RPM and Popping Dog Bones

[PowerDubs]

I've broken two rear rpm arms at the hinge pin, never broken an Arrma one,

My rear stock arm cracked in line with the pin on it's 2nd run....

 

[Notorious J]

My rear stock arm cracked in line with the pin on it's 2nd run....

I've had three go the same way. Has to be a flaw in the mold or manufacturing process. The joint opens way too easy. Switched the rears to RPM.

 

[slick2500]

As I have watched you and @olds97_lss posting these pics, I felt that I should mention one thing. The measurements should not be end to end. The plastic could be thinner or thicker where they wrap the hinge pins. On the fronts, the measurements should be taken from where the pillow balls screw in, to the "center" of the hinge pin hole. On the rears, it's from hole to hole. This measurement would give a more accurate distance, and determine if one is truly longer than the other. Agree or disagree?

True for the uppers but, I am pretty sure that if the stock lower arms would not have been bowed they would have also been 140mm just like the Rpms. I'll re measure them again at some point.

 

[Lazy Bushman]

Warning! Longish post here.

@Notorious J I did think about the measurement and risk of measuring top to bottom. When I measured mine against stock I inserted the pin across both (well half of each) and it was level and the length pretty much bang on exactly the same with less than 1mm variation. Below is the latest email I got from RPM when I got up this morning:

We're happy to try and help to the best of our abilities.

Let's start by addressing the "stock-versu-RPM" situation:

Thread - rppm-and-popping-dog-bones.12070 Post #3 by Notorious J states he runs all stock (no RPM) but axle issue is the same on his.

Thread - cvs-popping-out.10590 Post #3 image shows stock a-arms, not RPM, in reference to another users stock a-arm problem.

In our opinion, ARRMA designed the driveshafts a bit too short. Our shop Kraton with stock a-arms on it shows the drive pin in the drive cup at almost the center point of the slot at ride height. That's too far out when this is the furthest in the pin will go as the suspension travels. It should be much closer to the inner edge of the drive slot.

As for a solution, we would be under the impression that sliding the pivot balls in another millimeter or so would be the best fix. Our engineering team says that the dogbone at the outdrive would be best situated in the outdrive where the axle pin misses the inner edge of the slot by about a millimeter or so at ride height since that's where it would be the furthest in. Obviously the free movement of the axle carrier must be taken into consideration here but if you can get full free movement of the axle carrier (lock-to-lock at both ends of suspension travel) with the pivot balls turned in that far, then the problem should go away except on the most extreme of impacts. Another consideration to look at would be whether the driveshaft contacts the outer lip of the outdrive at full suspension travel.

My response is below and in it I outline what I think my personal issue was. There are still a few unknowns for me such as why does my left lower arm seem to becoming in contact with the drive cup and why does it only happen on one side only. I have also included pics of the dog bones measurements as well as how the dog bone now sits in the cup.

Again I appreciate your response. I do admit there have been a couple of issues with stock but a lot less than by the guys using RPM……now that said it may not be an RPM issue, it just appears to be the most consistent change made by people who have this issue on a regular basis.

I have done a bunch more investigation and comparison of all the parts on my vehicle since last email and while I haven’t tested the performance yet, I don’t think that in my case the issue was caused by the RPM arms (thankfully as I do like your stuff, wing mount is a looming purchase for me). I think your comment about the dogbanes is bang on. I am running GPM dog bones and discovered that it is about .3mm shorter. I replaced the one that was popping out regularly with a stock on and it is definitely sitting better! I would have replaced both with stock but I only have one good one as a spare but more on order. Combine this change with the shim removal and it is sitting much better now. Why however it is doing it more on one side than the other I don’t know. Maybe due to crashes etc my front left has a bit more flex….don’t know, but the front left arm is also a bit more chewed out where it appears to have come in contact with the drive cup, again this is speculation but I have a pic of that on that thread I started about RPM arms, maybe the arm impacting on the cup is another reason why this side is popping out but again I don’t quite know.

I will be updating the forum shortly with this info (cut and past to a degree) along with some pics if you are interested.

Lastly, I just want to reiterate that I really do appreciate you taking the time and communicating on this issue. It is very easy for a manufacturer to say “Not my problem, others haven’t complained” so I do appreciate what you guys are doing here.

