Re: Prototype Small Wheeled Shooter
 

Unfortunately, 2:1 is not an easy off-the-shelf gear ratio to come by. These small wheel shooters are super easy to build with a vex planetary and just about any kit motor. Available reductions are 1:1, 3:1, 4:1, 5:1, 10:1 and any combination of those you would like. You can still adjust the tangential velocity of the wheels by changing wheel size (2", 3", 4", 6" are easy from Banebots) or input motor. Bag motor spins at 14k rpm, AM motor at 16k, and Banebots 550 at around 19k Our best setup at the moment is a 5:1 Bag, 3:1 AM, and 1:1 Bag.

Just looking at the math, it's obvious we have a lot of slipping on the last wheel. By my calculations the tangential velocity of a 3" wheel on a 1:1 Bag motor is roughly 175 ft/sec. If a frisbee had no slippage when contacting a wheel in this type of shooter, I would expect it to leave at about 85 ft/second! This is waaay higher than what we are seeing, so I have no doubt that there is a lot of slipping going on.

Something interesting to note: we put a new frisbee into our two wheeled shooter (3:1 Bag, 1:1 Bag) and analyzed the marks left by the shooter wheels afterwards. It looked to me like the 3:1 wheel had more slippage than the 1:1 wheel, since the 3:1 had a shorter 'burn' mark left on the frisbee and shorter overall contact period.

Also interesting to note: given the frisbee compression and wheel spacing involved, the frisbee contacts two adjacent shooting wheels for a substantial amount of time. I'm not sure exactly how they all interact at this point...


TL;DR: I gave up on calculating this stuff, we're just going to go with quantitative results! Also, I need a better high speed camera.

Re: Prototype Small Wheeled Shooter
 

Trying slowing both motors down, to get faster exit speed. Easy enough to do: run them with motor controllers instead of straight off a battery.

Re: Prototype Small Wheeled Shooter
 

We will try slowing down the last motor and then experiment with the others as well. Thanks!

Re: Prototype Small Wheeled Shooter
 

You can also try speeding up the second wheel by putting in a BB RS-550. Or for prototyping purposes, one of the super-powered FP 801-0673 motors from last year. We prototyped with a FP and were getting some pretty impressive velocity. Mind you, we also have a larger wheel spacing, which means less time with the 'bee contacting two wheels.

Re: Prototype Small Wheeled Shooter
 

Better yet:

a) remove wheels 2 and 3, and adjust the speed of wheel 1 until you get the fastest exit speed (call it s1), then

b) keeping wheel 1 at speed s1, add wheel 2 and adjust its speed until you get the fastest exit speed (call it s2), then

c) keeping wheels 1 and 2 at speeds s1 and s2, add wheel 3 and adjust its speed until you get the fastest exit speed.

Re: Prototype Small Wheeled Shooter
 

Most logical process for dialing in the shooter that I have seen yet.

Re: Prototype Small Wheeled Shooter
 

This is where a Chronograph will come in really handy!
Whether you use of a single sensor or dual sensor doesn't matter, either will take out the subjectivity of the measurement and just give you solid measurements.

Re: Prototype Small Wheeled Shooter
 

While you are talking to them ask them about this law from Texas.....

If two trains going in opposite directions on the same track meet each other, one can't move until the other does.

:p

Thanks for the clarification on the FIRST rule ...

Re: Prototype Small Wheeled Shooter
 

Thanks to all have posted to this thread. We tested our version last night.

We had been running two CIMs at 1:1 with 6" wheels with mediocre results. We could score in the high goal but only if we were close to the wall.

Last night we ran the 2-7/8" Bane Bot wheels. Our set up is BB550 motors at a 19:46 reduction. Two wheels 4" apart. The disk is loaded at about 12" off the floor with an angle of about 40 degrees. Running the motors at 50% shot the disks over the top of the high goal from about 17' away. Higher speeds did not change the performance much.

We started with 10-3/4" spacing but were not happy so we added a piece of 1/4" poycarbonate. Current spacing is 10-1/2". No additional friction material.

