Spring loaded nut tool on Kickstarter

Eli Buzzell wrote: My thoughts exactly.

No problem guys, science is useless, right? Go back to your cave...

Don't know much about all the complicated stuff but I will buy one when available - I've skinned enough knuckles over the years.

Eric and Lucie wrote: No problem guys, science is useless, right? Go back to your cave...

Is science useless? Of course not. Is worrying about the science of a nut tool useless? Yes.

I can smell engineer from a good distance and it usually does not smell like fun. But hey I am just a knuckle dragger.

Little hammer is aid.

Eric and Lucie wrote: [...] * Tiny hammer on concrete: low energy, high force, short duration (hard impact) * big sledge hammer on mattress: high energy, low force, long duration (soft impact). Does that make more sense? I think that the value of this tool is that it is likely easier to hold snug against a nut in just the right place and at the right angle, without having to worry about hitting it with a rock of cam, or by hitting the nut with the tool itself. As a result, the energy of the moving mass will be transmitted very efficiently to the nut, and the shock will be very hard, so it will be able to reach a high force (more like the concrete wall than the mattress).

This is the main point of LittleHammer thanks Eric and Lucie. A stabbing strike at a nut with a passive nut tool means the palm is the mattress — creating a soft impact as it backs up the nut tool handle. Some designs make this more comfortable with covers or flat sections on the the handle but this doesn't help with the soft impact problem.

LittleHammer's small impact weight even with a short travel supplies a hard impact force you can connect directly and accurately to the nut. Given the wedge shape of a nut you don't have to reverse it far to release.

Eric and Lucie wrote: Sure, you could measure a force, but it would not in any way be a characteristic of the tool, but rather a characteristic of the nut placement you are working on. It's a bit like if you were trying to characterize a hammer by hitting something with it. If you hit a concrete wall, you will generate an incredibly high force even with a tiny hammer, but if you hit a mattress, that force will be many orders of magnitude smaller, even with a sledge hammer (but that force will act for a much longer time... while the mattress undergoes a large deformation). * Tiny hammer on concrete: low energy, high force, short duration (hard impact) * big sledge hammer on mattress: high energy, low force, long duration (soft impact). Does that make more sense? I think that the value of this tool is that it is likely easier to hold snug against a nut in just the right place and at the right angle, without having to worry about hitting it with a rock of cam, or by hitting the nut with the tool itself. As a result, the energy of the moving mass will be transmitted very efficiently to the nut, and the shock will be very hard, so it will be able to reach a high force (more like the concrete wall than the mattress).

Ah, got it. It would serve some utility to compare directly under controlled conditions, but I see your point.

Mike Brady wrote: Is science useless? Of course not. Is worrying about the science of a nut tool useless? Yes. I can smell engineer from a good distance and it usually does not smell like fun. But hey I am just a knuckle dragger.

As a fellow engineer (admittedly, an environmental engineer), I thought it was an interesting discussion, and particularly relevant given the discussion was about the physical properties of the tool.

Mike Brady wrote: Wow...you must be a blast to hang out with.

my thought exactly, first it was "oh yeah, I already invented that" then it went to "oh yeah, you dont understand force, let me explain".

I think this is pretty awesome the more I think about it.

scienceguy288 wrote: As a fellow engineer (admittedly, an environmental engineer), I thought it was an interesting discussion, and particularly relevant given the discussion was about the physical properties of the tool.

I thought the discussion WAS interesting but the discussion had turned into a discussion about the tools physical properties. It was originally posted as "Hey check out this cool idea".

As a machinist and fabricator it is my duty to rib engineers whenever possible. With that said, from someone who appreciates what is involved in creating and then producing things, I am not going to tell the people that are complaining about the cost of a tool that is being made on a very small scale that the cost is in fact reasonable, regardless of whether the tool has enough force to work well. If force is even the right word. :)

A word on the physics. While energy is an easy way to symplify the mathematics of this problem, the fundamentals of why this design works is impulse. Starting with F = ma (force = mass*acceleration), you can go through the following (high school physics) steps:
F=ma
F=m(deltaV)/t //t=time, deltaV=change in velocity
Ft=mv
This equation says that Force*Time (also called impulse) is equal to mass*velocity (also called momentum). Step two above is a lazy mans way of taking an derivative, and a better interpretation is that the impulse is equal to the change in momentum. In our problem, the change in momentum is that of the slide hammer. Immediately before it strikes the end of the tool, its velocity (and thus its momentum) is maximized (m*vbefore). Very soon after it strikes the end of the tool, its momentum is zero (m*vafter=m*0=0). This means that all of the momentum of the hammer is translated into impulse in this system.

