Attatching an axel to a wheel
 

I know the tile sounds a little childish, but I was wondering how do you guys attach your axels to your wheels so that the axel isn't free moving?

Re: Attatching an axel to a wheel
 

best way is with a slotted axel and a key.

Dont even think of using a set screw!

Re: Attatching an axel to a wheel
 

unless it holds the key stock in place

Re: Attatching an axel to a wheel
 

Exactly. Set screws can be quite good if used properly.

696 has always keyed the axle (and bore of the wheel) with a standard straight key/keyway. A few teams use a hex shaft and matching hex bore in the wheel. Other teams allow the wheel to free spin on the the shaft and affix a sprocket or whatever directly to the wheel.

Shaft collars, flanged bearings, e-clips, and whatnot are all good ways to keep a wheel from moving linearly along the shaft too.

Let me know if you have any more questions. :)

Re: Attatching an axel to a wheel
 

According to Mr. Bill (team Hammond, 71), if you don't want it to move, weld it. While this may be difficult due to the material the wheel hub is made of, some teams will weld the sprocket to the axle and then bolt the wheel to the welded sprocket.

This is an extremely robust method of attachment, though if anything breaks, the whole axle must be replaced including the sprocket.

Re: Attatching an axel to a wheel
 

If you want to avoid broaching a slot a round pin can be used. Examples can be seen Here.
Check out 2006 Robot CAD. Look at the wheel and shaft.

Re: Attatching an axel to a wheel
 

Pins are one of the weakest ways to go. Its difficult to calculate the impact shear forces a pin will see, in a collision for example.

Ive seen many axel pins break, and Ive seen a 0.5" diameter axel break where the pin was located, due to the reduction in cross sectional area the hole produces in the shaft.

BTW, they use pins on the props for small outboard motors - and they call them shear pins - they are intended to break if the prop hits a rock - saves the prop

A robot with failed drive train, motors spinning and bot going nowhere, is one of the most common failures you see at FIRST competitions.

Re: Attatching an axel to a wheel
 

Ken,
Are you are speaking of a pin located perpendicular to a shaft, as is the case of a prop shear pin, or a pin located parallel to the shaft, as the drawings show? I do not disagree with you, just want a clarification.

Re: Attatching an axel to a wheel
 

I was referring to perpendicular pins that take all the torque applied to the wheel. I have spent many hours replaceing those at competitions.

I clicked into the drawings and I think I found what you are talking about. The pin is wedged between the wheel and the shaft, to hold the key tight on the opposite side?

Why not tap the shaft and put a small bolt with a large washer on the end, to keep the key from slideing out? that would make it easier to remove / replace the wheel.

Re: Attatching an axel to a wheel
 

Ken,
The shaft is tapped and there is a bolt on the wheel to hold it on.
Look again.

Re: Attatching an axel to a wheel
 

so whats the purpose of the pin then?

Re: Attatching an axel to a wheel
 

we actually had to drill and tap hole at comp so $@#$@#$@# to keep the wheel from coming off the c clip channel was not deep enough and our wheel had about an 1/8" from falling off

Re: Attatching an axel to a wheel
 

This should make things clear as mud.

Re: Attatching an axel to a wheel
 

what did i say i must have typing turrets

Re: Attatching an axel to a wheel
 

Is there any reason a pin such as that would be used over a keyway? Or would it just be used if you didnt have the correct broach?

Re: Attatching an axel to a wheel
 

Im gonna guess and say that anyone can put the wheel over the shaft and drill out the hole for the pin, if you dont use a key

those square-drill-bits are too expensive for some teams :^)

Re: Attatching an axel to a wheel
 

The ol' bolt in place of the square key trick.

I like it. Even if you don't use it in the initial build, it's helpful to take note for quick repairs in the field. It DOES work, and works well.

Better than taping 7 hacksaw blades together and trying to cut a keyway because you didn't have an arbor and broach. At least thats what the students told me.)

Re: Attatching an axel to a wheel
 

The reason we use a round pin is that a key way can't be broached in a pocket. The broach must pass all the way through in order to cut the key way.

Re: Attatching an axel to a wheel
 

Touche.

Do you ever strip the threads on the axles or bolts due to torsional force on the wheels?

