Advice on Linear Actuators & angles of 'lift'

[Jocklandjohn]

The lifting roof I've built on my 110 has been very successful, except for the fabric sides which although robust & functional have proved very vulnerable on stormy days and very cold & quite prone to condensation in winter. So I'm looking at a wee bit of additional work to add rigid sides that will lift with the roof. This will put the total weight up over the limit of the current gas struts.

One other problem with the gas struts is that because of the way they need to be fitted to the roof, laying flat & parallel with the rooftop, they only really start to provide any 'push' once I've physically pushed the roof up past a certain angle at which point the gas struts take over and start to push. Of course when lowering the roof it's the opposite and the roof comes down under control until you hit that point where the struts cease to work and suddenly you're holding up a very heavy lump whilst trying to ensure the fabric sides don't flap out and get trapped.

So I'm contemplating fitting a pair of linear actuators. Ideally they would be fitted vertically so they can push straight up, and a pair of 220lb push would easily do the job if placed in the right location. However that may not be possible given the internal fittings I have which means the struts have to be located quite far back and the length of actuator lift is not sufficient to fully raise the roof, so I'm looking at fitting the actuators horizontally, in the same style as the gas struts.

I can see two obvious ways to do this - see drawings - one is a straightforward fixing to base and to lid and hope that the combined 'push' and the proper location will allow the roof to be lifted.

 

However I've also mulled over the scissors type addition which 'might' make the pushing action easier.  I've got a few inches of space between the base and the lifting top so just enough space to allow a folding scissors-type bracket to be located. This also has the additional advantage of allowing the roof to 'lock' in the upright position and be supported by the scissors bracket rather than all the weight being supported on the actuator (although it's possible to retain the gas struts too as they're in a different location). So the actuators are really only to overcome that initial horizontal aspect of movement where the maximum 'push' is required  on the way up, and 'support' on the way down.

 

I'm not an engineer but I know many of you are - so could someone with the relevant experience cast an eye on these options and offer an opinion please? Or maybe even something more appropriate?

[Cynic-al]

The closer to the back the easier it will be for them to lift the roof so get them as far back as stroke / space will allow.

To use it like the top drawing you need to vertically separate point A1 & B1 as much as possible. When the roof is down the closer point a1 & b1 are horizontally the harder job they will have at pushing the roof up. How much space do you have?

The second option is better again the lower the mechanism is the more force the actuator will need to lift the roof. If you think about a scissor car jack they're a lot easier to turn the handle when they're near the top than the bottom.

Thinking of a scissor car jack you can get 12v ones quite cheap, they lay pretty flat and give a good stroke and are supposed to lift a car. It's bacically doing what your trying to do just in a single component. Maybe an option? Just a random ebay search http://www.ebay.co.uk/itm/like/182722022898?chn=ps&dispItem=1&adgroupid=49522826281&rlsatarget=pla-543033447832&abcId=1128966&adtype=pla&merchantid=115507028&poi=&googleloc=1006679&device=c&campaignid=857333700&crdt=0

Also does it matter if the two sides don't lift at exactly as you can't be sure they will lift at the same speed. If the car jack was powerful enough maybe you could get away with just one?

If you put weights and lengths of everything then the forced could be calculated for you.

Edited September 25, 2017 by Cynic-al

[Dave W]

The scissors arrangement should work as you have it, on the proviso that the scissors never fully close. If the part anchored at B is allowed to be inline with the actuator when closed, it won't be able to open it.

You could also look at make A-B as a single strut, mount B in a roller guide setup and attach the actuator to B. That would reverse the operation so the actuator would pull to open and push to close. Again though, ideally you want a slight angle when closed so it never fully aligns with the actuator. If you want to see a manufacturer's version of the design, see if you can find a VW California T5 or T6, they have an electrically operated pop top that is controlled by a linear actuator.

From experience, when you buy linear actuators, remember to check their operating speed. I bought one to replace the ram on our rock'n'roll bed as it was exactly the same lengths so was a straight swap... only after fitting did I realise that it would take 50 seconds to go from one extreme to the other. It does the job but, in  hind sight I'd have paid slightly more for one that was double the speed !

[Jocklandjohn]

44 minutes ago, Cynic-al said:

The closer to the back the easier it will be for them to lift the roof so get them as far back as stroke / space will allow.

To use it like the top drawing you need to vertically separate point A1 & B1 as much as possible. When the roof is down the closer point a1 & b1 are horizontally the harder job they will have at pushing the roof up. How much space do you have?

