Struggling with the MATH

[Joe Jones]

So I have a situation where I need to raise and lower a six-panel window shield, using a linear actuator. The CABLE that will raise and lower the bottom of the lowest panel via a track along both sides of the window must raise the bottom 75". Each panel will be 12.5" tall x 37" wide.

The actuator will be situated above the window, mounted horizontally. Obviously I cannot use a RAM with a 75" stroke, so I have to double over the cable via pulleys to multiply the RAM's linear movement.

There is a total of 37" of width for the EXTENDED RAM an the pulleys, frame, etc. I figure a good actuator with a 450 lb. load and somewhere's in the neighborhood of a 12" stroke will accomplish this goal. The cable will be a LOOP and the RAM will both pull the panels UP into the folded position, and DOWN into the extended position which covers the windows. This will prevent someone from lifting the panels by hand.

So I need the geometry of the cable loop to accomplish this! The RAM will push and pull a narrow bar that will move a bank of pulleys away from a parallel and stationary bank, so the distance the loops stretch will equal the stroke of the RAM.

For some reason, I cannot figure out the geometry of this situation.

Joe

[robertspark]

sketch?

[Francisco]

With a 12.5" stroke on the actuator ram, and six cable "legs", you get the 75" stroke you need for the window shield. The narrow bar you envison as fitted to the actuator's ram would have to mount two sets of three pulleys, one for each leg of the actuation cable. Can work, but it will be difficult to make it compact and smooth enough; I'd suggest going with a rotary motor and a couple of drums instead.

Pulleys.png

[Joe Jones]

Great minds think alike! I have been working on this design today. I ordered all of the components from Amazon. A 12VDC motor with a 12 RPM gearbox for power (maybe too slow? ) the pillow block bearings, the 8mm steel shafts, the 1:3 belt reduction combination, the two pulleys, the stainless steel cable and the crimp connectors and tool, etc. I went back and also ordered a 40 RPM and 80 RPM motor, so I can swap out one for another to get the right speed.

I will work on the layout of the frame tomorrow. I figure I can make ONE working prototype, and then if it works as I hope, I will make them for the rest of the windows.

The idea here is for a 1/8" stainless steel 7x19 cable to wrap 1-1/2 times around the drive pulleys at the top. The lower pulleys on each side of the window will be the tensioning pulleys. Small crimps on the outer cables will trip stop switches that will prevent the motor from moving further, but it will allow the motors to run in the opposite direction.

I will automate them all, but for the moment I bought a polarity reversing momentary switch.

Joe

WINDOW SHIELDS GEAR MOTOR CONCEPT JPG.jpg

WINDOW SHIELDS SIX PANEL SIDE VIEW JPG.jpg

[Joe Jones]

sketch?

As I began to work on it, I chose to ditch the linear actuator and rotate a pair of round pulleys instead. The cable will wrap the pulley once before continuing around the closed loop. At the bottom inside (front) of each cable, the lower panel will be attached with a pinch bolt or ??? On the outside (rear) cable, a pinch connector will close the steel rope loop on each side.

When the panels are deployed (rolled down) they will be held in place by the track wheels, similar to those used on garage doors. For fire escape egress, I will use another cable down the center of the panels. Pulling down on a level on one of the lower panels will retract all but the top track pulleys, allowing someone to push out on the panels to escape easily to the ground.

I looked at the commercial offerings, but they are so BORING! These six panels will be cnc cut with designs that make them at least SEMI-attractive while covering the windows. I may go with the typical Kentucky decorum ... the windmill, the old barn, the hunter with his dog, etc. ... OR I may opt for a more uniform panel pattern of oak leaves, or whatever. Maybe ...

Joe

WOMAN AT BLINDS JPG.jpg

[robertspark]

WOMAN AT BLINDS JPG.jpg

hey if she comes with a set of the blinds put me down for an extra set!

[Joe Jones]

I figure if I am going to cover the windows with sheet metal, and I have the plasma table ... it is only a matter of deciding what pattern or design each window will have when down. The shroud around the top can also be cnc cut with a pattern to make it a bit more decorative.

Joe

[Joe Jones]

I ordered all of the components needed to make a working prototype for proof of concept. Now I am struggling with ... stainless steel vs. powder coated cold roll steel. Which one is more cost effective?