While in my case I'm thinking the problem isn't directly a RPM issue, I am going to keep an eye on it as I'm wondering if the extra flex at least is a contributor. I'm hoping not. I have definitely ordered a couple of sets of stock dog bones as well as some stock arms from Jenny's just in case. Hopefully I won't need them as the RPM's have with stood more punishment than my stock ones took before cracking for sure.

In terms of the pics you will see that the GPM bones are slightly shorter so the GPM's + Shim's would not have helped. The other is a pic of how the shaft now sits in the cup. Note the previous pic I posted of the shaft position was without the shims on the pillow balls and the result looks greater than the difference in measurement.

Sorry for such a long post but I wanted to be clear and fair on this and for people to see how RPM is in fact interested in our issues as they read this stuff (RPM I know you are lurking here!).

 

[Notorious J]

I've had three go the same way. Has to be a flaw in the mold or manufacturing process. The joint opens way too easy. Switched the rears to RPM.

Four as of this evening, but I hit a tree off a jump and bent the hinge pin as well. No fault of anyone but myself. Dam, I only have one right front lower spare left. Scuse me, gotta go visit my friends at Jennys ?

 

[martysmith223]

Four as of this evening, but I hit a tree off a jump and bent the hinge pin as well. No fault of anyone but myself. Dam, I only have one right front lower spare left. Scuse me, gotta go visit my friends at Jennys ?

don't feel bad man landed on my ass end from about 20 feet high broken gearbox case cartwheels for about another 20 feet now my servo is dead and my wing mount is all kinda bent ripped Lower screws out of the gearbox case that attach to the voltage towers guess that what broke the top two also ripped one side of the wind mount loose and broke the wing mount wheelie bar lol voltage tower strait as an arrow! but I'm down waiting on my hr gearbox case order it a few days ago so at least it was already on the way

don't feel bad man landed on my ass end from about 20 feet high broken gearbox case cartwheels for about another 20 feet now my servo is dead and my wing mount is all kinda bent ripped Lower screws out of the gearbox case that attach to the voltage towers guess that what broke the top two also ripped one side of the wind mount loose and broke the wing mount wheelie bar lol voltage tower strait as an arrow! but I'm down waiting on my hr gearbox case order it a few days ago so at least it was already on the way

all this happened about an hr ago lol

 

[SrC]

Just my observations.
Notorious V3:
On OE rear arms, I noticed my right side arm chewed up from the right side cup. Diff is not shimed on the left.
Left arm, not chewed up, but shows clear sign of intermittent contact by the left cup.
RPM arms measure out the same as OE. Checked when new. I haven't noticed either cups making contact to the RPM's. (yet)
RPM arms do stretch. Some don't mind. Some actually like the feel of flexible Arms. (don't know why) And some don't even notice it. And some others like myself don't like the flex at all. In my track days years ago, RPM was the rage, but the serious fast guys would rather use the OE composite arms on rigs such as Losi and Team AE. And they kept OE spares on hand in the pits. I liked the solid feel. Much more dialed and predictable feel. I know these Armas are not track rigs. Durability is all we want due to the abuse and the fun way we drive these. But I notice that too much flex, affects my driving style. Perhaps a moot point to most others. I get it.
I've tried these RPM arms as well. There is a trade off between flexibility and stiffness. Stiff snaps sooner, while flexible will snap under more severe load all while flexing like spagetti, which even affects damping to some extent.


Kraton V4: The flex of the rear RPM arms seem more apparent to me. It appears that the longer wheelbase exacerbates this. I prefer the OE arms on my Kraton. RPMs better for my Noto. My preference.
The Diff is shimmed on the V4( ring gear side) from the factory now. One shim only.

