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Problem with 2-part up-and-over sliding shutter automation

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Hi all 

I am finally getting to the point of having a working dome and shutter driver from an electronics point of view:

I have alpaca controllers and drivers for both, sensor switches in place for the shutter travel, encoder for the dome rotation, relay latch for unlocking the shutter, motor drivers for the opening motor.

I've also put in place a bicycle-wire based winch system to raise and lower the lower shutter on an endless rope system.

What's missing is this:

When winching, the lower shutter rises on the rails up the slot and under the lower shutter to a certain point and then brings the upper shutter with it by virtue of pressing under the bottom edge.

When the lower shutter raises to a certain point on the cycle, gravity takes over, the top part of the shutter unhooks from the lower part and slides down the back of the dome with a a crash into the buffers. 

I'd really rather that didn't happen, since the buffers and the dome they are attached to wont last long doing that regularly. 

I tried putting shock cord elastic between the two so the larger upper part couldnt run away but the lengths are wrong and wouldnt allow the shutters to close properly with the right length to prevent or at least dampen runaway.

What I am looking for is ideas to prevent this happening in a reliable way so the dome automation can do its job, night after night. 

What I find is writing about the problem also helps me think about it, so hope this is useful. 

The winch system:

The bicycle wire system has rollers on the inside of the shutter rail that guide the wire that is pulling the shutter up , which is fastened to the lower edge of the lower shutter. The wire goes up to the top of the dome, round a pulley and then back again, this time inside bicycle wire guide tube which mean I can more or less run it where I like with a small amount of give. In this case it runs back along the rail down to the winch. The wire wraps around the winch about 3 or 4 times and then fastens on the shutter again.


Something to make the upper shutter stick to the driven lower shutter on the way up and come apart on the way down ...

Something to dampen the crashing of the shutter into the buffer... 


hope this stirs your creative engineering juices. 





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Hi Mike, I would look at designing the Upper Shutter being driven via the cycle chain in a full loop thereby the motor drives the upper shutter, with the chain and motor stopping any slippage. The lower shutter I would re-design, pivoting on the bottom edge with linear actuators opening and closing the lower shutter.

As Julian as previously stated, a diagram would be helpful.



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Not sure of the relative weights of the components, but if the upper shutter is fairly light, how about a magnetic coupling between the two?

On the way up when the lower lip of the lower shutter engages with the upper shutter rare earth magnets link them together. This prevents the upper shutter slipping down. On the return journey, when the upper shutter reaches its end stop the winch pulls the lower sutter free and it continues on its journey.

It might be getter to do the same thing the other way round with the upper shutter lower edge linked magnetically to the upper edge of the lower shutter. The two shutters move as one until the upper shutter reaches its end stop. The winche then separates the magnets and continues to move the lower shutter to its end position.

A more mechanically complicated design would be to have the two shutters linked by a pivoted pin that passes through both lower and upper shutters in the closed position. The arm extends to the side of teh shutter and operates much like the trigger on a medieval crossbow as the upper shutter approaches its final poistion. the end of the arm away from the pin passes over some kind of ramp, cam, bump, that despresses the pivoted arm and withdraws the pin; allowing the lower shutter to continue on its way.

Edited by old_eyes
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Hi all

Thanks for the replies

I normally reply as I get them but it seems my notifications are not coming through. 

I appreciate the need for a drawing or diagram or photographs so I'll get on to that. 

Sloz - the dome already exists and can't use a lower shutter that folds out instead of folds up - there is not space during rotation. 


Old eyes - thats where my son and I were getting to something similar - magnets, torque dampers and rope, sliding frictional track, something to friction bind or toggle the top to the bottom with. Or a gravity activated clamp that catches when the shutters are almost horizontal ( ie on the top of the dome) but releases when getting back to vertical during closure. 

Next - some pics. 




Inside of dome - shutter closed. Insides are secured by internal rollers and uses a prong and electric latch to secure. Cord at top of lower shutter is an elastic rope to the end of hte top shutter in attempt to stop slide. It doesnt'.


Shutter fully open, lower retracted under upper and both back over the slot. Limit switch to left not yet engaged. Visible are two compasses for dome rotation measurement.


Shutters partially open, lower retracted under top and top about to break free and hit end stops. 


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next pic - view from outside.

You can see the top shutter edge lined with screws that hold a ptfe wiper blade , which is probably the ultimate cause of this problem.

The lower shutter is partially retracted under the upper. The shiny thing is the back of the monitor in the dome. 


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