Mantis: Elegant home brewed TTS

Design of a TTS system:

How can a tech toe be strong enough to hold a tele boot?
Many people (particularly those familiar with using dynafits as an AT binding) have questioned how a Dynafit toepiece can hold the boot without a heel piece. When using the toe piece for touring uphill the boot will pop out of the toe piece if it is not ‘locked’ so how can it deal with the forces generated when skiing with no Dynafit heel mechanism?

Figure 1

It is important to understand how the Dynafit jaws engage with the boot. The jaws, or pins, of the toe piece engage in the tech fittings (little ‘cups’) in the toes of the boot and the detail of the geometry is critical. The jaws open laterally to release the boot if the boot heel is pushed sideways, but in order to pry the toe jaw open, the tech fittings engage with the toe piece at an angle on the front, so that as the boot rotates laterally the jaws are levered open. The wall at the ‘back’ of the cup is not ramped, so the cup cannot be easily pushed forward out of the jaws. This means that if you take a boot and push the heel sideways the boot ‘pivots’ on one jaw and pulls backward out of the other as shown in Figure 1.

When used on it’s own, the toepiece releases with very little force applied to the heel. The magic is that when you add a compression spring that applies a force driving the boot forward then it stabilizes the system by driving the boot forward onto the toe piece and resisting any lateral torque applied to the heel.

Figure 2

Looking at Figure 2, you can see that if a force is applied to the heel as shown, then the boot is trying to rotate counterclockwise about point A. In order for the boot to actually rotate and release then the torque provided by the heel force has to overcome the torque generated by the compression force.

So for a release the following equation holds:

Heel force X Length of boot > (must exceed) Compression force X Width/2

If the force at the heel is not great enough to overcome the compression spring then the boot will not displace sideways and the boot stays attached to the binding.

Graph of release forces in a TTS binding

The interesting thing to note from this is that in theory a greater compression force requires a greater heel force to release the boot. This effect has been seen in some simple experiments. This shows that there is some control over the releaseablity of the binding, though in practice the forces required to get release torques greater than the equivalent to DIN 5-6 may be unrealistic to apply in practice. Note the green line shows the ‘typical’ preload on a tele heel.

Avoiding tippy toe
One of the ways in which a TTS system differs from 75mm or NTN is that the bellows are only compressed with the force that pulls the heel down from the compression springs and the weight of the skier. With no spring and no skier weight then you could rotate the boot with no bellows flex (it’s a free pivot right!). This is not the case in 75mm or NTN where, even without the spring, if you lift the heel you start to compress the bellows as a result of the front of the boot being ‘clamped’. This means that for TTS the effect of the compression spring is more critical to the feel of the binding and this has a few design implications:

  1. Moving the cable pivot forward / back by small increments has a very significant impact on the activity (flex resistance) of the binding.
  2. It is helpful to position the cable pivot lower than is typical on conventional bindings such that you get more spring engagement at low boot flex angles to replace the resistance that is lost due to the free pivot at the toe.
  3. It is typically necessary to have the cable pivot point further back than conventional bindings to replace the resistance that is lost due to the free pivot at the toe.
  4. Less active setups allow the toe to rotate too easily and the system seems to lack control
    Points 2 & 3 tend to result in a binding which requires more spring travel than conventional bindings. This is discussed later.

The Mantis uses a cable pivot that is positioned 70 mm behind the dynafit toe pivot. This set up gives a feel close to Hammerhead position 3 or a BD O1. Anything forward of about 55-60 mm results in a very neutral feel. Anything rear of 80mm was going off the Hammerhead scale.

Schematic of what distinguishes Mantis from “regular” TTS

Achieving Robustness
There are 2 areas where the Mantis differs from the commercially available TTS, including the range of travel of the compression springs and the spacing of the mount.

The spring travel is an important and relatively well understood dimension of a telemark binding. As the boot is flexed and the spring is compressed, the force resisting the rise of the heel increases. At the point where the spring bottoms out there is no longer any travel or compliance in the system and the forces in the system ramp up steeply. This has two effects, the boot heel cannot be raised any further (giving a hard stop feel) and also the stress on the rear binding mounting screws can become dangerously high. In this situation, a skier driving the boot forward aggressively can lever the binding out of the ski. The Mantis avoids this situation by using the longer springs of the AXL binding which have more travel than many of the alternative cartridge based springs. This is something first tried by Ben Kadas in his AXL TTS system. The AXL springs combined with a pivot point giving a fairly active system do not bottom out and allow a ‘knee to ski’ range of motion.

