Actuating existing hinge

Other Hardware Robotics
1

I have just bought a hinged wall mount for my bedroom TV (Microcenter linky) and would like to make a project out of motorizing it. There appears to be plenty of room in and around the arms to add mechanisms and linkages, I just need to figure out how to actuate the hinges.

One solution I thought of was inspired by those linkages bolted to the top of a door that pull it closed and also dampen the closing so that it doesn't slam.

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I'm fairly certain I've also seen one of these contraptions motorized so that it could open the door as well.

This linkage would be easy to use on the 1st (by the wall) and 3rd (on the TV plate) hinges that have only 180 degrees of motion. It has the advantage of being incredibly easy to make, I just need to get some flat steel bars from a hardware store and some bearings for the friction.

I need good, thin bearings though. The ones I saw on the Home Depot and Menards website look too think.

The middle hinge is going to be the hardest to deal with, because it has a full 360 degree range of motion with the bolt in the center of the hinge getting in the way of using the double-bar linkage on the inside. I can have the bar mounted on the outside so it goes around the hinge, but that looks ugly. The other downside is that the actuator would need the same range of motion as the hinge, so a nromal servo with 180 degree range would be out: I'd need a continuous rotation one.

So I came up with gear, either directly meshed or a spocket & chain. The upshot of that method is that a 2x multiplying ratio can let me use a 180 degree servo at the expense of doubling my torque requirement.

Problem is, I know less about gears than I know about motors. Where would I even be able to find gears in the sizes I need?

The other major problem is torque. I want there to be some amount of resistance so the mount stays in place with the motors deenergized. By my rough estimate moving it around myself, I may need a few to several ft-lbs or torque to power the arms. Where can I find servos that powerful? If there aren't any that are cheap, what about gears to make my own servo? I'm sure I'll be able to find something about motor control online that I can use to make my own controller (I've downloaded a ton of App Notes from TI, Atmel, Microchip, and other places).

So...bearings, servos, and gears. That's what I need help with.

Please?

2

Can you send more detailed photos of the mechanism...?

3

So...bearings, servos, and gears. That's what I need help with.

Servocity has everything you need.

4

Linear actuator(s) might be a good approch - plenty of force normally, nice and slow (so pretty safe).

5

jremington:
Servocity has everything you need.
MOTION - ServoCity

That place is exactly the kind of thing I was looking for. I'm not sure if it will have everything I need since I'm going to have pretty tight constraints on the motor and gear sizes, but it's a great starting point. Thank you. Any other places like this will be much appreciated.

Can you send more detailed photos of the mechanism...?


Full-res image link on my Google Drive.

I took some measurements with my calipers.

Wall-side bars, inner dimensions: 27.0mm H x 17.25mm W
Plate-side bar, inner dimensions: 35.5mm H x 16.4mm W

Center hinge:
bolt width: 10mm
spacer height + washers: 19.2mm

The plastic cover that goes over the wall mount has some room that I could put some mechanics and a box for the controller under. For the other hinges, I'd like to be able to build the servo assemblies inside the bars, though I realize that's a tight squeeze. The standard-size servo I bought to disassemble is about exactly as wide as the outside width of the bars, meaning I'd have to take the mechanics, motor, and controller out of the plastic case to work, if the motor would even fit inside at all.

I'm also concerned about noise. When I back-drove the cheap servo motor, it made that irritating whiny noise that is so characteristic of cheap motors. If I put that in the bars, it'll just become an echo chamber. How would I pick a quiet motor? Do I need a brushless one?

I realize that with these requirements I'll probably need to design my own servo motor module. I'm willing to do that if it's within my skills to do so. I've found a Microchip App Note among my huge stash about how to use a dsPIC to control a sensored BLDC, and it references several others that look promising for the purpose:

• AN885 – Brushless DC (BLDC) Motor
Fundamentals
• AN901 – Using the dsPIC30F for Sensorless
BLDC Control
• AN857 – Brushless DC Motor Control Made Easy
• AN889 – Brushless DC Motor Control Using
PIC18FXX31 MCUs

I've recently bought a Launchpad as well, so I may have the option of using some TI MSP variant for the motor modules. I need to use it for something, don't I?

6

Servos in general are loud. You can get multiple-rotation servos. Brushless servos are also available, but some have a whine from the motor PWM frequency.

7

Its the spur gears that are loud. A gear-less linear actuator might be pretty quiet (the sort with a leadscrew
through the centre of a stepper perhaps - use microstepping for a quiet stepper motor)

8

The problem is I don't think a linear actuator would be very good for this. How would I connect it to apply to force properly to turn the hinges?

Are spur gears inherently noisy, or is that just consequence of them being cheap plastic? Would a metal-geared servo be quieter?

9

Worm gear to the rescue :slight_smile:

And I've never seen those door things motorized, that's all kinds of horrible engineering with horrible leverage.

10

INTP:
Worm gear to the rescue :slight_smile:

I thought of those, since it looks like they give a good reduction ratio for their size. Only problem is I can't see how I'd mount them in an aesthetically pleasing way.

And I've never seen those door things motorized, that's all kinds of horrible engineering with horrible leverage.

Automatic door openers used with the handicapped button.

11

So what you do is put it at the top in a case :slight_smile:
Use a 3" gear on the door hinge line with the worm gear. Just make sure that the door is level and oiled.

12

Isaac96:
So what you do is put it at the top in a case :slight_smile:
Use a 3" gear on the door hinge line with the worm gear. Just make sure that the door is level and oiled.

I'm not mechanizing a door, it's a TV wall mount. My space is quite limited and there's 3 hinges with 2 different ranges of motion.

13

Sorry, forgot :-[
But you can probably do the same. How about a pneumatic piston for the 2nd hinge, with a small servo helping with the centering?
Actually, that wouldn't work so well. Use 1/5 scale RC servos-the sail winch servos will do about 5 turns.

14

Is this the kind of thing you're talking about, Issac? It's hard to tell from the page, but it looks like a winch servo is not the same as a continuous rotation one, right? I'm inferring from your comments and some of the stuff on that page that a winch servo is position based just like a normal servo, and not speed based like a continuous rotation one. Instead of mapping the pulse width range to an angle range like 0-180o, it maps it to 0-1,800o to cover multiple rotations. Is that correct?

If that's true, it would be perfect for me. Most of the servos I've found are much faster than I need, and don't have enough torque for my estimated need. Those that do are ridiculously expensive, like 100USD each. I've been seriously considering ways to hack a servo or use an already heavily geared motor and program my own servo controller for it. But this way I can take the multi-turn winch servo and just gear it down as is. Does it have additional reduction gearing to the potentiometer then? Will I be able to hack into it the same as a normal servo?

15

Exactly what I meant. Sail winch servos have multiple turn potentiometers (I think) and you can still hack into them.

16

I've had to put this project off for a while, but I am still slowly moving forward. I have ordered the Hobby King winch servo I linked above and will see if it is suitable for my needs.