Re: Prototype Small Wheeled Shooter
 

You forgot the other critical variable. What compression are you running?

Re: Prototype Small Wheeled Shooter
 

Thanks for all the discussion!

New shooter last night. Slow wheel is a CIM with a 2.5" soft neoprene wheel (1:1). Fast wheel is a mini-CIM with a 4" soft neoprene wheel (1:1). Compression and the spacing between the wheels are not optimized yet. We've ordered a taller 4" wheel and installing a top shield as the frisbee is definitely rising as it goes through. While we don't have the rotational speed that some teams are getting we managed a 53" distance (parallel to the floor start) before optimization.

Re: Prototype Small Wheeled Shooter
 

Here's some video of us testing our own variation of this idea. I'm not yet thrilled with how it's working out. We're not getting a lot of distance out of it.

http://www.youtube.com/watch?v=FR7ppSZ7VS0

The video shows a few different tests spliced together. I didn't edit out anything bad -- including language, thus the dumb music :) -- so what you see is what we saw.

In each subsequent test, we're dialing back power to the wheels.

The details:
Input wheel -- Banebots RS550 motor through a 3:1 Versaplanetary transmission driving 2 .8" thick, green Banebots wheels.
Output wheel -- BAG Motor through a 1:1 Versaplanetary transmission driving 4 .4" thick, orange Banebots wheels.
Bottom surface -- 1/4" delrin sheet
Wall -- 1x1x.063" Aluminum tube with 1" wide urethane flat belting double-sided taped to the inside face.
Compression -- 3/4" compression, I believe.
Loader -- 6" stroke, 3/4" bore pneumatic cylinder
Angle -- 30 degrees
Exit Height -- 22"

Any thoughts?

Re: Prototype Small Wheeled Shooter
 

We found the spacing to be very sensitive, we see best results at 10 and 3/8" with the banebot wheels.

Re: Prototype Small Wheeled Shooter
 

Is anyone seeing any statistical/quantifiable difference between results when you compare the different banebot wheels (orange/green/blue)?

Re: Prototype Small Wheeled Shooter
 

I don't have the data but we were measuring better distances with the green wheels but they were getting damaged by the discs to quickly for us. The blue wheels weren't that of a much difference in distance.

Re: Prototype Small Wheeled Shooter
 

thanks for the information!
One other thing.
Do you find that the Versaplanetary gear boxes get hot while you are doing your shooting testing?

We set up two tonight and it seemed that they were pretty hot after a relatively short time.

thanks

Re: Prototype Small Wheeled Shooter
 

We're running BAG motors through VERSAPlanetary gearboxes at 3:1 entry and 1:1 exit, both driving 2.875" blue banebot wheels off a .5" hex shaft. The 3:1 doesn't change temperature too terribly. The 1:1 gets fairly warm rather quickly. Not sure if it's something to be concerned about or not right now. Still have yet to put our shooter prototype through it's paces. Will do extensive testing tomorrow and Thursday.

Re: Prototype Small Wheeled Shooter
 

We set up two to run on the BB 550 motors (a 5:1 and a 1:1) and both seemed to get hot very quickly. We followed the directions on attaching the motors ... but it didn't feel quite right for either one... a little too much binding when we clamped down the screws...

We followed the directions on how to assemble from the website..

We are doing the same thing you are with the same size banebot wheels and the hex shafts... we will try more tomorrow night.
thanks for the help!!

Re: Prototype Small Wheeled Shooter
 

Bob,
It might also have to do with how the gearboxes were lubricated. Too much grease can cause of a lot of internal resistance and, of course, too little isn't a pretty sight unless you like metal dust. We use about a pea sized amount of grease per stage, either Superlube or Lithium is what we use but everyone has their favorite. Ours get warm but certainly not crazy hot.

Re: Prototype Small Wheeled Shooter
 

Our 1:1 boxes get uncomfortably hot after about 30 seconds or so. We definitely won't be running them full time.