The second option is better again the lower the mechanism is the more force the actuator will need to lift the roof. If you think about a scissor car jack they're a lot easier to turn the handle when they're near the top than the bottom.

Thinking of a scissor car jack you can get 12v ones quite cheap, they lay pretty flat and give a good stroke and are supposed to lift a car. It's bacically doing what your trying to do just in a single component. Maybe an option? Just a random ebay search http://www.ebay.co.uk/itm/like/182722022898?chn=ps&dispItem=1&adgroupid=49522826281&rlsatarget=pla-543033447832&abcId=1128966&adtype=pla&merchantid=115507028&poi=&googleloc=1006679&device=c&campaignid=857333700&crdt=0

Also does it matter if the two sides don't lift at exactly as you can't be sure they will lift at the same speed. If the car jack was powerful enough maybe you could get away with just one?

If you put weights and lengths of everything then the forced could be calculated for you.

Thanks Al - I've got exactly 3 inches between roof top and bottom to play with. And yes I understood the further-back-is-easier requirement as it played a big role in getting the gas struts properly located. Yes ideally both sides lift at the same time as the roof does flex and the sides may jam or rub if not lifted in alignment. Jack is quite a neat thing but dont think it will fit in the available space. 

 

37 minutes ago, Dave W said:

The scissors arrangement should work as you have it, on the proviso that the scissors never fully close. If the part anchored at B is allowed to be inline with the actuator when closed, it won't be able to open it.

You could also look at make A-B as a single strut, mount B in a roller guide setup and attach the actuator to B. That would reverse the operation so the actuator would pull to open and push to close. Again though, ideally you want a slight angle when closed so it never fully aligns with the actuator. If you want to see a manufacturer's version of the design, see if you can find a VW California T5 or T6, they have an electrically operated pop top that is controlled by a linear actuator.

From experience, when you buy linear actuators, remember to check their operating speed. I bought one to replace the ram on our rock'n'roll bed as it was exactly the same lengths so was a straight swap... only after fitting did I realise that it would take 50 seconds to go from one extreme to the other. It does the job but, in  hind sight I'd have paid slightly more for one that was double the speed !

Cheers Dave - is 3 inches enough? Might be really tight. Operating speed - yes I was reading the blurb on ebay and its something like 5mm a second for the cheap ones! Not quick but then they're not hugely expensive. I think I'll have a look at a VW and get some idea of what they've done. 

There is one huge factor here that might be to my advantage and thats the removal of the fabric sides - the current setup precludes an inner lifting mechanism in part because of the fabric (the gas struts are on the outside of the fabric, so don't interfere with it) so with the fabric gone I might be able to install actuators with more placement options. I still need to work around interior seating and fridge, sink etc. 

Although I wanted the actuators inside the vehicle to keep them clean and dry, I *may* be able to go external and conceal inside the outer skin but the problem with that is that the loading is then borne by the relatively thin sides as opposed to the very much more robust roof sections. 

Think I need  to get inside with tape measure and figure out precise locations where I might be able to install. But at least I know now that the scissors is viable, and I quite like the suggestion of A B being a strut and pulling to open. 

Thanks both of you.

[Soren Frimodt]

That Electric Jack uses a Worm gear setup, the easiest way to get plenty of torque and predictable speed (albeit a bit slow) What about using that principle of the worm gear and fit it at the pivoting point? Perhaps with a shaft through the entine length of the roof so it lifts evenly. I don't know if this is possible on your setup though, just a thought  

[Jocklandjohn]

7 minutes ago, Soren Frimodt said:

That Electric Jack uses a Worm gear setup, the easiest way to get plenty of torque and predictable speed (albeit a bit slow) What about using that principle of the worm gear and fit it at the pivoting point? Perhaps with a shaft through the entine length of the roof so it lifts evenly. I don't know if this is possible on your setup though, just a thought  

I think I'd struggle to fit that!  The ideal at the moment is looking like actuators in some configuration - might just manage a vertical push but thats not quite as easy as the less-efficient horizontal installation. 

[Soren Frimodt]

Okay, was worth a shot though.. I don't think the first option is really viable with a linear activator, it would struggle at the first part just like your gas struts, and it may well kill it if you tried. Option 2 seems the best from my point of view

[Jocklandjohn]

3 minutes ago, Soren Frimodt said:

Okay, was worth a shot though.. I don't think the first option is really viable with a linear activator, it would struggle at the first part just like your gas struts, and it may well kill it if you tried. Option 2 seems the best from my point of view

Yes I think you're right. I'll need to get some material sizes and weights and work out the actual weight to be raised, but it looks like it will be in the 80KG range, so I have a better idea of the forces involved. But certainly the actuators look like a flexible option.