Mount pattern is also something that is of concern to any potential TTS designer. The dynafit toe never takes much torque when used as an AT binding in conjunction with a Dynafit heel. This is because any lateral movement of the heel is supported by the heel piece directly – in essence the heel and the toe work in conjunction to reduce the forces on the individual mounting screws. With a TTS system the boot is clamped into the toe piece and becomes a lever so that if the heel is pushed sideways then it applies all the applied torque through the closely spaced Dynafit toe mount. Big skis, big skiers and burly terrain could result in the toe piece being levered out. To address this issue, the Mantis does two things. First, it uses the Dynafit Radical toe piece which has a slightly greater distance between the screws. Second, rather than mounting the toe piece into the relatively soft ski, the Mantis mounts into a carbon fibre plate using inserts. This plate is extremely strong and stiff with little chance of the toe piece pulling out. The plate is then mounted to the ski, using the NTN mount pattern which has screws much further apart so that the forces for any given torque are reduced. The use of this plate and extended mount pattern reduces the forces on individual screws by approximately 3 times over a TTS system using a conventional Dynafit toe piece mounted using its standard hole pattern.

© 2012
 

Related Posts
BackcountryTalk thread – TTS, strength, weaknesses, workarounds

17 comments

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    • PQ on 13Mar2013 at 12:08 pm

    Nice article, thanks.
    I like the idea of a carbon fibre mounting plate….
    I’ve been skiing with a relatively standard TTS system (direct mounting the tech toe to the ski, G3 heel bits) and really enjoying it.

    One thing that I would add to the discussion is the effect of the boot chosen. I suppose this is true for all tele bindings. However, I’m skiing the TTS using an Scarpa F1 AT boot and a current (black/orange) Scarpa TX-Pro (both 27.0). I prefer a more neutral binding so I’ve mounted the block well forward  (heel bar 5.25cm back from tech pins). With that same position, the F1s give super-active performance while the TX-Pros provide neutral performance (perhaps similar to a BD O1). 

    So… just something to consider when mounting your riser blocks. The ideal position for the heel pivot is crucial and you may well want to shift it for different boots. Also, remember that the mount position changes as boot size changes. Test things out before mounting!

    Loving it so far.

    • PQ on 13Mar2013 at 12:11 pm

    One other comment that is somewhat off topic – boots that are compatible with TTS (and NTN). 

    I’m LOVING the light weight, tourability and hikeability of the F1s. It brings me back to the days when tele gear was actually light and a joy to tour in! It is frustrating that the boot manufacturers push the telemark crowd to heavier and heavier gear when the alternatives are obvious. Obviously people will switch to AT when there is a >2kg boot/binding advantage. My F1/TTS setup is as light as any AT setup not using race boots or bindings…  I keep hoping to see Scarpa taking the discontinued F1 production line and altering that  to come out with a very light NTN/TTS boot.  I understand that it is a small market and boot development is very high cost. And, it is somewhat understandable that they delayed until there were lighter touring bindings available. But those bindings are there now. There are issues with the NTN Freedom for touring, but it is moving in the right direction. And TTS is looking pretty good…

    • teletilyouresmelly on 13Mar2013 at 12:40 pm

    Very cool!  So this is your design Ben?  Couldn’t quite tell from the article.

    • telemarkman on 14Mar2013 at 3:50 am

    Regarding the “NTN 2nd heel” version: How about just shortening the wire of an old superloop binding. could this work?

    • BenKadas on 14Mar2013 at 6:47 pm

    The NTN second heel offers no advantage over using the heel, this has been concluded from more than a few binding makers and frankenbinding makers, the second heel is a gimmick, nothing more. Superloops are too weak, but something with a side throw or a front throw could be incorporated into a TTS.

    • BenKadas on 14Mar2013 at 6:48 pm

    Oddly, both TTS homebrews were built by Ben’s, but this one was built by Ben, aka Bambi 🙂

    • BenKadas on 14Mar2013 at 6:55 pm

    Hey Bambi, nice job, very clean and professional. How much does the reinforced plate weigh?

    I really enjoyed reading the second page, pretty much the same conclusions I came to during my TTS experiments.

    As you found, retention using the NTN second heel (duckbutt) holds no advantage over retention using the standard heel, it was a gummick that caught the eye of many telemarkers, but we now know that it is nothing more than a gimmick.

    NTN did bring the AT toe and tech fittings into tele mainstream, for hat we can be very grateful. I have been skiing TTS hybrids and TTS for two years. I have had no binding failures, no binding pull outs, and I have had numerous releases.

    Simply put, TTS works, TTS is the future.

    • BenKadas on 14Mar2013 at 7:39 pm

    The difference may also be due to the location of the tech fittings on the F1 vs the TX Pro, the F1 has the fittings located for improved touring. Also, the F1 has shorter bellows travel, so it’ll bottom out faster, which could make it feel more active when in fact it’s simply run out of travel.

