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 Access Hatch and Nose Cone

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Matt Jacobs
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PostSubject: Access Hatch and Nose Cone   Sun Oct 03, 2010 8:22 pm

I believe we have an effective design for the main access hatch. It is functional and fits well. The addition of a tether from the sub body to the hatch would make it easier to use underwater. A short tether could be attached from the rear of the main hatch opening on the sub body to the rear of the hatch door. If we give the hatch door positive buoyancy, it would float straight up and out of the way during entry/exit.

My initial thought with the nose cone is to permanently fix it the sub body. I think that epoxy would produce an effective bond but if we were to damage the nose cone it would be very difficult to remove. An internal latch mechanism would prevent the drag produced by the preexisting bolt method. It should also be more resistant to the type of damage the nose cone sustained last year.

A flipper latch similar to the one below should work. I would like to purchase several different variations of this latch and test fit them to the sub. Let me know what you think.
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Dana
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PostSubject: Re: Access Hatch and Nose Cone   Mon Oct 04, 2010 2:37 am

Are you talking about tethering the two hatches together? We shouldn't need to open both at the same time. The rear hatch is in case of emergency. The front hatch is for planned getting in and out of the sub.
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Dana
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PostSubject: Re: Access Hatch and Nose Cone   Mon Oct 04, 2010 5:17 am

Wait, do you mean that the front hatch can open independently. But opening the rear hatch also opens the front hatch? I think that's a great idea.

But if the hatches are positively buoyant, we run into the problem again with losing a lot of buoyancy as soon as the hatches are released. I believe we will have support divers in the water that can grab the hatches. So neutrally buoyant should be ok. hmm, actually the support divers will be carrying the sub to the surface. I think it takes all four of them to inflate their BCs to get the sub to the surface. Maybe we just need to figure out a way to slide the hatches inside of the sub so that they won't fall out. So that one of the support divers can grab the hatches and put it in the sub before they surface.

Does someone who has actually been in the water with the sub want to comment on this?
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Dana
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PostSubject: Re: Access Hatch and Nose Cone   Mon Oct 04, 2010 5:20 am

how would you mount the flipper latch to the nose cone without using bolts? In the picture, the latch is mounted to the 2x4 with bolts. Good idea, but I don't think this gets around using bolts. Unless there is another way to mount it.
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Matt Jacobs
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PostSubject: Re: Access Hatch and Nose Cone   Mon Oct 04, 2010 9:43 am

I was still going to use bolts to attach the flipper latch. I was thinking we could use bolts with a flat,rounded head. That way the bolts are smooth on the outside and the nuts are on the inside of the sub. It looked like the previous method had bolts protruding slightly all the way around the nose cone. A larger diameter bolt would reduce the possibility of shearing them off again. We could also use epoxy instead of bolts, we just need to test it. I haven't used epoxy on fiberglass. It's hard to know if these latches will work with the sub and nose cone's curved surfaces. I need to get a closer look a the nose cone. When could we meet up next to check it out. I could pick up a few latches to test fit.

Sorry I didn't clearly explain about the hatches. I am just talking about the main access hatch. I think the hatch door will be a little difficult to maneuver underwater. A diver will have to hold it while the driver gets in and out. We could attach a short tether (about a ft.) from the sub body to the hatch door. If the door is given a slightly positive buoyancy, it will float vertically in the water and out of the way. The tether should be attached from the rear of the hatch opening on the sub body to the rear of the hatch door (opposite side of the release mechanism). This frees up a diver to perform other tasks and should simplify the loading/unloading process underwater. As long as the hatches are tethered to the sub, it shouldn't affect the overall buoyancy of the sub.
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Dana
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PostSubject: Re: Access Hatch and Nose Cone   Mon Oct 04, 2010 1:03 pm

Hold off on buying anything. Let's get some input from someone who has been on the sub in the water.
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Blue
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PostSubject: Re: Access Hatch and Nose Cone   Mon Oct 04, 2010 10:30 pm

Matt~

Respectfully I'm going to shoot down some of your ideas.