Re: Attatching an axel to a wheel
 

not for first but for occra. our team has been successfully just bolted our sprockets to our wheels. and the wheels have bearings. the shaft is in those bearings, and collars hold the wheels from moving sideways. so basically our shaft is free of our wheels/sprockets. simple and works well. if you had good bearings in the wheels, you can eliminate the bearings to hold the shaft. if you really wanted it to spin under sideloads(such as turning with 4wd or plain being pushed sideways), you can actually get bearings..... just cant remember the name of the bearing right now.... the kind for pressing loads. GAH. cant rememebr any terms lol. like tiny turntables ish..... sorry. i really cant rememebr the term right now. well anyways, if the sprocket is solid to the wheel, wheel and tire dont slip, and chain doesnt slip, wheel doesnt wobble=sprocket doesnt wobble, you're pretty much set.
not hard to do. but this has been working for us well in OCCRA.... where we dont experience as much torque and shtuff.. so i unno about first.

Re: Attatching an axel to a wheel
 

The type of pin that you have been discussing (running parallel rather than perpendicular to the shaft) is commonly known as a "Dutchman Pin." They are commonly used to attach large flywheels to drive shafts. Dutchman Pins have two distinct advantages over "conventional" pins, in that they are typically much stronger for a given pin size, and they require less material to be removed from the parent shaft - thereby leaving the shaft stronger (as with conventional pins, the diameter of the Dutchman Pin should not exceed 25% of the diameter of the parent shaft).

The shear strength of a conventional pin is calculated as: Pin Shear Strength = 2 * Pi * Pin_Radius^2 * Material_Shear_Strength

The shear strength of a Dutchman Pin is calculated as: Pin Shear Strength = Pin_Diameter * Pin_Length * Material_Shear_Strength

In a typical application where the pin is 25% of the shaft diameter, and the hub length (and therefore pin length) is the same as the shaft diameter, the Dutchman Pin will have a shear strength 250% higher than a conventional pin. For example, lets assume we want to attach a wheel with a 1" long hub to a 1" diameter shaft and a 0.25" diameter pin. The pin is made of tool steel with a shear strength of 45,000 psi. In this case, a conventional pin would shear at 4418 pounds, while the Dutchman Pin would survive past 11,250 pounds of shear force.

As the strength of the pin is determined by the total cross-section area of the pin, you typically do NOT want to use a bolt or threaded fastener as the pin. For a given diameter pin (as measured across the threads) the threads reduce the effective cross-section of the pin, thereby reducing the pin strength.

Dutchman Pins also offer some advantages over square keyways and keys, such as easier manufacturing (in some cases) and fabrication with more commonly available materials.

-dave

p.s. you can indeed broach a square keyway in a blind hole, it just takes a different technique than using a conventional broach set.

Re: Attatching an axel to a wheel
 

I'm guessing you'd have to grind a tool that is recangular in shape that is the thickness of the keyway you want. They you'd grind it sharp on the edge (sorry, I'm not describing this well). Think something like a lathe groove cutting tool. Then, I'd rig up something to put it in the spindle of a mill, align it to be parallel with a mill axis (lets say x), and lock the spindle with the brake and/or a very low gear. Then, with my gear already positined in a vice or whatever such that the ground cutter is directly over the gear diameter that is parallel with the x axis, I would make sure the y axis is locked in place. Then, I would proceed to move the cutter into the gear just a little bit, and pull down on the downfeed handle. Move the gear into the cutter a little more, and pull down once more. Each time, you "shave" off a little bit until you get the depth you want.

Is this correct for the most part?

PS. Substitute "wheel" or anything else in where I said "gear"

Re: Attatching an axel to a wheel
 

Close enough. That method will definitely work. Take the same idea, turn it sideways, and you can see how you would do it on a lathe (this is actually the preferred option - with the cutter mounted on the cross-slide - just because there is one less degree of freedom to worry about). Turn it sideways the other way, and you can do the same thing on a shaper. I have also seen it done "by hand" with a one-shot cutter and an arbor press. Drill out the majority of the keyway (as if preparing for a Dutchman Pin), then use the cutter to clean up the corners.

-dave

Re: Attatching an axel to a wheel
 

My prefered method is a hex shaft while hardest to build it has the best long term benefit=== I have never sheared nor seen a sheared hex shaft, they can snap like any other shaft but they are i beleive the strongest.

