Linear actuator to raise the bed?

[dverstra]

In a different thread, raising the bed with a linear actuator was mentioned. After a few searches to see if they are documented with pictures, I decided to ask if they exist.

Jim Godward mentioned it.
"I have used their actuators for a couple of applications, one to raise the bed in the MH, and have had excellent results and no failures yet after about 2+ years.  The one problem I have had is the minimum length for the throw I needed.  I had to install at an angle in order to get the throw I needed for the bed.  My other applications were designed for the actuator so there was no problem there.  Be sure to figure the additional force required if not mounted in a straight line with the movement required.

Just an engineer talking!"

Any pics that might help a NON-Engineer? 8)

 

[HotTommy]

I don't have a picture of an actuator on a bed, but maybe this will help.  This is a picture of a typical linear actuator.  On each end there is a round hole for mounting the actuator.  The smaller pieces are the mounting plates.  One would be attached to a stationary spot and the other to the underside of the bed.  The actuator would then be attached to the mounting plates by putting a pin through each plate and each of the holes in the actuator.
http://i00.i.aliimg.com/wsphoto/v0/1998553918_1/1500N-150KG-load-5-7mm-s-Speed-150mm-6inches-stroke-12V-DC-6-Multi-function-Electric.jpg

There are several engineering challenges alluded to earlier.

• There must be places strong enough to withstand the force of lifting the bed where you can mount the actuator.
• There must be enough space beneath the closed bed to fit the closed actuator.
• The actuator must extend far enough to lift the bed to the desired height.
• The actuator must be strong enough to lift the bed.
• The actuator must open and close at an acceptable speed

Actuators come in many specs so you can choose the one best suited for your situation.  To pick the right one you'll want to examine your bed to see how much room you have for it, where you can place the mounts, and how much force it takes to lift your bed.  Keep in mind that the force required of the actuator will not be the same as the force you use to lift the bed unless the actuator lifts the bed at the same place and with the same motion that you use.  That's where the engineering comes in.  If you post your findings, we can help you figure which actuator would be suitable.

 

[dverstra]

If the actuator was mounted similarly to the gas cylinder the currently holds it up, the stroke of the actuator would need to be the same, correct? I'll have to check and see if an actuator could fit there.

 

[HotTommy]

If the actuator was mounted similarly to the gas cylinder the currently holds it up, the stroke of the actuator would need to be the same, correct? I'll have to check and see if an actuator could fit there.

Without seeing it, my guess is yes, it would be the same.  ..... BTW, why do you want to use an actuator instead of the gas cylinder setup?  And is there more than one gas cylinder?  And would you want to keep or remove the gas cylinder?

Another thought -
There is an electrical engineering facet to this project too. For example, it is unlikely you will be able to mount the actuator so it reaches the end of it travel just as the bed comes to rest in its down position.  Rather than than have the bed stop above its fully down position, you'll likely want the actuator to have a little bit of travel left when the bed comes to rest. If you continue to provide power to the actuator after the bed stops, the motor will apply force to the actuator and mounts until the bed is raised again.  Over time this could cause things to be pulled out of position.  ... One solution is to install an electrical switch that will remove power from the down circuit of the actuator when the bed is fully down.  Plainly that adds another level of complexity to the project. .... My point is that this project may be more difficult than your imagined.  Think twice before you commit to doing it.

 

[bucks2]

If the actuator was mounted similarly to the gas cylinder the currently holds it up, the stroke of the actuator would need to be the same, correct? I'll have to check and see if an actuator could fit there.

Not necessarily. The gas cylinders are positioned and designed to hold the bed up once you've lifted it. They don't provide all the force needed to lift the bed. While an actuator at that angle and using the same mounting points might work short term, it will put more strain on the hinges and the actuator mounting points than is necessary.

Here's the reason, using my bed gas cylinder locations as an example. The mount on the bed frame is only two inches lower than the mount on the bottom of the plywood the mattress sits on. So the actuator is almost parallel to the floor when the bed is down. When the bed is raised the top and bottom of the actuator are  7 1/2" away from vertical, when the bed is down the gas cylinders ends are 18" apart.

The actuator will push straight out, if you used the same mounting points,  it would have tremendous leverage to push the plywood towards the end of the bed, pulling the hinges apart and very little leverage to push up. IMHO you'll need to mount the bottom of the actuator at the bottom of the space under the bed, floor level if possible. I'd have it angled slightly, pushing towards the hinges. You'll also want it more than halfway from the hinges to the end of the bed that goes up so that the force pushes the free end up rather than pushing the hinge end up. 

