A Linear Actuator *or* The Magic Door!

Being that things warmed up and I was trying to get some stuff put away in my shop, I decided to tackle the linear actuator and get it in place.

The linear actuator, extended.
The linear actuator, extended.

Now some of you may be pausing (or going to the search engine of your choice) and asking ‘what the heck IS a linear actuator?’  Well, it is a screw/worm gear drive that pushes/pulls a shaft along a straight line, into and out of the housing.  These are the things that move lots of slide-outs on modern RVs and trailers.

But, you might also ask, if you don’t have a slide-out, why would you need a linear actuator?  Well, one of the problems with our bus, when we got it, was that there was no way to lock it.  The emergency doors had handles, but they had no key-locks though, they could be locked with a padlock on the interior handle or by installing a keyed household deadbolt through the door to interfere with the existent deadbolt inside, which is what we did to the back door.   The front door locked like a dream, as it was one of the swing-lever accordion doors.

The front door, with the swing-latch in the closed and locked position.
The front door, with the swing-latch in the closed and locked position.

As you can see, this is really secure.  Even if someone broke the glass to get in, they’d have to reach up and unlatch the handle by the gear shift in order to swing the door in.  You might also note the cloth by the latch – one of the problems with the door is that the latch has worn and it rattles while you drive.

The swing arm in the open position.
The swing arm in the open position.

Anyhow, you might note the long rod that connects the swing arm in the center to the door.   When the swing arm is moved to open the door, the rod gets pulled in and pulls the door accordingly.  In looking at it in the right way, if the swing arm was a static unit, in order for the door to open, the bar would have to shrink, optimally about 13″ to open the front door fully.  It just so worked out that Firgelli Automations sold not only a linear actuator with the motor integral to the unit (rather than mounted alongside), but also a remote kit.

Firgelli 12 Inch Stroke Sleek Rod Linear Actuator – 150 lbs Force


List Price: Price Not Listed
New From: 0 Out of Stock
Used from: Out of Stock

4 Channel Remote Control Systems


List Price: $79.99 USD
New From: $79.99 USD In Stock
Used from: Out of Stock

Now, I chose the higher-powered 12″ model rather than the 14″ one, as I didn’t want to stress the door by pushing it too far, and the bar just wasn’t long enough to take the length of the fully opened 14″ one.  But the high-powered one has a push/pull strength of 150#, and a stopped strength of 300#, which seemed pretty strong as a replacement for the 5/8″ steel bar.

Threaded bar end and the hinge at the door.
Threaded bar end and the hinge at the door.

In looking to replace the bar, I needed to save the threaded end that attached to the hinge at the door, and the collar end that attached to the swing-arm.  These were easily enough cut away with the angle-grinder, and leveled (as best I could).

This is a picture of my 12" linear actuator, open, against the cut bar.
This is a picture of my 12″ linear actuator, open, against the cut bar.

I laid these out against the actuator and things looked pretty good.  But where I had planned to weld right to the actuator, it turned out that the fittings on the actuator were aluminum, so I had to create some pockets of angle-iron that would be the way to attach it.

Parts of angle iron for the connector pockets.
Parts of angle iron for the connector pockets.

These had to be cut down, welded, ground a bit more, welded again, then ended with some flat plate and drilled so that they would attach to the actuator.  As the bar-end of the actuator was not a nice, square piece but rounded as the bar was, and then rounded to allow for a swiveling action that I really didn’t want,  I had to make the pocket that would connect to the threaded rod not only a tight fit, but also longer so that it wouldn’t swivel or flex at all.

The connector cups, fitted and drilled to be attached to the actuator.
The connector cups, fitted and drilled to be attached to the actuator.

So after a little extra work, I had everithing ready to put together.  The connector pockets needed to be painted to keep down rust on the new grinds, and I decided to go with the brass paint, for the fun of it.

Here's the new linear actuator in place!
Here’s the new linear actuator in place!

The linear actuator bar wend in place great, however I discovered that if the round, extendable actuator bar with the screws on it moves and allows you to screw it into the door fitting, you’re actually unscrewing it from the motor and it’s a bad thing ™.  Luckily, the bar screwed right back into the actuator, and all I had to do was detach the other end from the swing arm and then screw the whole bar in and it worked out fine.

The remote, inside the door switch area.  The wires for the linear actuator go out through an existing hole in the bottom.
The remote, inside the door switch area. The wires for the linear actuator go out through an existing hole in the bottom.

I decided to use the space inside the door switch area of the swing arm to mount the remote, which worked well, as it already had a power line and ground screw in place.  The best thing about this placement is that the wires from the actuator don’t hang up on the swing arm when I use that.  With the actuator fully extended, the door operates normally.  With the swing arm locked, it works like this:

True it doesn’t open quite all the way, but it’s enough to get into and out of the bus, and the full extension of the linear actuator closes the door up snug enough that the door handle doesn’t chatter because it’s loose and worn anymore.

Now, all I need to do is get a DPDT swtich to run the door from inside, and it will be perfect.  But for right now, I have a keychain remote door lock for the bus!