[Mike4703]

I have two solar panel arrays that are on a square frame that is hinged on the bottom front side and held up at the appropriate angle by two adjustable supports from the top corners to the base. Very simple, like a door laid on its side hinge on the bottom. I want to convert to a mechanism to remotely raise and lower the panels. We occasionally have high wind and like to have the panels down flat when this happens. I'd like to use a simple linear actuator but when I try to design this I run into a mechanical leverage problem. At the beginning of the lift from horizontal the angle of the lift causes the forces to mostly be in the horizontal direction which tends to rip things apart. The problem is that the base frame is only 10 inches off the roof so there no room to mount the actuator vertically so it would push up and down. The actuator needs a stroke of about 24 inches so it is a long one. How do you push upward with no room underneath for the retracted actuator. I've tried to think of all sorts of bell cranks, pullies, folded levers, etc and they all suffer from the problem of starting the motion with a unacceptable mechanical disadvantage which would break the framework.

[txcncman]

Why can't you use a scissor lift type mechanism built into its own steel frame?

[lukewarm]

The frame looks pretty rigid, what about moving the actuator connection point closer to the pivot point to cut down on the stroke you need. Use a 8 inch stroke linear actuator?

[lukewarm]

You could also mount the bottom of the actuator to pad of the leg closest to the pivot point and add a slight drop bracket on the panel to give better leverage. I'd sketch up what I mean but I'm away from the shop right now.

[Geof]

Do what I have seen on heavy dump trucks with the same problem; use two pairs of actuators.

One pair are very short stroke pushing straight up about one third of the way from the pivot point. These are not attached to the panel, only the frame and only raise the panel to a few degrees of tilt. By that point the mechanical disadvantage of the longer actuators is reduced so they take over and push the panel the full way.

[Spencer Clayton]

Why can't you use a scissor lift type mechanism built into its own steel frame?

I like this idea, especially if it is just one set of scissor linkages on the edge to be raised with the base of the linkage mounted to a hinge running sideways.

Lateral thinking always amazes!

[tjbaudio]

Do what I have seen on heavy dump trucks with the same problem; use two pairs of actuators.

One pair are very short stroke pushing straight up about one third of the way from the pivot point. These are not attached to the panel, only the frame and only raise the panel to a few degrees of tilt. By that point the mechanical disadvantage of the longer actuators is reduced so they take over and push the panel the full way.

This was one of my first thoughts.

The other was to use longer actuators and let part of them stick above the panel. When flat they would be 90 deg to the surface and have 100% lift available. You could play a little with the exact geometry.

I would also consider just moving the actuators closer to the center of the sides. Go from [\] to [|]

[txcncman]

See if this helps:

[Mike4703]

Thanks for thinking about this. The suggestion about two actuators would work; one short pushing straight up and then one using a scissors type arrangement to take it the rest of the way. Hoping to use just one however.

By the way I didn't mention at first that there is only about a foot and a half of space behind the thing, so the scissors would have to be across, so it would all fold up underneath.

The scissors by itself would only work, as implied here, if I built a strong mechanism using steel as the initial forces with the geometry forced by the dimensions of the existing framework will generate very large initial forces on the joints.

Don't really want anything sticking up above the panels when they are down.

I was trying to design a cam mechanism that would push up initially and then engage the scissors so one actuator would do two jobs, gets mechanically complex. I think I will just have to decide which compromise I want to go with. There is no real simple way to do this, even though it's a simple task.

I saw a pre-made frame to do exactly what I am trying to do now that was way overbuild, very heavy, and had dangerously strong helper springs built in all because of this initial movement problem. Used only one actuator though.

[txcncman]

LOL@"By the way I didn't mention..." Yeah. Whatever. Do the math. Good luck.

[Mike4703]

Sorry about that--one little detail that changes the whole picture! Here's some math. The array weighs about 80 lbs. If the lift point is about half way from the hinge then you need 160 lbs to lift it. A scissors lift with 4 inches of height at start and 20 inches long has a 5:1 mechanical disadvantage, so need 5 x 160 lbs = 800 lbs of force horizontally to move it. This is made of 1 x 1 x 1/8 in aluminum tubing. Doesn't take much imagination to see that things will be severely bent applying this kind of force to joints and fittings.
Moving the lift point all the way out to the top of the frame cuts the force in half but then need still to design it so it all fits underneath--thus some kind of hinged scissors lift attached sideways which gets mechanically complex. And still needs some help getting started.
The other route is to use multiple actuators timed to first push up then complete the movement.
In the meantime I've gotten the idea to use gas struts to push up, sized to overcome most of the weight when its folded down. Having trouble finding the right sizes though in my first searches.
The big problem through all of this is any kind of linear actuator or strut needs as much space underneath as as the upward stroke--this is why they sell the tracking solar arrays with pole mounts to get them up off the ground.

