I’ve had a few people on the trail ask me this question,
but I didn’t really know the answer. Why does the
Hunter frame have two forks on each side? I thought
that it would make the frame narrower, and thus easier
to ride in some manner, but I wasn’t sure.
Triangles my good man. Triangles are the strongest structure there are (ie. bridges, cranes, large antennas etc.) I believe the double fork with the connection at the top is supposed to make it stronger. And if I am totally wrong, atleast you can lock it up so no one could steal it, unlike a regular uni, where only your wheel is safe.
-David Kaplan
I would really like to know the answer to this if anyone knows. When I look at the hunter frame I only see it’s disadvantages. I know there must be a good reason for the thing looking the way it does. To get things rolling on this discussion, here are my concerns with it’s design. If anyone sees where I have reasoned wrong, or can shed some light PLEASE respond.
First, if you remember from basic strength of materials, the deflection of a beam is the integral of M/(EI) evaluated over the length for which you are concerned with deflection. For simple bending this is simply My/(EI) where M is the applied moment, y is the beam length, E is the material’s Young’s modulus and I is the moment of inertia.
Now consider you are making a unicycle frame and are curious how large the diameter of the lowers should be. For a given material the and moment and length, only the moment of inertia may change as you decide on a diameter. Now the moment of inertia for a hollow tube is : pi(od^4-id^4)/4. (correct me if I’m wrong). This means that the relationship between tube diameter and deflection is roughly forth order. Meaning that a tube of twice the diameter is on the order of magnitude of 16 times as stiff.
So you have the hunter frame with two tubes that are like half the diameter… (like 8 times less stiff?)
so maybe the idea is that you want a naturally more compliant ride without a seat post shock. My suspicion is that the second piece to the frame is to increase the resistance to buckling. (from the same basic engineering class the critical buckling load is
(pi^2)*EI/(KL)^2. Where K is the “effective length factor”.) So the second piece of the frame, by grabbing the first in the middle, may be attempting to constrain the movement to achieve a lower K (higher buckling mode). However, if this is the case, I think there will be huge stress in the welds from this geometry as the second piece will see nearly pure bending. I don’t have time to fire that guy into ANSYS to see, but am curious if anyone out there has broken these frames. If so, where on the frame and how did it fail?
-gauss
Re: Hunter frame question
This is exactly right- a wide frame risks hitting the legs.
Christopher
From my limited experience with Lewis’s, the Hunter is a tank. From what I’v heard from others, the Telford and DM Vortex are equaly strong; the integrity of these frames are well established. They were all made by professionals- 2 of them by pro frame makers. I don’t think they will be slaping themselves in the head, Gauss, when it is brought to there attention that they neglected to take into account the air speed of an unladen african sparrow.
Christopher
haven’t seen the telford, but if you look at the DM Vortex, it is a very different, and I’d venture to say, much more effective geometry than the hunter.
Gauss-
WHAT IN GOD’S NAME DID ALL THAT MEAN? YOU HAVE PROVEN YOUR INTELLECTUAL SUPERIORITY! Now, never speak again.
-David Kaplan
Then you will probably think the Telford is even less likely to function properly- and it is easly the most coveted and beloved of the three! Check it out here:
http://www.telford-design.com/descript.htm
Christopher
against the requests of some I must reply and note that the Telford is a beauty. I might also ask you all to note that in the telford and vortex it is easy to see that the load applied by the rider is more or less evenly distributed among the supports. Where as, in the Hunter, it doesn’t seem to be. I never claimed that this IS the case, but only, that it is my suspicion, whatever that is worth. I only wanted to know the truth about the thing. I don’t think I’m “intellectually superior” just thought that there are more than a few of you that have seen those equations before and would understand where I was coming from. If you haven’t, I tried to explain them pretty well, so that you could see that I wasn’t some shoot from the hip fool who hadn’t given any thought to what he was saying. In fact, I have talked to several people about the hunter frame, some with with P.h.ds in mechanical engineering, who don’t understand what is up with the hunter. I apologize if I offended anyone, by questioning their choice ride. Again, I am just really curious about this thing, and thought that someone out there would know, and that this was the appropriate forum to ask in as I have always been very impressed by the depth of everyone’s knowledge here. Rysling’s response, really helped me to understand the motivation for it. Thank you for that.
also, look at the telford and picture how the reaction forces work, The rear two supports are in compression. Being swept allows the thing to absorb shock (much like some bicycles were designed to do a few years ago). The front two supports respond in tension (think of the seat tube as a see saw pivited about where it joins the seat stay). There is, as far as I can see at a glance, little or no moment (twisting) at any of the welds, which are tig welds. the curved seat stays reduce the overall stiffness (in a good way) and don’t stress the welds as much in bending.
