CAD uni drawings?

General
21

Re: CAD uni drawings?

This is great, they do produce nice stuff. I like the BMX frame, I see
potential there!

Roger

The UK’s Unicycle Source

----- Original Message -----
From: “Neil” <Neil.4zxjz@timelimit.unicyclist.com>
Newsgroups: rec.sport.unicycling
To: <rsu@unicycling.org>
Sent: Tuesday, May 21, 2002 10:17 AM
Subject: Re: CAD uni drawings?

>
> AccordNSX wrote:
> > *There site is here.
> > www.airborne.net
> > *
>
> Woohoo! Boy their frames are purdy…nice ‘n’ shiny too :slight_smile:
>
> > *
> > If you check out some of their frames and bikes, you can clearly see
> > that they do some pretty impressive stuff. I don’t see any of our
> > requirements being much of a problem for them. Their frames are made
> > in China by a commercial division of China’s aerospace and satellite
> > manufacturing organization. <— sounds cool to me. *
>
> You’re right there - It doesn’t look like they’d have any problems with
> any kind of design we come up with: bendy bits, straight bits, flat bits
> etc. Excuse my technical terms but my head is in the clouds after
> checking out their site :wink:
>
>
> –
> Neil - Total member
> ------------------------------------------------------------------------
> Neil’s Profile: http://www.unicyclist.com/profile/19
> View this thread: http://www.unicyclist.com/thread/18185
>
>

> rec.sport.unicycling mailing list -
www.unicycling.org/mailman/listinfo/rsu
>
>

22

Not knowing a huge amount about titanium, I’m wondering exactly what benefits a Ti frame would bring to a uni frame other than being made of an exotic and costly material… Please don’t get me wrong - the thought of a Ti frame gets the old pulse rate really fired up - but I ask the following playing the devil’s advocate in a bid to make sure that I / we are getting excited for all the right reasons…

Suppose you want to have 3 pieces of tubing made from aluminium, chromoly and titanium and all of equal strength:

From what I know of aluminium it is much lighter (but weaker) than chromoly. So you have to increase the thickness of the alu tubing to compensate for it’s weakness. But you still end up with a lighter piece of tubing than the chromoly one.

The titanium tube would be lighter and than chromoly one. But lighter still than the aluminium one?

If the aluminium tube is the lightest of the 3, and just as strong as the others, then shouldn’t we be looking at aluminium rather than titanium? This question is easily shot to bits if the Ti tube is lightest of all… but it is something I don’t know for sure… so thought best to ask.

Cheers,
Neil

23

This page from the airborne site explains the advantages of titanium and compares the performace with other materials.

24

Here’s some links to bike frame material pages that helped me get to grips with what material choice actually means to a frame. It’s worth keeping in mind that these pages are talking about bikes so some of the good / bad points they mention don’t necessarily apply to a uni frame. I never realised there was so much to it!

Sheldon Brown
A simple and easy to understand explanation of materials with their pros and cons:

Bike 101 – Frame Materials
Much like Sheldon’s page but prettier:
http://www.caree.org/bike101framematerials.htm

Titanium – the Ideal Material for Bicycle Frames
General info about titanium and comparisons between it and other materials:
http://www.vanguardtitanium.com/titanium.htm

MTB Frame Metals
Bike based comparison of frame materials and how good they are for different riding styles / types:
http://www.mtbbritain.co.uk/frame_metal.html

What You Really Really Want
A magnesium frame! This page is describing a Salt Cycles magnesium frame. It says the magnesium alloy frame is “34% lighter than aluminium and 50% stronger than titanium”. Hubba hubba. It doesn’t say much about the stiffness of the material other than, “The damping characteristics of this alloy rival the best titanium frames on the market”.
http://www.aardvarkcycles.com/product831.html
The frame is made by Salt Cycles in Utah, USA but their web site doesn’t provide anything other than contact info:
http://www.saltcycles.com/indexSalt.htm

What I can make out from the above is that there’s a particular material that best suits a particular riding style: XC, DH etc. Aluminium is stiff and light but can be subject to fatigue. Steel is cheap and strong but heavy. Titanium is light and strong but does flex. The magnesium frames sound the best of all but are subject to the flex of titanium. I guess each of these materials have draw backs that can be overcome with good design though.

