Rpm a arms for 3s and 4s models, let's see your broken a arms.

[Ginglehopper]

I think Rpm needs to redesign these a arms as they always fail in the exact same spot. I want to see your photos of your broken Rpm a arms to pass along to Rpm.

View attachment 83433

I know I broke one in that same spot. I'll see if I have a picture.
Yep! Same spot. This is with the front Senton 3s BLX arm.

 

[slick2500]

Adding another one to the list https://www.arrmaforum.com/threads/what-did-you-break-today.8928/page-213#post-706627

 

[Velodromed]

Adding another one to the list https://www.arrmaforum.com/threads/what-did-you-break-today.8928/page-213#post-706627

Aw man I wanna post it myself

 

[Hector_Fisher]

Adding another one to the list https://www.arrmaforum.com/threads/what-did-you-break-today.8928/page-213#post-706627

Posted this already elsewhere, but figured I'd add to this collection!

 

[Velodromed]

Posted this already elsewhere, but figured I'd add to this collection!

View attachment 209265

What were the temp and conditions again? Just so it’s part of this thread…

 

[Hector_Fisher]

What were the temp and conditions again? Just so it’s part of this thread…

60ish degrees outside, drifting around a small gravel parking lot, 5 to 10mph. Hit a protruding stump.

Now that I'm looking at the previous pictures on this thread, I'm not really surprised it broke where it did.

 

[Velodromed]

60ish degrees outside, drifting around a small gravel parking lot, 5 to 10mph. Hit a protruding stump.

Now that I'm looking at the previous pictures on this thread, I'm not really surprised it broke where it did.

Yeah it’s a good thread.

 

[GRC]

Typhon 3s front arm. Same spot as everyone else. It was a bit chilly, around 45 degrees. I usually try not to jump under 50 degrees. This is why.

 

[Michael24]

Broke all four same spot over the course of the winter. BRCC long jumping they only broke if I landed on packed snowmobile tracks awkwardly. -20c 50ft jump 20ft high. Just disposed of them the other day.

 

[Hector_Fisher]

Okay guys... I've got a theory here... I'm just spit balling, so call me out if I'm off my rocker:

What if the process RPM uses to cast their arms leave some amount of residual stress in each arm? Think like preload. The arm is already tight. In one of the pictures, the plastic just before the break is bent, but there were no vertical forces involved? Is that evidence of residual stress? Looking at my breakage on the back side, it quite literally exploded at the rear leg of the arm. For how tame of a hit that was, definitely seems like there was some additional forces at play. Would that make sense as to why boiling works? Relieves the residual stress?

If you want to get into the material sciences portion of it--one size of the smaller chunk has striations, revealing that there was an initial flaw that was slowly widened by successiv stresses--and the other side..... is completely different failure mode... doesn't realky look like fatigue stress cracking. Not sure what technical terms you would use to describe it, other than explosion.

Sorry if this bores you, but this fascinates me.

 

[slick2500]

Okay guys... I've got a theory here... I'm just spit balling, so call me out if I'm off my rocker:

What if the process RPM uses to cast their arms leave some amount of residual stress in each arm? Think like preload. The arm is already tight. In one of the pictures, the plastic just before the break is bent, but there were no vertical forces involved? Is that evidence of residual stress? Looking at my breakage on the back side, it quite literally exploded at the rear leg of the arm. For how tame of a hit that was, definitely seems like there was some additional forces at play. Would that make sense as to why boiling works? Relieves the residual stress?

If you want to get into the material sciences portion of it--one size of the smaller chunk has striations, revealing that there was an initial flaw that was slowly widened by successiv stresses--and the other side..... is completely different failure mode... doesn't realky look like fatigue stress cracking. Not sure what technical terms you would use to describe it, other than explosion.

Sorry if this bores you, but this fascinates me.

View attachment 209894

View attachment 209896

View attachment 209897

View attachment 209898

Rpm molds their arms they aren't cast. But I am pretty sure the process isn't 100% perfect.

Boiling them doesn't make a difference, the ones I posted had been boiled.

 

[Hector_Fisher]

Rpm molds their arms they aren't cast. But I am pretty sure the process isn't 100% perfect.

Boiling them doesn't make a difference, the ones I posted had been boiled.

