Motorizing a TV mount

[benskiskull]

TL;DR Summary

I'm searching for ideas on how to motorize a tv mount arm, my own ideas so far run into barriers fairly quickly (insufficient torque, mounting problems, etc.)

Let me preface my question by a disclaimer: I don't know for sure if the format of this question fits this forum, I hope it does. Here it goes:I recently bought a tv mount from Amazon, which is basically a swivel arm with a joint in the middle. Pictures to illustrate (red are joints):

What I would like to do is motorize the whole thing (every joint). There are some challenges along the way I haven't been able to solve though, mainly because of the high joint stiffness (I haven't measured, but per my estimation I need some 3-4 kg of force, sorry, 30-40 Newtons pulling on the tv mount platform to extend the arm). Let me present some of the ideas I went through:

1. Somehow actually put a motor on each joint. Issues: High joint stiffness and small leverage at the joints means high required torque, means big and heavy motors, not good. Also, attaching them would be pretty annoying, especially at the middle joint, as you can see, transfer of torque to the second segment sandwiched in the middle would not be fun.
   
   
2. Some form of linear motor / pneumatic cylinder / between the arm segments and the wall and tv mount, like an excavator. Issues: High joint stiffness and small leverage again means high required force. Not only that, but at angles around 0 and 180 degress, the force applied by those actuators would be multiplied by nearly 0, as most of the force would not produce torque. Also: Those actuators can't contract to length 0 and they take up space, meaning that generally, the arm propably would not be able to contract all the way.
   
   
3. Some form of rope-pulley system. Different sub ideas:
   --3.1 Have all of the pulleys either at the wall mount or the tv mount, all attaching to different points on the other side. With 3 pulleys, I should be able to constrain the whole system. Issue: Since the pulleys can only pull, not push, I would need to have, for example, springs between the arm segements pushing them apart, so that the pulleys can pull against that force and fix the system in place (otherwise, the arm could only close, not open). Springs would have the same torque issue explained beforce, and they would also produce a non constant force depending on the arm segments angle.
   
   --3.2 Have all pulleys at the wall mount and let ropes go along the arm, attaching at either side of each joint and turning them that way. Propably best solution, but again, the issue of needing very high pulling force while needing at least a decent leverage everywhere (meaning a large pulley on each joint? ugly) remains.

I'm kind of out of ideas at this point, do you guys have further ideas / suggestions, or remarks on my ideas so far? I would be very grateful for answers.

 

[Baluncore]

Welcome to PF.

Don't motorise the hinge axis, use secondary links.
Look for; "linear actuator 12V".

 

[Lnewqban]

Welcome, @benskiskull !

How do you plan on remotely controlling the movement(s) of the mechanism?

 

[benskiskull]

Welcome to PF.

Don't motorise the hinge axis, use secondary links.
Look for; "linear actuator 12V".

Thank you! What exactly do you mean by secondary links? As for linear actuators, I'm aware of them, so far I just haven't considered them seriously because of the aforementioned force requirements, they would have to be quite beefy. But can you show me what you mean by secondary links?

 

[benskiskull]

Welcome, @benskiskull !

How do you plan on remotely controlling the movement(s) of the mechanism?

Propably with a ESP32 and a web interface being controlled with my smartphone, using a self written app.

 

[Baluncore]

But can you show me what you mean by secondary links?

You have two links, with three joints, so you need to control three joints. If you could eliminate one of the links, you would reduce the number of joints. There are too many degrees of freedom available.

What positions or orientations do you require for the TV screen ?

 

[berkeman]

I recently bought a tv mount from Amazon

Can you upload a picture or two of this mount? Or link to the Amazon page? (Use the "Attach files" link at the lower left of the Edit window to upload files)

What I would like to do is motorize the whole thing (every joint).

Can you say why? Why do you want to be able to move the TV around in viewing angle? How quickly do you need to move it?

 

[Juanda]

Can you upload a picture or two of this mount? Or link to the Amazon page? (Use the "Attach files" link at the lower left of the Edit window to upload files)
Can you say why? Why do you want to be able to move the TV around in viewing angle? How quickly do you need to move it?

In addition to those questions, @benskiskull can you tell us what are the tools and resources you have available for the job? A 3D printer? Drills? A lathe?
I'm trying to figure out how hard can you go with the modifications to the frame.

You mentioned you have a lot of resisting torque which is a problem. Maybe you'd solve it by modifying the frame to accept low-friction bushings or bearings so that smaller motors would do the job (assuming the frame and joints are strong enough to resist the bending moment).

 

[benskiskull]

Thanks @berkeman, of course, the amazon product is here. As for your other question: Part of the reason I want to do this is fancyness, another part of it is that I'm planning on mounting the tv on the wall above my desk, and that desk is pretty deep, bending over it to extend the tv arm would be pretty annoying. As for the speed, it doesn't have to move very fast. I'm imagining something like a 10 second period from fully closed to fully extended. 20 seconds would be slow, but still barely acceptable.

@Juanda, ty as well for your answer. As for tools, I have the most essential tools for working on wood and metals etc (a handsaw, a drill with steel drilling bits as well, a dremel for finer cutting / grinding, etc). I have access to a 3d printer as well, and I sometimes have access to a simple inverter welder, although I would prefer alternative methods, as welding is quite a skill to learn IMO, and I would struggle with transporting the arm to the welding location. Welding smaller things would propably be fine (bolts, nuts, small pipe segments, stuff like that).
Your point on the resisting torque is a good one. I will try if loosening the screw holding the lower and upper part of the first arm segment together in the first non fixed arm joint is going to make it less stiff.

 

[Juanda]

Your point on the resisting torque is a good one. I will try if loosening the screw holding the lower and upper part of the first arm segment together in the first non fixed arm joint is going to make it less stiff.

It'll probably make your frame a little wobbly though. The point of bearings/bushings is to provide rigidity in all directions except the one in which they allow motion.
If instead of using them you simply add clearance, your frame will be able to move in ways it shouldn't such as sagging down. That of course is in addition to the greater friction you'd have compared to using bearings/bushings.

Also, be aware that if the screws are not torqued, they could completely come out depending on the functioning of the mechanism. Does the head rub with the surface as the frame rotates? That could cause it to loosen more as you use it...
Other concerns arise once bolts/screws lose preload such as fatigue but I don't know how loaded that mechanism is. I'd be surprised if it doesn't have a huge safety factor built in from the factory.

Is it a screwed joint or a bolted joint? If it's bolted, as a precaution, I'd install locking nuts such as DIN 985 or similar. And I'd install the screws so they can't fall out. Basically, installing the bolt from above so if anything falls it'll be just the nut.

If it's a screwed joint, adding locking features is more annoying but still possible. The cheapest (and probably most unreliable) option is to use PTFE tape on the threads. There are also adhesives for that specific purpose, helicoils, tapered screws, and many other options.