DIY Kraton 4s suspension arms.

[Zlayer]

I broke a rear arm yesterday, and had seen a solution on here earlier where a member here (Sion Jones) had made some out of plastic. I know they are sold out everywhere so I tried the diy method. I used a cutting board which is nearly identical in thickness to the stock arms. I have ran it for a few minutes including a few small jumps with good success so far. I hope these are at least as durable as the stock ones or even more so! Now that I know this works I’m going to make some out of black cutting boards (and smooth them out) and maybe some other colors too. If I make lots of them it won’t be a big deal if the break. I can make between 10 -20 of them out of one cutting board!

 

[DoNoHarm]

You know what cutting board material is probably the best household plastic to use. I’ll be surprised if it’s weaker than stock.

 

[Zlayer]

You know what cutting board material is probably the best household plastic to use. I’ll be surprised if it’s weaker than stock.

It feels stronger, but still a bit flexible.

 

[Zlayer]

I just ran it some more and it “was” doing great while just driving. I hopped it a few times off a 1.5’ gravel pile very slow and easy and it broke right where the stock one does. I don’t think it’s an issue of material, but rather, there isn’t enough material where the pin goes through (same problem with stock arms). I don’t think there is clearance for anything thicker. I fear using the aluminum arms will break the chassis where the pins attach to the body. This problem renders this car pretty useless for anything other than ripping around a parking lot with no bumps. I don’t know what kind of magic arms Richduperbash (YouTube) got on his, but the car I’m using would NOT have survived what he’s Putting his through. It sucks a lot because I based my decision on getting the 4s on his tank tough launching videos. I will of course try again though.

 

[Zlayer]

I have found a possible solution using limiting straps as a way of reducing stress off the part of the arm that the hinge pin goes through. I will test a few different materials. This would be a solution for stock arms or my super sleek space age DIY version. Pics and observations to come. Arrma needs to compensate me for this R&D ? just kidding (no I’m not. This product is a disaster at $400).

 

[D3MON]

as you said i would shy away from aluminum for obvious reasons, almost wish there was a mult-material arm, i.e. some sort of allow at each end, and composite in the center to give that flex, and fail point when absolute necessary, and just sell replacement center pieces, i understand logistically this would be insanely difficult to design, between the connection points of the different materials unless some sort of hollowed out insert with through-screws, almost like a sleeve. probably over thinking that though.

 

[slick2500]

I have found a possible solution using limiting straps as a way of reducing stress off the part of the arm that the hinge pin goes through. I will test a few different materials. This would be a solution for stock arms or my super sleek space age DIY version. Pics and observations to come. Arrma needs to compensate me for this R&D ? just kidding (no I’m not. This product is a disaster at $400).

They need to redesign the bulkhead to allow for an a arm with a solid hinge pin boss and to allow for a thicker hinge pin boss.

 

[DoNoHarm]

I told you all, truck isn’t designed for this speed!! I told you! ????

And I agree, the bulkhead needs some sort of a redesign because the arms just don’t have enough meat on them. You’d like to think that some engineer knew this would be an issue but had to be kept quiet because of a higher level management..

 

[bicketybam]

Thankfully I didn't need to drop $400 to figure this out. The lighter 3s trucks have the same issue. It only made sense that a heavier truck with longer arms would be even worse.

 

[Zlayer]

Thankfully I didn't need to drop $400 to figure this out. The lighter 3s trucks have the same issue. It only made sense that a heavier truck with longer arms would be even worse.

I didn’t have that information. All I had heard was “Arrma tough, Arrma tough, Arrma tough!”?

 

[Zlayer]

I have a better understanding of why these arms break so easily now. It’s not just a matter of weak bosses where the hinge pin goes through, but a lack of lateral support forwards and backwards. Both breakages I’ve seen on YouTube (ausieRCplayground and another I can’t remember) landed on the tail nose up. This pushes the suspension arms forward where there is no support in that direction. The toe links are in the center line making them good for up and down support but not front to back. I have come up with this function over form solution to help alleviate the lateral forces. I used zip ties from the arms to the wheelie bar which should prevent forward movement some. I’ve did some descent jumps and haven’t broken in this configuration despite landing on the tail like mentioned before. Also note worm gear clamp holding the arm to the hinge pin. That, I hope, will hold strong. Also it doesn’t limit up and down suspension travel, just lateral.

 

[Zlayer]

I’ve did some more descent jumps off my ramp. I’m being cautious, but my confidence in this setup is growing. I’ve worked up to some 10-15’ jumps 7’ish high with some backflips here and there. Higher and faster will come, and I need to do a trip to the skate park now.

 

[DoNoHarm]

Very smart! I think the best way to fix this design flaw is to have an aftermarket hub carrier to accept a rear toe link goinf from the suspension arm pin to that hub carrier. Then the a arm will no longer be subjected to forward (and reverse) torque. Toe links aren’t the most durable alternative, but I bet it’ll be way better than factory.