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Author: Subject: Design for a prop catcher
HappyFather

posted on 2/1/11 at 11:43 PM Reply With Quote
Design for a prop catcher

Hello!

I'm building an Aries Locoblade with a Fireblade engine and a MNR Reverse box. I read a bit about issues with props going lose and the damage they can do and since I plan to drive around with my child, I really would like to have this issue covered.

So, prop catchers... A couple of questions:

* Do I need one (from reverse box to diff) or two (to also cover front prop)?
* Any pictures of catchers in place so that I can see how they were bolted into place without messing with the brake pipe and how the catchers look?
* How can I make a catcher? Or should I get it made?

I guess for now that covers my doubts... Thank you all for reading!
HappyFather

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blakep82

posted on 2/1/11 at 11:50 PM Reply With Quote
well, props really should have one in any place where a prop can break, so that means both front and back props could really do with it.

for my car, the racing regs say they have to have a steel hoop fitted in the tunnel, thats litterally what mine had. i thick steel bar bent round the tunnel, welded to the chassis, should work ok, but if the prop breaks slightly forward of that, its not going to help a lot lol.

the best kind i'd say would be for the prop to go inside a tube, but that adds weight.

theres no perfect design really. a couple of 25mm wide maybe 3mm thick bits of flat bar welded up and over the prop inside the tunnel would be ok though





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marcjagman

posted on 3/1/11 at 12:22 AM Reply With Quote
I'm going to use 1 1/4 inch wide by 1/8 thick for mine. 6 in total, 4 down the tunnel and 2 at the front.
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irvined

posted on 3/1/11 at 12:57 AM Reply With Quote
If your going to fit them, then fit two of them.

I haven't made any yet, but there are some pictures on these threads:

http://locostbuilders.co.uk/forum/14/viewthread.php?tid=119907

http://www.locostbuilders.co.uk/forum/31/viewthread.php?tid=133580

I intend to make mine using some 3mmx25mm strip, in a sort of =0 shape at the front of each prop shaft. My feeling is that its more likely to come off at the front end (Where it meets the gearbox) and if it comes off at the front it will keep turning as long as the wheels are moving, whereas if it comes off at the rear it will keep turning until I press the clutch.

HTH


David





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907

posted on 3/1/11 at 08:29 AM Reply With Quote
Hi All.

First of all I should say that this post is purely MY opinion, and I'm not trying to have a go at anyone.
It is not my intention to offend anyone.

I don't have first hand experience of a prop breaking but I did see the damage done to the swing arm of a GPZ 550 when
the chain snapped, part of which wrapped around the rear wheel and thrashed the steel frame into an unrecognizable
shape. The rider (my son) walked away. Very lucky.

If you roll 3mm strip into a ring, or form it into a hoop shape, you will be able to flex it out of shape with just bare hands.
Imagine hitting it several hundred times a second with say a 1kg hammer.

In one of the links above Iank says, quote,
"The problem is once free they are pretty much equivalent to a sledge hammer being smashed into the tunnel." end quote.

I would say that he isn't that far out.

I would think that a minimum thickness for the hoop/ring/frame should be 6mm, with it braced to the chassis with similar
thickness material on edge.

Like I said, just my opinion.

Cheers
Paul G

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chunky2772

posted on 3/1/11 at 10:11 AM Reply With Quote
hello happy father if you send me your e mail adress i will send you some pics of my prop shaft catcher. ive tryed posting pics on here but nothing works for me! send to bigchunky27@yahoo.co.uk and you can post them up for everyone to see.
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MikeR

posted on 3/1/11 at 10:30 AM Reply With Quote
I'll u2u you my email address. If you send them to me, i'll post them on the forum.
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plentywahalla

posted on 3/1/11 at 10:55 AM Reply With Quote
We used to fit these on boats where there is a propshaft between engine and Z drive or jet drive. If one goes awol it would punch a hole in the hull bottom.

The general rule is the closer to the shaft the restraint is, then the less energy it will need to contain. Also perfectly round is best as it will encourage the shaft to keep spinning concentrically.

The usual design was a split ring with bolted flanges so it could be easily disassembled.

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RichardK

posted on 3/1/11 at 01:15 PM Reply With Quote
I know of a builder who has used a tractor exhaust clamp as part of his prop catcher design, maybe something to think about.

Cheers

Rich





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HappyFather

posted on 4/1/11 at 08:47 AM Reply With Quote
Thank you, Chunky2772! Here are his prop catcher pictures (I hope I scaled them down enough).

