Balancing a Pneumatic wheel
 

We've got 2 6" Andymark pneumatic wheels on our shooter, and we were having some major issues with vibration due to the air spigot throwing off the weight distribution. We removed the innertubes entirely and filled them with bubble wrap which helped some, but it still vibrates badly because the tire doesn't seat particularly well without inflation. For teams that are using pneumatic shooter wheels, what did you do to balance them?

Also, did anyone find a different type of wheel to be superior?

Re: Balancing a Pneumatic wheel
 

We are using a single 8" pneumatic wheel and the team taped a few small nuts/bolts into the spoke opposite of the filler tube. Works fine.

We were running the tire without an innertube but discovered it flattened out too much and it was difficult to get a good grip on the disk.

Re: Balancing a Pneumatic wheel
 

We used 1/4 oz tire weights from Harbor Freight - they're adhesive backed and worked like a charm!

Re: Balancing a Pneumatic wheel
 

Two long bolts on the holes opposite of the air nozzle, with washers stacked on them. Our sweet spot was 9 washers on each bolt, give or take a few for others depending on bolts/nuts and such.

Am I the only one that watches lunch with Andy?

Re: Balancing a Pneumatic wheel
 

Step 1: Take the inner-tube out.
Step 2: Fill the tire with pool noodle which has been cut in half.
Step 3: Thank your friendly M'Aiken Magic mentor from South Carolina.
Works like a champ, promise.

Re: Balancing a Pneumatic wheel
 

Remind me to wear my kevlar vest to any event you're at.

Seriously, don't forget to take into account that these wheels are running at speeds they were NOT designed for. Make sure anything you attach to them can handle the speeds.

Re: Balancing a Pneumatic wheel
 

Do what we did: Just take the tubing out! Literally. Just the hub and the rubber tire. No inner tube. It works beautifully.

Re: Balancing a Pneumatic wheel
 

Well we've probably run the shooter wheels, in total, for over 2 hours of run-time and nothing has ever gone wrong (this is actually an insane amount of time considering robots are typically not run for very long times).

When you couple the strong adhesive and with the centripetal force of the wheel, there's no way these puppies will fly off.

Re: Balancing a Pneumatic wheel
 

I know team 3130 removed the whole inner tube and replaced it with pool noodle and had great success with it.

Re: Balancing a Pneumatic wheel
 

I think if the weights will work on sport bikes that they will be fine on a robot wheel :) a 2006 yzf r6 has a top engine rpm of around 21,000RPM. The sixth gear reduction ratio is 1.074. Dividing 21,000RPM/1.074 will produce the RPM of the rear wheel. This comes out to be 19,553RPM. I don't think the shooter wheel is hitting that speed lol Now i realize you may do the math and realize nobody ever drives that fast but when the bike is doing 250MPH, people do drive that fast on the track, the rear wheel is spinning at abut 3,703RPM which is faster then any shooter wheel is spinning. So Andrew you are just fine using wheel weights :)

Re: Balancing a Pneumatic wheel
 

3703 < 5000 So I'm not seeing your point. I know one of my wheels is geared close to 7500 rpm. Now, I'm aware I'm not hitting that speed but I'd be willing to bet you that it's well above 3700rpm. And frankly, I don't care if it "should" be safe. I care that it is. I care that teams took some time to put in safe guards to prevent shrapnel hitting people because I'm selfish and I enjoy the use of all of my limbs.

Re: Balancing a Pneumatic wheel
 

That's well over 1200 miles per hour. I don't think the wheel itself would survive, much less stick-on weights.

Based on reports I've seen here, some frisbee shooters are spinning their wheels at 6000 RPM or higher. 5000 RPM seems common. Whether or not you use wheel weights, if you're running a wheel at several thousand RPM, you'd better have an effective containment system to protect the outside world in case something spontaneously disassembles itself.

Re: Balancing a Pneumatic wheel
 

I believe those are the smaller wheels, not the pneumatic. If someone is spinning that pneumatic wheel over 4,000 RPM then the are lucky they still have a wheel.

Re: Balancing a Pneumatic wheel
 

Something to consider is that the way most teams practice is not indicative of an FRC match. Their is significantly more vibration, impact, and otherwise dynamic loading that the robot will see during a match compared to the loads it sees when you drive around picking up frisbees without the full contact of a typical match. Any field reset volunteer could tell you about the buckets of stuff they have to pick up off the field.

I think many people are running tires at 1:1 off a CIM and just assume they are getting close to a no-load free speed. If they were to put a tachometer on it I bet they would find their true rotation rate is significantly slower.

