Bicycle Spoke Design

http://www.astounding.org.uk/ian/wheel/

This is the one i refer to. This is finite element analysis using a software called Ansys. But is there a way to calculate those forces without Finite element analysis?

A slide rule. :)

You could compute the sum tension and compression on each spoke for a given load at a point.

However, you must also take into consideration that the rim contributes to the system.

Sounds like a very long and arduous set of manual calculations.

yea, u may be right.. but still id like to hear what other people have in mind.

Those numbers are not believable. It is not possible for large compression to occur in a bicycle spoke; it would just buckle.

Wby would you try to re-invent the wheel???????

Im not re-inventing a wheel.. that'll be pointless.. to be honest, this is my assignment to design the wheel, i have to state the technical reasons of why i choose to use this number of spokes...

Does your assignment have a deadline?

I like deadlines. I just love the whooshing sound they make as they fly by.

I can't help you.

I never did my own homework.

You are awesome.. xD
Nah its okay..

If you chose a wheel with three spokes only you might have a chance with the manual calculations. I'd start there and go to four if need to.

Good luck!

Now that concept seems to be proven by trial and error. Its up to OP to finalise the calculations.

I would argue that because it exists it works. And because it works I dont have to prove it.

Hahahahahahaha!

Apparently political spokesman is an easier gig than bicycle spokesman.

Tighten them all up two more turns, and then recalculate. That prospect alone should tell you this is not an easy problem.

no more annoying tightening

That's a great illustration of what I'm talking about!

It has 8 spokes.. why?... purely arbitary 'cos it's easy to draw, do, imagine, construct, measure etc. Doesn't need maths or CAD to make the decision to have 8 spokes, and doubtless the design and mold tool were all done with CAD... but based on an arbitary decision.

Del

I just liked the color

Ah, now the colour is designed by extensive use of maths, CAD, physics and finite elephant analysis... honest

Del

What, no 'impact group' of sociologists & style gurus?

GA

The only caveat I'll add is that today's student should be made to perform at least one simplified iterative calculation by hand to understand why computers are tasked with the process. Calculating the loading of the spokes of a bicycle wheel by hand is IMHO a cruel and unusual punishment but everyone has their vices.

To your very valid point about why reinvent a wheel. As I presume you know from your bow construction, the availability and quality of any fabrication material changes with time. How something was made previously may not be possible at another time. Knowing what are the critical attributes for a design is the fundamental of all engineering. It is also so very easy to become infatuated with the theory and numbers. Nothing trumps theory like disagreeing experimental data. (I think I am paraphrasing Feynman.)

I agree with you.

All the calculations one does become road kill once you start to spoke a bike, or motorcycle wheel.

Design yer heart out, but when it comes down to tensioning, Bicycling - Wheelbuilding: check spoke tension using ...

I remember parts of my short lived musical career. One thing I do remember is that when the roadies got finished tuning the guitars with the strobe tuners, the players would "fine" tune them to their liking.

Del, one of the best responses I've read in a long time.

Cheers

I don't see how there is an answer since you could tighten all of the spokes without any change.

Or tightening one spoke changes the stress on all the others.

This becomes an infinitely variable, insoluble problem.

No, having a definable set of infinities is a solution. That is different from not being able to define anything.

In this case once one adds the non-linear condition that a spoke will snap above a certain level of tension then the maximum load on the axle is knowable with a certain tension.

Yes but, a snapped spoke introduces a completely new set of variables.

Still doesn't change the original condition. It just introduces a new problem. The goal of the exercise is to identify what is knowable not to induce despair that nothing can be known. Too many religions already do that.

Well, if that's the goal all OP needs to do is keep reading Ian's web site. It's all laid out for them.

The simplist non-determinist mechanics problem that I know of is...

What is the force on each of the incompressible legs of a four-legged table?

If you assume the floor is perfectly flat and the legs are exactly the same length, the weight would split equally four ways. Any deviation and 2 or 3 of the four legs would support the weight. (I always manage to pick this kind of table whenever I visit a fast food restaurant.)

No-one would carry out an iterative calculation beforehand on the folded beer mat needed to achieve a viable engineering solution.

Us non-engineers would just say that a fat person will put more stress on the spokes than a skinny person.

To calculate it, I would weigh the person exerting the force, add it to the weight of the bicycle, and divide that number by the total number of spokes on both wheels.

Assuming that all spokes are tensioned equally. There may be a slight downward adjustment needed for the stress that the rim itself absorbs.