While keyways are nice they have flaws such as loose keys and the key exploding since all the torque is applied at that one point

For practicality i would use a similar method to that which secures the tires to the axles of your car, there are four to eight pins which are parellel to the shaft and are inserted into the wheel, very strong(it can withstand whatever you car dishes out and i challenge you to build a competition legal robot that dishes out more torque than my 1979 Trans Am, so much that it can snap through and average hub built correctly and like i described)

Re: Attatching an axel to a wheel
 

"Exploding" keys are not always a flaw. Most of the time I would consider them a safety feature. If the key breaks it just saved some other part of your drive train like a shaft or some gear teeth. I would much rather replace a key in a wheel hub in the heat of competition than rebuild a gearbox. Sometimes it is not always about designing everything in your drive train to withstand unlimited torque than it is about designing a built in safety that is easy to fix. I would much rather have to replace a U joint on my 4 wheel drive truck than have to rebuild the transmission or rear end.

Re: Attatching an axel to a wheel
 

On the note of u joints did u know that they have these clutch things that are slightly weaker than u-joints and u put them like between the yolk and the axleshaft and they can supposedly be switchede in like 10 minutes while a u-joint**cringe**

Re: Attatching an axel to a wheel
 

Another note on shaft collars... use clamping style collars and preferably the two piece type. Shaft collars with set screws will mar the shaft which is no fun!!

Buy a simple broach set to broach 1/4" - 1/2" items. A wise investment along with several pieces 3/8" and 1/2" keyed shafting. MSC Direct has this for about $100. It's served us well for 4 years now. You may need an arbor press, although with most pieces you can press the broach through with a simple drill press (not running of course) and some cutting oil.

Re: Attatching an axel to a wheel
 

Do you have any pictures of this design?

Re: Attatching an axel to a wheel
 

U mean the hex shaft?

Basically instead of the shaft being round it is a hexagon shape so that when u slide on a wheel, gear etc. it can slide along the shaft but cannot spin, for a great look at it open up the transmission FIRST sent you this past year and you will see a small hex shaft going through one or two of the gears.

for a hub its easy:
These are from jeeps since there are the most taken apart vehical, you dont need anything this beefy on your robot though

http://www.thedieselstop.com/content...nt/image24.jpg
http://jeephorizons.com/tech/xj44/axle9.jpg
http://jeephorizons.com/tech/xj44/axle10.jpg
http://jeephorizons.com/tech/xj44/axle11.jpg

Re: Attatching an axel to a wheel
 

Do you know of any other ways of attatching the axel to a wheel. It doesn't have to be an easy way.

Re: Attatching an axel to a wheel
 

This would depend largely on the material that your wheel hub is made of. Plastic of poly-carb. hubs can be "sandwiched" between two discs that securely fit around the spokes of the wheel (try looking at the "wheel-chair wheels" from past years), then attach the metal discs to the axle by any of the previously mentioned methods (pin, key, WELD!)

If the hub is metal, the wheel hub can be directly broached or pinned.

Re: Attatching an axel to a wheel
 

Does anyone know of any place where they would sell gears with a hex bore in them?

Re: Attatching an axel to a wheel
 

If you want to buy from AndyMark, they have limited tooth count selection of hex bore gears.

I can't recall ever seeing any from a major supplier that are hex bored, however.

Re: Attatching an axel to a wheel
 

Many tool supply places will sell hex shaped broach tools. If you have an arbor press in your shop it may save you some money in the long run to have the broach tool and just buy standard gears.

Re: Attatching an axel to a wheel
 

A good undersized 1/2" Hex Broach retails for a few hundred dollars, and since you won't use that often, I'd suggest just finding a nearby machine shop with broaching capabilities and ask them to do it. We've done this before and they've been happy to help. We've also managed to get a broach donated, so we can now do it ourselves on our press, be we've only used it once.

Re: Attatching an axel to a wheel
 

Thanks every one for the input. We were actually thinking of making the hex with a CNC mill. It would have a fillet on the corners but we think we can put the same fillet on the shaft using a lathe. What do you guys think about this?

Re: Attatching an axel to a wheel
 

The last few years, we've just used Skyway wheels with a 5/8 keyed bore, and 5/8 shaft with a keyway already cut (MSC). We typically use a bearing on each side of the wheel/sprocket (pillow block arrangement), with split shaft collars outboard of those to prevent the axle from moving laterally. Simple, strong, inexpensive and requires no machining. Only a little sanding occasionally if things are too tight. We have relied on those aluminum pillow block housings that were used in the kit or available for several years, so now we might have to have some machined if we can't find them.

Amazing how working in a wood shop can reduce your machining requirements.