Who better to ask than the man himself?
It would be great to hear the thinking behind the design choices he made- let us know what you find out.
Christopher
Ok, I was just playing with you. I didn’t mean to hurt any feelings. Please accept my apology. Pretty please:D
-David kaplan
I believe that the primary design constraint for the Hunter frame was the desire to use standard bicycle frame tubing. The small diameter tubing is what is used for the rear triangle on a bike. That design also happens to keep the frame narrow. The result is synergy.
The Bay Area California muni guys would know more about the history and reasons for the design of the Hunter. I think it was Bruce Bundy who started the whole thing with the Hunter frame.
RE: Hunter frame question
> haven’t seen the telford, but if you look at the DM Vortex,
> it is a very different, and I’d venture to say, much more
> effective geometry than the hunter.
The DM Vortex was designed after the Hunter and Telford, using things
learned from those designs and looking to improve upon the concept. Both
David Mariner and I came up with nearly the exact same design when asked to
take the Hunter/Telford concept to the next level.
If my understanding of the history is correct, here is how the Hunter came
about:
Most unicycles (nearly all unicycles at that time) are made of cheap,
low-quality tubing. If you’re going to have a frame custom made, it would be
better to use some “real” bicycle frame tubing. But the main tubing of a
bike frame is pretty fat, and would stick out too much on a unicycle frame.
So how about thinner, rear triangle tubing? Okay, but one is not enough. So
two side by side will make up for the lack of thickness.
The Hunter frames are made by Rick Hunter, a famous bike frame maker in the
Santa Cruz area. They were ordered by Bruce Bundy. I don’t know how they
reached the design that was used, but it seems to work fine. Stress-wise,
the front fork seems to take most of the weight, but most of the issues
quoted in the messages on this subject were talking about issues that aren’t
really issues for unicycle frames.
In short, unicycle frames don’t break. What we need at this point are frames
that are big enough to fit the tires we want, yet not so wide as to bang on
peoples’ legs. Also they need to be stiff enough so the tires don’t rub, and
so the seat doesn’t flex left to right.
Off the top of my head I can’t think of any examples of broken Hunter,
Telford, or DM Vortex frames. Or nearly any other type for that matter. I
broke a Miyata Deluxe frame once, but that was from a trick where I was
standing on the uni on its side. I think I put my freestyle frames to more
abuse than my MUni frames.
Continuing the frame history, the Hunter design came first. Based on that
concept, Geoffrey Faraghan came up with the Telford design. For this
unicycle he wanted two main things, a seat post angle similar to a mountain
bike, to allow for mountain bike suspension posts, and a more elegant,
aesthetic look than the utilitarian Hunter frame.
Geoff may not be a professional frame maker, but he is a perfectionist, and
the Telford frames are beautiful and very well crafted. The problem with
Telfords has always been getting one, as the demand continues to exceed the
supply.
Based on the success of the Hunter and Telford designs, David Mariner (DM)
wanted to make a similarly high-tech MUni frame. So he took the small tubing
concept to what is probably at or near its logical limit, with a simple “V”
design pointing straight down to the wheel.
Bronson Silva had a DM Vortex prototype, which looked very similar to the
Hunter. I believe this was a concept testing model. Bronson used that one
for a long time, but has recently replaced it with a Kris Holm.
I still ride and love my DM ATU, but it’s about time I moved up to a 3" tire
(and one less excuse for not riding the gnarly stuff when everybody else,
including Beau, does…). My Wilder is on order!
Stay on top,
John Foss, the Uni-Cyclone
jfoss@unicycling.com
“My p____ just grew an inch!” David Poznanter, after riding an insane
downhill mud/wood obstacle in the pouring rain
Re: Hunter frame question
All good comments by John. The history is correct as far as I know. The
initial design of the Hunter was largely Bruce’s. He was riding the first
prototype in Dec 1997 and it was ridden yesterday in Santa Cruz and at Sea
Otter by Louise, a beginner who will try anything. It couldn’t be in better
hands.
The only frame I know of breaking was Bruce’s Semcycle Deluxe 26" that I
broke going uphill in '99. It broke down by the bearing holder - snapped
right through. But none of the Hunter or other frames specifically designed
for Muni seem to have any problems like that. All the other parts, but not
the frames. Has anyone else broken a frame?
—Nathan
“John Foss” <john_foss@asinet.com> wrote in message
news:mailman.1017083450.422.rsu@unicycling.org…
> > haven’t seen the telford, but if you look at the DM Vortex,
> > it is a very different, and I’d venture to say, much more
> > effective geometry than the hunter.