[Dave W]

One other thought regarding the linear actuator, you could, potentially use a ram as well to assist in the first part of the lift if you can't get the angle. The actuators have 

58 minutes ago, Soren Frimodt said:

That Electric Jack uses a Worm gear setup, the easiest way to get plenty of torque and predictable speed (albeit a bit slow) What about using that principle of the worm gear and fit it at the pivoting point? Perhaps with a shaft through the entine length of the roof so it lifts evenly. I don't know if this is possible on your setup though, just a thought  

Essentially that's all a linear actuator is, uses a worm gear to turn the motors rotation into a linear movement. Hence the cheaper ones are quite slow but have a lot of torque (1500 Newtons with mine, which will lift 150Kg ish). At 5mm per second over a 400mm movement you just need to be patient !

[Dave W]

1 hour ago, Jocklandjohn said:

Cheers Dave - is 3 inches enough? Might be really tight. Operating speed - yes I was reading the blurb on ebay and its something like 5mm a second for the cheap ones! Not quick but then they're not hugely expensive. I think I'll have a look at a VW and get some idea of what they've done. 

I think it would be, yes, you don't need much of an angle, just enough to ensure that the actuator and lever aren't directly in line. Even a small initial deflection will be enough to ensure the actuator is able to move the lever. On my bed it's only offset by around 1/2 an inch.

[Bowie69]

You could use two sets of actuators, one short set to get over the force 'hump', mounted vertically,  then another set to do the rest of the lift as you have above.

Then, you don't need really long actuators poking down into the living space.

Or, you could retain gas struts and use the short actuators to help you lift/lower the first part?

I had been thinking about some sort of cable drive, like an electric window mechanism , but struggled to find anything on Google...

[Jocklandjohn]

5 minutes ago, Dave W said:

I think it would be, yes, you don't need much of an angle, just enough to ensure that the actuator and lever aren't directly in line. Even a small initial deflection will be enough to ensure the actuator is able to move the lever. On my bed it's only offset by around 1/2 an inch.

Slowness is irrelevant to be honest - after being trapped by the elbow when lowering the roof in a forest miles from anywhere in the highlands one day when the wind caught it - rescued by my 8 year old son who was JUST able to put his head agains the roof inside with his knees bent and then straighten, which lifted it a few inches - I'm happy to watch and wait in safety! 

[Jocklandjohn]

Just now, Bowie69 said:

You could use two sets of actuators, one short set to get over the force 'hump', mounted vertically,  then another set to do the rest of the lift as you have above.

Then, you don't need really long actuators poking down into the living space.

Or, you could retain gas struts and use the short actuators to help you lift/lower the first part?

I had been thinking about some sort of cable drive, like an electric window mechanism , but struggled to find anything on Google...

I did think about the short actuators to do the initial lift - but I'd then need to add stronger gas struts because the addition of the hard sides will make it too heavy and as it is at present I'm at the max size/strength for the diameter of strut tube I'm using because they fit in the gap between inner and outer folds of the lifting roof & base. If I go stronger they go up in diameter and then they'd have to come inside and be in the space where the actuator can go!  Hence using the actuators to do the heavy lifting but keeping the relatively light gas struts to take some of the strain - they're there and working fine so makes sense to leave them.

I'll pop up some images later on today or tomorrow to show the set-up and space available.  But keep the suggestions coming - very valuable!

[Dave W]

If you're looking for a nice looking switch to control all this, I can recommend the CBE step switch, designed to be used to raise and lower the access steps on a motorhome it takes a single 12v input and switches the output to the motor internally so you just need two wires in (12v) and two wires out to the motor and the switch does the rest. the wiring diagram that comes with it also has an allowance for end stop switches although I've never bothered using those in my case.

The CBE stuff gives a nice finish to the interior with lots of different options regarding modules you can use with them and surround colours.

[Jocklandjohn]

Thanks for that - might be worth a look when I get to fitting.  They don't seem to be too expensive either. 

2 minutes ago, Dave W said:

If you're looking for a nice looking switch to control all this, I can recommend the CBE step switch, designed to be used to raise and lower the access steps on a motorhome it takes a single 12v input and switches the output to the motor internally so you just need two wires in (12v) and two wires out to the motor and the switch does the rest. the wiring diagram that comes with it also has an allowance for end stop switches although I've never bothered using those in my case.

The CBE stuff gives a nice finish to the interior with lots of different options regarding modules you can use with them and surround colours.