Rotisserie design 101, moment resisting connection at the pivot shaft? Options

[bondo]

I'm in the midst of over-designing a rotisserie.

The basic idea of a rotisserie is that the bolt on parts that go where the bumpers mount extend a shaft from the center, which acts as a pivot.

What I need to know is, is a 914 strong enough that those "shafts" coming out from the front and rear just need to be held up off the ground, or do they also need to be held straight and level? I basically need to know what forces are placed on the uprights... whether it's just a vertical force, or a vertical force plus moment.

[McMark]

In my experience vertical plus moment.

If you're building an 'engine stand' type rotisserie (lift into place) then it's not a big deal. The one like this that I used was AWESOME! Great balance and easy to turn. No problems, probably because of the increased bracing for the vertical.

If you're going to use an adjustable height setup (crank to raise, etc) then you have a problem with binding in the raise/lower action as well as reducing the size of your bracing for the vertical. So that's where the moment becomes a problem. If you're going to do a raise/lower rotisserie, I would weld on a top cross brace to keep the posts vertical.

The rotisseries from Eastwood are really nice. I've seen one in person and they are really well constructed. more info here

[bondo]

In my experience vertical plus moment.

If you're building an 'engine stand' type rotisserie (lift into place) then it's not a big deal. The one like this that I used was AWESOME! Great balance and easy to turn. No problems, probably because of the increased bracing for the vertical.

If you're going to use an adjustable height setup (crank to raise, etc) then you have a problem with binding in the raise/lower action as well as reducing the size of your bracing for the vertical. So that's where the moment becomes a problem. If you're going to do a raise/lower rotisserie, I would weld on a top cross brace to keep the posts vertical.

The rotisseries from Eastwood are really nice. I've seen one in person and they are really well constructed. more info here

Cool, thanks. Just what I needed to know. Hmm, top brace... I should have left that piece of rectangular tubing the full 20 feet long. (IMG:style_emoticons/default/biggrin.gif)

[VaccaRabite]

If you are building one, keep it simple instead of complex.

Eastwood's twirler is complex, as it has to work for a lot of different cars. it sells, if I remember correctly, for around $1200. I built mine for $250.

You do need a steel bar that goes across the bottom of the structure for stability. I would not make it adjustable height. Make a fixed height and look at some of the lifting mechanisms that folks here have made to raise and lower thier tubs on it. Frankly, a stripped 914 tub is light enough that 2 guys can lift it pretty easy.

Zach

[woobn8r]

Why not actually use two engine stands as a base....
they are useful again after your chassis is finished.

[VaccaRabite]

Why not actually use two engine stands as a base....
they are useful again after your chassis is finished.

You have to cut the engine stands. You could use them as engine stnads afterwards, but they would be really tall. Also the bases get modified to support the car.

If you look at mine, you can see what I am talking about. The ornage bits are the engine stand. The grey bits were the steel stock that I welded in.

(IMG:http://farm1.static.flickr.com/120/253639040_5d6c95a1ab.jpg)
(IMG:http://farm1.static.flickr.com/110/253639016_fd4c58f1d4.jpg)

As you can see, even with the added height, there is not a lot of clearance for the body to go all the way around. Also, the stands are rather chopped up.

Frankly, for the $30 from Harbor Freight for a new engine stand, just buy a third and use it for its intended purpose.

Zach

[woobn8r]

I see yer point....
I was thinking of an adjustable height (slip fit with a pin), but had not considered the width of the base being outside the dimensions of the chassis....

tangerine makes a rotisserie ($900), ...and it breaks down for shipping purposes...

[bondo]

If you are building one, keep it simple instead of complex.

Haha... I'm building what may be the most complex rotisserie ever made. Hint: binding will not be a problem. (IMG:style_emoticons/default/biggrin.gif)

The total cost will end up being around $200-$300, but I did get much of the materials for free.

[John]

If you are building one, keep it simple instead of complex.

Haha... I'm building what may be the most complex rotisserie ever made. Hint: binding will not be a problem. (IMG:style_emoticons/default/biggrin.gif)

The total cost will end up being around $200-$300, but I did get much of the materials for free.

Cool no binding. Did you put a gearbox with a crank at one end and a big bearing at the other end to precision turn the car?

We need pics.

I have seen some pretty complex fixtures at manufacturers facilities where one man can turn over a very large weldment with the use of a gearbox at one end of a sort of rotisserie.

[bondo]

If you are building one, keep it simple instead of complex.

Haha... I'm building what may be the most complex rotisserie ever made. Hint: binding will not be a problem. (IMG:style_emoticons/default/biggrin.gif)

The total cost will end up being around $200-$300, but I did get much of the materials for free.

Cool no binding. Did you put a gearbox with a crank at one end and a big bearing at the other end to precision turn the car?

We need pics.

I have seen some pretty complex fixtures at manufacturers facilities where one man can turn over a very large weldment with the use of a gearbox at one end of a sort of rotisserie.

No pics until it's done... (IMG:style_emoticons/default/biggrin.gif)

But I will say that it involves part of a P-38 Lightning. (IMG:style_emoticons/default/happy11.gif)