How strong an actuator you will need depends on where you can mount it. Different MH's have different depths of space under the bed. The angle of the push will determine how much force will be needed. The closer to vertical you can get, and still have enough rod travel to raise the bed to the height needed the less force will be needed. It may be more than you think. Go to the middle of your bed and lift it. That's the force the linear actuator will need. It's a lot more than lifting at the end.

HotTommy wrote while I was composing my missive. The answer to the actuator pulling or pushing too far is the adjustable limit switches available on the actuators. They can be adjusted after installation to close exactly to the position you want.

Ken

 

[Lou Schneider]

Usually gas struts are mounted so they go over center as the bed is fully closed.  Since they're always pressing outward, shortly before the bed closes the mounting point on the bed platform reaches it's minimum distance from the mount on the other end, then as the bed is fully closed it moves away, i.e the arc goes over center and the extension force is now pressing the bed closed.

Another way of describing this is when the bed is fully closed, the actuator is pushing downward on the bed.

The same thing happens with the spring lifts for cabinet doors that open vertically - the door mount extends further inward than the cabinet end, so shortly before the door fully closes the arc goes over center and the spring presses the door closed.

You don't want this with a linear actuator - you want the actuator to remain uphill, pointing in the direction of the lift, during the entire operation, even when the bed is fully closed.

 

[zippinbye]

Here's and anecdotal tale from a boat hatch lift I once had.  Many boats, especially off-shore/"go fast" boats, have linear actuators installed on the engine hatch covers.  A visit to a marine manufacturer website might provide some insight for transfer of technology to a RV bed (Donzi, Wellcraft, Fountain, Eliminator, etc.).

I had an actuator on a Sea Ray Pachanga sport boat.  The upholstered fiberglass hatch was around 5' x7' and probably weighed quite a bit more than an queen mattress on plywood. Much like many RV beds, the structure surrounding the engine hatch could be viewed as a box.  One end (say the head of your bed) had a piano hinge attaching to the hatch to a vertical bulkhead. The actuator was mounted on centerline. At the "foot end," bulky portion of the actuator (motor/drive, cylinder end) attached high on the bulkhead.  The piston end fastened about half way out on the hatch's overall length (center of the bed).  My actuator rested nearly parallel with the hatch, when the hatch was closed.  Although I never could see inside, I believe the actuator lay perhaps five degrees below parallel, lower on forward bulkhead end. I'm no engineer, but I believe that would be considered a significant moment-arm, and by nature contained significant piston throw distance.  It probably opened over 50 degrees.  Both ends were secured with clevis pins and the power supply had a cannon plug; quick removal was easily accomplished.

The advantage of such a mounting orientation is minimal encroachment into your storage space, compared to angular or near-vertical resting positions.  On centerline, the assembly would occupy just the top portion of your bed base, only the length of it's closed dimension (side mounting might be possible, but I think there would be a lot of torsional flexing of the mattress base plate).  The main concern would be sufficient structural integrity at the attachment points.  Somebody smarter than me could calculate the loads involved. If I were installing in my 5th wheel, I would build plywood plates at both attachment points, to spread the load.  It might be necessary to internally brace the foot end of the bed box.  In my case, the batteries are perhaps a 4 foot electrical run.  I could direct-wire with a switch (sort of obscured) in the bed foot bulkhead, or employ solenoid switching and place the control just about anywhere.  If the piston throw exceeds any clearances or desired opening distance, then some sort of automatic limit switch would be wise.

As a side note, the actuator in my boat was an identical brand and model line as that on an old-school, ground mounted satellite TV array I owned back in the day (remember all those free signals?).  I kept the satellite actuator for spare boat parts (motor mainly), but the boat actuator never faltered in 14 years.  The boat actuator was longer, but I'd place money on being able to adapt a satellite positioner for an RV bed. Could be cheap or free with a little hunting for an idle satellite system.

Hope that helps.  It didn't help me.  Now I have another RV mod running through my mind!

 

[dverstra]

Without seeing it, my guess is yes, it would be the same.  ..... BTW, why do you want to use an actuator instead of the gas cylinder setup?  And is there more than one gas cylinder?  And would you want to keep or remove the gas cylinder?

Maybe I just need to get a heavier gas spring. MaryAnne can't lift it and it is reasonably heavy for me.