Re: Prototype Small Wheeled Shooter
 

I have found them to get warm but never as hot as our drive CIMs or anything like that. I think most of the 1:1 heat is from the bearings but I have no way to know that.

One of the reasons we are choosing to run BAG motors is so far they have taken all the heat we have thrown at them, which is mostly being stalled several times in a row from failed collector tests. We ran BB550 on our collector last year and stalled it once for 20 secs or so and smoked the motor. The BAGs are expensive but we don't have to replace it this competition season it'll be worth it.

I'm interested to see how the bearings in the VPs hold up over the course of the season. We'll have spares gearboxes on hand but hopefully won't have to use them.

Re: Prototype Small Wheeled Shooter
 

Bob, we're running the same ratios as you using the AM 9015 motors. We had some binding issues initially too. I emailed Vex and got an immediate reply from Paul Copioli with the very helpful technique to loosen the mounting bolts slightly and run the motor. When the motor and gearbox sound like they're running smoothly tighten the screws. That technique solved our binding issues.

By the way, if anyone else is using a AM 9015 motor from this year's KOP with the VerasPlanetary you'll probably need to use the 1/4" spacers with any gear ratio as the knurled length of the shaft is shorter than an AM 9015 motor from last year. Paul said they designed the AM 9015 collar to grip the knurling, but with the shorter knurled length it's trying to grip an un-knurled portion of the shaft. The 1/4" spacers put the knurling in the collar.

A very big mahalo to Team Spectrum for sharing their design! We were already headed down the same path, but learning about the Banebots wheels with the VersaPlanetary gearboxes sure got us to our final design a lot quicker.

In our latest round of testing we shot some upside down discs successfully into the middle and high goals from up close using the same wheels speeds as a right-side up disc without a cover. Upside down shooting was more sensitive to feeding though. If it wasn't fed quite right the disc would pop up from the first wheel. We'll probably add a cover to take care of this issue.

Re: Prototype Small Wheeled Shooter
 

Bob, when I set up a BB 550 (motor was purchased two years) in a 10:1 VP, I had trouble getting the gearbox to spin while powered. I could turn the shaft by hand (with a wheel on it - slightly difficult), but when I put it on a power supply, the shaft wouldn't spin at all and the current spiked rather quickly. I did not find this problem with the BAG motor installed 1:1. After much testing individual components, I eventually spaced the BB 550 motor plate from the gearbox with thin washers. This appeared to relieve some pressure between the motor (either the shaft or the face of the motor) and the gearbox. I notified VEX support and Paul sent me two things to try:

"1. As you suspect, the RS-550 shaft that you have may be a bit longer than we have tested and the end of the shaft may be pressing against the gear. To test this, please remove the input sun gear while the motor is installed to see if it sticks into the same space the gear should be.

2. The clamping hub and bolts are fighting each other. In order to get around this, try only using to bolts to mount the motor plate and tighten them after you have tightened the coupler."


I did not try either though, because my team had decided to go with a double BAG motor setup. Maybe you're seeing something similar?

Re: Prototype Small Wheeled Shooter
 

The versaplanetary gearboxes come "fully assembled". Should we be opening them up and adding grease?

Re: Prototype Small Wheeled Shooter
 

Yes, we recommend a light coating of white lithium grease to ensure longevity.

Re: Prototype Small Wheeled Shooter
 

I just put our motors and gearboxes through an "intensive" test. 12 volts straight from a battery to the 3:1 gearbox and the 1:1 gearbox (Both driving BAG motors.) for 1 minute 25 seconds. 3:1 Gearbox is noticeably warmer than the 1:1 gearbox. BAG Motors are warm but nothing to be concerned of, if their construction mimics that of a CIM. Do not have access to any temperature sensing probes.

*3:1 gearbox was freshly greased with white lithium grease (NLGI #2). 1:1 gearbox has not been greased yet outside of stock greasing.

