Quick release buckle strap with controllable release of tension

[Robbwal199]

Looking for products / ideas on a strap (max 30 cm length) which has a quick release buckle (like in bike helmets) halfway up the strap which can be released without a person manually touching/altering the buckle themselves. For eg: a wireless system where clicking a button on an app releases the buckle (unrealistic but gets the point across)

 

[berkeman]

What range of tension does the strap need to be able to handle? What other release mechanisms are you considering? Can you say what the application is? (Does it involve life safety, for example)

 

[berkeman]

BTW, is this related to your previous thread about the head/neck injury testing in vehicle crashes?

https://www.physicsforums.com/threads/turnbuckle-release-mechanism.1057808/

 

[Robbwal199]

What range of tension does the strap need to be able to handle? What other release mechanisms are you considering? Can you say what the application is? (Does it involve life safety, for example)

Yes, it is the same application as in previous forum but didn't want to bombard viewers with too much information; I can filter any ideas based on if I think its feasible in terms of safety, tension needed etc.

 

[berkeman]

Okay, so you want a way to disconnect the restraint strap that is synchronized with some moment during the collision process, right? Have you found any good candidates so far?

 

[Robbwal199]

Okay, so you want a way to disconnect the restraint strap that is synchronized with some moment during the collision process, right? Have you found any good candidates so far?

Exactly that if possible.. if not fully synchronized with a specific moment, at least someway controllable. No good candidates as of yet.

 

[berkeman]

What is the range of hold force that you need? You could just use an energized solenoid to hold the 2 strap ends together until you want to disconnect them, and shut off the power to the solenoid at the exact moment you want to release the tension.

 

[Robbwal199]

What is the range of hold force that you need? You could just use an energized solenoid to hold the 2 strap ends together until you want to disconnect them, and shut off the power to the solenoid at the exact moment you want to release the tension.

Giving a guess, tension needed would be equivalent to an average man having to exert 50% of his strength to pull a light 20cm strap.. I'm unfamiliar with solenoids - firstly, how practical would it be to fit this into a 20cm long strap? Retraction upon de-energizing disconnects the straps how?

Cheers

 

[berkeman]

Giving a guess, tension needed would be equivalent to an average man having to exert 50% of his strength to pull a light 20cm strap..

That's a lot of force, probably on the order of 100 pounds? That's more than a typical bicycle helmet strap buckle can reliably hold against, IMO. That would take a pretty big solenoid; the one in the picture below is only 65 ounces worth of holding force.

I'm unfamiliar with solenoids - firstly, how practical would it be to fit this into a 20cm long strap? Retraction upon de-energizing disconnects the straps how?

A solenoid would fit fine in this application, as long as the hold force was not too big. Basically an electrical coil is energized to pull in and hold a ferrous cylinder:

https://en.wikipedia.org/wiki/Solenoid_(engineering)

https://www.galco.com/53753-82-delt.html?utm_source=adwords&utm_medium=cpc&utm_campaign=[EM] Standard Shopping | A1 | Top 50% Products | In Stock - G&utm_term=&utm_content=156551831946&utm_id=20873210055&utm_device=c&utm_network=g&utm_mt=&source=AdWords&gad_source=1&gclid=Cj0KCQiAtaOtBhCwARIsAN_x-3JJKOPuZrbUpF2OGp8AH0HyB_PZdTLOOjZDGzWSFZnkR5mkYflNMIcaAmESEALw_wcB

 

[berkeman]

If you really need to hold against 100 pounds of force, then some other buckle/release mechanism will likely be needed instead of just a solenoid.

 

[Robbwal199]

Thanks for that Berkeman, based off your recommendation and my lack of familiarity, I'll rule out the solenoid.

Possibly more relevant to my previous forum:
Going back to my previous idea as in Picture 1 attached, the ratchet strap reduces length between platforms and tilts the head forward. The bottom hook on strap is machined so that it is barely holding onto its anchor. In order to help with consistency of the hook coming off the anchor point to relieve all tension, I believe adding a fixed mechanism as in Picture 2 could help. A horizontal bar/wire (drawn in black) positioned just before the hardstop impacts the lower half of the strap (below ratchet). This will displace that impact point on the strap to the right as we look in the picture, which will accordingly kick the hook to the left as we look, and help it off the anchor point.

If this does work it achieves two things: 1. greater consistency in alleviating tension. 2. release of tension is before impact/hardstop and does not require the impact to release tension (without new bar/wire, hooks coming off anchor is dependent on force generated by impact).

Let me know if you understand this (I gather its very difficult to follow) and if so, do you think this could work / help?

 

[Tom.G]

A bit of clarification would be helpful. Is the release to be based on Force or on Position (along the track)?

If Positional release is acceptable, use ordinary cam lock buckles with the release handles facing the trailing end of the sled. With appropriate cord(s) attached to the release handle(s) leading back to the launch point. The cords get tight, open the cam lock buckle, and your the head is free.

I recommend a single release mechanism to avoid problems of trying to get two of them to release at exactly the same time.

(above found with:
https://www.google.com/search?hl=en&q=cam+lock+straps)

Cheers,
Tom

 

[Robbwal199]

@Tom.G The release needs to be solely positional relative to the track i.e. it releases tension at the same point positionally.

I can see the potential of this cam lock buckle idea but don't fully understand. See picture attached.

Is the orientation of the buckle correct? Where does the cord attach to the buckle / how does the tension in the cord release the buckle?

 

[Tom.G]

The buckle must be positioned so that the lever you would lift to release the buckle is facing toward the starting end of the track.

