Lazyweb,I need a better motor for my curtain automation. I've tried several models, and they all only last two or three months before they strip their internal gears. So my current procedure is, "buy a new motor every two months." This is not a good system.
I figured the motors would just stall out before stripping gears. They are straining, but never reach the point where they actually stop turning. But no, eventually something cracks.
I'm driving the motors with with this board, which is 12vdc and has a 1.2a max stall current, so I've tried these motors, and stripped the internal metal gears on all of them, multiple times:
- 227:1 1.1A
- 378:1 1.1A
- 227:1 2.1A (which is technically out of spec for the driver, but worked-ish)
I'm kind of puzzled by this, because except for the 227:1 1.1A, they are not stalling out! They strain a bit at the end, but they keep turning. I expected that the failure mode I would be repeatedly experiencing would be that the motor is fine and the driver board melts. But somehow, even without the motor ever getting stuck, it's just shattering internally. (Applying power directly results in the shaft not rotating at all, or rotating only partially then getting stuck, so it's definitely that the gearbox has committed internal suicide.)
I need to find a quiet, fast motor with like, 350+ oz-in torque. Bidirectional, constant speed. And if it has more than a 1.1A stall, or if it needs more than 12vdc, I need to find a driver board to run it with. I don't even really know where to look. You'd think lots of people would want to move heavy things with a small box.
Suggestions?
Never used one of these before, but it seems to meet your specs.
https://www.amazon.com/Dayton-Model-1LNG7-Motor-12VDC/dp/B004VYQ3K2
Huh. Pricey. Also 9 RPM means, I think, 4 minutes to close the curtain. So that's less than ideal.
For that price you could pick up a big NEMA34 stepper motor
http://www.automationtechnologiesinc.com/products-page/nema-34/nema-34-high-torque-stepper-motor-640-oz-in-55
Is the oz-in rating on steppers "real"? Because early on I tried one of these that is rated at 179 oz-in and I could easily stop it with my fingers. But the regular electric motors rated at 240 oz-in, I can't. So i wonder if something else is going on there.
Also a stepper seems like overkill since I'm not doing positioning or anything precise. Just: go, stop, reverse.
And how do I tell what RPM a stepper like that would do?
Steppers have maximum torque when holding still. The torque drops off rapidly as motor speed increases.
http://www.automationtechnologiesinc.com/wp-content/uploads/downloads/2016/08/KL34H280-55-4AT.pdf
So, running at 600rpm that'll deliver 240 oz-in (while drawing 5.5A).
A stepper is totally overkill here, my thought was more: If you could get a beefy stepper for $60 then you should be able to get a regular DC motor for much less than that.
With that said, when I did a CNC conversion on my milling machine I used NEMA23 570 oz-in motors for X&Y axis and they deliver significantly more torque than I can apply with my fingers. So, I'd keep steppers in mind as a backup plan.
Huh, a jwz post in my field.
Bigger motors last longer. You're already using Pololu components, so you might as well buy one of their 37D motors: https://www.pololu.com/category/116/37d-mm-gearmotors and pair it with one of their bigger controllers: https://www.pololu.com/category/10/brushed-dc-motor-controllers
You'd guess that a higher reduction gearbox wouldn't last as long as a gearbox with lower reduction, since the gears in the higher reduction box have smaller teeth, and there's more of them. For long mechanical life, buy a bigger motor and gear it down electronically, rather than use a small motor and gear it down mechanically.
Have you tried oiling up the curtain rails? Or using a lighter weight curtain? Could the curtain rope be replaced with a pulley so the effort to move the curtain is less but takes longer to move it?
Yes, I oiled the rail. No, it can't be lightened. Building a block and tackle sounds like a giant pain in the ass.
Saw this post recently, might be of some use (not sure if 5 cm / sec is fast enough but 1 kg is probably enough load):
http://41j.com/blog/2016/10/moving-a-1kg-static-load/
Try contacting these guys: http://www.anchorelectricmotors.com
they're under different ownership now so can't guarantee that they haven't changed but they used to be more than accommodating for helping with these sorts of problems / projects, they'll have access to a ton of stuff not generally available online, so might be worth a shot.
This may be a) considered cheating and b) more money than you want to spend but maybe you need to replace the track with one designed for automation. Somfy has a very good reputation in this space and is used in lots of commercial boardrooms etc.