We will assume the maximum velocity of the hammer is fixed (the spring system is frictionless, and the spring is strong enough to ignore the effects of gravity), and thus the momentum change is fixed at Vbefore*m (where m is the mass of the slide hammer, more on this later).
Inspecting the other side of the equation, if we assume momentum change is fixed, than decreasing the time increases the force on the system. In other words, if the time it takes to change the momentum (the time it takes the hammer to go from Vbefore to 0) is very small, the force is very large. Alternately, if the time is much longer, the magnitude of the force applied is much smaller. For the case of the littleHammer, the time is very very small. I tried to find some information on the duration of this impulse. After watching a lot of slow motion videos of hammers hitting things and looking up specs on impact hammers, I decided to just ballpark it. According to this surprisingly detailed paper, duration of a clap clapping a human hand takes about 200uS. The time for the hammer to impact the end of the device is probably similar to that duration, and slamming a nut tool onto a lodged piece is likely an order of magnitude slower than than a clap (2mS). Additionally, the impact velocity of the hammer is likely higher than what someone could practically generate with their hand in a real world situation. Net: even if the hammer is signifcantly lighter than a persons arm, considering the duration of the impulse and the velocity of the hammer, it is likely to produce similar force.

In order to dislodge a stuck piece of gear, you need to apply a threshold force to overcome the deformation of the metal. Lets try to solve for this force based on the parameters of the problem. Energy is a very useful concept when solving problems like this, because it can vastly simplify the math. Instead of trying to solve for the equations of motion of a spring (mx''=kx') and taking the derivative of the result to substitute for the velocity in our impulse equation, we can just remember that energy is conserved. In this case, when the hammer is pulled back, the user stores potential energy in the spring. Assuming a linear spring, this energy is 1/2kx^2 where k is the spring constant and x is the displacement from an uncompressed spring. When the spring is released, the energy converts from potential to kinetic energy, which is 1/2mv^2, where m and v are as above. Setting these equal and solving this for v:
1/2kx^2 = 1/2mv^2
v^2 = k/mx^2
v = sqrt(k/m)x
and substituting into the equation above, solved for force:
Ft = m(sqrt(k/m)x)
simplifying:
F = sqrt(km)x/t

This shows that the applied force of the hammer on the piece is directly proportional to how much the spring is compressed, and only proportional to the square root of the mass of the hammer. The time (t) is fixed by the physical properties of the materials, so the only way to increase force is to increase the mass , the amount you pull back the spring, or the spring constant
From looking at the schematic and watching the video, the wieght seems to be pulled back about 5cm, and i'd guess the wieght of the brass hammer to be about 80 grams (more the half of the entire wieght). Assuming a strong spring (16lb/inch = 2800 N/m) and substituting:
F = sqrt(2800N/m*0.08kg)*0.05m/0.0002s = 3740 or 3.7kN
Assuming a human hand/arm wieghs 15 lbs (6.8kg) and you can get the nut tool moving around 15mph (6.7m/s) before you hit it yields a force of
f=mv/t = (6.8kg*6.7m/s)/0.002s = 2278N or 2.2kN
Obviously these are ballpark estimates, and it would be interesting to get real data, but I think it shows that the littlehammer is at least in theory capable of producing similar force to a human using a traditional nut tool.

Mike Brady wrote: I thought the discussion WAS interesting but the discussion had turned into a discussion about the tools physical properties. It was originally posted as "Hey check out this cool idea". As a machinist and fabricator it is my duty to rib engineers whenever possible. With that said, from someone who appreciates what is involved in creating and then producing things, I am not going to tell the people that are complaining about the cost of a tool that is being made on a very small scale that the cost is in fact reasonable, regardless of whether the tool has enough force to work well. If force is even the right word. :)

Meh, saying cool idea or this idea is useless is only interesting for some time. Discussions regarding testing of physical properties are far more involved!