So, for a Ti frame, it sounds like it’ll be strong, lighter than steel / chromoly but heavier than a slightly weaker aluminium one. So it’d be best suited to an extremely hardcore frame – like what I imagined in the first place! In the bike frame world it seems like the flex of Ti is desirable for certain riding styles. However, I don’t know of any unicycle riding style that actually benefits from frame flex. So I guess this would be something that would need mentioning to Airborne so the tubing choice can be steered towards producing a stiffer ride. From their web site it sounds like they are well aware of sorting flex issues.

25

Not an expert here but I think aluminum frames get their strength from large diameter tubing. This is a no-no in a uni frame, especially a rough-terrain uni, since we are pinching the frame between a fat tire and padded-up legs. Sounds like titanium is the perfect choice - strong, light, very good shock/stress absorption. There’s no need to thicken it up to make it stiff like a bike frame, because we are not using it to transfer power, at least to the extent that a bicyclist uses the frame. Basically a mountain uni frame just connects the seat to the wheel, except for the “chicken climb” technique, where there is some power transfer going on. But if a flexing plastic Miyata handle is good enough for MUni hill-climbing (it probably isn’t the best that can be achieved), then the stiffness of the material used for the frame is not that critical.

So the chief design criteria with respect to performance are: 1) lightness for hops and jumps, 2) strength enough to bear the rider’s weight and the shock of drops that hit the already air-cushioned seat, 3) shatter-resistance to endure UPDs on rocks and pavement. 4) sufficient stiffness to do steep hill climbs and lunges without loss of power or functionality (such as twisting to pinch the tire, etc.).

Other non-performance criteria are: 1) cost, 2) maintainability, 3) availability.

In the MUni frame, it seems to me that titanium’s true nature, light and strong with good elongation, can really shine.
I have a titanium cook pot for long-distance backpacking. It flexes very very easily, but who cares? all it has to do is hold water and noodles. It does that very well, and is much lighter than the stainless I no longer carry. It cost a bit, but it was a one-time investment and gets a lot of use.

How workable is it in the home basement shop for modifications and repairs? Is it possible to find machinists that can work titanium for small jobs? Is it harder to find a titanium machinist than a cro-moly machinist?

26

I’m no expert either that’s for sure. Come on experts - where are you?

The all aluminium Wilder frame works a treat mind you - the only aluminium frame I know of. I’m not sure how it’d hold up to excesive drops on the forks on rocks over a long period of time but I have a good amount of faith in Scott it’s designer.

[/B]

Sounds good to me. I’m not sure about the perfect choice bit though. Perfect for someone who needs the ultimate bomb proof uni perhaps. I’m nowhere near needing that kind of frame (that doesn’t mean I don’t want one!) and, were it not for the lack of brake mounts, my Wilder would be my idea of perfection: stiff, strong, great clearance without getting in the way and 636g.

Given how even cheap frames hold up I personaly feel that it’s the design that’s the clincher followed by weight. I have a feeling that a Ti frame will only turn out to be a few hundred grams lighter than, say, the KH24. If said Ti frame turns out costing a few hundred USD more then it’s simply not worth it. Saving 300g is not a huge saving really - you can do save this much simply in your choice of pedals… a much cheaper option :wink: This is just my personal feeling and others may well disagree.

[/B]

You’re bang on in my book.

I’m not entirely sure where all the forces go when landing drops (cranks, hub and bearing mounts probably see the worst) but I’d hope they don’t all go in through the seat :wink:

Good point about finding a machinist. Although, if a Ti frame broke to the point of needing a machinist I think I’d be looking for an ambulance first of all :wink:

27

Neil, Thanx for the links- I had most of 'em already, but from an aluminium/carbon perspective.

As has already been mentioned, not much, if any, weight advantage will exist. Scott really did do a great job with the Wilder; when drawing up weight estimates for an aluminium/carbon hybrid, I used the Wilder as a bench mark- a tough target to beat! Of coarse, the Wilder ‘lacked’ a flat crown and brake bosses…

A very well made/properly treated chrome alloy frame can come close to the Wilder, and has other characteristics that might make it choice (or so I’m told- the stats looked good).

