Monday, October 11, 2010

Top Transplant - Lifting the Top

At this point in my documentation, I need to deviate from counting the "days" I've been working. Due to changes in work demands, a sick infant, and my wife's waning patience at being left for whole days or weekends at a time while I toil away at my buddy's shop, I'm just not getting whole days to work on the project. The upside is that since things have reached a certain level of completeness (see the last update), I was able to bring the van home again, and work on things for an hour or two here and there in the driveway. Progress comes in bursts, on afternoons when I can get away from work a little early and weekends when the baby naps or I can leave her with Mommy for (shorter) periods of time.

Instead, I'll try to capture "projects" as they are completed. Please remember that some of these projects span many days of short bursts and are often interposed with other projects, so things may appear out of order slightly.

Here then, I will cover the saga of "Lifting the Top". My goal, at the outset, was to be able to raise and lower the top on electric power, since I wanted my wife to be able to operate the top as easily as opening a sunroof. With the GTRV design, after releasing the latches, you must lift the top for 8-10 inches before the gas springs kick in and raise the top the rest of the way. When lowering the top, you have to hold it a bit above "fully closed" while you tuck the corners of the tent fabric away from the latches. For me this means putting my shoulder up against the top and standing up a bit. My wife is obviously smaller, and not quite as strong, so I was hoping to avoid this for her.

As always, more/bigger pictures on Picasa web album.

The problem with electric lifting actuators in this situation is packaging. The GTRV top is very low profile (lending the "Garagable" part to "Garagable Top RVs"), which doesn't leave much room for a bulky actuator. I was excited, then, to find these "tubular" actuators from Firgelli Automations.

The trick to this design is that the drive motor is contained within the actuator tube. This makes for a compact design, one that doesn't take up much more room than the gas spring that was included in the original design.

First I tackled the upper brackets, where the actuator hits the pop-top. These brackets came from Firgelli, and I thought they were nice and compact until I started messing with them and found some oddness. First, the drilled holes weren't exactly square to the material, which made tapping them less than fun. Why tap? Well, I was concerned that if the mechanism ever failed while in the "down" position, it would be difficult (or impossible) to service the actuators since they'd be trapped under the cap, and a burned actuator would prevent me from raising the top manually. So instead, I tapped the brackets themselves then used button-head cap screws from the outside to bolt everything up. This way, if there was a problem I could simply unbolt the bracket from outside and raise the top manually. Its a good thing I did it this way.... read on.

The Firgelli brackets weren't going to work on the van-side of things. They advertise "almost 180 degrees of rotation" from the bracket. I only needed about 40 degrees, but in an arc that wasn't compatible with the pinch-points on the brackets, so I had to make my own. I started by clipping a couple of corners from some 2" x 3/16" bar stock, then transferred over the critical measurements. The red is layout fluid, which when brushed on, makes it easy to transfer marks and measurements over to the steel. This is one of those things that (as an Electrical Engineer, not an ME or pro-machinist) I was glad to learn about when I was building Battlebots back in the last decade.

After a bit more cutting, a little drilling and grinding, and some less-than-ideal welds, I have a couple of these brackets. These are the first project done by my "new" old welder. I've had this welder since the aforementioned Battlebot-days, got from another Bot-builder friend, but I'd never gotten off my butt and set it up until now. It's an old SIP design from Italy, with a few quirks which I will get around to fixing later, but for a hobbyist like myself, it should do ok.

After paint, I made a couple of pads from cork/rubber gasket material. These should help seal against leaks and keep the roof damage to a minimum.

The lower bracket and actuator in place, complete with stainless sheet metal screws.

In the up position, everything was looking good. The actuators, even "unlocked" had enough holding power to keep the roof up without any struggle. "Locking" the actuators by shorting the motor terminals was built-in to my design and proved more than adequate to keeping things from moving. I started "small" by just moving the actuators a few inches, and everything was fine.

After I tried to run the actuators all the way down, though, I found a significant problem. After a bunch of blown fuses and swear words, much probing, and disconnecting and reconnecting of wiring and bracketry, I was able to find the problem: The actuators aren't really built to take the load I was putting them under, despite the 150lb rating. The motor assembly is held in the actuator tube by a pair of plastic (!!!) standoffs that fit the extruded profile of the tube. Under heavy compression load, these standoffs were compressing and sliding, and the motor was hitting the cap on the actuator tube, pinching wires and shorting things as it happened. There may still be hope for this design, if I can get some metal motor mounts machined up, but for now the electric lift design was DOA.

With a heavy heart, and 8 extra holes in the van roof :(, I gave up and fitted the original GTRV gas springs to the top. This isn't a "bad" design, it just wasn't what I was hoping for. Once again I have the problems of manually lifting/holding the top while raising/lowering, but so does every other GTRV owner...

On the upside, I was able to get to this point prior to the San Diego ExPo Meet-n-greet, so I was able to show off a mostly-functional pop top! :)

More to come...


ned said...

hey there, what lenght are your actuators? - I'm thinking of doing similar to my land cruiser.
also, did you find you needed sideways stability across the front the roof , or were the actuators enough to keep it firm?

kind regards,
ned .

Herbie said...

Ned, they were the 18" stroke actuators (Part # FA-05-12-18"), which I notice aren't on Firgelli's website any more. I think the overall length was right around 36" or so, but I'd have to dig up a saved copy of the datasheet to be sure.

Sideways stability was fine - the hinges do most of the work there. With the gas struts that are currently fitted (remember that the actuators were a bust due to the loads involved), there's a little side to side movement if you push on the top or something, but generally the hinges hold everything in line. I'm planning to upgrade to a set of double-shear hinges soon, and that should firm things up even more.

As for your LC, I'd try to find a way to calculate all the loads at ALL points in the movement of the top before you commit to these actuators. As you can see from my experience, they aren't well designed to handle high-compression loads and they certainly didn't have enough strength to raise the top from fully lowered. The gas struts need a little help at the beginning, but at least they tolerate all the loads.

ned said...

many thanks, good info. the poptop i bought is from a T2 and with have to be cut to shape. also its currently got lifting bars, so ill have to start from scratch with the mechanism. i want electric though!!! haha, i wouldnt think it was nifty otherwise. do you have a link to somewhere i can view these double shear hinges you speak of?

reckon ill just get actuators with a quite high lifting force, im not concerned how they look.

Cole said...

Did you ever get this working ?