>
> The DM Vortex was designed after the Hunter and Telford, using things
> learned from those designs and looking to improve upon the concept. Both
> David Mariner and I came up with nearly the exact same design when asked
to
> take the Hunter/Telford concept to the next level.
>
> If my understanding of the history is correct, here is how the Hunter came
> about:
>
> Most unicycles (nearly all unicycles at that time) are made of cheap,
> low-quality tubing. If you’re going to have a frame custom made, it would
be
> better to use some “real” bicycle frame tubing. But the main tubing of a
> bike frame is pretty fat, and would stick out too much on a unicycle
frame.
> So how about thinner, rear triangle tubing? Okay, but one is not enough.
So
> two side by side will make up for the lack of thickness.
>
> The Hunter frames are made by Rick Hunter, a famous bike frame maker in
the
> Santa Cruz area. They were ordered by Bruce Bundy. I don’t know how they
> reached the design that was used, but it seems to work fine. Stress-wise,
> the front fork seems to take most of the weight, but most of the issues
> quoted in the messages on this subject were talking about issues that
aren’t
> really issues for unicycle frames.
>
> In short, unicycle frames don’t break. What we need at this point are
frames
> that are big enough to fit the tires we want, yet not so wide as to bang
on
> peoples’ legs. Also they need to be stiff enough so the tires don’t rub,
and
> so the seat doesn’t flex left to right.
>
> Off the top of my head I can’t think of any examples of broken Hunter,
> Telford, or DM Vortex frames. Or nearly any other type for that matter. I
> broke a Miyata Deluxe frame once, but that was from a trick where I was
> standing on the uni on its side. I think I put my freestyle frames to more
> abuse than my MUni frames.
>
> Continuing the frame history, the Hunter design came first. Based on that
> concept, Geoffrey Faraghan came up with the Telford design. For this
> unicycle he wanted two main things, a seat post angle similar to a
mountain
> bike, to allow for mountain bike suspension posts, and a more elegant,
> aesthetic look than the utilitarian Hunter frame.
>
> Geoff may not be a professional frame maker, but he is a perfectionist,
and
> the Telford frames are beautiful and very well crafted. The problem with
> Telfords has always been getting one, as the demand continues to exceed
the
> supply.
>
> Based on the success of the Hunter and Telford designs, David Mariner (DM)
> wanted to make a similarly high-tech MUni frame. So he took the small
tubing
> concept to what is probably at or near its logical limit, with a simple
“V”
> design pointing straight down to the wheel.
>
> Bronson Silva had a DM Vortex prototype, which looked very similar to the
> Hunter. I believe this was a concept testing model. Bronson used that one
> for a long time, but has recently replaced it with a Kris Holm.
>
> I still ride and love my DM ATU, but it’s about time I moved up to a 3"
tire
> (and one less excuse for not riding the gnarly stuff when everybody else,
> including Beau, does…). My Wilder is on order!
>
> Stay on top,
> John Foss, the Uni-Cyclone
> jfoss@unicycling.com
> www.unicycling.com
>
>
> “My p____ just grew an inch!” David Poznanter, after riding an insane
> downhill mud/wood obstacle in the pouring rain
Re: Hunter frame question
On Mon, 25 Mar 2002 10:57:41 -0800, John Foss <john_foss@asinet.com>
wrote:
>“My p____ just grew an inch!” David Poznanter, after riding an insane
>downhill mud/wood obstacle in the pouring rain
In places where John nor anyone in this group of course ever ventures,
such growth is offered for considerable sums of money. Just riding an
insane obstacle is definitely an el cheapo method of obtaining a
larger p____!
Klaas Bil
“To trigger/fool/saturate/overload Echelon, the following has been picked automagically from a database:”
“GSS, meta, 20755”
I heard back from Rick today. Here is what he had to say on the subject.
Hey Chris
Thanks for the mail… Hmmm you want me to disclose my intellectual property to a
chat group ! Oh well here goes… basically the double tubes keep the overall
width to a minimum especially once I started making the uni’s with clearance for
3.0 tires. If the frame were any wider people would be knocking their knees. The
hoop style stays are also stylied after the bicycle frames that I build along with
the wishbone piece. This made sense to me as it works great for
bicycles. I am not
an engineer so any analysis is a little over my head. I rely on real
world testing
and so far not a single failure of any kind, fatigue or yield. I think
most the of
force on a uincycle goes directly through the pedals into the cranks and
hub. The
hub strength was the main concern early on when people started taking
the uni’s on
trails and of drops and such. I guess originally another feature of the wishbone
rear end was to act like a handle as well, mainly when you are off the cycle or
jumping off it , I wanted to make it distinctive looking also. I feel a
proper
design will incorporate alot of things… strength and durability for
starters then ergonomics and style.