Of course the cord(s) must remain slack after they open the buckle until the sled hits the end stop.

Assuming the buckle is on the lower strap, attached to the sled, a few possibilities would be:
1) Make the lower strap long enough to leave slack in the strap + cord(s) at end-of-travel.
2) Attached the fixed end of the strap (right end in your image) to an extension spring. The spring of course would need to be strong enough to open the buckle but weak enough to not materially affect the sled speed.

Cheers,
Tom

p.s.
Another approach comes to mind:

1) Put hook(s) on the lower end of the hold-down straps.
2) Put the hook(s) into slot(s) or holes(s) in the bottom of the sled.

(or put wing(s) on the sled to accept the hook(s)​

3) On the base of the apparatus, have a protrusion that sticks up to release the hook(s) as the sled passes.

 

[Robbwal199]

@Tom.G
Cheers for those suggestions Tom, couple things to point out:
I'm unsure on how the buckle could be positioned perpendicular to the direction of the straps threaded through it.
Implementing slack to the straps would be not be possible given their purpose in tensioning to tilt the head forward.
This also affects the cord needing to be slack after opening buckle, not possible?

Re the other approaches mentioned:
The straps currently have hook attachments on their ends already, you might have missed them in images.
Attaching hooks directly to the platform and not to an anchor point on the platform is doable, but finding a protrusion / mechanism to release hooks as they pass is difficult eg: protrusion only intervenes at perfect moment of hooks passing, and does not impact rest of sled.

I'll refer you back to my original idea; the straps, full of tension by ratcheting, have hooks on either end, attached to anchor points as in photo attached. The lower hooks are machined away so that their connection to the anchor is minimal, ready to fall off. When the sled reaches the endpoint, the sudden deceleration and momentum of system will release those lower hooks off the anchor points, alleviating all tension in straps as required. Issue with this is consistency of the release of the hooks, as well as the fact the hooks only release in response to the impact. Ideally, they release just before the endpoint.

In order to increase consistency and attempt to release the hooks before the endpoint, a new idea is to add a fixture just before the endpoint of the actuator (picture 2 drawings in red and black). The straps full of tension collide with a small bar (drawn in black) running horizontally across the track. The tension filled straps will be forced to alleviate this added tension created by the collision with small bar (black) by finding their point of weakness -> the lower hooks barely hanging on, forcing them off their anchor points and relieving all tension.

Let me know your thoughts/questions on this idea.

Thanks,
Robert

Edit: I'm unconvinced by this new idea as new fixture may just increase the grab of the lower hooks by introducing momentum in wrong direction of release.

Any suggestions on some sort of wireless actuator to be placed between straps and pink neck to "jab" the strap in direction of the end of the track, introducing momentum to release hook from anchor?

 

[Tom.G]

A wireless machanism should be possible, but how about instead of a radio receiver you use a light sensor and a light beam across the track to trigger the strap release. (probably a little cheaper)

Of course any mass added to the sled will decrease its acceleration, as will anything on the track to force the hooks off will decrease its speed.

Looks like a case of "You pays your money and takes your choice."

Cheers,
Tom

 

[Robbwal199]

@Tom.G

Yes, the issue of adding the weight of an additional actuator would hinder performance too much.

Going back to your idea re replacing the ratchet with a buckle, is there any buckle which could be released non-manually... or if a push button buckle was used and a fixture placed at the end of the track protruded to hit the button (possibly wouldn't generate the localised force needed to push the button properly)

 

[berkeman]

Yes, the issue of adding the weight of an additional actuator would hinder performance too much.

You may have considered this before, but what about just using a taut string that gets cut as the assembly passes a certain point in the track. A sharp pair of crossed razor blades should give you a reliable severing of the string with minimum disturbance of the motion, and very light weight for the moving assembly.

 

[Tom.G]

or if a push button buckle was used and a fixture placed at the end of the track protruded to hit the button (possibly wouldn't generate the localised force needed to push the button properly)

https://www.amazon.com/Buckles-Plastic-Tactical-Backpack-Accessories/dp/B07LGS5WLT?tag=pfamazon01-20

Then attach a piece metal to the handle as shown above in Pink. (You may want the strip of metal wider than sketched though.)

Your fixture at the end of the track could then open the cam-lock buckle.

Cheers,
Tom

 

[Robbwal199]

You may have considered this before, but what about just using a taut string that gets cut as the assembly passes a certain point in the track. A sharp pair of crossed razor blades should give you a reliable severing of the string with minimum disturbance of the motion, and very light weight for the moving assembly.

Have considered this before, but finding a string capable of holding sufficient tension while also being narrow / weak enough to be severed instantaneously is extremely difficult.

 

[Robbwal199]

View attachment 338954https://www.amazon.com/Buckles-Plastic-Tactical-Backpack-Accessories/dp/B07LGS5WLT?tag=pfamazon01-20

Then attach a piece metal to the handle as shown above in Pink. (You may want the strip of metal wider than sketched though.)

Your fixture at the end of the track could then open the cam-lock buckle.

Cheers,
Tom

Thanks for that suggestion Tom, is the picture attached along the lines of what you were thinking of?

 

[Tom.G]

is the picture attached along the lines of what you were thinking of?

Yes.

finding a string capable of holding sufficient tension while also being narrow / weak enough to be severed instantaneously is extremely difficult.

Maybe Fishing line? Available in a wide variety of strengths.

 

[Robbwal199]

Thanks for that suggestion Tom, is the picture attached along the lines of what you were thinking of?

@Tom.G Just wanted to say cheers Tom, we are in the process of implementing something along the lines of your suggestion quoted.