Interesting that, instead of the commonly recomended U shaped strap of steel, this is a plate. In a way, this design seems easier to attach to the car without getting in the way of brake and fuel pipes.

chunky2772 prop catcher 1
chunky2772 prop catcher 1

chunky2772 prop catcher 2
chunky2772 prop catcher 2

chunky2772 prop catcher 3
chunky2772 prop catcher 3


What do you guys have to say?

Thank you all for the participation this thread has been having!
Best regards,
HappyFather

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Bluemoon

posted on 4/1/11 at 09:11 AM Reply With Quote
^^ I like the idea, but I think the plate is quite thin (looks it in the photo). One nice thing about it is it's a design that could be retro-fitted without welding, also it's a "close fit" so the prop can't get that out of line, which is I guess is the will tend to stop the prop to hammering away at the chassis. Definatly better than just a "hoop"..

Dan

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chunky2772

posted on 4/1/11 at 08:13 PM Reply With Quote
That flat plate is 3mm st/st and the two halfs off tube is also 3mm st/st powder coated black this design is super strong and will withstand any prop shaft failing. Im that confident ill put my weeks wages on its strength.
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RichardK

posted on 4/1/11 at 08:23 PM Reply With Quote
I like that

Nice work

Rich





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Bluemoon

posted on 5/1/11 at 12:23 PM Reply With Quote
quote:
Originally posted by chunky2772
That flat plate is 3mm st/st and the two halfs off tube is also 3mm st/st powder coated black this design is super strong and will withstand any prop shaft failing. Im that confident ill put my weeks wages on its strength.


Cool look's thin in the photo, was guessing <1.5mm 3mm sounds more like it.. May have a go at doing something similar.. Only issue is that I have riveted my body panels on (minus the top of the transmission tunnel) making fitting "interesting/near impossible!", thought I might regret that at the time I was pulling the rivets and using PU ;(

Dan

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chunky2772

posted on 5/1/11 at 09:03 PM Reply With Quote
I wouldent feel safe in any home build without a propshaft catcher in the trany tunnel. I think this is a must have in any kit car. one member on here posted pics of the damage done to his car after the prop gave up on him and it completely trashed his car. Im not taking any chances with mine! my car smokes the tyres in 1st 2nd gear so you can just imagine the power going through that shaft.
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designer

posted on 5/1/11 at 09:53 PM Reply With Quote
That is the best prop catcher I have seen.
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spdpug98

posted on 6/1/11 at 03:39 PM Reply With Quote
Looks like a great bit of kit, I have just started taking my 4 year old out for rides in the car and it has made me think a lot about getting a prop catcher fitted

So I have decided to get a couple made up for my car even though it means taking the seats and the tunnel cover out again twice (once to measure then once to fit!). Have you bolted the plates straight through the chassis uprights or just used rivnuts, I am thinking of bolting straight through the rails





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chunky2772

posted on 6/1/11 at 08:07 PM Reply With Quote
Ive just used rivnuts but bolts through the chasiss should be better. For your own piece of mind get a square of 3mm st/st or mild steel sheet stand it on edge and wack it as hard as you can with a big hammer see how much damage you do to it then you can make your own mind up just how strong it is. Remember the sheet is gona be stronger again with that half segment of tube welded to it.
A hoop round the propshaft has no strength. That plated design also stops fuel,brake, and electrics being damaged.

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spdpug98

posted on 6/1/11 at 08:36 PM Reply With Quote
quote:
Originally posted by chunky2772
Ive just used rivnuts but bolts through the chasiss should be better. For your own piece of mind get a square of 3mm st/st or mild steel sheet stand it on edge and wack it as hard as you can with a big hammer see how much damage you do to it then you can make your own mind up just how strong it is. Remember the sheet is gona be stronger again with that half segment of tube welded to it.
A hoop round the propshaft has no strength. That plated design also stops fuel,brake, and electrics being damaged.


Thanks





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David Jenkins

posted on 6/1/11 at 09:19 PM Reply With Quote
That's a "Doh! Why didn't I think of that" idea!

Nice and simple, and an easy retro-fit for a built car like mine. I think that'll be a project the next time I'm working in the transmission tunnel.





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HappyFather

posted on 7/1/11 at 07:45 AM Reply With Quote
Thank you all for your contributions and specially to chunky2772 for showing his design. It has been receiving so much praise that I'll just copy it for my car!

And when I get on the road, I'll have one less worry when I take my (now three, by the time I finish the car maybe five years old) kid for a spin.

The best to all of you!
HappyFather

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