DIY Converting a manual penthouse to electric (A possible solution?) - Page 2

shenrie · 02-08-2017, 07:59 PM

Quote:

Originally Posted by boywonder

Caution: the helper springs will shoot out and fly across the street or bend the supporting cover plate when really compressed with wood.....don't ask me how I know this....

^^^ thanks for mentioning this. springs are dangerous. all sizes, all shapes. i watched one of my dads friends lose and eye when i was 3-4 years old. i dont remember much from that age, but ill never forget that. ive had some close calls screwing with vehicle springs and was being careful. honestly, im lucky to still have all my appendages...

all that safety stuff aside, cool idea. look forward to seeing what you come up with.

Nrobert10 · 02-08-2017, 08:01 PM

So I was going down the same path when I just installed my pop top. You all are much better at the math of it all.

The question I have is why would you need the long spring and chain at all? My original thought was to remove the large spring, mill out the other side of the track and make a shuttle. The lifting bar would have a shoulder bolt and guides on both the inner rail and outer rail to help reduce binding. The actuator would connect directly to the shuttle to lift and lower the top. I thought about leaving the small helper spring to get it started.

Figuring out the math behind it was well beyond my knowledge.

boywonder · 02-09-2017, 05:24 AM

Here is the answer without using any math.....

You need the long springs to bias the weight of the top toward what I'll call "neutral bouyancy".

Think about it this way....we have gravity acting downward all day long.....So picture getting in the van and lifting the top with no springs installed. It will take a superhero to get it up, and it will come crashing down when you let go.

If the spring load is too high, then the top would stay popped up and you could hang from the roof and it wouldn't come down.

When the spring rate and preload are correct, the top will stay in any position that you place it, from all the way down to all the way up.....this is what we want, same for a garage door BTW.

When this condition is achieved, we are essentially just overcoming frictional losses of the pivots, sliding elements etc when lifting and lowering the top....at least on paper. The reality is that the geometry of the crossbars and where the springs attach make things somewhat non-linear, that's why we need trig and free-body diagrams.

So with the weight of the top balanced with the springs, the forces required to lift and lower are small compared to not having the springs to balance the weight..essentially the forces need to be high enough to overcome friction and deal with the non-linearities of the geometry.

When the actuator force requirements are low, the actuators can be smaller, cost less and use less power, just like people who are lifting the top (except for the cost part

).

The other benefit of the springs is that if an actuator fails, the weight of the top is balanced and won't come crashing down and injure and maim you or your loved ones.

boywonder · 02-09-2017, 05:36 AM

Quote:

Originally Posted by boywonder

When the spring rate and preload are correct, the top will stay in any position that you place it, from all the way down to all the way up.....this is what we want, same for a garage door BTW.

...quoting myself here.....

If you are going through garage door openers, the odds are high that your garage door springs either need to be adjusted, or replaced with springs with a different spring rate.

An easy way to check this is to disconnect your door opener with the garage door closed. Then lift the door and close the door manually. The effort required to lift and close the door should be about equal. You should also be able to partially open the door and the door should not continue to open or turn around and close.

If your door is difficult to open manually and speeds towards the ground that's a recipe for a short lived opener...since it's not designed to lift the weight of the door, only to overcome the frictional losses to lift and close when the springs are adjusted properly.

Nrobert10 · 02-09-2017, 06:18 AM

Makes sense. That's why I love this forum so much knowledge to be gained everyday!

BrianW · 02-09-2017, 07:28 AM

RE: Penthouse weight. On SMB's site, they say a Penthouse for a Sprinter weighs 345 pounds, so I assume an E-van PH would be around the same.

"The Penthouse Top installed adds about 345 pounds" Sportsmobile Custom Camper Vans - Penthouse Tops

Not sure if that includes the weight of the PH bed or not. And obviously you'd need to add in any additional accessories like roof tracks, solar, etc.

MSD · 02-09-2017, 10:14 AM

I really like this thread… Keep it going

boywonder · 02-09-2017, 01:25 PM

Quote:

Originally Posted by BrianW

RE: Penthouse weight. On SMB's site, they say a Penthouse for a Sprinter weighs 345 pounds, so I assume an E-van PH would be around the same.

"The Penthouse Top installed adds about 345 pounds" Sportsmobile Custom Camper Vans - Penthouse Tops

Not sure if that includes the weight of the PH bed or not. And obviously you'd need to add in any additional accessories like roof tracks, solar, etc.

As an interesting design exercise, we can calculate the PH weight based on the spring loads and see if we are in the ballpark. I estimate that my RB roof probably weighs 250-275lbs....that's a swag...but if it really weighed 345 lbs, it would have taken more than 4 people to heave it up on the roof during the install.

Flakwagon · 02-09-2017, 01:30 PM

I'm assuming the 345 includes the hardware, which we are not lifting. I'm going to get a scale and measure the lifting force needed. I'm also going to lower the top as far as I can and find the "neutral" point and measure the angle of the bars and tension in the springs. With that information I should be able to reverse calculate the weight of the top and then the force required for an actuator.

Flakwagon · 02-09-2017, 10:08 PM

I got myself a spring scale. I measured about 170# to get it moving. I also found the neutrally bouyant point in the top and was able to take measurements of the springs. Going to run the numbers back wards and see if both equations give me the same answer.

I didn't have time to run all the numbers and come up with an exact answer. But I have everything I need now. We should know tomorrow if this will work or not.