Re: Balancing a Pneumatic wheel
 

The TechnoKats robot this year uses the pneumatic tires from AndyMark. I think the operator typically calls for 3000 RPM, but it can go to 5000 on command without trouble.

The final output wheel on the TechnoKats shooter has a Spinbox in "overdrive" configuration on a MiniCIM motor. It definitely exceeds 5600 RPM when run full power (the cRIO stops getting a good signal from the encoders above that rate).

The wheels are well balanced (though there is still enough vibration to matter) and there is a shield in place to keep debris from flying out if something comes apart at speed.

Re: Balancing a Pneumatic wheel
 

Here's how I did it:

I also used stick on lead weights for RC airplane balancing, but I simply did not trust just double sided sticky tape to hold them inside the wheel.

I stuck the weights on where they needed to go and then I used 30 minute epoxy as the final balancing "weight". This also helps to secure the weights in place.

http://www3.towerhobbies.com/cgi-bin...&I=LXK204&P=ML

The fourth picture is what happens after you spend time balancing the wheel and the tire decides to spin the tube inside the wheel resulting in an unbalanced wheel...

Re: Balancing a Pneumatic wheel
 

What centripetal force? In the rotating frame of the wheel, there is a centrifugal force, which tends to push the weights away from the center of rotation. It's working against you, not with you. I don't know what adhesive you're using, but I would feel safer if you have a cover over your shooter wheels.

We used nuts and bolts, with various amounts of washers, at up to three points around each wheel. And a cover over the whole shooter assembly.

Re: Balancing a Pneumatic wheel
 

My apologies, I meant centrifugal.

I don't know how this works against us though.

Considering our weights are on the very outer edge of the plastic hub, pushing them outward away from rotation keeps them more solidly in place.

Re: Balancing a Pneumatic wheel
 

And also flying out of the wheel, into the limbs of other people.

Re: Balancing a Pneumatic wheel
 

Introducing the 2014 FRC game....

Re: Balancing a Pneumatic wheel
 

Let's talk more about the feasibility of it than joking around about it.

I don't see a way for them to fly out.

Re: Balancing a Pneumatic wheel
 

I wasn't joking. I would never trust adhesive on a high rpm flywheel. If it isn't good enough to hold on bumpers, why is it good enough for a shooter?

Re: Balancing a Pneumatic wheel
 

To be honest, why not put the wheel on a shaft between a pair of bearings? It takes almost all of the imbalance out of the system. Try McMaster 5913K71 bearings for 1/2" shafts...

Re: Balancing a Pneumatic wheel
 

For one, I can't even pull the weights off with my bare hands. It's a pretty tough adhesive. I need pliers to even come close to tearing them off.

For two, the centrifugal force of the wheel keeps them lodged. I don't see any way for them to come out when you pair the two of these together.

Imagine being on a gravitron, except also being taped to your seat with a super strong adhesive. Are you going to get anywhere?

Re: Balancing a Pneumatic wheel
 

Regardless of how you balanced your tire it is possible for anything to fly off including bolts with washers used for balancing or even the whole wheel so shield your spinning items if possible to protect from flying objects.

BTW tire shops use adhesive weights for balancing car tires.

http://solutions.3m.com/wps/portal/3...beMJV74VR9N7gl

Re: Balancing a Pneumatic wheel
 

No. Such. Thing.

Re: Balancing a Pneumatic wheel
 

While that's technically true, it's a convenience term for the outward force component of rotational inertia. It exists for the intents and purposes of describing and calculating behavior. You got his point :rolleyes:

Re: Balancing a Pneumatic wheel
 

Has anyone looked into Dyna Beads?
There used mainly for balancing motorcycle tires. Should work for us.

http://www.innovativebalancing.com/index.php

Here is a Youtube video showing how they work.
http://www.youtube.com/watch?v=eq263AYgyYg

Re: Balancing a Pneumatic wheel
 

Not an actual force, but you understand exactly what I'm saying and the concept I'm referring to.

Re: Balancing a Pneumatic wheel
 

I do not think responses like this really add anything to the discussion at hand. If you wouldn't phrase it that way when talking to your grandmother, it probably isn't the way you want to say it on CD.

As others have said, it is certainly a physics concept and being able to explain the difference between centripetal and centrifugal force is a key indicator that you understand what a reference frame is, and how they work. In college, particularly in Orbital Mechanics or Mechanism design this intuitive understanding becomes very important as the vector math gets real crazy, real quick. Any good physics textbook should have a reasonably in depth explanation, an old xkcd comic does a decent job in a blurb, and of course Wikipedia goes into much more depth.