Again, a repeat: frame material should be chosen for more than weight considerations. If felxure is that great of a factor, ‘more’ material may have to be used (read weight). I like to climb (really!)- flexing would be an issue. I suppose for those crazy people doing long drops, rubbing the wheel on landing would suck, too…

These are the main reasons I see to go with Ti:

Tough/Maintanance (read: oxide) free.

Bragging rights- it’s FREAK’N TITANIUM!

The Airborn badge, with the dropping bomb, looks cool.

I’m not willing/able to poney up $1000 bucks (or whatever) for bragging rights- I’d rather have another wheel and drooool over somebody elses Ti frame.

BTW: Cannondale aluminium forks have been used for a couple unis…

Anyway, my 2 cents:

The crown should be flat or angled for gliding. Boiler plate would look cool for this.

No less than a centemeter clearance on the sides of the tyre, preferably a bit more, with 2 cm on top. Dismounting because of mud accumulation is a drag.

24 and 20" frames (so that Lewis will by one). Making both should be no BFD.

An ice dispencer.

A decent underseat sub-woofer and MP3 player, preloaded with ‘Ride of the Valkeries’.

Christopher

28

Re: CAD uni drawings?

On Tue, 21 May 2002 08:15:39 -0500,
U-Turn <U-Turn.508ny@timelimit.unicyclist.com> wrote:
>
> > So, for a Ti frame, it sounds like it’ll be strong, lighter than steel
> > / chromoly but heavier than a slightly weaker aluminium one.
>
> Not an expert here but I think aluminum frames get their strength from
> large diameter tubing.

Stiffness rather than strength, and as you identified the stiffness is a
lot less critical in a unicycle than a bicycle.

> very good shock/stress absorption.

The shock absorption merits of titanium are over-rated I think. It’s
going to be several orders of magnitude less than the shock absorbing
action of the tyre (unless you’ve gone for solid steel tyres, I suppose).
This topic is debated ad nauseum on the bicycle tech groups, if you really
want to go into it.

If you’re looking for a unicycle to cross the kalahari I think steel wins
because you’re more likely to find a local who can weld it up for you when
it breaks. Otherwise, I don’t see titanium as having any particular
disadvantages other than cost, and it might be lighter, and it will
certainly seem flashier.

regards, Ian SMith

|\ /| no .sig
|o o|
|/ |

29

I thought that Ti was difficult to machine but relatively easy to weld. Am I mistaken?

30

RE: CAD uni drawings?

> There’s no need to thicken it up to make it stiff like
> a bike frame, because we are not using it to transfer
> power, at least to the extent that a bicyclist uses
> the frame.

Yes and no. A tremendous amount of twisting force is applied to the frame as
you pedal, especially if you hold the front of the seat. Any MUni frame
should be built with this in mind.

A good frame should also be able to take a reasonable amount of side force,
such as from a crash where you land on top of it while it’s on its side.
This type of force (not applied in this way) broke one of my freestyle
frames once.

> But if a flexing plastic Miyata handle is good
> enough for MUni hill-climbing (it probably isn’t the best that can be
> achieved), then the stiffness of the material used for the
> frame is not that critical.

Yuck. I don’t like anything flexing except suspension, a tire, or an air
seat. My Miyata seat sits on top of a custom post that connects to the front
bumper bolts with a gusset, keeping it stiff. This is based on a string of
broken Miyata posts in the past, in addition to wanting a more efficient
transfer of power. Pictures:

> How workable is it in the home basement shop for modifications and
> repairs? Is it possible to find machinists that can work titanium for
> small jobs? Is it harder to find a titanium machinist than a cro-moly
> machinist?

Yes. Titanium can be a pain to work with. Hopefully the frame is what it
needs to be when it arrives in the box… :slight_smile:

I’d love a titanium frame. I already have a carbon one, and am waiting on my
aluminum one from Scott Bridgeman. But for the near future, any titanium
frame production will be of a custom or small-lot nature. Nobody is going to
mass-produce anything with only 10 or so riders saying they want one.

But MUni continues to gain popularity, and as more people find out about our
fun sport, odds are we’ll be able to get better, more affordable parts for
all around the unicycle, including the frame.