Kyle Tarry wrote: Yes, different placements will vary significantly, but it's not possible to quantify or test every placement possible, so why try? The value in measuring the force under controlled circumstances is it gives you the ability to compare measurements of other techniques (such as tapping with a nut tool, or tapping with a cam on a nut tool) under the same controlled circumstances, and therefore gives you relative information. Just because a test does not perfectly mimic the real application doesn't make the test useless. I think you could devise a test (or a few tests) that mimic a stuck placement fairly well, and get some decent comparable data from different methods.

That was my thought. Material hear strength is measured in controlled conditions in the lab using devices that don't test every single force that will be experienced, but those measurements are still used in designing products. The point here, I think, is to assess the forces/impulses involved using this product relative to those generated during the use of a regular nut tool. Even if it doesn't consider every placement, it will still be generalizable to some extent and control for a lot of confounding variables (e.g., how stuck is the nut placement? How deep is the crack? How strong is the user?).

mikejohnson1 wrote:A word on the physics. While energy is an easy way to symplify the mathematics of this problem, the fundamentals of why this design works is impulse. Starting with F = ma (force = mass*acceleration), you can go through the following (high school physics) steps: F=ma F=m(deltaV)/t //t=time, deltaV=change in velocity Ft=mv This equation says that Force*Time (also called impulse) is equal to mass*velocity (also called momentum). Step two above is a lazy mans way of taking an derivative, and a better interpretation is that the impulse is equal to the change in momentum. In our problem, the change in momentum is that of the slide hammer. Immediately before it strikes the end of the tool, its velocity (and thus its momentum) is maximized (m*vbefore). Very soon after it strikes the end of the tool, its momentum is zero (m*vafter=m*0=0). This means that all of the momentum of the hammer is translated into impulse in this system. We will assume the maximum velocity of the hammer is fixed (the spring system is frictionless, and the spring is strong enough to ignore the effects of gravity), and thus the momentum change is fixed at Vbefore*m (where m is the mass of the slide hammer, more on this later). Inspecting the other side of the equation, if we assume momentum change is fixed, than decreasing the time increases the force on the system. In other words, if the time it takes to change the momentum (the time it takes the hammer to go from Vbefore to 0) is very small, the force is very large. Alternately, if the time is much longer, the magnitude of the force applied is much smaller. For the case of the littleHammer, the time is very very small. I tried to find some information on the duration of this impulse. After watching a lot of slow motion videos of hammers hitting things and looking up specs on impact hammers, I decided to just ballpark it. According to this surprisingly detailed paper, duration of a clap clapping a human hand takes about 200uS. The time for the hammer to impact the end of the device is probably similar to that duration, and slamming a nut tool onto a lodged piece is likely an order of magnitude slower than than a clap (2mS). Additionally, the impact velocity of the hammer is likely higher than what someone could practically generate with their hand in a real world situation. Net: even if the hammer is signifcantly lighter than a persons arm, considering the duration of the impulse and the velocity of the hammer, it is likely to produce similar force. In order to dislodge a stuck piece of gear, you need to apply a threshold force to overcome the deformation of the metal. Lets try to solve for this force based on the parameters of the problem. Energy is a very useful concept when solving problems like this, because it can vastly simplify the math. Instead of trying to solve for the equations of motion of a spring (mx''=kx') and taking the derivative of the result to substitute for the velocity in our impulse equation, we can just remember that energy is conserved. In this case, when the hammer is pulled back, the user stores potential energy in the spring. Assuming a linear spring, this energy is 1/2kx^2 where k is the spring constant and x is the displacement from an uncompressed spring. When the spring is released, the energy converts from potential to kinetic energy, which is 1/2mv^2, where m and v are as above. Setting these equal and solving this for v: 1/2kx^2 = 1/2mv^2 v^2 = k/mx^2 v = sqrt(k/m)x and substituting into the equation above, solved for force: Ft = m(sqrt(k/m)x) simplifying: F = sqrt(km)x/t This shows that the applied force of the hammer on the piece is directly proportional to how much the spring is compressed, and only proportional to the square root of the mass of the hammer. The time (t) is fixed by the physical properties of the materials, so the only way to increase force is to increase the mass , the amount you pull back the spring, or the spring constant From looking at the schematic and watching the video, the wieght seems to be pulled back about 5cm, and i'd guess the wieght of the brass hammer to be about 80 grams (more the half of the entire wieght). Assuming a strong spring (16lb/inch = 2800 N/m) and substituting: F = sqrt(2800N/m*0.08kg)*0.05m/0.0002s = 3740 or 3.7kN Assuming a human hand/arm wieghs 15 lbs (6.8kg) and you can get the nut tool moving around 15mph (6.7m/s) before you hit it yields a force of f=mv/t = (6.8kg*6.7m/s)/0.002s = 2278N or 2.2kN Obviously these are ballpark estimates, and it would be interesting to get real data, but I think it shows that the littlehammer is at least in theory capable of producing similar force to a human using a traditional nut tool.