Casting-metal, molding-plastic, yeah I was typing fast. But you got the point. Boiling does do SOMETHING though. I just boiled one of these arms from the same package and compared back to the other in a new-boiled vs new-stock flexibility with attached weight (once they were both at room temp). The boiled one is more flexible (didn't use a ton of weight to exaggerate it). I don't know exactly how or if you can extrapolate that to assume increased durability. But they are more flexible.

I know there are casting defects. That was evident from the picture before on the non-shattered side. I'm sure that doesn't help the breakage.

 

[Hector_Fisher]

Posted elsewhere, but including here. Again.

 

[Just a hobby]

The only rpm arms I never broke were for my baja 5b ss. My losi baja rey they broke,bottom only top ok. But the tires camber is out of wack way too negative.
My kraton, and Granite arms started to sag then broke. If you can catch the sagging of the arm when it's just a little bent and switch the arms from left to right they will last longer. Otherwise all break in the same spot. The arms need more plastic to them not a skeleton of a arm same thickness as stock won't work.
Hope this made sense?

 

[slick2500]

The only rpm arms I never broke were for my baja 5b ss. My losi baja rey they broke,bottom only top ok. But the tires camber is out of wack way too negative.
My kraton, and Granite arms started to sag then broke. If you can catch the sagging of the arm when it's just a little bent and switch the arms from left to right they will last longer. Otherwise all break in the same spot. The arms need more plastic to them not a skeleton of a arm same thickness as stock won't work.
Hope this made sense?

Yup it needs to either be filled in or at least have gussets in the corners.

 

[Just a hobby]

I noticed summer is to hot making the arms bend and stay bent fast. Winter they just snap. 60 degrees to 70 degress no more no less. I've been doing a 15 to 20 minute boil on just the first inch on the suspension pin chassi side only of the stock arms. Seems to help some.

 

[SrC]

RPM has recommended boiling their Nylons many years past.
And periodically I may even re-boil them and straighten them out, if I do a tear down. I don't have these exact RPM arms. I don't have a 4x4 rig. But yeah cold weather will make them shatter like glass, no matter what. And the 6s arms tend to warp, stretch out or bend. NG. RPM Nylon tends to work better or worse depending on the mold designs for specifics rigs. I never broke one RPM arm on any of my RC10T's for instance. Yet have snapped many 6s Arrma wing mounts and 6s arms. Less so than the stockers however. I bil them also. RPM will replace for free any of their Nylon parts if you send the broken ones back to them. They recycle the Nylon of the Broken ones. Don't even need a receipt. Just need some patience to receive the the replacements.

 

[Just a hobby]

I forgot about my hpi blitz,never broke a arm on that. Rpm refused my arms twice. When a arm broke in the street and showed some road rash. Just snapped dropping off a high curb. I knew it was going to break. I just don't run rpm on 4×4 trucks I jump.

RPM has recommended boiling their Nylons many years past.
And periodically I may even re-boil them and straighten them out, if I do a tear down. I don't have these exact RPM arms. I don't have a 4x4 rig. But yeah cold weather will make them shatter like glass, no matter what. And the 6s arms tend to warp, stretch out or bend. NG. RPM Nylon tends to work better or worse depending on the mold designs for specifics rigs. I never broke one RPM arm on any of my RC10T's for instance. Yet have snapped many 6s Arrma wing mounts and 6s arms. Less so than the stockers however. I bil them also. RPM will replace for free any of their Nylon parts if you send the broken ones back to them. They recycle the Nylon of the Broken ones. Don't even need a receipt. Just need some patience to receive the the replacements.

6 pound rc trucks rpm is OK. Anything over 10lbs and you do even light jumping and the arms stay bent and twisted for good. Then snap in the same area.

 

[SrC]

Yeah RPM is very specific in their warranty. If there is much road rash, normal wear, etc. They are considered worn out despite them cracking or breaking. I never ran into any problems with my replacement requests. Turn around time has taken a month or so FWIW. If they are all chewed up or worn when they snapped, I just buy another set. But I have had more RPM replacements over the years then I can count. They have had that warranty for over 20+ years now. And still honor it. My last replacement was about a year ago, for 6s wing mounts. I always have spares on hand anyway.

 

[Just a hobby]

If I didn't snap and bend shock shafts on almost every rpm broken arm. I would still use rpm. Maybe the Granite will get them again,but my 3s kraton never again. I'm about to order the v2 arms and longer rods. And eventually v2 shock towers and v2 outcast chassi. I believe v2 arms and v1 chassi need a little sanding and fitting to work.