Our team is planning to use 2 775pro motors on 10:1 veraplanetary gearboxes driving 4" orange grip stealth wheels. we found that this should be enough power in our tests, but i wanna hear the communities input?
what are your thoughts? should flywheels be needed?
heres a link to the current “cannon” CAD model: https://a360.co/3beuBDR
A 775 pro tops out at 18,730 rpm +/-10%. On 10:1 gearboxes, that means the wheel will run around 1800 rpm. Not sure if this is enough speed, it really depends on what shot you are trying to hit. For reference, we are making 25 foot shots with ~6000 rpm and 4 inch wheels.
Most of those are not actually topics about shooters in 2020. They just have the words somewhere in the discussion. This is a specific question about 775 pros, which hasn’t been asked.
I believe our team is “shooting” for a distance of about 10 feet or so, around the white line (mind the pun)
its also nice to see a team number so close to our own, only 5 teams between us!
2 or 3 775-Pros on a 2:1 or 3:1, 4 inch wheel.
For the first 2 weeks we were planning on using 2 775pros due to funds and we were able to shoot 38+ feet in a pretty straight arc. This was with 2-2.5" of compression geared 2:1, with two 4 inch green stealth wheels sandwiched between two colsons. We have since spent the money for Neos and shoot harder now but 775pros will easily make a good shooter.
that seems to work great!, our design called for a Parallel shooter with about 2.5 in of compression, we just got the parts and haven’t been able to prototype yet so we’re kinda throwing a dart in the dark and hoping it’ll stick!
We have been using two 775pros 1:1 and it is fine
We are using a 775pro on a 1:3 gear reduction. It can reach the 2 pt with the bumpers against the wall (~2ft distance from shooter to wall) and barely the 3 pt with a 12” bump stop. Our experimental calculations predicted it to be way more powerful, but the ball compression and flywheel made it considerably less efficient in practice. I don’t think a single 1:10 could reach the 2 pt from any distance unless you somehow make your shooter super fine tuned. Adding a second motor like you mentioned probably wouldn’t help, because you arent adding any more RPM, just torque. 1:3 is definitely enough torque in our testing, so adding more wouldn’t contribute to anything.
we are using a parallel shooter and switching to 3:1 with this new knowledge, we may even just do a 1:1 but we need to experiment
At only 10 feet out I think you will be fine. We’re doing a vertical rather than horizontal two wheel shooter but otherwise have a similar design (4" stealth wheels, 2.5" of compression). In testing we were able to score from up close as well as the initiation line using just hand drills direct driving the 1/2" hex shafts, with the drills having a max of ~1800 RPM.
If you have an easily reconfigurable gearbox I would like at dropping the reduction to maybe 5:1 so that you have a little more speed available for range if needed. There’s no need to go crazy fast with 1:1 type gearings if you aren’t trying to score from back by the control panel.
“Less efficient” sounds like the ball is slowing down your shooter wheel on it’s way through, which more torque would help you solve?
(Shooting wheel diameter plays a huge role in all of this - diameter drives surface velocity drives torque requirements. If you’re spinning a 3" wheel, your results make sense - if you’re spinning 4" or 6", there’s definitely room for improvement.)
How carefully have you characterized what’s going on?
We’re at about 80% of our theoretical exit velocity (26ft/s measured* exit velocity out of 33ft/s theoretical on a 66ft/s surface speed** single wheel hooded shooter), and 95 has gotten closer to 110-130% by making their hood more slippery with less wrap.
*Taped a 1 ft grid, filmed shots across it with a smartphone, calculated based on “grid cells crossed per timestamp” - it was way easier than it had any right to be. And we got a real exit angle out of it too, about 6 deg lower than theoretical.
**calculated at 90% of free speed; we have an encoder, so I can see our RPMs drop another ~10% as the ball passes through with open loop control. This is most of our losses; we haven’t gotten closed loop control working yet.
On topic: OP, calculate the desired surface speed of your shooting wheels at ~80% of free speed and you might find the 10:1 is placing you slower than you want. OTOH if you’re doing a parallel wheel shot, you need half the surface speed of the hooded shooters for the same exit velocity, so something slow could be fine.
Make sure your components are rated for 18k RPM before implementing 1:1…
My bad, definitely forgot to include some things.
Our flywheel is two 4” AM stealth wheels right next to each other. There are two “forks” to form a hood.
Im now pretty sure the main speed decrease is due to the backspin created by the hood, so a parallel shooter like OP describes wouldn’t have this issue. Our shooter is currently good enough, so I never investigated further. My mistake.
The reason I say 1:3 is enough torque is that when we used two 775pros on 1:3 reduction we saw no noticeable change in distance to when we used just one 775pro.
775’s should be fine, however in my own experiences 10-1 versa gearboxes break a fair amount and I would recommend a different ratio.
We also have a 9:1 kit in case they do break, although I think our team is going to re look at our ratios for our design, We don’t meet on Sundays but we can check tomorrow morning, I’ll update then how it worked (or didnt) to our teams liking
so just an update: while we never got to put it through competitive stresses, we did test it a whole lot, The shooter was constantly able to shoot 4 balls in quick succession with only a little ball drop (not enough that we were worried). the gearbox reduction seemed to hold up great during testing with very minimal wear, we are still considering the 9:1 over the 10:1 depending on what changes next year
This topic was automatically closed 365 days after the last reply. New replies are no longer allowed.