Small diameter tubular linear actuators

[Superchunk]

Hi there,

I'm trying to design a little lifter for my shower chair so I can better reach the shower etc.

This is the shower chair: https://www.theospreygroup.co.uk/produc ... ower-chair

The castor legs are already height-adjustable by sliding further in or out of the steel frame so was just thinking of popping in 4 actuators for the castor legs. I am pretty light weight (40 kg) so will need about 150 N thrust per actuator or maybe a bit less. The problem is however the diameter. The current castor leg diameter is 18mm, so ideally I need a tubular actuator of this diameter or less.

I found these which are 16 mm, but are no longer available and only carry 80 N : https://www.aliexpress.com/item/1005006251480630.html

Does anyone know where I can find actuators within this spec, or any advice for a better lifter design, or if I should just scrap this whole project?

[Burgerman]

How will these be mounted?
You cant just fit a caster to it.

You need a mechanism that holds the casters and takes all the forces. And an actuator to actually provide ONLY the lifting force. And it needs to be watertight. I honestly dont think this is going to be simple.

A SEAT elevator is probably easier. And a compressed air type one that you sit on might do better in a shower.

Seems like moving the shower closer or lower would be easier?

[Superchunk]

The current castor legs are mounted with an e-clip and pin through a hole in the steel frame. Was going to mount the actuator the same way.

Seems like moving the shower closer or lower would be easier?

Yeah, but what's the fun in that eh?

A SEAT elevator is probably easier.

Thought of that, seat is welded to the frame, the only adjustable points are where the castors are.

[Burgerman]

They are not able to take lateral loads. They will buckle. Only force it the direction they are designed for. You cant just add to the caster fork length.

I meant like an air cushion on top of your seat.

[shirley_hkg]

You haven't thought about synchronize them too, so you shall tip over.

Also , waterproof is another issue.

Finding tubular actuator is subtle .

[Superchunk]

You haven't thought about synchronize them too, so you shall tip over.

Also , waterproof is another issue.

Finding tubular actuator is subtle .

I will be using an esp32s3 with voltage regulators and PWM h-bridges to control them so syncing/electronics isn't the issue for me. Is there any actuator that's 18mm or less diameter? I couldn't find any, where are you looking?

[Superchunk]

They are not able to take lateral loads. They will buckle. Only force it the direction they are designed for. You cant just add to the caster fork length.

I meant like an air cushion on top of your seat.

Need a hole in the chair so I can poop before showering lol. I'm not sure where the lateral load would be? All the load would be vertical from me sitting on it no? The castor legs are just a steel tube, there's no fork that surrounds the wheel, the bearing surrounds the leg.

[Burgerman]

It will collapse the moment you push it. All the force needed to push the chair is resisted by the fragile actuator. And that is a smaller diameter hollow bar that extends. And a caster is not central. So already exerts a side load just from your mass befor you try getting someone to push the chair.

Try is. Bet you it collapses! Those things are tiny and cannot take any side loads. Not even a few lb. Next problem is that they turn. So your fixed wheels will also rotate!

[Burgerman]

I will be using an esp32s3 with voltage regulators and PWM h-bridges to control them so syncing/electronics isn't the issue for me. Is there any actuator that's 18mm or less diameter? I couldn't find any, where are you looking?

Speed is LOAD dependent. So the one with the highest load will go slower than the lightest loaded ones. So you will tip over to the side that is more loaded, loke towards the drain, or if you lean one way... Or to the rear if that has more weight. And all 4 wheels will point in completely different directions. And they will bend as soon as you attempt to push it.

[Superchunk]

It will collapse the moment you push it. All the force needed to push the chair is resisted by the fragile actuator. And that is a smaller diameter hollow bar that extends. And a caster is not central. So already exerts a side load just from your mass befor you try getting someone to push the chair.

Try is. Bet you it collapses! Those things are tiny and cannot take any side loads. Not even a few lb. Next problem is that they turn. So your fixed wheels will also rotate!

Ah I see now, thanks for explaining. The pushing force is essentially transferred through the castor leg/actuator to the castor.

So what are my options here then to raise/lower this chair?

[Superchunk]

I will be using an esp32s3 with voltage regulators and PWM h-bridges to control them so syncing/electronics isn't the issue for me. Is there any actuator that's 18mm or less diameter? I couldn't find any, where are you looking?

Speed is LOAD dependent. So the one with the highest load will go slower than the lightest loaded ones. So you will tip over to the side that is more loaded, loke towards the drain, or if you lean one way... Or to the rear if that has more weight. And all 4 wheels will point in completely different directions. And they will bend as soon as you attempt to push it.