Stay on top,
John Foss, the Uni-Cyclone
jfoss@unicycling.com

“Vehicularly-Injured Sperm-Count seat: better known by it’s abbreviated
name, Viscount.” David Stone, on saddle preference

31

I am no expert on this subject but extremely interested in anything that adds comfort without sacrificing efficiency. From my experience with most for mentioned materials, the benefit realized with each depends on your riding style and situation.

For example, both aluminum with titanium have different characteristics as described in each website, but what is important is each lends itself to the sport in different areas. Aluminum typically is a very harsh ride, mostly due to the oversized tubing needed to compensate for low strength properties. It seems to be the material of choice in criterium racing because it is extremely stiff, both laterally (side to side) and radially (up and down). Inherent with criterium racing is lots of high toque sprinting coming out of corners, and starting and keeping up with multiple breakaway attempts. The goal is a bike that is unforgiving so that all torque applied is realized in speed output. Because the bike is radially stiff as well as laterally, one feels every bump in the road, which in fast short races is not a bad thing. A mass marketed aluminum bike called " Giant" is extremely popular at our SLC criteriums

Titanium on the other hand is much more popular in longer road races or endurance riding, than aluminum. The properties of titanium lends itself to this sort of riding. If the frame is designed properly it should be radially forgiving, removing much of the road shock that can be punishing over a long race, but remaining laterally stiff, so that most power is realized in speed output.

Titanium is the material of choice with serious tandem riding, however rarely seen because of its high cost. Because the stoker is sitting directly over the rear wheel (similar to a unicycle), road shock can be punishing. Due to their long lengths, choosing a material and designing the frame to be laterally stiff but radially forgiving is a challenge. A well-deigned titanium tandem is by far the most comfortable ride mostly due to the material’s shock absorbing properties. Most important is that when properly designed, lateral integrity is not sacrificed. A tandem manufacture called “Co-motion” makes the best I have seen.

In short, I think a lot has to be taken into account before a material is selected for a unicycle. The method in which unicycle frames are designed does not lend itself to absorbing shock, no mater the material. We are expecting to find a material that is forgiving without “angles” that are crucial for absorbing shock no matter the material. Most unicycles I see are straight up and down void of angles, which is great for lateral strength but offer nothing in radial forgiveness. We are expecting the length of the tube positioned vertically to offer all its properties. A well-designed bicycle frame uses precise angles to get the most form the material chosen. Telford is a start but even he did not design his frame with the idea of radial forgiveness.

I am confident a frame can absorb shock making riding more pleasant, but at this point I don’t think the answer is in the material, but rather in better frame geometry. I nominated Harper for this project. After all his genius only comes around every hundred years. Foss said so.

dan

32

Re: CAD uni drawings?

On Tue, 21 May 2002 07:30:44 -0500, Neil
<Neil.506kz@timelimit.unicyclist.com> wrote:

>However, I don’t know of any
>unicycle riding style that actually benefits from frame flex.

Semcycle claim that their “standard” model has a very smooth ride by
design because of the somewhat flexible frame.

Klaas Bil

“To trigger/fool/saturate/overload Echelon, the following has been picked automagically from a database:”
“Achmed Jibril, rebels, Rand Corporation”

33

RE: CAD uni drawings?

> Bragging rights- it’s FREAK’N TITANIUM!

Amen!

> The crown should be flat or angled for gliding.
> Boiler plate would look cool for this.

Do that many people really glide on MUnis? This is an important
consideration for a Kris Holm, who basically does everything on a MUni, but
I think most of us have freestyle or other unicycles for those type of
activities. If not, the KH frame is an excellent choice for any MUni fan. In
other words, I don’t put a very high importance on a MUni frame’s ability to
support gliding, one-footing, or stand-up skills. Brake mounts should be
considered, however, on any new high-end MUni frame design. Not everybody
wants or needs them, but people who do won’t consider your design otherwise,
and those are the ones often riding in the toughest places.

> No less than a centemeter clearance on the sides of the tyre,
> preferably a bit more, with 2 cm on top. Dismounting
> because of mud accumulation is a drag.

…Get it, “drag?” I think those numbers sound about right.

> A decent underseat sub-woofer and MP3 player, preloaded with ‘Ride of
> the Valkeries’.

