Linear Actuator - Please Help!

[gregog]

Hi All,

I'm hoping that somebody on here has some knowledge and wisdom that they could bestow upon me. I am looking to, hopefully, purchase two linear actuators (with a method of controlling and driving them) for use in an upcoming production. At this point, I should say I have never worked with actuators before.

 

 

The actuators will be used to drive a 6 metre aluminium bar (mounted horizontally with an actuator at each end) up from stage height, to the desired height of approx 1200mm.The desired effect is to look like a ballet bar, which will not be used. Purely aesthetic.

 

At the moment I do not know how I will power this, so I am looking for advice on the purchase of two actuators and a motor and way of controlling the actuators - whilst maintaining a low cost. The load would not exceed 100kg, so weight is not an issue. The speed is negotiable, as the application is for use on stage, so can be worked around. As such they would be indoors and do not require to be waterproof etc.

 

Has anyone ever used actuators in a show, or know of anything that would suit this purpose? If anyone can recommend anything that I could use, where I could perhaps purchase some from or give me any kind of information, it would be amazing! I have, of course, had a google and found several companies that sell actuators - but after calling one company (RS - named and shamed) a lovely woman on the phone told me "I'm not desiging it for you" and then stopped talking to me. All I wanted was the costing of purchasing two actuators and was telling her what they'd be used for to ask for help with a motor! So I thought best ask some friendly faces in the industry.

 

Many thanks in advance,

Gregog

[ImagineerTom]

Linea Actuators are an incredibly complicated and costly way to do what you're trying to do - is there a specific reason why you NEED to use actuators, why you need a fully remote-controlled system or even why you couldn't just use a bar on 2 bits of string?

[Brian]

Garage door opener? Or electric gate actuator?

[gregog]

I don't have to use Linear Actuators at all, they were just something I was aware of and know come in variable sizes for the amount of travel I need.

Two bits of string would definitely not be suitable. I definitely want a way of being able to operate the bar electronically. It doesn't have to be remote controlled, providing it goes up when I want it to and down when I want it to, then that is perfect.

 

Thanks for the ideas Brian, will have a look into these!

 

As I said in my post, not familiar with actuators myself - just knew "of" them and that they would suit the purpose, very open to other suggestions and ideas though, so please keep them coming.

 

gregog

[musht]

to the desired height of approx 1200mm....load would not exceed 100kg, so weight is not an issue.

 

6m long load weighing 100kg to 1.2m at low cost, sounds a big ask, does it have a 1.2m hole to drop into?

 

Problem being a lot of linear actuators are made for high accuracy with hig cost.

 

Satellite positioner jack motors spring to mind , 1200mm would be very big, acme lead screw might take you somewhere.

[ImagineerTom]

Two bits of string attached to simple/cheep electric winch then....

 

Actuators (mechanical, electromagnetic or pnumatic) are VERY susceptible to sideways forces and if you drill in to the tech spec's you'll find they all suggest that a secondary system is installed so that the actuator is ONLY handling the travel motion ie you're going to have to build a secondary support system/track to actually guide the bar and take any forces that aren't perfectly parallel to the actuator. Whilst you're not intending anyone to use the bar I can assure you that at some point someone will lean on it / knock it / stumble against it and that will probably be enough to knock an un-supported actuator out.

[Brian]

If the load on the bar, and the mass of the bar, are going to be constant, could you counterweight the assembly? Your actuator would then only have to do a much smaller amount of work.

[Giles Favell]

If you sort yourself out a sliding/telescopic post, you'll find HIWIN do some very nice 12V linear actuators, plus battery pack and control which, with a small amount of imagination can have the lift multiplied (via pullies or chain and sprockets) to give you what you require. The rams are well engineered, self-sustaining and reliable and are of the type that are used on hospital beds. The biggest they do is about 5kN (500kg ish) with a stroke of 500mm or so. Cost approx £175 per ram, plus battery and control.

http://www.hiwin.com...ators/lan3.html

[cedd]

Does the bar have to lift vertically out of the stage? Perhaps a false stage surface (which you'd probably have to do anyway to cover a vertical lifting bar) and a hinge arrangement so that the bar folds up and when lowered, lays on its' side in the stage. That way your actuators don't need to be too long.