Happy Trails
Rick
Re: Hunter frame question
It’s not really el cheapo. To develop that level of skill typically takes
years of hard work and will require hundreds or more likely thousands of
dollars worth of unicycle stuff. Anything that is easy or cheap
automatically isn’t worth anything so the length stays the same (or even
goes down).
You should’ve heard those guys on that ride though…“Oh S#%$ I crashed on
that little drop?! Must’ve lost at least an inch.”
—Nathan
Sorry this is un-PC, but that’s real life for you.
“Klaas Bil” <klaasbil_remove_the_spamkiller_@xs4all.nl> wrote in message
news:3c9fb155.13971167@newszilla.xs4all.nl…
> On Mon, 25 Mar 2002 10:57:41 -0800, John Foss <john_foss@asinet.com>
> wrote:
>
> >“My p____ just grew an inch!” David Poznanter, after riding an insane
> >downhill mud/wood obstacle in the pouring rain
>
> In places where John nor anyone in this group of course ever ventures,
> such growth is offered for considerable sums of money. Just riding an
> insane obstacle is definitely an el cheapo method of obtaining a
> larger p____!
>
> Klaas Bil
RE: Hunter frame question
> Anything that is easy or cheap automatically isn’t worth
> anything so the length stays the same (or even
> goes down).
>
> You should’ve heard those guys on that ride though…“Oh S#%$
> I crashed on that little drop?! Must’ve lost at least an inch.”
I probably shouldn’t go here, but…
After a few of these comments, Scot Cooper said something about scoring the
obstacles on a “penimeter.” We all got a laugh out of that one.
Then on Sunday, we were talking to Dangerous Dan from Vancouver. He was
getting ready to present a show at Sea Otter, where he and two other
Flowriders (www.flowriders.com) were going to ride on wooden ladder bridges
and beams, the highest of which was at least a third higher than this one:
http://www.flowriders.com/1389.htm
Dan was mentioning how the wind was making things “sketchy.” After we were
done talking to him, I commented that sketchy is a relative term. For me, a
beam 3’ off the ground is sketchy. So his 18’ (or however high) bridge was a
little sketchy? But it rates a thousand on the penimeter!
My pictures from Sea Otter, including ones similar to the link above, will
be up eventually, after I get caught up on all the pictures before that…
please be patient.
(http://www.unicycling.com/ofoto/muniphotos.htm)
Stay on top,
John Foss, the Uni-Cyclone
jfoss@unicycling.com
“My p____ just grew an inch!” David Poznanter, after riding an insane
downhill mud/wood obstacle in the pouring rain
RE: Hunter frame question
Rick Hunter wrote:
> most the of force on a uincycle goes directly through the
> pedals into the cranks and hub.
I know Rick isn’t reading this, but that’s okay, he knows what he’s doing.
Yes, the biggest stresses on a mountain unicycle are in the pedals, cranks,
and hub. I think the two biggest stresses on a mountain unicycle frame are
twisting, left and right as you pedal, and pulling, the force going from the
seat handle and pulling at the point of the bearing holders.
Of course the frame supports the rider when seated for regular riding, but
mostly we are not on the seat when doing the challenging stuff. Especially
drops, we hope!
In a well-executed drop, the frame probably gets very little stress at all.
everything’s happening to the wheel, and you are hopefully not landing on
the seat.
Pedaling uphill and powering over obstacles I think are where the real
stresses come in. My carbon fiber MUni frame broke (due to a defect in
manufacture where not enough adhesive got into the tube joint) from hard
uphill pedaling. As you crank hard from one side to the other, holding or
pulling up on the seat, the frame is being wrenched from side to side with
basically all the strength of your biggest muscles. It puts a lot of
twisting force on the frame! My carbon frame was repaired, with aluminum
pins to assist the glued joints and to help resist against the twisting
force.
The pulling up type of force happens whenever you hop, or otherwise pull up
on your seat. Depending on the shape of your seatpost and frame, this puts a
pulling force on the whole frame, as well as a rearward flexing force that
could have some long-term effects wherever the weak part of the frame may
be.
Lastly, a unicycle frame (for any type of riding) has to be laterally stiff,
meaning to keep the fork crown from moving side to side over the tire. This
is the cause of tire rub, and the reason why you need lots of clearance on a
flexible frame, like a Schwinn. The stiffer your frame, the less flex you
will get, and the less tire clearance you need (not accounting for mud). In
this area, tubular frames are going to fare better than flat steel (or
aluminum) frames, unless those flat frames are real thick.
Stay on top,
John Foss, the Uni-Cyclone
jfoss@unicycling.com
“My p____ just grew an inch!” David Poznanter, after riding an insane
downhill mud/wood obstacle in the pouring rain