Electric roller door near disaster
 

Opened the remote control electric roller shutter garage door last Wednesday to get the car out, after getting it out I pressed the open button by mistake. The door opened more (it shouldn't have, the limit ought to have prevented it) and jammed against the roof and motor just kept going.


I switched it off and needing to go out, I left it as it was because the manual crank handle did nothing.


On my return, I left the car out, unjammed the door by teasing it down a bit at a time and it suddenly came crashing down at high speed. Would have been serious if anyone or an animal had been in its path.


It uses a tube motor, inside a tubular barrel to wind the door onto. Once down, the shutter door can be easily disconnected from the barrel and the barrel with the motor inside removed.



The tube motor is quite a clever and intricate design, it includes the motor, limit switches, a three stage planetary gearbox and a slip ring system to transfer power to the motor which has a stator which rotates with the tube.



Opening up the tube motor, I found the cause of the failure - It relies upon a 3/8" shaft for the drive to 'push against', the 3/8" shaft had been turned down to reduce its strength to form a weakness, turned down to around 1/16" diameter. Idea is that the shaft snaps if the motor is overloaded, but I am surprised it has lasted as long as it has, around ten years since I installed the roller door. I think the shaft was much weaker than it ought to have been.



To get it back to normal working as quickly as possible, I ordered a new tube motor on Thursday, delivered and installed yesterday morning. I will repair the shaft of the original one to keep as a spare.



It is an identical door to the Crocodile door advertised on TV by that builder, but I paid a fraction of what Crocodile would likely charge for the same door.



Point is - if that bit of 1/16" diameter shaft snaps, there is absolutely nothing to stop a roller door coming crashing down at high speed and they are heavy.

I dont know anything about roller doors, although my old employer had them on the warehouses of his premises. I always assumed them to be a basic motor with a gear, and a gear on an axle carrying the shutter. Around the axle on the shutter, there was a chain, which allowed you to 'shuffle' it onto a wheel welded to the gear, so if the motor or power failed, you could manually raise and lower. Therefore there must have been some form of clutch arrangement within. I never had to use it.

Another employer, again with a roller shutter, manual though this time. If I recall, you had to pull down on something, and then pull the chain to raise and lower. This pull, acted on a pivoted lever which I assumed locked into a gear tooth, so once released it would lock the door.

I imagine these types would be a lot noisier than a tube motor (which until I read your post, I had never heard of!) It got me thinking of them - safety etc. With no engineering experience nor motor experience (except from model railway, scalextric and a rear sun blind) - could it be converted to a worm gear arrangement. Should it snap again, the worm gear would lock it in place? (and perhaps be a compromise on noise)

The motor and all of its associated bits, is in a 45mm x 600mm -ish tube. That then fits inside what they call the barrel, the outer tube around 75mm x the width of the door. Tube motor and barrel are locked to together, driven against the fixed bracket at one end of the barrel, force of the drive being taken by the 3/8" shaft I mentioned earlier, designed to break on overload.


It seems to be a very good design, apart from this weakness in the design which allows the door to come crashing down if the deliberate weak part snaps. Both motor and manual winding system are disabled if this snaps, so until the new tube motor arrived and I had it installed, I had no way to open the door.