Re: Prototype Small Wheeled Shooter
 

All,

There are several items that contribute to heat in a VersaPlanetary gearbox. The #1 thing that is different than other gearboxes you are used to is the thin wall of the ring gear section. The ring gear is aluminum and very thin so it conducts the heat very quickly and gets hot quickly. In addition, the thermal mass of the aluminum is less than the steel gears and bearings so it will get hotter much faster than the internal steel gears.

Also, the output shaft is also aluminum to that thing gets pretty hot, too.

The BAG motor has the same internal construction as a CIM motor and that is why it is able to dissipate heat in a similar way. It does not rely on convection cooling like a RS550, RS775, or AM-9015 so it is happy to remain at an elevated temperature. However, the aluminum VersaPlanetary case is sucking a lot of heat from the motors and acting as a heat sink. The VersaPlanetary housing gets hot, but it is nothing to be concerned about.

The bearing speed rating is over 20,000 RPM so this application should not over task the bearings.

In short, the gearbox getting hot is primarily related to the thin aluminum case and is not a concern.

Paul

Re: Prototype Small Wheeled Shooter
 

Thanks for clearing that up Paul.

Re: Prototype Small Wheeled Shooter
 

Here is our final shooter design before mounting it on the robot.
Before the hood was added today, we were able to consistently shoot at 31 ft./sec. We will optimize it now that the actual assembly is complete. We hope to squeeze another 5 Ft./sec out of it.

http://www.youtube.com/watch?v=cpHcM...ature=youtu.be

Re: Prototype Small Wheeled Shooter
 

Awesome video, I like the feeder, very simple. What are the specs? 3:1 and 1:1? Compression? Wheel Separation?

Re: Prototype Small Wheeled Shooter
 

Here is our shooter as of Monday. Standard stuff, 1:1, 3:1, bag motors 'bout 3/8 compression right now with a rubber strip on opposite side.

We designed it to use two or three wheels but found the third wheel added little for the amount of complication it added. We also tried 3" Colsons but switched back to the Bane Bots. You never know, durability testing may make the Colsons more attractive.

Sorry for the shaky cell phone video.

Big thanks to the folks at 3847 and everyone else who shared on this thread.

Re: Prototype Small Wheeled Shooter
 

Yes, 3:1 and 1:1. Wheel separation is approximately .25". Currently the compression is around .5", but we will be optimizing that using a chronograph today, getting actual numbers instead of just observation.
Although, even if we leave it exactly where it is, it is already acceptable for our game play strategy.

Re: Prototype Small Wheeled Shooter
 

Question for those of you running a close spacing between the wheels do you notice any issues with discs being in contact with both? Currently our wheels are approximately 1.5" apart and I'm wondering if it its worth re-manufacturing the attachment at this point.

Same as most people: 1:1 and 3:1 Bag motors, orange BB wheels, and using a piece of of roughtop on the fence with about .25" compression.

Re: Prototype Small Wheeled Shooter
 

I'm thinking the same thing. There's currently, on ours, something like 2.5 nineteen our wheels, as we were discovering significant wear on our 1:1 wheel. Same setup as others - 3:1 and 1:1 bag motors, 2.87 blue banebots wheels, 9/16th compression, gaffers tape on the compression wall, AND A COVER over the wheel (picture to be posted in an hour) and were getting absurdly less distance than anyone else

Re: Prototype Small Wheeled Shooter
 

We aren't running tiny wheels but smaller than most, and it was my engineering intuition that says having the frisbee touching both wheels has to be detrimental to overall performance as that pretty much necessitates one wheel slipping. Ours is designed so this isn't possible and the shooter does seem to perform quite well with minimal wear on the green banebots wheels.

Additionally, roughtop as a backstop is probably not the best material. Roughtop actually has pretty poor friction on plastics

Re: Prototype Small Wheeled Shooter
 

This seems like it would be true. The initial prototype design came about for the design requirement of being able to mount our shooter/collector on a lift so it had to be insanely small and light. I'm glad other teams have found a use for it but our specs were never meant to be taken as optimal for all situations. In fact we only ever plan to shoot from behind the pyramid as our max distance, most of our shots should only travel about 4 feet total before entering the goal.