Re: Balancing a Pneumatic wheel
 

Ok, centripetal vs. centrifugal is an easy mistake. If your weights are on the outer edge, that still sounds scary. Do you mean that they are on the inside of the outer rim? In other words, if you imagine a smiley face painted on the non-adhesive side of the weight, would it be facing towards the axle? That would be okay. If it's facing away from the axle, that's very scary; if it's facing parallel to the axis of rotation, that's a little scary.

Maybe you could post a photo?

Of course, if your team is convinced that it's safe, then you only need to convince the inspectors, not me.

Re: Balancing a Pneumatic wheel
 

OK, time to add a few words of sense to this discussion.
1. Adhesives, particularly double sticky tape are not fasteners. We can argue industrial adhesives but so far I have not seen anyone discuss these yet.
2. The tread of the pneumatic tires you are discussing cannot take the force of the wheel speeds that will be generally encountered. I believe the operative phrase is "destructive disintegration". Have you noticed how hard it is to find any speed data on these tires?
3. The imbalance and vibration is telling you something, you are not listening.
4. Just because you haven't witnessed parts leaving the flywheel yet, doesn't mean it won't happen.
5. Most of you are using motors that free speed above 15,000 RPM. Coupled to a 3:1 transmission, what numbers do you get? Direct drive on a 775 is over 7,000.
I think you guys need to rethink your designs to be sure. Not pretty sure, not 'oh it will never happen' sure, really sure. Please remember that inspectors will be looking at your robot with this in mind...
R08
ROBOT parts shall not be made from hazardous materials, be unsafe, cause an unsafe condition, or interfere with the operation of other ROBOTS.
I am sure that if your design should cause any flying debris, an inspector will be asked to either disable your mechanism until such time as you can prove it won't hurt anyone or anything, or whatever it takes to prevent a re-occurrence. Now is the time to be really sure, not during competition.

Re: Balancing a Pneumatic wheel
 

For the tire wheel weights, mounted on the inside of a wheel: They are being used exactly as the MFR intended in a less severe than typical application. In this case the supplied double sided sticky tape is tested & sold for this application. Of course they need to be properly applied to a clean surface.

(squirrel alert) Industrial adhesives: Our shooter board & bumper backing is made of thin wood strips glued together with industrial adhesive. Fiber reinforced composite matrix to my materials professor. Plywood to my Home Depot salesman.

Re: Balancing a Pneumatic wheel
 

We are using the spin box with standard .500 keyed hubs and mounting hardware. The problem that we have found is the plastic hubs are out of round. No level of balancing would cure this issue, we tried. The id bore is to large for the hub and the thru bolt holes are to sloppy. This hub was not intended to spin at 5K rpm. We are now attempting to turn a new set of hubs out of HDPE and a drive shaft from 6061. We are hoping we can tru the hub and shaft. Our current setup runs and shoots OK but the vibration causes issues with the camera. As we progress I will post pics and CAD files if anyone is interested.

Re: Balancing a Pneumatic wheel
 

In Newtonian mechanics, the term centrifugal force is used to refer to one of two distinct concepts: an inertial force (also called a "fictitious" force) observed in a non-inertial reference frame, and a reaction force corresponding to a centripetal force¹.

Centripetal force is the force exerted by the wheel rim on the balancing weight, pushing the balancing weight toward the center of the wheel. It's what makes the balancing weight following the circular path.

Centrifugal force is the reaction force exerted by the balancing weight on the wheel rim in response to the centripetal force. It is a real force.

So Ksafin's only mistake was that he should have said "centripetal force" instead of "centrifugal force", because he was referring to a force acting on the weight.

¹wikipedia

Re: Balancing a Pneumatic wheel
 

Our AndyMark hubs are round. Since they appear to be injection molded parts, I would expect them to be consistent. We are mounting them to a 5/8 dia Andymark hub with #10 screws. We made a 1-1/8D x 5/8D insert for the other side of the hub to keep it true to the shaft. If you are using 1/2 shafting, a 1/2 bearing would work there as well.

Re: Balancing a Pneumatic wheel
 

Hi Al,

There are many teams using these pneumatic tires on their shooter but I am getting the impression from your various posts that you are deeming them unsafe to use in this application. My concern is that you as a inspector or someone else will rule them illegal during inspection based on what you specified. This will in turn render a robot's shooter useless until another "more safe" wheel is used.

