Drilling and tapping case for solenoid

[mbryner]

As mentioned on a few previous posts, I'm adding a Murphy 1 1/2-inch throw solenoid to my 6/1 to open the fuel rack and passively close it on normal shutdown or emergency shutdown.   It seems the easiest is to attach a thin stranded aircraft cable to the tensioning spring on the governor mechanism.   The cable will thread back to the solenoid.   The energized solenoid holds the cable tight at the required spring tension for 650 rpm.   If the solenoid is de-energized the cable falls slack and the engine stops.   There is insufficient room to the left of the spring to mount the solenoid and multiple holes would have to be drilled in the crankcase, so I just mounted the solenoid in a vertical orientation to the engine base frame.   Then the cable will have to go through a pulley to make a 90 deg turn from vertical to horizontal.   If I attach the pulley to the stud the spring is on in the picture below, the spring will be angled downward and not in line with the governor mechanism anymore.   I was planning on drilling a hole in the crankcase approx where the red dot is.   Does anyone see any problems with that?   How thick is the iron there?   It's not easy to determine by looking in the crankcase.   It's directly below the camshaft.   It's preferable to not plunge through and have to clean out the crankcase from drilling shavings, but if that's what it takes...   Thanks.

Marcus

[d34]

Just a thought, I dont have a clue if this would work for you.  Why not get a shorter spring with the same tention and mount the pully on the stud that is there?

[bschwartz]

Are you SURE the engine will shut down with the spring tension released.  It would be a bad day if your system were to sense a problem, release the spring, and the engine only slowed down a lot, but not shut off.

[mbryner]

@d34:  Thanks.  Great idea.  But how do I know the spring constant is the same?   If I don't get the same spring constant won't the engine rpm bounce around?

@brett: Well, I'd be using it for routine shutdown, too, so if it doesn't work I'll notice pretty quickly!   Seriously though, if you take out any tension on the spring, there's nothing to pull the fuel rack open against the flyweights.   I got the idea from Jens from a previous thread: http://www.microcogen.info/index.php?topic=1780.msg21695#msg21695   Hmm, I'll double check tomorrow.

[LowGear]

Isn't it more energy efficient to energize the solenoid when things fail.  Is the solenoid strong enough to pull the rack closed?  Yes, I know this is a little like putting the generators in the basement a couple of hundred meters from the ocean.  The only catastrophic failure scenario here would be a dead battery. 

Casey

[mbryner]

Casey,  not less efficient if you use the solenoid for routine startup and shutdown.   A solenoid doesn't take much power to hold on:  hold on to keep running, let go and engine turns off.   Anything fails = power lost = engine passively turns off because no more fuel.

[AdeV]

Marcus,


Looking at that picture, I'd estimate you have at least an inch of solid iron there, plenty to drill & tap a decent sized bolt.

[Carlb]

Isn't it more energy efficient to energize the solenoid when things fail.  Is the solenoid strong enough to pull the rack closed?  Yes, I know this is a little like putting the generators in the basement a couple of hundred meters from the ocean.  The only catastrophic failure scenario here would be a dead battery. 

Casey

What happens if a mouse eats through the wire or the solenoid fails.   I think energizing the solenoid to keep the engine running would provide a "fail safe" situation.

carl

[LowGear]

Hi,

Thanks for listening.  I'm back on the team.  Normally On.

Can we set it up so it could be over-rided(?).  OK, this is the first step towards Kaos but "back doors" can make life a lot easier.

This is where I ask if anyone has seen Captain JB Weld?

Casey

[mbryner]

Thanks all.   Jens, that is what I needed to know.  98% is OK.  

If it is a concern (it isn't any more for me) you could add a secondary safety.

I can add a small/weak spring pulling on the opposite side of the rack to make it 100% reliable.   That's easy.   I'll do some experimenting today.  

Here's a pic of what I tried first.   It worked but wasn't reliable enough and the Allthread rod was bending.

[Thob]

I think I would use the bolts on the left of the crankcase cover just below the spring attach point.  Make a bracket that holds a pivot point below the spring attach point, and use a right-angle lever similar to the governor linkages.  Attach the spring to the new lever and allow the lever to rest against the existing spring attach point in the "run" position.  The other arm of the lever goes to the left and has a cable that goes down to the solenoid.  You can add a spring to pull it up at that point, if needed.

Please excuse the crudity of my drawing.

I'd would also vote for keeping it fail-safe such that if the solenoid power fails, a wire breaks, or anything mechanical breaks it shuts off.