Surely there must be a telescoping rod, with air lock?

[Jack D S]

I would've thought such a thing exists, but I can't find any. Have you heard of something like this...?

A simple extending telescoping rod, but it is airtight, and at one end, the cylinder can be closed or opened by the user to respectively lock the rod in position, or allow it to extend/contract.

Or alternatively, do you know any other solutions for a simple telescoping rod that can be locked into position at any length. The locking mechanism should be at a single point to lock the whole rod (as opposed to many existing rods that must be locked at each tier that extends). A bonus is if it can be operated by a simple button, trigger or mechanical switch (not a twisting or screw mechanism that requires two hands, or multiple turns to tighten).

Much appreciated!

 

[berkeman]

Welcome to PF.

A simple extending telescoping rod, but it is airtight, and at one end, the cylinder can be closed or opened by the user to respectively lock the rod in position, or allow it to extend/contract.

I don't think that storing air at 1ATM ("closing the vent") will be very rigid. It will act like a pneumatic spring with that 1ATM air stored in the chamber.

Or alternatively, do you know any other solutions for a simple telescoping rod that can be locked into position at any length.

Maybe like the door closer mechanisms on screen doors, etc? They have a little mechanical tab that can be used to lock the door at any position, IIRC.

https://www.amazon.com/Standard-Pne...ble-Aluminum/dp/B09YNRTX7T/?tag=pfamazon01-20

 

[Jack D S]

I don't think that storing air at 1ATM ("closing the vent") will be very rigid. It will act like a pneumatic spring with that 1ATM air stored in the chamber.

Agreed, but for this project, that little spring movement is ok.

PS. Thanks for the welcome, and for the link. Let me check that out...

 

[DaveE]

My initial impression is that you want a hydraulic system, sort of like the steering on your car. It probably doesn't work for you for any number of reasons. But it's an idea, anyway.

 

[Baluncore]

Or alternatively, do you know any other solutions for a simple telescoping rod that can be locked into position at any length.

What is the range of length needed, shortest - longest ?
How many stages may it have?
What forces must it apply, axial or radial?

 

[Jack D S]

To answer your questions, I am happy to give (almost) full disclosure here.
The project could be akin to a book stand or laptop stand with an elevating platform. The idea is to use these extending rods attached to opposite edges on a pivot. Thus, when the rods extend (along a diagonal) the platform raises. And being that they attach to opposite ends allows for the platforms to fold almost flat against each other when the rods are contracted.

Attached is a basic image to portray the concept.

Ideally, the all the rods (being open or closed (ie. locked into position or adjustable)) should be controlled by a single point, and ideally using only a single hand manoeuvre.

What is the range of length needed, shortest - longest ?
How many stages may it have?

At their most condensed the rods would be around 30 cm.
They should be able to extend to two or three tiers, so approximately double or triple the condensed length, obviously a bit less though for the overlapping areas.

What forces must it apply, axial or radial?

The platform should be able to support approximately 10kg, though around 50kg would be great. So, given the structure, that is kind of an axial / lateral force. It need not have to endure sudden impulse forces. The overlaps of the tiers must be enough to sustain this force too.
Small movements (bounce) is ok.

That's why I thought to simply open or close airtight cylinders. This could be operated via cable, or similar mechanism. And in fact, the weight on the top platform pressing down could assist in plugging the cylinder closed perhaps.

I'm happy to hear your thoughts.
Thank you for the replies already so far.

 

[berkeman]

Attached is a basic image to portray the concept.

That structure is not very resistant to racking forces left-to-right. Have you considered other placements of those 4 supports to improve that? Or maybe the addition of 1-2 more supports to make the structure more resistant to racking?

 

[Jack D S]

That structure is not very resistant to racking forces left-to-right. Have you considered other placements of those 4 supports to improve that? Or maybe the addition of 1-2 more supports to make the structure more resistant to racking?

Yes, thank you for the observation. I have indeed taken that into account. That image was only to explain the general structure.

(To counter the racking forces, I am most considering embedding the rods into wide rectangular cartridges. So that their rigid width should prevent side swaying.)

 

[DaveE]

How about something with mechanical advantage and one actuator? Roughly like this:

 

[Jack D S]

How about something with mechanical advantage and one actuator? Roughly like this:
View attachment 347707

Good thought, but one of the key functions that my project needs is that the top platform can inherently also tilt at an angle different to the base plate:

Pivots and simple locking telescopic rods would be great for this. I'm just surprised to see that there isn't a telescopic rod that locks the rod from only one point.

What would it take to manufacture it bespoke?
Would it be difficult to make it so it is adequately air-tight?

 

[Tom.G]

Good thought, but one of the key functions that my project needs is that the top platform can inherently also tilt at an angle different to the base plate:
View attachment 347712

Pivots and simple locking telescopic rods would be great for this. I'm just surprised to see that there isn't a telescopic rod that locks the rod from only one point.

What would it take to manufacture it bespoke?
Would it be difficult to make it so it is adequately air-tight?

You could make the extendable legs as hydraulic pistons with a reservoir to hold the fluid when the legs are collapsed.

A manually operated spool valve could be used to connect the legs to the reservoir when adjusting position, and to isolate the the legs from each other and the reservoir when in the locking position.

The reservoir could be bladders in the fixed-length legs for compactness.

Cheers,
Tom

P.S. If you start selling it, I expect a commission!

 

[Lnewqban]

Welcome, Jack!

For vertical movement plus tilting the top, you will need two independent controls.
Take a look at electrical linear actuators, which have a self-locking mechanism.

 

[jack action]

Good thought, but one of the key functions that my project needs is that the top platform can inherently also tilt at an angle different to the base plate:
View attachment 347712

This is how they do it in the industry:

​

Combined lift & tilt:

(source)

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​

It seems easier and safer to design multiple components, each with a well-defined and predictable position/force/moment combination than to have an infinite amount of position/force/moment combinations acting on a single component.

 

[berkeman]

Pivots and simple locking telescopic rods would be great for this. I'm just surprised to see that there isn't a telescopic rod that locks the rod from only one point.

There are telescoping rods with a twist-lock feature:

and other locking mechanisms:

 

[jrmichler]

The project could be akin to a book stand or laptop stand with an elevating platform.

Have you considered a heavy duty tripod? They are heavier than simple camera tripods, are adjustable for height and angle, and shrink down to a small size. Here's a random link to a tripod that's rated for a 10 kg load: https://www.amazon.com/dp/B0B2KGQ7BL/?tag=pfamazon01-20.

 

[DaveE]

one of the key functions that my project needs is that the top platform can inherently also tilt at an angle different to the base plate

OK, so you have height and tilt as the adjustable parameters? Then I would think about two actuators, maybe like @jack action 's post. Four seems unnecessarily complex and expensive. Perhaps with alignment/synchronization issues. i.e. extra work for someone that only wants to control two things.