Yes, these tires were not specifically designed to be used under these circumstances but I have yet to hear of one coming apart. I agree that great care needs to be taken in how they are mounted and balanced. Also, it is highly recommended some sort of shield be used to prevent any flying debris should something come loose.

If a team takes these steps, do you see them capable of being used in a safe manner?

Re: Balancing a Pneumatic wheel
 

How are you evaluating "less severe?" These weights are sold for auto & motorcycle tire balancing. An automotive tire will rarely see over 1000rpm. Small trailer tires may be as much as double this but no where near 3k-5k rpm. I'm surprised no one is discussing the Dynabeads mentioned in an earlier post. Much better balance solution for this application. They claim to deliver precise balance and they are contained. I have not used them but I've seen a number of credible reviews on them from the motorcycle community.

This still doesn't allow teams to use components beyond their rated capacities. Even with the best balance solution, if the wheel/tire falls apart, they are all dangerous. If the vendor description of the item has a 5000 rpm recommended limit, that should be considered the maximum safe operation condition.

Regards,

Re: Balancing a Pneumatic wheel
 

I don't really think its fair to say that its the maximum safe operating condition. Manufacturers often leave a very large margin for error. Its also problematic for components such as the AM pneumatic wheel, which doesn't spec a 'recommended maximum rpm'.

The AM pneumatic wheels were DEFINITELY not designed for operation at, or anywhere close to 5000rpm. Neither are the banebots wheels many have used in their shooters. Nor ANY wheel I've seen in a wheeled shooter, though I would consider MOST shooters currently mounted on robots in their bags 'reasonably safe'. If they haven't blown themselves apart in testing, they likely won't during competition. Could it happen? Sure, there's wear and other things that aren't considered in my extreme oversimplification. I think robots should be designed to contain a failing shooter wheel, but restricting operation of robot parts to manufacturer provided values/use cases is just problematic.

Re: Balancing a Pneumatic wheel
 

Centrifugal force (or centripetal depending on your point view) Depends on tangential velocity not RPM. Motorcycles & cars see easily 50 m/s which is more than our wheel, at least, is spinning.

All the wheels I have seen use on the Frisbee shooters are being used "off label" from what the manufacturer intended. Liability laws being what they are, I doubt you will get buy in from them if you asked.

So it is incumbent on us to make sure our robots are safe. This very much includes making sure they are no loose bits on the wheel that can fly off and hurt some one. Also that you are not spinning the wheel at a speed that will make it come apart.
Also checking the shooter wheel should be part of everybody's pit check list before every match.

Re: Balancing a Pneumatic wheel
 

It depends on both.

F = mv²/r .... or .... F=mrω²

Centripetal acceleration:

20" at 120mph = 11,330 m/s² ....... 8" at 5000 rpm = 27,854 m/s²

see attached Motorcycle vs Shooter Wheel centripetal acceleration calculator

Re: Balancing a Pneumatic wheel
 

50 m/s is about 110 mph. Motorcycle and car wheels that operate at such speeds are not made of polycarbonate and grey rubber.

Re: Balancing a Pneumatic wheel
 

I will grant you a 110% I will not put an Andymark pneumatic wheel on my motorcycle and try to go 110 MPH. I don't think my poor Volvo would go that fast either. The analogy breaks down pretty rapidly. :]

Here is a article on plastic car wheels. Doesn't really transfer to robot Frisbee shooters

Re: Balancing a Pneumatic wheel
 

Shu,
I am not saying that inspectors will make any decisions on the use of a particular tire. We cannot tell it's use during the inspection process. I am discussing the use of certain of the mentioned methods of attempting to correct vibration and balance. Again there is no way for inspectors to determine during the process if your design is safe or not.
What I am trying to point out is that certain assumptions for high speed rotating objects may lead to unsafe conditions during play on the field. I don't want to see any team disabled by or for an unsafe condition and I certainly do not want to see anybody injured. From my calculations, many shooter designs exceed by more than 5 times the rotational speed of car tires. Even devices designed for road tires may not retain their design characteristics at your rotational speeds. Now is the time to be sure. For reference I suggest you look to videos of drag racing vehicles in the burnout box prior to a race. Be sure to take a close look at the tire profile during the burnout process.

Re: Balancing a Pneumatic wheel
 

Also, anybody that has spun up one of the AM pneumatic wheels 1:1 off a CIM with no air in the tire will tell you that the rubber of the tire deforms rather alot. It quite visibly pancakes at that speed with no air pressure to help it hold shape.

