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Not being able to find spares suck. Maybe not a problem in the world of associated, kyosho and tamiya, I don't know, but definitely a problem if you have a schumacher cougar (or topcat or cougar 2). Anyway, I was reminded of how after my first ever accident with my first car the control arm would easily come loose in a crash since the front bulkhead was cracked. So I worked with that idea and went to work on an already broken control arm.
the slot is narrower than the pin (obviously or it would be rather pointless) but wide enough that when enough force is applied it will open and let the pin out. Now if I had had a 3D printer capable of printing nylon I would print a few arms and test this idea. But I don't. And with the lack of spares I'm not going to do this to one of my somewhat healthy control arms. Might try it on one of my damaged bulkheads since those are still available as spares and using one of my leftover right C2 control arms (previous owner seems to have had a habit of breaking the left arm)...

anyway, just wondering if anyone has tried this before and if it works the way it's meant to (that is, it works fine under normal circumstances and in a crash the arm comes off without any actual damage)?

my guess is that it would work, but depending on how wide that slot is will dictate how trackworthy it is. In other words, maybe just slicing the arm with a hacksaw blade width is enough to just allow the arm to pop off only under really extreme crashes. otherwise if the gap is too much, simply tagging a berm or barrier would pop the arm out preventing you from finishing that race.

PerKr wrote:anyway, just wondering if anyone has tried this before and if it works the way it's meant to (that is, it works fine under normal circumstances and in a crash the arm comes off without any actual damage)?

If you crash, do you want the entire arm to tear off, or do you want it to make it through to the end of the race? Not saying one is better than the other, but that's the question, I think.

Coelacanth wrote:

PerKr wrote:anyway, just wondering if anyone has tried this before and if it works the way it's meant to (that is, it works fine under normal circumstances and in a crash the arm comes off without any actual damage)?

If you crash, do you want the entire arm to tear off, or do you want it to make it through to the end of the race? Not saying one is better than the other, but that's the question, I think.

indeed. I'd personally prefer having the arm come off (in a controlled non-destructive manner) in every hard crash than having parts break in every other hard crash. At least when spares are not readily available. others might think differently.

I haven't measured the opening I cut in the arm. More than a hacksaw blade. I think the pin is 3.2mm (should have measured, but a 3.2mm drill bit fit nicely in the holes) so the slot is probably in the 2-2.5mm range. Too small of an opening and the resulting cantilevers will have to open too far and might break because of that. Too large of an opening and the arm will come off too easily.

We do have a simple 3D printer at work. It won't do nylon, it's more ABS like and won't take much of a beating, but maybe I could use that to provide me with open-ended arms for testing...

My concern with that idea is that each time the arms fall off, that stress point you've introduced would further weaken, so that they'd be popping off with the smallest jumps or bumping into competitor's cars. The same thing happens with ball joints. The more they pop off & on, the more easily they'll pop off. That slot you cut may seem narrow, but under the duress of even basic racing, I bet the arms will fall off too frequently, and you'll be saving the arms...but not being competitive as you'll always be limping along on 3 (or less) legs before finishing races.

An interesting idea, and a commendable thought for possibly recycling previously throwaway items.... but I honestly think that the responses here are about right.... once you cut into the strength point of the arm, you're going to lose the strength that was there, and you're going to have arms popping off like your buggy is the Scarecrow in the Wizard of Oz. That's the main reason why those arms break at that point all the time, rather than anywhere else.... that's where the stresses are mostly located.

For me, I just grab another pair of arms from the pile.....
But then, I'm weird like that!!!

Alex

Alex, I was thinking the same as you, but I think he's actually referring to breaking the bulkhead, which is probably a much bigger pain and more costly to replace than the arms...but also everything that was said is also true. I don't think pre-slotting the arms is a good solution, either.

Didn't one of the Schuey's Maybe Cat2000 have an O-ring setup for the Front arms, for crash survivability? I know they did it for wing mounts, but I swore one of the cars came with it for the front Arms...

Incredible_Serious wrote:An interesting idea, and a commendable thought for possibly recycling previously throwaway items.... but I honestly think that the responses here are about right.... once you cut into the strength point of the arm, you're going to lose the strength that was there, and you're going to have arms popping off like your buggy is the Scarecrow in the Wizard of Oz. That's the main reason why those arms break at that point all the time, rather than anywhere else.... that's where the stresses are mostly located.

For me, I just grab another pair of arms from the pile.....

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But then, I'm weird like that!!!

Alex

that's 8 alloy tubs in your parts pile?

There will be some relaxation from breakoffs, that's for sure. But I honestly don't think anyone really knows just how strong the pivot area needs to be and how many break-offs are required before a slotted arm is rendered useless. I guess I'll be looking into testing that with the two damaged C2 arms (broken at the outer pin) and some 3D-printed parts.
edit: I'm not disagreeing that it might not work but I'm also not agreeing that it won't. You guys bring up some valid points.

Beau: I think all CAT models up until and including the Bosscat had the O-ring front suspension. Not sure but I think the topcat had that feature as well. Pretty nice idea.

edit2: I'm referring to both the arms and the bulkhead. The bulkhead is still available from schumacher, unlike the arms.

Beau S wrote:Didn't one of the Schuey's Maybe Cat2000 have an O-ring setup for the Front arms, for crash survivability? I know they did it for wing mounts, but I swore one of the cars came with it for the front Arms...

All the early Cats up to the BossCat had the Crashback functionality... rubber bands or o-rings on the front end, to enable the whole front arm and upright assembly to swing in an arc backwards from the perpendicular. No longer in use from the Cat 2000 onwards.

Alex

EDIT: You beat me to it, PerKr.... and yes, that is all those tubs in my junk pile. There's a few Nitro 10, a few TopCat / Cougar and Cougar 2. Some are more bananas than chassis plates now......

Alex

PerKr wrote:edit2: I'm referring to both the arms and the bulkhead. The bulkhead is still available from schumacher, unlike the arms.

Okay, when you said that, I retract part of my earlier statement, only to say this:

Does anybody else here see the irony of someone worried about damaging their hard-to-replace control arms by cutting them up?

Coelacanth wrote:Does anybody else here see the irony of someone worried about damaging their hard-to-replace control arms by cutting them up?

Schumacher people are a special breed, Kyosho-boy......



Alex