DIY Projector Lift

[TroelsL]

Hi,

Let me first describe my project. I wish to create an in-ceiling hidden compartment for my home theatre projector. For this purpose, I will try to make a scissor lift using a horizontally mounted linear actuator and a pulley. I am sure this project sounds less than daunting for you, but bear in mind that I have little experience in electronics.

My question is this: Is this project too ambitious for a novice?

Currently, I know little other than the actuator seems to be the best approach for lowering the projector 30-50 cm (12-20").

I also have a home automation system, which has 24v programmable outputs, which I can hopefully to control the actuator.

I'm hoping that this will be simply enough to do, as it would be ideal to be able to control the lift using the existing home automation system. Any thoughts?

 

[davenn]

hi there
welcome to the forums

I don't know if you know that these units are available commercially ? it may pay to check out prices if you come to realise that building one may be too difficult

Personally, not something I would attempt unless it was a kit assembly ... a bit too mechanical for me

Dave

 

[Gryd3]

... a bit too mechanical for me

This is probably what will stump you/us. The electronics part is easy to think out, draw out, and calculate.
The mechanical portion of this has many many solutions and different options for hardware. It can easily be under-engineered or over-engineered.
If you have the mechanical portion down, we can help with motor drivers and such

 

[TroelsL]

Thanks for your replies (and the welcome). The mechanical part seems manegeable to me. I'm basically stealing the idea from this video:

The scissor should manage lowering it without skewing it, but my biggest concern is ensuring that it is lifted back up to the same height so that it aligns nicely with the ceiling. I assume here that the actuator will shut down (rather than burn itself out) when it cannot retract further.

I realize that these are available commercially, but I have thus far been unable to find a solution that aren't insanely expensive. Also, they all seem to be either wirelessly controllable (IR or RF), or need a switch on the wall. I'd greatly prefer something that can integrate with my home automation.

I'll do a bit of thinking/drawing and testing and see if I can build something that aligns nicely on the workshop floor before I start installing it in the ceiling.

 

[TroelsL]

I managed to come up with a much simpler design. Basically, I'm just lowering a box from the ceiling. The box will have no sides, and 4 cylinders (one at each corner) will ensure that it does not shift position while being lowered. This reduces my problem to being able to wire the actuator correctly. I have also managed to program my home automation system to give a 24V pulse to two different outputs, which I hope is what the actuator will need.

I could really use some help from you guys in choosing the right actuator though. Is this the right place to ask, or should I start a new thread in a different category?

I'll ask here, and move it if requested.

My best effort leads me to this one:

http://www.linak-us.com/products/linear-actuators.aspx?product=LA31 HOMELINE
(DataSheet available at link)

It is a 24V actuator with more than enough lift to raise and lower even a heavy (15kg) projector. My questions are:

1. It specifies "Built-in limit switches (not adjustable)". Does this mean that it will automatically stop when it reaches either extreme? So even if I leave the power on for a few extra seconds, I won't destroy it?
2. How do I wire this? As mentioned, I'm a bit of a rookie. Should I expect 3 wires (ground, and one wire for each direction)?
3. Linak is a wholeseller, so I can't buy directly from them. If I search ebay for LA31, I get a bunch of results, but they seem like cheaper, Chinese versions of this. Is LA31 some sort of standard term for this type of actuator?

Any help is much appreciated.

 

[Gryd3]

1. It specifies "Built-in limit switches (not adjustable)". Does this mean that it will automatically stop when it reaches either extreme? So even if I leave the power on for a few extra seconds, I won't destroy it?
2. How do I wire this? As mentioned, I'm a bit of a rookie. Should I expect 3 wires (ground, and one wire for each direction)?
3. Linak is a wholeseller, so I can't buy directly from them. If I search ebay for LA31, I get a bunch of results, but they seem like cheaper, Chinese versions of this. Is LA31 some sort of standard term for this type of actuator?

Any help is much appreciated.

I took a look at the spec sheet for it and was unable to determine a wiring diagram unless it is in another resource.
1. The built-in limit switches could be internal to prevent excessive movement to prevent damage, or they could be broken out so that they can be interfaces with a controller. I am unsure.
2. The actuator should have at least 4 conductors: 2 conductors for the hall effect sensor used for positioning, (Ground and signal) and 2 more conductors for motor control which would need to be driven with an H-Bridge. (Note, I could NOT find a wire diagram or hookup requirements of any kind of the specs PDF so this is an educated guess based on the bare minimums that could be provided.)
3. Unsure. Linear actuators are not my domain

 

[TroelsL]

I took a look at the spec sheet for it and was unable to determine a wiring diagram unless it is in another resource.
1. The built-in limit switches could be internal to prevent excessive movement to prevent damage, or they could be broken out so that they can be interfaces with a controller. I am unsure.
2. The actuator should have at least 4 conductors: 2 conductors for the hall effect sensor used for positioning, (Ground and signal) and 2 more conductors for motor control which would need to be driven with an H-Bridge. (Note, I could NOT find a wire diagram or hookup requirements of any kind of the specs PDF so this is an educated guess based on the bare minimums that could be provided.)
3. Unsure. Linear actuators are not my domain

Ok, thanks for that information.

I don't think there is a wiring diagram as they are expecting you to buy their controller, not wire it yourself. Should anyone be able to recommend any other actuator (preferably available in Europe), that would also be appreciated.