Re: Prototype Small Wheeled Shooter
 

Thank you very much about this post, we use a small wheeled shooter too now, and it can shoot up to 40 fit ( 2 bag cims, no gears )!
you helped us alot! :)

Re: Prototype Small Wheeled Shooter
 

What compression, wheels, and wheel separation are you using?

Re: Prototype Small Wheeled Shooter
 

every wheel uses one bag motor with no gear, and i dont realy sure about the wheels, i never saw any wheels like them, they made of some kind of spong .. here's a picture we got in fb, it doesnt explain alot, but still..
http://www.facebook.com/photo.php?fb...type=1&theater

Re: Prototype Small Wheeled Shooter
 

Something or another like this? Our team used a similar product back in 2010 for our ball magnet. Worked great.

Re: Prototype Small Wheeled Shooter
 

Because of the buggy BAG motor problem, we have switched our motors over to a BB775 at 3:1 for the first shooter, and a AM-9012 1:1 for the second wheel. The first wheel is at 90% power while the second is at 85%.

We are shooting the high goal from the back of the pyramid with ease so we are pleased with the result.

We also made the compression on the first wheel about 3/16 less than the first wheel to aid in our ground loading. This change did not effect distance at all.

Re: Prototype Small Wheeled Shooter
 

While this post is regarding using the VersaPlanetaries with a pneumatic wheel, I figured I would post it here after all the other postings about powering shooter wheels off of the VersaPlanetary.

My team's competition robot is currently running a two 8" pneumatic wheel linear shooter directly driven by CIM motors that were attached to a machined step shaft via a coupling. We found this setup to cause extreme vibrations and our small couplings would often come loose.

I believed that these vibrations (which I thought had to do with the lack of concentricity with our setup) also caused y-variability with our shooter so on our practice robot we are trying to run the 8" pneumatic wheels directly off of the 3:1 VersaPlanetary with an RS-550 on each. Looking at the motor curves, I figured that we could get close to the ~4500 r/min that we had with the CIM with this setup. Perhaps I am wrong.

When we tried powering the VersaPlanetary (with the Pneumatic wheel attached via 1/2" shaft and 1/8" keyway) using an FRC battery, the wheel would quickly get up to speed however after about 10 seconds a burning smell developed and we could see smoke coming out of the gearbox, not the motor.

We applied white-lithium grease moderately and did our best to follow the instructions for assembling the gearbox and motor.

From those more experienced than I, should I even be trying to direct drive a pneumatic wheel with the VersaPlanetary at 3:1 with the 550? Do you even think I could get the wheel up to 5000 r/min?

On to the smoke problem- should I try spacing out the motor mounting plate? It is not too hard to spin the output shaft by hand however it is pretty jerky. We inspected the gearbox afterwards and it appeared fine. Should we just try reassembling the motor onto the gearbox?

Also, it heated up quickly when powered on.

Hopefully Paul Copioli will see this and offer some advice.

Thanks!

Re: Prototype Small Wheeled Shooter
 

Andrew,

Don't be so sure that the smoke isn't coming from the motor. The VP is designed to have vents to the motor form the motor mounting plate. Smoke form the motor could definitely look like it is coming from the VP.

With that said, my team is running 2 VPs on our shooter with 8" pneumatic tires and have seen no such smoke. We are using RS775 motors with 5:1 and 3:1 There really isn't anything inside the VP that would smoke very long before seizing.

I suggest you look at the current the motor is drawing while just attached to the VP. Some people have reported problems getting the RS550 motor lined up properly while installing into the gearbox. That could be causing excessive loading on the motor causing it to overheat.

Paul

Re: Prototype Small Wheeled Shooter
 

When we were first running our shooter with 3:1 Versaplanetaries with BAG motors, the gearboxes would get very hot, while the motor (and the wires to the motor) were cool. We tweaked the spacing of the sun gear on the output shaft just a little, and that solved the problem.