Regarding dog bone clearance within the drive cup slots, I noticed that the more slop you have at the camber links as well as the inner hinge ins(C block to D block and outer hinge (hub carrier) pins, you have a better chance for losing a bone. I can tell you there is much slop out of the box to contend with in my opinion. V3 or V4. I understand why Arma does this. Just a byproduct of their pricepoint. That's ok.
My Tekno MT uses OE CVD's both front and rear. I have considered modding a cvd set setup for the rear on my Armas. I know it can be done if it hasn't been done already. This eliminates dog bones popping at the rear and controls deflection at the drive cups. I've lost several bones to the weeds. I actually found a lost one by chance at my local spot that I lost several months ago, Although rusty, It was in perfect shape. I paint my dogs safety yellow now. Making it very easy to spot. Since painting them, my rig hasn't ejected one. Go figure. But I know it will happen. $20.00 for a pair of dogs gets expensive after a while. I tend to lose them in the weeds before I bend them or wear them out.
These bones eject at high rpms when they let go because of snapped arms or camber rod ends and they will end up 50 feet in another direction.

 

[martysmith223]

Just my observations.
Notorious V3:
On OE rear arms, I noticed my right side arm chewed up from the right side cup. Diff is not shimed on the left.
Left arm, not chewed up, but shows clear sign of intermittent contact by the left cup.
RPM arms measure out the same as OE. Checked when new. I haven't noticed either cups making contact to the RPM's. (yet)
RPM arms do stretch. Some don't mind. Some actually like the feel of flexible Arms. (don't know why) And some don't even notice it. And some others like myself don't like the flex at all. In my track days years ago, RPM was the rage, but the serious fast guys would rather use the OE composite arms on rigs such as Losi and Team AE. And they kept OE spares on hand in the pits. I liked the solid feel. Much more dialed and predictable feel. I know these Armas are not track rigs. Durability is all we want due to the abuse and the fun way we drive these. But I notice that too much flex, affects my driving style. Perhaps a moot point to most others. I get it.
I've tried these RPM arms as well. There is a trade off between flexibility and stiffness. Stiff snaps sooner, while flexible will snap under more severe load all while flexing like spagetti, which even affects damping to some extent.


Kraton V4: The flex of the rear RPM arms seem more apparent to me. It appears that the longer wheelbase exacerbates this. I prefer the OE arms on my Kraton. RPMs better for my Noto. My preference.
The Diff is shimmed on the V4( ring gear side) from the factory now. One shim only.

Regarding dog bone clearance within the drive cup slots, I noticed that the more slop you have at the camber links as well as the inner hinge ins(C block to D block and outer hinge (hub carrier) pins, you have a better chance for losing a bone. I can tell you there is much slop out of the box to contend with in my opinion. V3 or V4. I understand why Arma does this. Just a byproduct of their pricepoint. That's ok.
My Tekno MT uses OE CVD's both front and rear. I have considered modding a cvd set setup for the rear on my Armas. I know it can be done if it hasn't been done already. This eliminates dog bones popping at the rear and controls deflection at the drive cups. I've lost several bones to the weeds. I actually found a lost one by chance at my local spot that I lost several months ago, Although rusty, It was in perfect shape. I paint my dogs safety yellow now. Making it very easy to spot. Since painting them, my rig hasn't ejected one. Go figure. But I know it will happen. $20.00 for a pair of dogs gets expensive after a while. I tend to lose them in the weeds before I bend them or wear them out.
These bones eject at high rpms when they let go because of snapped arms or camber rod ends and they will end up 50 feet in another direction.

the Cvds will fit on the kraton I have a set ready to go on just havnt done it yeah cause my kraton is already down waiting on parts I'm not sure what cant use the cvds like this but I'm positive the kraton can

the Cvds will fit on the kraton I have a set ready to go on just havnt done it yeah cause my kraton is already down waiting on parts I'm not sure what cant use the cvds like this but I'm positive the kraton can

without modifications if I'm correct

 

[SrC]

Thanks for the cvd info. Yea it's a no brainer. Expensive but worth it. And you are not going to find Tekno parts with RC dismantlers. They work with RTR's . More profitable and in demand.

 

[Lazy Bushman]

I haven’t had an issue with my backend at all and it is running stock. I have hearof running the front CVD’s in the rear and I have a couple of sets coming from Jenny’s (I think a couple). One will go to racking off the GPM’s and the other I might put on the rear

 

[Primarrma]

I haven’t had an issue with my backend at all and it is running stock. I have hearof running the front CVD’s in the rear and I have a couple of sets coming from Jenny’s (I think a couple). One will go to racking off the GPM’s and the other I might put on the rear

I've been really disappointed with gpm stuff too, most of the stuff I've got rid of.