This is not possible. It's not possible if the wheel is suspended or stationary but when a force is applied it is impossible.

Start with pin jointed frames in mechanics, this works because there are no bending moments, all forces are along the struts. When solid frames are used with fixed joints then it is like jacking up a large object with 20 jacks, one pump and the whole system changes unless there is some flexibility like a lump of rubber under each jack.

A prestressed spoked bicycle wheel is like this, one screw on the tensioner and it's all changed, and there's no way to find the tension in any one spoke without putting stress gauges on each one, it certainly cannot be calculated.

So the question of what happens when a force is exerted say a rider gets on or leans over around a bend causing sidewards forces is quite a silly one to ask, it's a dynamic fast changing picture and any computer simulation or finite element analysis would need lots of assumptions like equal tension on all spokes, no interaction from the rim and results would be purely theoretical.

I am not sure why you feel it is not possible. I would be amazed if it has not been done before and done without the aids of calculators, let alone computers.

I am reminded of a story where someone got the original blueprints for a 1960s Porsche 904 race car and subsequently modeled the tubular frame of the car in a high end CAD package to check the original design for stress. He wanted to build a replica of the car.

What amazed the builder was how close the original design was to the limits of stress tolerance. Somehow those engineers accomplished with slide rulers what we take for granted performing in some CAD package.

Pre-computer design seems to be a lost art, but before your cross it off as impossible you might want to reflect on your ancestors and how they managed problems like these. Every technical hurdle is just an opportunity to be crossed.

I think the lesson for the original poster is to learn the actual processes required to design the spooked wheel. It probably is not as important that he comes up with the exact right answer, but to at least understand the principles and he will have a much greater appreciation for the power of CAD and what is going on under the hood in the end.

AH -

The wheel is spooked... and now gone! No more calculations.... no more problem! :)

I see I mis-spoke! :-)

Sorry can't resist!

But good!

Yeah. I got a good laugh! :-)

Consider bicycle steering dynamics. These are not fully understood. We know angular momentum, rake of fork, steering angle, trail, rider position, all have a lot to do with it. But we don't know a lot. This sort of complicated problem has only been looked at seriously quite recently.

A bike wheel is similar, it is very complicated. Spokes stretch and the elbows bend. The nipples and eyelets at the rim can change things, its possible to put washers on both ends of the spoke, there are a million types of hubs and rims, there are different lacing patterns...

The modern trend is a super stiff rim that is very deep and less spokes, spokes that don't do much. These can be fine, but can't be repaired and brought back to true when slightly bent.

The OP should be reading Jobst Brandt, and Gerd Schraner - the two gurus of bike wheel building. Jobst Brandt is more of an engineer and has modelled bike wheels and so is probably most helpful to an engineer. Schraner is more the art and history of bike racing. His is free online: http://www.scribd.com/doc/26719057/Gerd-Schraner-The-Art-of-Wheel-Building I'm sure Jobst Brandt is free online somewhere too.

Also the quick answer for how many spokes to use is 36. 36 is the best number of spokes in nearly all cases. (except very small wheels less than 20" nominal diameter) 28 spokes is not a good idea. 32 is just manufacturers being cheap. Generally.

It is said that to steer a bike you must (sub-consciously) momentarily steer in the opposite direction, how does this square with being able to ride a bike no hands.

You shift you weight (e.g wiggle your backside sideways), if you lean a bike one way the wheel angle changes (e.g the handlebars move).

Have you never pushed a bike by holding just the saddle? (Whilst carrying strings of onions draped on the ze 'andle bars? )

Del

This is one of the hottest topics in motorcycle training, where it is known as countersteering. It becomes relevant at higher speeds only. At low speeds there are two methods of initiating a turn
1. Lean sideways to fall into the turn. This is obviously what you have to do when riding no hands. The handlebars should fall into the turn, though this is less reliable with the steep rake on mountain bikes.
2. Turn the handlebars into the turn.
At higher speeds countersteering comes into play. This is a surprising use of the gyroscopic property of the front wheel. It is called precession, and the effect is that when the handlebars are turned to the left (a movement of yaw) the wheel drops to the right (a movement of roll). It can be demonstrated by holding a dismounted front wheel by the axles, getting someone else to spin it and twisting the axle as if turning handlebars. This is extremely important for initiating a rapid turn on a motorcycle, but TBH I am not so sure of the extent of the effect on a pedal cycle.