The nose cone being permanently mounted to the sub is a bad idea for many reasons...If and when* the nose cone breaks it will be close to impossible to remove the existing resin and fit a new cone in its place. Also if the nose cone falls off during the race and not replaced you can no longer participate until the shield is fixed (this is obviously for safety concerns). So you can imagine that if our permanent nose cone shattered like it did at the last competition we would have to perform surgery until it is fixed ruining the rest of the week for potential racing.

The idea for the nose cone is therefore to have some type of design that incorporates a *non-fastener* type of mount. Something that if ran into the wall at full speed will be able to fail and not destroy the mounting mechanism. So you can put a fresh one in place without having to worry about fixing anything.

I actually like the flipper latch idea for the rear hatch ONLY. As Dana said the rear hatch will be completely sealed during racing and really should only need to be open to switch out batteries or do minimal work on the drive train or electronics package. However if these latches are on the outside of the sub the possibility for them busting off is very high as well. Also you have to consider the drag they will impose if mounted on the exterior of the sub...especially being so close to the propeller this drag will ultimately destroy the flow seen by the prop. If you were to mount on the outside i would recommend finding some stainless steel ones in addition to finding some streamline ones.

You have some really great ideas and yeah like you said I'm not sure if these will work on a curved surface, but def look into it. Also just making the bolt larger will not solve all of the problems since the bolt didn't shear, but actually ripped through the polycarbonate nose cone destroying our holes for mounting. Countersunk screws are also a good idea but I'm not sure if you can countersink the hull of the sub with the amount of material that is there.

Brian

Let me know if you want more input.

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Dana
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PostSubject: Re: Access Hatch and Nose Cone   Fri Oct 08, 2010 9:25 pm

Here are the current latches on the sub

Lip on the sub that mates to the hatch:


Mount for the rear side of the front hatch:


latch on the front side of the hatch:


pulling on the latch to release the hatch from the sub (inside view)


pulling on the latch to release the hatch from the sub (outside view)






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Dana
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PostSubject: Re: Access Hatch and Nose Cone   Mon Oct 11, 2010 2:41 am

At the meeting today, we threw around the idea of tethering the front hatch to the sub, so that when we are in the water, the hatch will not completely detach itself from the sub.

After getting out of the sub a few times, I think the current latch mechanism works fine. Once Morford (via text message) explained to me how to get out, it was pretty easy. If we go with the current latch mechanism (or any other mechanism that involves mounting the hatch at the front and back) we need to add clips to the sides of the hatch so that the sides stay firmly on the sub when in the water. This will cut down on drag forces.

If the current latch proves to be too difficult to operate underwater, we talked about modifying the latch so that it can be opened from above. Since the pilot's head is inside the nose cone, the pilot has to reach behind to get to the hatch, since the latch is on the hatch. The modification would add an alternate way of opening the latch so that the pilot does not have to reach back as far. we may have a similar latch, just moved up so that the pilot doesn't have to reach back as far, or on the handlebars.

Also, we talked about the rear hatch and the buoy (omg and found some crazy stuff in the closet in the garage - an old buoy, lots of control surfaces, etc). We talked about having the dead man's switch work like a bicycle hand braking mechanism.


Awesome meeting!
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Dana
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PostSubject: Re: Access Hatch and Nose Cone   Mon Nov 22, 2010 3:24 am

I asked Turner about the steel to plastic epoxy that some of you were looking at. Here is what he said

The nose cone has never been done before [attempting to mount with epoxy] but because of the thermal cycles it goes through, mechanical methods will work better than an epoxy, especially when under any stress. We can still test it, because its not like its going to damage the nose cone or anything like drilling holes would. We did attach hooks to the sub and they all eventually fell off after a bit, but we can try again.
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