Slide-Mounted Generator Lock Design

[reslife]

I have a generator that is fastened to a rail/slide assembly that can be pulled out from the vehicle to have maintenance done to it. Someone suggested using a quick release pin (

http://www.mcmaster.com/#standard-quick-release-pins/=l17wjw)

to secure the generator in place. My question is this: how do I determine the pin that will work? I know the weight of the generator, but I'm not sure how to account for the force of an impact. Please let me know if this question if unclear.

 

[hydtools]

What are you using now to keep the generator in its stowed position?

Ted

 

[reslife]

Hard to describe in words, but basically it's two pieces: an metal piece shaped like an 'S' on one side of the slide, and a straight piece on the other slide. The bottom of the 'S' meets the straight piece and they are secured with a bolt. The issue with the existing design is that the bolt isn't always tightened, so the metal faces aren't touching, thus loading the bolt in shear.

 

[MikeHalloran]

Those pull pins are really intended to work in shear, not in a direct pull. Their detents are just there to keep them from falling out.

Absent photos of your installation indicating otherwise, I'd suggest replacing the bolt with a padlock, because generators may fall out from vibration, but they more often walk away, ahem, with assistance.



Mike Halloran
Pembroke Pines, FL, USA

 

[reslife]

Right, so the plan is to replace the bolt with the pin (which will be loaded in shear). I'm just not sure how to determine how strong the pin has to be. I like your suggestion about the padlock!

 

[hydtools]

Pick a pin the same size as the bolt, if the bolt is in shear.

Ted

 

[dhengr]

Reslife:
You neglected Mike’s most important suggestion, and that was some photos or sketches showing how the generator is oriented on the truck, what the slide track looks like, dimensions, weights, C.G’s, etc. etc. We can’t see it from here, and have no idea which impact loads or vibrations are applied which way, and to what. Neither the bolt or the pin will likely work well in single shear; but the bolt is probably stronger than the pin, and would work better in single shear when properly tightened. If the bolts aren’t being reapplied properly, what makes you think the pins will be? And, they better be secured to the frame with a light chain/cable or they will just fall off the truck when not reinstalled. Can you redesign the locking mechanism is some way so the pin just holds it in place without really being loaded during the vibrations and impacts? The pins with spring loaded detents are not particularly strong against pull-out and they require a fairly fine fit in the hole too.

 

[reslife]

Good points dhenger, thanks for the response. Here is a picture of the setup:

This is looking from the rear of the vehicle, forward. There are pins in it now just to see how it looks, but it typically uses a bolt (which as I said, is rarely torqued). The logic behind using the pin over the bolt was that the bolt requires proper torque to mate the surfaces. The pin (which would be secured by a cable) could just be inserted and then loaded in shear. I always thought that bolts shouldn't be loaded in shear? Perhaps a pin isn't the best way to secure this?

 

[MikeHalloran]

That's a _very_ cheesy assembly. ... and it may be assembled wrong, to boot.

The plates through which the pins pass are way too far apart to put the pins in pure shear; the pins are also in bending and tension when the slide tries to move.

It's not clear if this is possible, but either the 'plate' or the 'box', or maybe both, should be bolted to the inside face of the mating structural angle, not the outside face. The idea is to get the near faces of the pin holes to within half a diameter of each other, less if possible.
The slide assemblies may or may not allow that.

In any case, I would reinforce the 'box' part with a solid block mostly filling its interior. Aluminum might work, steel would be better in some ways. Basically, a prismatical block filling the interior of the tin box at the left, with a through hole match- drilled to the existing hole in one wall. I'd secure it with at least four sturdy flat head screws entering from top and bottom through the flanges. Or maybe by welding. That way a long pull pin could be fully supported for most of its length, and it wouldn't be possible for the pin to assume an angular position as shown.



Mike Halloran
Pembroke Pines, FL, USA

 

[reslife]

Totally agree, same thing I said when it came in. Not quite sure who designed it all, but I was basically told to "fix" it. You make some good recommendations! Thanks!

 

[dhengr]

Reslife:
You said.... “The logic behind using the pin over the bolt was that the bolt requires proper torque to mate the surfaces. The pin (which would be secured by a cable) could just be inserted and then loaded in shear. I always thought that bolts shouldn't be loaded in shear? Perhaps a pin isn't the best way to secure this?”

What logic? Bolts are commonly used in shear, and the important thing is that you properly mate the surfaces by tightening the bolts, so the bolt can act correctly in shear, at a real faying surface. You don’t really have a sound connection if the bolt is flopping around in two loose holes and across a 1/8 or 3/16" gap as in your two track halves. And, that’s why the pin is kinda a half-a$$ed connection too, and worse yet, it doesn’t draw the two pieces together. The above is a bolt or pin in single shear (one shear plane through the bolt, one faying surface, same plane) with two lapped side plates (your two track halves). When you have the loose gap, the bolt in also being loaded/stressed in bending and maybe in tension across the gap, and is not bearing uniformly in its side plate holes. A bolt in double shear has two shear planes through the bolt, two faying surfaces, and two side plates and one center plate. With the whole system in tension or compression, causing the shear on the bolts, and consequently putting the bolts into bearing on the holes in the three plates.

That whole system looks pretty new. Are the sliding tracks strong enough to hold up over time, under the vertical, lateral and longitudinal loadings they might see? The pins you’ve picked are not a better solution than bolts. Mike is saying about the same thing I’m trying to explain. That loose gap connection is just a bad detail all the way around. Maybe the workers are not tightening the bolts for fear of pinching the rollers on the sliding track system. At the rear of the track half fixed to the generator, cut a shim piece a couple inches long which fills that gap, and weld it to the web of the track. Chamfer the front corner so that you get a tight fit-up during the last few inches of longitudinal slide movement. Match drill this shim and then use a bolt which can now be tightened, with any wrench, no torque requirement. Maybe add a cotter pin so the nut can’t vib. off. Alternatively, at the front and the back (which we see) of the two track halves fixed to the generator, make four pairs/sets of sloped blocks (two front sets, two back sets) several inches long and a little wider than the track. The idea is that the last inch or so of longitudinal track movement starts to ramp up these blocks, unloads the slide tracks a bit, and puts the generator on solid mounts during transit. Then drill a vert, hole through the back end of track and the two sets of rear blocks and drop vert. pins into these holes. Weld the bot. blocks to the deck and the top blocks to the underside of the track rail, use a small slope. Make the bot. front blocks higher than the bot. rear blocks, so that the front top blocks will move over/past the rear bot. blocks during assembly.

 

[hydtools]

Check with Onan for their recommended installation for their generator.

Ted