I this case I would carefully word my research and calculation into this format for a presentation that could possibly get you noticed. http://www.youtube.com/watch?v=rLDgQg6bq7o

A friend of mine who worked for Caterpillar commented that the six spoke wheels would crack but the five spoke ones wouldn't. It would be interesting to find out why. You would think the six spoke ones would be stronger but maybe they were too rigid.

More likely stress distribution.

In the movie Apollo 13 when things went wrong everybody pulls out their slide rules and start calculating furiously. Who would have thought a slide rule could have been so dramatic?

Why do you think they call it tuning a bicycle wheel? You almost have to be a musician to to assemble a wheel perfectly. Assuming everything is perfect to begin with all the spokes in the wheel should emit the same tone when plucked or struck with an object. My method is to go around the wheel squeezing the spokes in pairs and feeling the tension that way. I have gotten some wheels that were so far off I don't know how they even functioned.

I've seen video (i think on a TV show) of a machine assembling spoked wheels exactly as you describe. i think the spokes were strung by hand then put on this machine which tightened all of the nuts then used a little solenoid to strike each spoke & adjust until they all sounded the same.

I've never used a wheel building machine myself. But we talk about machine built wheels at work a lot and I've talked to people who have used them.

I do think you are correct that lacing the wheel is usually done by hand.

Then the robot tries to balance the tension.

For a good wheel a human then fine tunes it. There are a lot of really cheap machine built wheels that come on surprisingly expensive new bicycles ($1200) that are terribly off balance in tensioning. If a wheel has off balance spokes the high tension spoke is more likely to break. If spokes are too loose then tension is not adequately shared between spokes and breakage is more likely. And the wheel may loosen itself.

One of the major "art" factors in wheel building is the pre-stressing of the spokes. I have no doubt that at the factory the spokes come with some pre-stress to stretch them closer to their final dimension. As is similar with bike cables. However they still will settle and stretch a signifigant amount during use. A good wheel builder must stress the wheel by hand (by over stressing each spoke) to get it to settle. Also the elbox of the spoke must conform to the hub flange and this is highly variable depending on fit for each hub.

I don't think any machine has been very good at pre-stressing the spokes so far.

A friend of mine was trying to invent a box for manually pre-stretching spokes in a more uniform and quick way than the usual hand building method. His first prototype was plywood and not nearly rigid enough to be effective. I'm not sure if he has since re-attempted.

What is the ideal number of spokes required to make the "motorcycle sound" when a playing card is applied?

When a balloon is applied?

Playing cards are old hat, what you need is cable ties round the frame tube and the strap cut to the optimum length to hit the spokes.

I once used the Queen of Hearts and when I took it off, her crown was gone,her hair was mussed, but she was smiling!

None of the bicycle wheel videos on YouTube involves any calculation other than spoke length.

Coming soon: 3D printed bicycle wheels, complete with tire.

In a classic wheel - thin spokes and thin rim

The hub is suspended from the north spokes which pull on the rim above the hub which make the rim go oval which pull on the east west spokes which pull on the hub laterally in opposite directions. The rim transmits the compression forces in a circular manner to its base whilst the lower spokes stop it from buckling. The lower spokes do not transmit compression as they buckle over that length.

The rim is strong enough to resist the bending over what distance ? How many spoke distances ? So that is your design parameter for the rim. Also lateral buckling but we might just ignore that for the moment as it is solved by the angled spokes.

Then work out how many spokes cover that kind of distance and so work out the spoke size (probably dependent on the threaded area as it is less than the spoke itself and has an additional factor for the thread).

To begin with, you can perhaps ignore the pretension. But give it a thought later as it does turn your tension only spoke into a partially compressible spoke due to the tension field added by pretension. Note that the distances are very small to achieve the pretension and the buckling shape of the rim does have significant movements.

Modern wheels - Thick rim and thick spokes

This is more or less the opposite of the above. The spokes work in compression. The rim is alot stronger so as to resist the bending between spokes which is a greater distance. This is an easier problem to solve as you can assume that all the spokes work all the time in both tension and compression. The calculation of the rim is easier too.

I guess its just fun to actually go through some basic numbers and get a feel for the way a wheel works. See if your FEA is telling you something ok or not really ok.

We haven't even gone into the dynamic loadings which happen so quickly that maybe the spokes do work in compression for a fraction of a second. The ovalising of the wheel is a key factor for slowing you down while you're racing.

More questions than answers the deeper you go into the subject. But that is the nature of the beast.

Also, I would like to suggest you FEA Simulation to exert to the bicycle wheel, which can help you the most rather than anything else.