Good luck finding a player that can handle the shocks. Don’t worry too much
about riding shocks, it’s rolling/bouncing down the side of the cliff I’m
worried about…

John Foss, the Uni-Cyclone
jfoss@unicycling.com

“Vehicularly-Injured Sperm-Count seat: better known by it’s abbreviated
name, Viscount.” David Stone, on saddle preference

34

RE: CAD uni drawings?

> The shock absorption merits of titanium are over-rated I think. It’s
> going to be several orders of magnitude less than the shock absorbing
> action of the tyre (unless you’ve gone for solid steel tyres,
> I suppose). This topic is debated ad nauseum on the bicycle tech
> groups, if you really want to go into it.

On a bicycle, quite a bit of ride dampening can be done by a (non-suspended)
frame. That’s because the frame has lots of parts that aren’t vertical. On a
unicycle frame, even a Telford, all the tubing basically goes up and down.
There’s virtually nothing to work with there, shock absorption-wise. I think
the benefits of titanium would be roughly in this order of importance:

  1. Woah, it’s freakin’ titanium!
  2. Good strength-to-weight ratio
  3. It’s titanium
  4. Won’t rust
  5. Check it out – titanium!

Something like that. Numbers 3 and 5 might need to be ranked higher…

JF

35

RE: CAD uni drawings?

> >However, I don’t know of any
> >unicycle riding style that actually benefits from frame flex.
>
> Semcycle claim that their “standard” model has a very smooth
> ride by design because of the somewhat flexible frame.

Yes, it has been advertised that way since its introduction in 1985. But I’m
still trying to figure out how a seat that can twist to the left and right
will give me a smoother ride.

The one area in which the frame is probably helpful is in long rides, where
the flex can alleviate some of the chafing you can get from legs rubbing
against the sides of the seat.

John Foss, the Uni-Cyclone
jfoss@unicycling.com

“Vehicularly-Injured Sperm-Count seat: better known by it’s abbreviated
name, Viscount.” David Stone, on saddle preference

36

Re: RE: CAD uni drawings?

Since I’ve learned to glide, having a flat crown is a priority for me on whatever unicycle I ride. Gliding is just so much fun. Since my MUni is the uni I ride the most, I do use the flat crown on my KH frame quite a bit, even though I have other unicycles that I can glide with. I like the flexibility of being able to glide during/before/after a MUni ride, if I find a nice place for it.

Ben

37

Re: CAD uni drawings?

On Wed, 22 May 2002 09:42:23 -0700, John Foss <john_foss@asinet.com>
wrote:
[color=darkred]
>> >However, I don’t know of any
>> >unicycle riding style that actually benefits from frame flex.
>>
>> Semcycle claim that their “standard” model has a very smooth
>> ride by design because of the somewhat flexible frame.
>
>Yes, it has been advertised that way since its introduction in 1985. But I’m
>still trying to figure out how a seat that can twist to the left and right
>will give me a smoother ride.
>
>The one area in which the frame is probably helpful is in long rides, where
>the flex can alleviate some of the chafing you can get from legs rubbing
>against the sides of the seat.[/color]

I doubt it would matter much in that respect. When I’m thinking long
rides, I’m thinking flat roads, hence little torque, hence negligible
twist. The twist isn’t that much anyway. I own one of these flexible
beasts but wouldn’t want to judge on the flex issue because I seldom
ride anything else (yet).

Klaas Bil

“To trigger/fool/saturate/overload Echelon, the following has been picked automagically from a database:”
“IRS, Security Evaluation, DES”

38

RE: CAD uni drawings?

> whatever unicycle I ride. Gliding is just so much fun. Since
> my MUni is
> the uni I ride the most, I do use the flat crown on my KH
> frame quite a
> bit, even though I have other unicycles that I can glide with. I like
> the flexibility of being able to glide during/before/after a
> MUni ride, if I find a nice place for it.

So that makes at least two. Plus I took some video clips of Brett Bymaster
trying it out on a KH on our last group ride. He’s not used to the knobby
tire though; his gliding experience is with smooth tires on pavement.

On pavement, a knobby tire detracts from gliding, as it’s hard to reduce the
friction enough for a shallow slope. But you need a knobby on dirt, because
a smooth tire will carry too much of the dirt between it and your shoe,
taking away your control. So it can indeed be fun to glide down an unpaved
slope with a knobby tire that keeps your foot gripping…

JF