https://www.harborfreight.com/10-ft-x-1-in-self-bonding-super-tape-63949.html
We have a similar shooter, (2" diameter wheels/roller combo), and a mini-cim seems to work well, which spins a bit under 6000 RPM.
What kind of compression are you running?
About 1/4", I believe, though one side is a PVC roller, and the other is thriftybot compliant wheels.
Spacing was a challenge, because our shooting rollers also double as our intake rollers, so it our set-up wasn’t optimized for one or the other, but compromised sp that bother worked.