This does not appear too difficult given the proper forethought that I am sure to get on this forum 8)

If the system malfunctioned, would I be able to lift it without the actuator working? Hmmm... in the DOWN position I would not be able to access it.

 

[Kevin Means]

Having access to the actuator in case it malfunctioned was an important consideration when I installed one in my generator slide out tray a few days ago. I'm just thinking out loud here but if I were going to install one to lift a bed, I'd first cut a hole in the bed-board under the mattress, adjascent to where I was going to install the actuator. That would give me access to the actuator if it failed. Just a thought. 

Kev

 

[HotTommy]

I agree with the above comments about changing the mounting geometry for an actuator versus a gas lift. ... Gas lifts are positioned so they don't start to help lift until the bed has been move upward a little by the person.  That keeps the bed from popping up at inopportune times.  If your bed is heavy for the entire range of motion then a stronger gas lift might help.  If it is only heavy for the first few inches, it is unlikely a stronger gas lift will solve that problem.  If the problem is only during the first few inches of lift, I keep thinking there must be a simple, elegant solution that doesn't require something as complicated as an actuator.  But I can't put my fingers on it.  Perhaps someone else has the answer.

 

[Lou Schneider]

If the problem is only during the first few inches of lift, I keep thinking there must be a simple, elegant solution that doesn't require something as complicated as an actuator.  But I can't put my fingers on it.  Perhaps someone else has the answer.

Change the geometry of the gas lift so it doesn't go over center and hold the bed closed.  Then add a mechanical latch to keep the bed from popping up.

 

[dverstra]

Part of the difficulty with lifting the bed is that the mattress extends past the plywood by about 8 inches or so. When it needs to be lifted, you have to reach under it a little to pull up on the plywood. That puts you in an awkward position to lift from.

 

[Lou Schneider]

Extend the plywood to the end of the mattress?

 

[dverstra]

Extend the plywood to the end of the mattress?

What's the fun in that? 8) Seriously, the corner of the mattress gets crushed a little in the final few inches of bringing the slide in. I don't think this is the original mattress in the coach. I suppose that I could cut a 45 degree on that corner.  Maybe I can just extend a handle of some sort. Then again that might be too easy.

 

[Rene T]

How about a piece of 3/4" plywood about 4" wide and about 12" long. Attach it to a door hinge and fasten the hinge to bottom side of the bed plywood on the foot end using 1/4-20 round head bolts. Put the heads of the bolts on the side of the mattress so it doesn't tear the mattress. You could even glue a pc of canvas over the screw heads as a added prevention or counter bore holes for the heads.  The length of the handle would be just long enough so that it extends 3 or 4 inches beyond the end of the mattress. If it's cut and installed in the right position, it would just swing down and lay flat against the bed frame box and just off the floor a little.  Sand the handle real good and apply a couple of coats of polyurethane.

 

[HotTommy]

A swing out / slide out handle would both give your body better leverage and move the lifting point farther from the hinge to reduce the amount of force needed for the lift.  That sounds like the simple, elegant solution I couldn't think of.

 

[dverstra]

You see...I told you. With the "proper forethought" , this problem can be solved ( and economically)

 

[HotTommy]

That was fun.  But next time, IF you want to spend less time solving a problem, start with a description of the problem rather than a description of one of many solutions.  ... But I'm not complaining.  Uncovering and solving this tech mystery with such friendly people was a good way to spend part of a cold almost winter day.

 

[Jim Godward]

Maybe I just need to get a heavier gas spring. MaryAnne can't lift it and it is reasonably heavy for me.

This does not appear too difficult given the proper forethought that I am sure to get on this forum 8)

If the system malfunctioned, would I be able to lift it without the actuator working? Hmmm... in the DOWN position I would not be able to access it.

The problem is the initial effort to lift is not reduced with the heavier spring.  We went from an 80# pair to a 120# pair of gas springs but no joy as my wife still could not lift the bed to start it up.

 

[Jim Godward]

Having access to the actuator in case it malfunctioned was an important consideration when I installed one in my generator slide out tray a few days ago. I'm just thinking out loud here but if I were going to install one to lift a bed, I'd first cut a hole in the bed-board under the mattress, adjascent to where I was going to install the actuator. That would give me access to the actuator if it failed. Just a thought. 

Kev,

Good thought and one I have not solved because of esthitics and approval of the boss.  I think I have a solution but till I actually do it, I'll keep quiet about it.