 

[olds97_lss]

Happened again for me today after removing the thick washer and moving the top shim to the bottom. Same left side. Will have to wait for the footage to compile and my migraine to dissipate before I know what kind of landing it was... considering how infuriating my savageX was being for the 2 hours before I ran the outcast... I'm guessing it wasn't a "happy" landing.

I changed the shock oil out back to stock (associated 80wt) since my last run. I should have left it stock as I like it better. It hops less now after big jumps. At the time, I was just used to the savage flux plush landings and hearing the outcast hit the ground like a rock was unsettling. Nearly a year later and I'm over that now. Would much prefer the more responsive suspension.

I'll be grinding the ends off the arms a mm or two before my next outing to try and help the ball popping out issue.

 

[slick2500]

Thanks for the cvd info. Yea it's a no brainer. Expensive but worth it. And you are not going to find Tekno parts with RC dismantlers. They work with RTR's . More profitable and in demand.

Yeah I just want to confirm that the front cvds will fit in the rear of the Kraton. Outcast and Talion. I've been running front cvds on my Outcast since like October or November of 2017, I don't even remember but I have had zero issues with them.

 

[Lazy Bushman]

Happened again for me today after removing the thick washer and moving the top shim to the bottom. Same left side. Will have to wait for the footage to compile and my migraine to dissipate before I know what kind of landing it was... considering how infuriating my savageX was being for the 2 hours before I ran the outcast... I'm guessing it wasn't a "happy" landing.

I changed the shock oil out back to stock (associated 80wt) since my last run. I should have left it stock as I like it better. It hops less now after big jumps. At the time, I was just used to the savage flux plush landings and hearing the outcast hit the ground like a rock was unsettling. Nearly a year later and I'm over that now. Would much prefer the more responsive suspension.

I'll be grinding the ends off the arms a mm or two before my next outing to try and help the ball popping out issue.

It is my left side that pops as well. I have bought the Kraton away with me for the weekend hoping to test it out. no where near by to jump etc, but it was also popping landing wheelies as well

 

[SrC]

No front popping CVD bones on my V3 Noto or V4 Kraton as of yet.
But the first thing I did out of the box was set up my caster, camber and toe. I removed both lower black washer shims at the lower pillows. I left the upper right side plastic shim where it was and replaced the upper left plastic shim with one of the extra Black metal washer shims. I did this to both rigs. Using my alignment guage it appeared they both required the same shimming. The suspension design geometry is not symmetrical left to right out of the box. I needed .5-1.0 mm more shimming on the left side upper. Same for both rigs. Curious if anyone else noticed this.
This gave me near perfect camber at -1 degrees L/R. My steering angle castor stayed good lock to lock. Then set my toe at +1-+1.5 degrees (toe out). Hard to adjust due to all the inherent control arm slop. I stayed with front stock upper and lower arms. Droop setting is very key here also as it controls arm deflection. My droop screws at the front are screwed in level to the arm. This also prevents snapped shock ends. My rear droop is not set as extreme, just enough to prevent shock end carnage. Extreme arm deflection is usually where/when the dogs pop out. My CVDs sit proper in the cups with this setup. I only seem to break the rear arms and have a set of rear RPMs here I played with. I've played with RPM arms for years past. They do better on some brand rigs than others. Overall they are too flexi for my taste. And RPM nylons do stretch for sure. I stay away from alloys. Been there done that. Composite arms can be more rigid and lighter. I like that. As long as they don't become a nuisance part that snaps a lot. Then you have options. Driving style will determine that.
I can see trying the Fr. upper RPM arm in conjunction with the OE lower arm. This may reduce some inherent upper arm slop. I may try that.