That's fine, I've made motor load compensators before, it's more the mechanical side of things that I suck at!

[Burgerman]

No you dont understand. Without positional feedback info, and 4 seperate controllers and some programming to make that work, theres no way to keep them in synch. The chair will end up with the actuators all at different lengths.

But it wont work for mechanical reasons either. Several of them. I use small actuators like those in hobby stuff over the years. They can be snapped in half in your hands. No way they would take anything like the force a caster will give them once extended even if you do not move an inch.

They work only with the forces in a straight line between mounting bolt holes. No bending forces at all is allowable on them. They are not strong in a bending direction.
Even if you were to use far bigger ones. You will need to mount casters or wheels on a frame where the mechanical height change is on some hinges or mechanism. And the actuator simply powers this. Between two points pushing or pulling. And preferably to keep the electronics sane, with a single bigger actuator. Preferably laid down to save space.

[shirley_hkg]

The extension tube (piston) of most actuators are free to turn, if not anchored.
They will then just turn with the drive screw rod but won't extend.

[Burgerman]

And the wheels will all point in different directions!

[Superchunk]

interesting, so what if I just leave the castor and their forks as they are, and put 2 holes in the frame to mount both ends of the actuator above it, would that work?

[shirley_hkg]

Just some thought .

https://youtube.com/shorts/nyNyBAprnXo? ... XkVP025M1W

[Burgerman]

interesting, so what if I just leave the castor and their forks as they are, and put 2 holes in the frame to mount both ends of the actuator above it, would that work?

Do they slide up and down already?

Then if they were about 10x more powerful, AND they had position feedback sensors, and you used 4 seperate power modules and some logic that made them all follow the same height position together, then it might if your mechanicals move freely. Remember that if they have a max lift of 8kg that means you should only be trying to use them to lift 4kg. And the amount you need will not be equal across all 4. So you will need 4 very powerful actuators.

[Superchunk]

interesting, so what if I just leave the castor and their forks as they are, and put 2 holes in the frame to mount both ends of the actuator above it, would that work?

Do they slide up and down already?

Then if they were about 10x more powerful, AND they had position feedback sensors, and you used 4 seperate power modules and some logic that made them all follow the same height position together, then it might if your mechanicals move freely. Remember that if they have a max lift of 8kg that means you should only be trying to use them to lift 4kg. And the amount you need will not be equal across all 4. So you will need 4 very powerful actuators.

Do what slide up and down already? The castor legs? yes, manually. I am aware that the force is an issue but I am looking and trying to find actuators that suit this spec although I am struggling tbh, not exactly sure where to look other than aliexpress.

[Raro]

I have seen this shower chair is electrically adjustable, as the video shows, it raises from 44.5 centimeters to 64.

https://youtu.be/znE37b7APD4?feature=shared

[Burgerman]

Look at the actuator size. Thats because they must be substantial.

[Raro]

I suggest you buy the complete chair, maybe it will serve you better than the one you have He will see if it suits him...

[Raro]

I don't think I wrote very well, I hope you understand.

[slomobile]

I just came across some long tubular actuators and ordered them https://www.amazon.com/dp/B0D25CRZBQ I have no idea how to control them yet. No idea if they will work for your application. But there they are. If anyone knows how they work, point me in the right direction.
Notice how the actuators mount with ball ends so they don't get side loaded.

It doesn't seem to me that you fully appreciate the lateral forces that happen when you extend the legs, and how actuators aren't capable of handling substantial lateral forces. But it isn't for me to judge.

[Superchunk]

I just came across some long tubular actuators and ordered them https://www.amazon.com/dp/B0D25CRZBQ I have no idea how to control them yet. No idea if they will work for your application. But there they are. If anyone knows how they work, point me in the right direction.
Notice how the actuators mount with ball ends so they don't get side loaded.

It doesn't seem to me that you fully appreciate the lateral forces that happen when you extend the legs, and how actuators aren't capable of handling substantial lateral forces. But it isn't for me to judge.

Thanks for posting this, I don't think the diameter of these is small enough to fit. I have however abandoned this project due to the lateral forces problem and motor weight loading. I would still love to do it but I need to come up with a better solution.

[slomobile]

What if you leave the shower chair as it is, but install something like this motorcycle lift https://www.blackwidowpro.com/motorcycl ... /bw-1604a/ on the floor of your shower. Motorize it, and make some cradles to engage with the lower horizontal bars on your shower chair and pick it up.

[Superchunk]

Could theoretically just attach an actuator to the wall and build a cradle then no? shower chair forklift lmao