The Glydea system can handle up to 132 lbs of drapery and has simply dry contact control (so all you need is a relay connected to your Arduino). The downside is it looks like it will be $800 or more (depending on the weight of your drapes and therefore which motor you need.
I looked in to Somfy once, and all in, it would have been like $2k or more. (I have a big window. It's my only window.) So that's just a stupid amount of money, even compared to burning a $17 motor every couple of months. Also their protocol is some proprietary RF bullshit that is not "load this URL to close the curtain." So I'd be trading an Arduino motor torque hassle for an Arduino RF beacon hassle or something. Yay.
I thought cost might be the problem as it sounds like you have a big window, and I am guessing that your drapes are "block out", so that means heavy, which is I guess why you keep going through motors.
According to the manual The Glydea system has basic "dry contact" switch inputs as standard, so you don't need to work with any protocols. Just 3 pins that you short to ground for open/close/stop.
from my favorite source for such things:
https://www.sciplus.com/p/CAR-SEAT-312VDC-GEAR-MOTOR_49248
or
https://www.sciplus.com/p/12-VDC-2500-RPM-AUTOMOTIVE-SEAT-MOTOR_49249
or this one, which I don't think will blow your board like those others might. It seems that board will power 3 phase.
https://www.sciplus.com/p/12VDC-BRUSHLESS-MOTOR_53799
McMaster has a variety of DC gear motors. http://www.mcmaster.com/#dc-gearmotors/=14k5856
Scroll down past the $500 ones, unless you really want to spend $500.
If you want more power, switch to an H bridge. I have used the Simple H before and had good results (won $1.125M) http://www.robotpower.com/products/simple-h_info.html
Look up brushless servo motors. They are perfect for this application. Upside is lots of torque at variable speeds with no gears, will probably last well into the next technological epoch. Downside is they are freaking expensive.
There is nothing about this application that calls for a brushless motor.
First thought: NEMA23 geared stepper at about 15:1. Might work with a cheap arduino-compatible driver like A4988 or any of those kinds of things.
example:
http://www.omc-stepperonline.com/gear-ratio-151-planetary-gearbox-nema-23-geared-stepper-motor-23hs222804spg15-p-146.html
Or buy cheaper from China.
Second thought: windscreen-wiper motor or car-seat motor.
If you're doing basic DC motors, don't need speed control and driver current is an issue, ditch the electronic driver and use a pair of 10A relays - super-easy.
For higher current (a few amps to dozens of amps) brushed DC motor control: you don't need a traditional silicon H-bridge if you are OK to miss out on variable speed control. You can get away with two SPDT relays instead, it's much cheaper and simpler.
Wire them like this:
+V GND
| |
| |
+ | . . | +
. x x .
. \ .
. \ . Relay one
. \ .
. | .
+ . . | . . +
|
|
|
Brushed DC
Motor
|
|
+ . . | . . +
. | .
. / .
. / . Relay two
. / .
. x x .
+ | . . | +
| |
| |
+V GND
Another advantage: there's no 'wrong' position for the relays (everything is forced to go through the motor, you can't short out the driver like you can a silicon H-bridge).
Con: I have not shown the driving circuitry for each of the above relays. You need to push current through a couple of pins on a relay to turn it on. If your control circuitry can't provide full coil current on its own (most likely) then you will need a small transistor (any common NPN will do, eg P2N2222) and a resistor on the base pin. Either way it's also a good idea to put a diode across the coil for 'flyback' protection too. Look up relay driving circuits (keyword 'Arduino' helps with searches) if you are not familiar.
Automotive relays come in all sorts of current ranges and should be easy to get. Even scrapped ones from an a car wrecker's.
Source: I design & make my own H-bridges. Feel free to ask any questions.
Woops, it looks like the (code) (/code) tags do not protect spaces.
Fixed diagram: http://halestrom.net/misc/spdt_relay_motorcontrol.txt
The reason why the gearboxes are stripping before the motors stall is that when gears are turning, that creates additional stress on the teeth beyond the force at 0 RPM at a given torque. So if you matched a gearbox to the stall torque of a given motor, you would be oversizing the gearbox.
Where to buy steppers with "oversized" gearbox, then?
Gears
https://www.precisionmicrodrives.com/application-notes/ab-024-introductory-gear-equations
try using something with a planetary gear? spur gears are much more fragile.