 

My initial thought was as Brian's - garden gate actuator. The problem being I doubt you'll find one of sufficient length to do a vertical lift.

 

If you need to go vertical lift then assuming you have the full height below the stage, you could do a chain drive using motors. Attach a pair of drive chains to the bottom of each upright, running up either side of it until they reach the stage floor where they go over diverter sprockets and off to motors. Then you just need to pull the chain in to lift the rod up. I've done this successfully with rising mic stands (mine were a 2 stage telescopic affair, but we won't go there!).

 

Take a look at the door lifts from Q division for a project using a similar principle.

[gregog]

Hi all,

Thanks for your suggestions and input, very much appreciated and I'm looking into a few of them!

 

The bar is going to be mounted on the front edge of the stage, with the actuators (or whatever I use) attached on the front edge of the stage (solid wall) into the orchestra pit. So depth is not an issue. However, this does mean that I can not use any type of flying as I don't have that capacity, nor do I want any lines spoiling the sight lines.

I am also unable to have it lay on its side, as on stage I will have a double barrell revolve - so I can't impede this with a bar.

 

The difficulty, with the location of the bar means that using motors and a chain to pull the chain to lift the rod is that I have limited access into my pit. God forbid me asking a muso to do something like that! As such, thats why an electric device like an actuator I thought would work best. Still very open to suggestions though, because I really think actuators are going to be well expensive!

 

I've been on the phone for a while this morning, with a guy discussing actuators and I do think the price is going to influence me greatly. As I will be attaching to the front of the stage, I can create guide rails for the "ballet bar" to help with any potential side loading, although as previously stated, there shouldn't be any load on the bar.

 

I'm going to have a look into garden gate actuators and see if this is feasible, although I would agee in that the travel is going to be an issue.

 

Thanks for your help, keep it coming!!

 

Gregog

[cedd]

You may find that pneumatic rams are your friend here. I seem to recall they're cheaper than linear actuators, come in a variety of lengths and are a very neat solution when lowered (no motors sticking out of the side). Of course they come with their own problems;

 

Using two rams to raise the bar will need some clever setting up to make sure they both rise at the same speed.

 

A compressor will need to live somewhere, albeit remotely if necessary. With a large enough reservoir you could maybe get away with running it before the show and just storing the air.

 

Depending on how heavy the bar is, you may get away with a single acting ram, which the weight of the bar lowers for you, which simplifies the job but also means you don't have any positive way of lowering the bar - it relies on gravity.

[timsabre]

You may find that pneumatic rams are your friend here.

They can be really hissy... might not be too good for this application.

[kerry davies]

Mounting a garage door opening system below or to one side of the stage seems favourite to me. Mounting vertical bars in guide tubes on the front of the stage raised by the cables from door openers just "feels" the simplest, pre-engineered solution.

[themadhippy]

if its going into the pit why not go old skool and have a couple of black clad chaps(or chapesses) in the pit to raise and lower the bar,if you want realism they could even make a hissing sound

[Giles Favell]

I should be very cautious about using pneumatic rams for this. One of the dangers of compressed air is its compressability. If for any reason the device sticks, you will get a build-up of pressure - until there is enough force behind it to break free - and then it will drive up very quickly and hard. If anyone or anything is in the way, they will get hurt. This is one of the reasons why air rams are not commonly used ( as well as their low power and lack of controllability compared to conventional hydraulics).

Electric motor in one form or another is likely to be the safest and cheapest. (other than people/counterweight ). Linear actuators of an affordable kind won't give you a stroke of more than about 500mm, though that can be multiplied up either by lever or by pullies and wire. Garage door type mechanisms are usually guided roller chain type, and should be quite easy, as Kerry says.....