 

[TroelsL]

I found some more information on the LA31 actuator. It's not a wiring diagram, but it mentions a 'Reed switch' and shows a small diagram (shown below). It is on page 100 here: http://catalog.linak.com/Linak/ENGLISH/USERMANUAL/LINAKLinearActuatorsandElectronicsUserManualEng/

Is this sufficient information, or should I look for a different make/model?

 

[Gryd3]

That gives us enough info. It is exactly what I was expecting.
Spec sheet says the actuator should be run at 10% duty cycle for continuous use, or can be run completely on for 2-min, but will require a lengthy rest time.
The motor will require an H-Bridge to drive. If the spec sheet claims there are limit switches, they appear to be internal to prevent damage from attempting to move the actuator further than designed. I will attempt to verify this.
As far as the actual control goes. You can use the reed switch to determine it's location (as well as if it is still moving)

Is your plan to use 4 of these? Or are you still considering a scissor lift?

 

[TroelsL]

Great. I vaguely understand the figure. I will go google 'H-bridge'

The duty cycle won't be a problem. Basically, it will lower the projector for less than 1 minute, then be shut off for at least an hour or so (duration of a movie).

My plan is to use a single actuator. The cylinder/rods will guide the box, and keep it from hitting the ground in the event of total failure. The actuator will be tethered to a wire, which is at the center of the box. I will draw up a sketch to better explain that part.

Another problem may have arisen though. I'm reading the manual of the output module of my automation system (in Danish only, I'm afraid), and it states that it is a 24 V DC module, which supports 8 low current components (12-48 V DC), each with a consumption of max 500 mA. I need to figure out if that is enough for the actuator, or I will need a separate power supply. I assume this makes the wiring more complex.

I do have the option of getting an electrician to do the wiring. And I will have to do so, as I cannot legally touch 230V outputs.

 

[Gryd3]

Another problem may have arisen though. I'm reading the manual of the output module of my automation system (in Danish only, I'm afraid), and it states that it is a 24 V DC module, which supports 8 low current components (12-48 V DC), each with a consumption of max 500 mA. I need to figure out if that is enough for the actuator, or I will need a separate power supply. I assume this makes the wiring more complex.

I do have the option of getting an electrician to do the wiring. And I will have to do so, as I cannot legally touch 230V outputs.

You can handle this two ways:
Use the automation system to 'trigger' your own circuit. Your own circuit will take care of timing the opening / closing and optionally monitor the reed switch and cut power if there is no pulses being detected. (Indicates a jam, or end of travel)
Use a relay and have your automation system take care of timing the motion. (May not be able to monitor the reed switch, or may require additional circuit to send a signal to the automation system when the reed switch detects full open/close or jam.

 

[Colin Mitchell]

Look at the principle for lowering a container from a semi trailer.
Use two of these.
It's very similar to an over-centre toggle.
It will pull right up to the ceiling.
You will need only one actuator.

 

[TroelsL]

I have just been told by someone who has experience with the LA12 actuator from Linak that the reed switch is not for end stops, but for being able to position the actuator. Since I don't need this capability, I'm hoping that will reduce the complexity. Otherwise, I could perhaps use an Arduino (as I am more at home in software development than hardware).

I will find out if this is also the case for the LA 31 actuator. Otherwise, I could use the LA12. That would pose another problem as it only extends 15 cm (6"). But I can solve that problem on my own.

 

[TroelsL]

Ok, I think I have managed to come up with something that should work. I learned a great deal in the process. Should I be wrong, please so tell, and I'll have learned some more

This is what I came up with. S1 and S2 are the outputs of my home automation system. The left power source is a 24V 5A DC power brick. The middle power source is the 24V DC 500mA output of the home automation system.

Next step will be to find the right components for the job. (Assuming that I won't kill anyone with this wiring)

 

[Gryd3]

Looks good to me.
Only possible change would depend on the 24V power brick you are using. Does it have a ground by chance? At rest, the motor is connected to 24V at both it's terminals. In an automotive application this would be asking for trouble, if either wire shorted to ground you'd have a fault. This is only the case though if your brick actually has a path to ground, and should be no problem if there is a transformer in use.
Someone else may have a clearer outlook on this.

 

[TroelsL]

I have yet to order the power brick. I must admit that I don't entirely understand when this can become a problem. I would prefer to be on the same side though.

Are you talking about if either wire internally in the PSU were wired to ground?

 

[Gryd3]

Are you talking about if either wire internally in the PSU were wired to ground?

Yes exactly.

It would not be a problem otherwise, and if this was the case, your motor would be at rest 24V above the ground reference. Simply swapping the two relay's neutral position will let you pick if your motor rest at 24V or 0V. Again, only a concern if the power supply's output is not isolated from mains or earth ground.
I may be paranoid, I was hoping someone would jump in with real world advice as I am basing my information on a similar device for automotive purposes. (Window and electric lock drivers)

 

[Vidno]

Troelsl,
Did you build it finally? I too saw that video you referenced and I started (almost finishing actually) building one.
My lowering distance needs are much more than the one on the video so I ended getting a 16" actuator and a 5 inch pulley wheel on a 5/8" shaft. This way I can get a lift distance of about 7 plus feet.
My design is basic. I also use scissor arms but only to stabilize the platform.
I wanted to see what you have done and exchange ideas.

 

[davenn]

hi vidno
welcome to EP

unfortunately Troelsl, never returned to the forums since his last post
so we never did find out how he got on


Dave