I realize that this is a ballpark figure, but are these values significantly different? I.e., are we talking tank vs bicycle or Honda Civic vs Subaru Forester (a strange metaphor, I know, but I think it conveys my question)?

mikejohnson1 wrote:A word on the physics.

Thet's quite a long demonstration for a climbing forum...
One thing I get from it is that the lighter the steel part of the tool (resisting the shock) and the heavyer the hammer, the more efficient it gets (the sum of masses from the impulse theory, remember ?)
The nut tool in the movie seems to be a little thick (and heavy) though...

I'm loving the physics discussion, I don't know the correct language but have been thinking about it in terms of the peak of the impact force over time. LittleHammer's advantage over a hand strike is that it gives a sharper peak, a small amount of force in a short period, transferred metal to metal.

With the hand strike, though it has the weight of the arm, the peak force is spread over a longer period as the flesh of the palm takes up the impact (backing up the tool handle).

It was using a cam for a hammer that I realised even though it didn't weigh much connecting that force directly to the stuck nut made it work. I'm not too happy about whacking a highly engineered cam like that, and also like to think the second could have an ascent without hanging on the rope to sort stuck gear, testing themselves at that grade.

LittleHammer is at its best in aid climbing but also great for climbers seconding to have some help — I learnt climbing seconding a friend that heavily seated every piece so I had some struggles removing gear when I was already freaking out about the climbing.

I've had some engineer climbers contact me and offer to model the forces so hopefully will have some data soon… weather I can understand it is yet to be seen!

I've devised this test for the less technical minded like myself.

climbdesign.files.wordpress…

I normally do not get involved in these types of discussions, especially when the equations start flying all over the thread.

My advice: I'd keep down the path that you are as it seems your product is on the right track. If you want to really wring out the performance in a quick manner, setup a DOE (design of experiments) using different nut loading situations (i.e. a nut that has been placed and set by hand, a nut that has been "fallen" on with a weight equal to around 180 lbs dropped from a certain distance, etc.).

You can calculate to your blue in the face, but there are details missed when you try and simplify the problem as I suspect some have in the posts above. If you want to go down the analysis route to determine the stresses on your tool and potential force generated, get a competent mechanical engineer / designer that has design experience related to your product and have them run an FEA (finite element analysis) simulation on your design. You will get a lot closer to the real world numbers by doing this. From this point, you can fine tune your design based on the results, run a real-world lab test to confirm the numbers from the FEA, then rinse and repeat.

It's easy to over simplify a problem using basic physics. You want an engineer looking at designs like this, not a physicist.

Kyle Terry is right about assumptions as well.

I agree with the general sentiments. I happen to be a physicist working as an engineer... I just did the calculations for fun. I'd say the general theory is correct (short impulse= high force==better at unsticking nut) but the best way to optimize the design is going to be by experiment. I don't think measuring or calculating or modeling the force is strictly necessary in this design, probably best to try out a bunch of weights/springs/lengths, etc... Sounds like you already did that, and I think the concept is great.

We wanted this nut tool BAD last Saturday! It would be great if you could attach it to your wrist and unlock nuts ninja style! Kapoung!

Three pages? Of this and no one said-?

"Put a palm sized rock in your chalk bag"
.?
that's the old way but not very safety conscious
So do not carry rocks in your chalk bag,

but
use any hard surface , cam head or the outside edge of that #10 hex from the belay.
I have a dedicated piece, a ,Clog Wab' a Hex like nut with thick walls it is from the 1970s that always does the job. (Back in the day we all had hammers in our packs . . .)

if you are a weak second or the leader fell and set the piece of gear, get a fefe hook ( thanks Jake!)
Place a piece of gear near as possible to the stuck piece, and hang off that while working to free the stuck piece.

Or wait did you hear? there is an app for that
I will collect a spring loaded Nut pick for the Novelty, and for what it is worth I will wait to get one used on EBay.