[vegipete]

How about a screw drive? Mount a hinged nut top center of the panel. Attach a 2 + whatever foot threaded rod to a motor. Hinge mount the motor to the roof frame under the nut. When the frame is lowered, the threaded rod will still be sticking up in the air. A long plastic nut would be preferred.

[TomB]

I'd mount the panel frame to a pivot rod and have a 6" long bar sticking down and out front when the panel was down. With a small electric motor connected to the back support and piece of allthread extending to a swiveling nut on the extension bar I would be done. Run the motor ccw and the allthread would pull the nut and end of the extension closer thus raising the panel. Reverse the motor an the panel would lay back down.

Somebody else can check my back of the envelop arithmetic but it seems to that the panel would need about 160 ft.lbs torque to raise. It seems to go about 40 degrees so a 6" long extension would swing +/- 20 degrees from vertical. That would mean the pull on the end would require about 341lbs. Using an acme .75" dia by 10 threads per inch rod would therefore require 22.5 ft lbs of torque. That is in the range of small electric motors and trivial to a small gear motor. A standard piece of 1/2" diameter allthread would work just as well as the acme rod but I couldn't remember the normal threads per inch and it would change the motor torque requirement.

Tom

[Mike4703]

I could use the threaded rod mechanism if I can find one made of stainless steel and I can make it lay down flat if needed. This is on top of a fifth wheel trailer and there can not be anything sticking up if it needs to move. I could make it so the panel attachment point can be uncoupled from the nut on the rod, and make the motor end so it can pivot. For wind protection purposes I suppose it doesn't matter if there is a rod still sticking up as it doesn't have any wind resistance.
I'll search for SS threaded rod. Stay tuned.

[Mike4703]

Plenty of SS threaded rod on ebay. The 1/2 in is 13tpi. As I thought this thru though I realized there is another reason not to have anything sticking up above the surface of the solar panels. These are high voltage panels and even a small shadow on one cell can cause the whole panel to fail. The shaded cell turns into a resistor in series with the rest of the cells and starts to heat up and can be ruined in a short time. Then the whole panel is trash. This could happen even if the panels are flat. I would have to remember to shut off the circuit breakers before lowering them or any time the rod would cast a shadow. So still looking for a way to push up from below.

[txcncman]

Don't park near trees or power lines that can cast shadows either. And hope a bird does not land on it or poop on it. Or wind blown leaves either.

[vegipete]

Plenty of SS threaded rod on ebay. The 1/2 in is 13tpi. As I thought this thru though I realized there is another reason not to have anything sticking up above the surface of the solar panels. These are high voltage panels and even a small shadow on one cell can cause the whole panel to fail.

The threaded rod can't cast a shadow on the panel it lifts because it is mounted on the wrong side. Ie, in the northern hemisphere, the rod would be due north of the center of the panel. (Assuming the hinge at the base of the panel is aligned east-west.)

[Mike4703]

txcncman, please don't post if you are just going to be obnoxious.

[Mike4703]

That's right. If the rod is on the north side, it will not be casting a shadow on the panels. Because of the mobile nature of this installation the hinge line will not be exactly east west, but the rod can be mounted back on a flange to give a little lee way. I was thinking initially that the rod would be sticking up between the two panels somewhere between the hinge and the free edge, as this would minimize the length of the rod and again make everything mount beneath it, but it doesn't have to. Also would give more room to design a way to fold it down for travel when needed. This is sounding better. The problem now is that the free end is over four feet above the frame when opened up. That's a long rod to be sticking up unsupported when the panels are down. I attached a drawing that has close but not exactly correct dimensions to help visualize the problem. If you look closely there are lines showing the locations of a threaded rod and a scissors mechanism that moves by bringing the bottom of the lever arms towards the center.

[underthetire]

How about air bags?