Re: Balancing a Pneumatic wheel
 

Something that seems a little odd to me is that alot of teams used very similar shooter designs last year, and I don't remember seeing as many worries as I have seen this year. Would the wheels being horizontal vs vertical make that much of a difference?

BTW both last year and this year we used 2008 KOP Grey wheels, and we had no trouble running them at 5k rpms either year.

Re: Balancing a Pneumatic wheel
 

The discussion is centered on the pneumatic tire/wheel which I don't think was widely used on last year's robots as part of the shooter.

Re: Balancing a Pneumatic wheel
 

We found that the valve stem was being pushed outward by centrifugal force.

So we put a zip tie around the valve stem and the bolts holding everything together. Seems to work well. Has been reliable.

We are only running about 3000 rpm. We are not trying for real long shots.

Re: Balancing a Pneumatic wheel
 

We did the same but with a few wraps of a fishing line

Re: Balancing a Pneumatic wheel
 

Had same issue. Elegantly solved with strategically placed duct tape toroid. :)

Re: Balancing a Pneumatic wheel
 

After some thoughtful offline conversations.....

Al is more likely to inspect your robot than I am. Take heed of his words.

Regards of who inspects your robot. It is your job to make sure it is safe. This means:

1. making sure anything attached to the rotating bits is well attached and is not going to come off.
2. making sure your shooter is not going to come apart from rotational forces or having your frisbee jammed into it.
3. Making sure the shooter is well attached and the shafting and bearings are adequate for the job.

Apologies in advance if this sounds the least bit preachy. I am looking forward to seeing amazing things this year.

Re: Balancing a Pneumatic wheel
 

^^^This^^^

A couple of years ago, I leaned over my lawn tractor with the engine running and slipped and caught myself by placing my hand squarely on the spinning debris mesh on the top of the engine. Not fun. I was "single handed" for several weeks after that.

So I would add #4:

4. put some sort of guard over the spinning wheel to protect wayward hands and contain pieces that might come flying off due to failures.

Re: Balancing a Pneumatic wheel
 

Good add.

Re: Balancing a Pneumatic wheel
 

A major concern of mine regarding high speed rotating wheels that I stricktly enforced with the 4134 kids was loose clothing and long hair. Hanging untucked shirts, hoodie strings and espesially long hair pose significant saftey issues. Most of time the kids know where there hands are, but not the strings on their hoodie.

Re: Balancing a Pneumatic wheel
 

Yikes. Great point.

Re: Balancing a Pneumatic wheel
 

Dangling chains, bracelets and chums, too.

Re: Balancing a Pneumatic wheel
 

Basic rules of our build site. If you are in the build area
closed toe shoes
safety glasses
hair pulled back
No danglies
hoodie strings tucked in.

Re: Balancing a Pneumatic wheel
 

Watches too. I usually have my watch and a band that tracks my activity over the day on my left wrist. When I'm anywhere near that shooter both of those are put in my computer bag. Neither of those are even loose but they are things attached to my person that increase risk and, again, I'm rather fond of my limbs.

Re: Balancing a Pneumatic wheel
 

This isn't only an issue with fast spinning wheels. A drill press will run at 1000 RPMs, if not faster... get a string or hair caught in that, and the students head will be pulled in before you can blink.

Re: Balancing a Pneumatic wheel
 

This is why my wedding ring stays in my dresser. I regularly work with rotating equipment & hot circuits (which you should never to begin with). I am paranoid that I will leave it some place.

Re: Balancing a Pneumatic wheel
 

I have to second the "pool noodle" fix. We went the way of balancing the wheel but did not like the potential catastrophic results that might ensue. We tried the pool noodle and an increased speed gearbox on a cim. We were slamming the frisbee into the wall 51 feet away with only a 10 degree elevation of the shooter and a drop of 20 inches.
I can't see why anyone who now knows this would chance an injury resulting from flying debris when this can be done quite easily. I can't see of any circumstance where a tube is necessary and not replaceable with a noodle. (I guess if the whole mechanism is "buried" and too difficult to change it might be understandable).

Re: Balancing a Pneumatic wheel
 

Several things we found essential for being successful with this tire (over 100ft. range, full court shooter).

• Machined 8lb. billet steel wheel that serves as 1/2 the rim
• Machined rim to reduce wobble
• Dynamically balanced assembly
• Upper bearing for support (reduced vibrations majorly)
• Machined tire for a profile with maximum frisbee contact
• Inner tube was essential to adjust frisbee tension (we found a specific air pressure that is increased as the tire wears)

We are powering the semi circle shooter with a mini cim and spin gear box, mounted with a machined aluminum motor mount.