If I make them out of stainless, they will be really expensive. 30 windows at $800.00 each? A $24K project?!? The stainless hinges alone would be over $1,600.00. 48 feet of either SS angle or square tubing x 30 windows is 1,440 feet of framing at $??? per foot. Then each window gets 23 sq.ft. of front shield, presumably also stainless steel. That is 690 sq.ft. of sheet metal, and then there are also fold down covers for the entry doors

I know that if I make these out of ALL stainless, they will not rust, and maintenance will be minimal, with an occasional power wash and some lube on the hinges. But then I have these large SILVER covers over my windows. Not really attractive for the neighbors. It wouldn't matter for a tornado warning, but for a vacation leave, the silver shields might be a bit harsh on the eyes.

If I use cold roll steel and powder coat everything, I can make them more subdued in appearance. But I am worried about long term maintenance issues ... largely rust, among them.

What are your thoughts?

Joe

[cstroke]

If you choose to go with steel make sure to do a zinc powdercoat primer first then the powder coat.
Also make sure the powdercoater sand or shot blasts the bare metal first.
You can get alot of years out of powder with the proper prep.

[Joe Jones]

If you choose to go with steel make sure to do a zinc powdercoat primer first then the powder coat.
Also make sure the powdercoater sand or shot blasts the bare metal first.
You can get alot of years out of powder with the proper prep.

Wow. More work. More expense.

You make a good argument for stainless steel!

Joe

[rdj357]

If you still want subtle, powder coat the stainless.

[Joe Jones]

If you still want subtle, powder coat the stainless.

Thanks. I did not know that stainless CAN be powder coated.

Joe

[rdj357]

It's a great underbase for candy colors - obviously that's not in the subtle direction LOL. But absolutely, all these stainless steel tumblers running around here are powder coated. We sell thousands of them a year.

[Joe Jones]

It's a great underbase for candy colors - obviously that's not in the subtle direction LOL. But absolutely, all these stainless steel tumblers running around here are powder coated. We sell thousands of them a year.

Huh. I hadn't thought about that. I have a red brick house, so I want them to blend in, at least a little bit! I don't want boring roll down panels that look like self storage doors. I want something that has SOME pizazz. The image below is just an example of what a window shield might look like... Of course the large cat openings would be closed with metal, using lines to imply the torsos.

Joe

CAT PANEL EXAMPLE.jpg

[Joe Jones]

Most of the components for the gear motor assembly have arrived. Now I am waiting for a nice, laser cut box frame to mount them! I reversed the motor mount after taking this photo. It will make it easier to remove it from the box when the bolts are not behind the motor.

Joe

GEAR MOTOR PRE-ASSEMBLY JPG.jpg

[AREA]

Looks like your plan is coming together Joe. Is this what you need the parts machined for?

[Joe Jones]

Looks like your plan is coming together Joe. Is this what you need the parts machined for?

No. I have so many projects in various stages of completion. This part is for the PlasmaCam tables, and I was advised by one prototying company to get a patent on it before I get too deeply into it. I could do that I guess, but I will talk to a local patent attorney in Bowling Green to look into it. The piece will greatly improve the function of the table. So I ordered 10 of them, to install onto my own PlasmaCam table to see how it works, and run it through the paces. If it works as well as I suspect it will, I will patent it and market it to all of the PlasmaCam table owners. If it doesn't work, well ... then I wasted a thousand dollars

Joe

[Joe Jones]

I now have five different geared motors, all physically identical, but at different RPM outputs; 5, 12, 40, 80 and 160 RPM. I suspect that I will use one extreme or the other. I will either use the belt pulleys (20/60) to reduce 160 RPM to 53.33, or use the 5 RPM motor to increase the rpm to 15, or some other combination. I have a lot of options now, to find the ideal speed for these window guards to roll up and down.

Joe

[Joe Jones]

The two plates from Send-Cut-Send arrived. They are perfect. I am going to assemble the drive motor for the first test unit, and then weld up a window shield with ordinary (read: cheap) metal. If it works as I suspect it will, I will then build shields for all of my windows out of stainless steel.

Joe