z-ya Posted October 25, 2011 Share Posted October 25, 2011 I had one of these fail on the race car this weekend (this is the 510 version, but the S30 version is the same design). The other was not far behind. I think I know why they failed. Let's see who can figure out how and why. Quote Link to comment Share on other sites More sharing options...
900ss Posted October 25, 2011 Share Posted October 25, 2011 I had one of these fail on the race car this weekend ... Let's see who can figure out how and why. You hit the tyre wall at 80mph Quote Link to comment Share on other sites More sharing options...
RB26powered74zcar Posted October 25, 2011 Share Posted October 25, 2011 I have a new pair I've been saving for a couple years, and was going to install them with my other goodies I'm installing right now... Waiting to hear why! Quote Link to comment Share on other sites More sharing options...
jasper Posted October 25, 2011 Share Posted October 25, 2011 Tension rod ear of contol arm due to torquing/rotating motion of control arm, as a result of sway bar resisantance. ??? Quote Link to comment Share on other sites More sharing options...
z-ya Posted October 25, 2011 Author Share Posted October 25, 2011 Tension rod ear of contol arm due to torquing/rotating motion of control arm, as a result of sway bar resisantance. ??? Very close. It broke at the yellow line. My guess is that sway bar pulling up, and pushing down on the control arm caused it to flex at the weakest point. It should be a boxed design like the OEM control arm. The Techno Toy Tuning arms are boxed, and a better design. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 26, 2011 Share Posted October 26, 2011 Gigantic stress riser at the end of the round tube that's welded to the flat plate. That's the narrowest part of the plate, the welds look like they have some undercut, and I'm betting the end of the tube was left open. The plate just worked like a hinge right at that junction with cracks starting from the center and working out. Quote Link to comment Share on other sites More sharing options...
z-ya Posted October 26, 2011 Author Share Posted October 26, 2011 Gigantic stress riser at the end of the round tube that's welded to the flat plate. That's the narrowest part of the plate, the welds look like they have some undercut, and I'm betting the end of the tube was left open. The plate just worked like a hinge right at that junction with cracks starting from the center and working out. Exactly. The other side is bent up, and the TC rod end is also bent. Even if the tube was closed on the end, I still think it would have failed. I like the idea of a boxed design like the OEM ones. I'll post some close ups of the failure when I have them. Quote Link to comment Share on other sites More sharing options...
JSM Posted October 26, 2011 Share Posted October 26, 2011 Yikes was the failure on the track? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted October 26, 2011 Share Posted October 26, 2011 (edited) Thats exactly where I figured it would break. Just closing the tube with a cap, or pinching it, and welding the end of it to the plate would have helped a bit. A vertical gusset, top and bottom, is the way to go there Edited October 26, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
EvilC Posted October 26, 2011 Share Posted October 26, 2011 Here is the TTT control arm for visual for those who don't know their products: Looking forward to close up pics of this failed part. Also would like to see the bottom section too. Quote Link to comment Share on other sites More sharing options...
wrcbonk Posted October 26, 2011 Share Posted October 26, 2011 I agree with JohnC. You can't just weld "this to that" and walk away. The flat stock and the cylinder may not even be the same type of metal. The weld gouged the stock pretty bad. 2 cents Bonk Quote Link to comment Share on other sites More sharing options...
Lazeum Posted October 26, 2011 Share Posted October 26, 2011 (edited) It is definitely a poor design. This control arm is supposed to work in compression/traction mode + side loading due to compression rod. It requires high section inertia which the flat plate cannot not provide. Risk is to see the arm bucking under load (with stab bar helping in this way). In addition to that, the ball joint is making the outer side quite stiff also, compression rod ear is also making the flat part stiffer next to ball joint which pusses stress even more the failure point. You can also put in the equation the material properties of the metal. With the welding operation being close to the weakest point, it probably does not help. Either except if you quench the part right after to avoid metal to cool down slowly. Material properties are probably the lowest at welding location. Edited October 26, 2011 by Lazeum Quote Link to comment Share on other sites More sharing options...
z-ya Posted October 26, 2011 Author Share Posted October 26, 2011 Yikes was the failure on the track? Yes, and like I said, I was looking for some new underwear. Not the first failure I have experienced on the track. I've also experience brake failure. Sluggish steering is a lot easier on the nerves than brake failure. Quote Link to comment Share on other sites More sharing options...
z-ya Posted October 26, 2011 Author Share Posted October 26, 2011 The guy that designed them is coming over Saturday to look at everything. I think we are all in agreement, there are major flaws. He promised to make good, and firstly was concerned about the driver (which is of most importance). Stay tuned. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 26, 2011 Share Posted October 26, 2011 This book is good: "Construction of Tubular Steel Fuselages" by Vex Aviation. You can get it from here: http://www.actechbooks.com. He can keep the same basic design but use a solid bar with a cut slot for the flat plate junction and then weld the solid bar into the hollow tube using a scarfed joint. The tip of the solid bar that's welded to the plate should be rounded and welded all around with no undercut. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 26, 2011 Share Posted October 26, 2011 He can keep the same basic design but use a solid bar with a cut slot for the flat plate junction and then weld the solid bar into the hollow tube using a scarfed joint. The tip of the solid bar that's welded to the plate should be rounded and welded all around with no undercut. Sounds heavy. Not to mention, he'd then presumably have to drill and blind tap for the turnbuckle, which is a lot more difficult than welding in a threaded bung. Quote Link to comment Share on other sites More sharing options...
z-ya Posted October 26, 2011 Author Share Posted October 26, 2011 I think there should be a gusset on the top and bottom of the control arm to minimize any flexing caused by the forces the sway bar exerts on it. I don't understand how just capping the end of the tube and welding it will prevent this joint from being the weak point. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 26, 2011 Share Posted October 26, 2011 I just tried to come up with a solution that worked using his existing design. Without seeing the failure I'm assuming that the plate itself is strong enough to handle the loads. I'm assuming the failure was caused by a concentration of stresses that produced a crack(s) and then that crack(s) propagated out and reduced the yield point of the plate until it failed. This failure took time to occur and wasn't just an instant failure. By in essence making the tube a solid clevis and then welding the plate into the slot of the clevis you're eliminating the stress concentration and resulting crack propagation point. Again, I'm assuming that the builder wants to continue with the basic design. EDIT: "I think" this design is lighter then the TTT LCAs. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 26, 2011 Share Posted October 26, 2011 Regarding the gusset, there's nothing to weld the gusset to on the top and bottom of the LCA as designed. Are you thinking about a truss? Quote Link to comment Share on other sites More sharing options...
RB26powered74zcar Posted October 26, 2011 Share Posted October 26, 2011 Looks like the pair I have was revised or something. They look different.... Quote Link to comment Share on other sites More sharing options...
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