    • PQ on 14Mar2013 at 9:30 pm

    No, it isn’t bottoming out. The F1 boot/binding system is stiffer right at the start – and remains so through the flex of the boot. I believe it is related to your first point – that the race boots have a short sole and, I believe a slight set-back of the tech fittings. Therefore, it is the essentially the same effect of using a significantly smaller boot – it shifts the pivot point of the riser blocks further back – making the binding/boot combo more active. I think the new F1 flex is actually stiffer as well. So the combination of those two things make it a more active combination compared toa pair of softer, well-used, larger soled TX-Pro.

    My point is that the performance of the system is sensitive to many things. That isn’t bad – but it does complicate setting things up. It also suggests that having movable spring pivot points is critical for a production binding.

    • Ben A on 15Mar2013 at 2:08 am

    @ TTYS – Yes this is a design that I put together last summer. I had been tinkering with test rigs for quite a while but was motivated to spend some money prototyping after seeing Ben K’s ‘Dyna AXL’ on this site. I’ll make it clearer on the article.

    @Ben K – The riser weighs 92g per binding. That weight is the price you pay for the more robust mount + the ability to use it in the NTN mount pattern.

    @telemarkman – a short cable works like a charm for the second heel while skiing but it does have the disadvantage of not disengaging as cleanly and so you need more travel on the preload to ensure that it disconnects for tourmode. I have not yet decided whether to go with the cable or a solid claw.

    @PQ – I am very interested in the F1 as a much lighter boot option – can they drive larger skis or are they limited to lighter weight gear? I’m also wondering how much flex the TLT5 has in the toes, and whether that could be easily modified to allow more flex – I have not got my hands on a pair to see what limits it’s range of motion. If possible then it strikes me that a TLT5 boot could probably provide almost as much control as a TX_pro with a 1.4 kg weight saving.

    Ben

    • BenKadas on 16Mar2013 at 7:39 am

    Cutting weight is tough as the heavy parts (springs, cables/wires, toe piece) are constants, so then if you start adding brakes, a quick throw in/out release, it quickly adds up. Teleskier is correct, NTN has the “convenience” apects covered, but at that convenience comes some costs: higher weight, fragility, and lower performance. Which is why the TTS needs to stay like it is, simple, durable and light.

    The one thing that I feel is not mentioned enough is release. Sure, there are releasable telemark bindings, but they are either clunky or suffer from poor performance. NTN is not releasable, though some claim to have releases, it is still not a releasable binding, nor was it designed to release. TTS on the other hand does have a toe piece designed to release and it will release, as it has for me more than a dozen times. Given time, there will be a toe piece designed with an adjustable release!

    The potential for TTS is huge! The ability to design a toe around a true free pivot, where release and retention can be seperated, and where the retention can be varied by user preference (underfoot cable, side mount wires), these are things that NTN cannot do in it’s current iteration.

    Toe boxes are so yesterday 🙂

    • gfd on 26Mar2013 at 2:33 am

    hi,
    i think it will work with a hammerhead to, if you cut the 75 norm wings off and install the techtoe on top of the plastic shim. now you have 5 cablepins to move the force of the binding.
    i’ll do this when i get a tech boot with bellows cheep.

    greets from snowing munich
    matsch

  1. Hi Matsch,

    ich arbeite seit zwei Jahren an einer TTS Lösung mit der Option das Fersenteil der Dynafit auch für alpines Fahren und Steighilfe zu nutzen. Das Ergebnis kann ich villeicht schon beim tf-skitest in Tux zeigen. Hast du Interesse an einem Gedankenaustausch? Wohne auch in MUC. Schau Dir mal den Beitrag über meinen Prototyp bei tf-friends an.

    Gruß

    Heino Jahn

  2. Sorry for my first Reply in German. I am working for two years realizing a TTS including the Dynafit Heelpiece to have two options: Tele and/or Alpine. News and Pics soon on Facebook.

    Greetings also from Munich
    Heino

    • Gary Mann on 11Dec2013 at 12:09 pm

    Any chance of

    • Einbekker . on 23Mar2014 at 3:23 pm

    I’d like to get also a TTS plate but how to!?

    • Mattias Lindh on 31Mar2014 at 3:25 pm

    Are there any news on this binding or what is happening to the wasatchski-company’s TTS? It seems they are still on beta-models and i cannot find the bindings in stores. I totally agree with the pros of the Mantis concept! Anyway of getting hold of those CAD-models for milling? 😛 That’d be excellent squared! Keep up the good work.

  1. […] makes it ripe for a host of DIY variations, some of which have been publicized on this website (Mantis). And Spike continues to attract interest, again, for simplicity and functionality. The biggest […]

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