 

[slick2500]

No front popping CVD bones on my V3 Noto or V4 Kraton as of yet.
But the first thing I did out of the box was set up my caster, camber and toe. I removed both lower black washer shims at the lower pillows. I left the upper right side plastic shim where it was and replaced the upper left plastic shim with one of the extra Black metal washer shims. I did this to both rigs. Using my alignment guage it appeared they both required the same shimming. The suspension design geometry is not symmetrical left to right out of the box. I needed .5-1.0 mm more shimming on the left side upper. Same for both rigs. Curious if anyone else noticed this.
This gave me near perfect camber at -1 degrees L/R. My steering angle castor stayed good lock to lock. Then set my toe at +1-+1.5 degrees (toe out). Hard to adjust due to all the inherent control arm slop. I stayed with front stock upper and lower arms. Droop setting is very key here also as it controls arm deflection. My droop screws at the front are screwed in level to the arm. This also prevents snapped shock ends. My rear droop is not set as extreme, just enough to prevent shock end carnage. Extreme arm deflection is usually where/when the dogs pop out. My CVDs sit proper in the cups with this setup. I only seem to break the rear arms and have a set of rear RPMs here I played with. I've played with RPM arms for years past. They do better on some brand rigs than others. Overall they are too flexi for my taste. And RPM nylons do stretch for sure. I stay away from alloys. Been there done that. Composite arms can be more rigid and lighter. I like that. As long as they don't become a nuisance part that snaps a lot. Then you have options. Driving style will determine that.
I can see trying the Fr. upper RPM arm in conjunction with the OE lower arm. This may reduce some inherent upper arm slop. I may try that.

My Rpms have sooo much slop on the top it's not even funny.

 

[Primarrma]

No front popping CVD bones on my V3 Noto or V4 Kraton as of yet.
But the first thing I did out of the box was set up my caster, camber and toe. I removed both lower black washer shims at the lower pillows. I left the upper right side plastic shim where it was and replaced the upper left plastic shim with one of the extra Black metal washer shims. I did this to both rigs. Using my alignment guage it appeared they both required the same shimming. The suspension design geometry is not symmetrical left to right out of the box. I needed .5-1.0 mm more shimming on the left side upper. Same for both rigs. Curious if anyone else noticed this.
This gave me near perfect camber at -1 degrees L/R. My steering angle castor stayed good lock to lock. Then set my toe at +1-+1.5 degrees (toe out). Hard to adjust due to all the inherent control arm slop. I stayed with front stock upper and lower arms. Droop setting is very key here also as it controls arm deflection. My droop screws at the front are screwed in level to the arm. This also prevents snapped shock ends. My rear droop is not set as extreme, just enough to prevent shock end carnage. Extreme arm deflection is usually where/when the dogs pop out. My CVDs sit proper in the cups with this setup. I only seem to break the rear arms and have a set of rear RPMs here I played with. I've played with RPM arms for years past. They do better on some brand rigs than others. Overall they are too flexi for my taste. And RPM nylons do stretch for sure. I stay away from alloys. Been there done that. Composite arms can be more rigid and lighter. I like that. As long as they don't become a nuisance part that snaps a lot. Then you have options. Driving style will determine that.
I can see trying the Fr. upper RPM arm in conjunction with the OE lower arm. This may reduce some inherent upper arm slop. I may try that.

Are you measuring camber with the tyres on, or with a measurement disk wheel?

My tyres are not square the whole way round so I would find I'd adjust something, move the car and it would be different? Or it may be the slop in everything?

 

[SrC]

Are you measuring camber with the tyres on, or with a measurement disk wheel?

My tyres are not square the whole way round so I would find I'd adjust something, move the car and it would be different? Or it may be the slop in everything?

It's hard to set up the toe due to the slop. I agree. I could get a around plus 1 to 1.5 degrees. Give or take. As long as they are close with the battery in place and servo on . Def want toe to be positive. Ever so slight is fine. I tried aligning with wheels off, but it doesn't matter with the slop and all. I leave the 4 wheels on. And constantly compress and settle the suspension between adjustments. These Armas are not track rigs, which I am more acustomed to. But, getting them close to setup really does help and make it drive more predictable. Out the box, camber was extremely negative riding on inner tread knobs, and not even left to right. Puts undo stress at hub and bearings. It will drive out of the box, but until you align it front and rear, you won't realize it's driving potential. And, the front tires will def. wear on the inside. Leave the rear tires with 2 to 3 degrees negative camber. Again the rear camber links are sloppy. So just get it close. The rear toe although fixed is a bit inconsistent left to right. Just my observation. Not tragic. Don't forget to set your Droop after all else is complete.Then take one more final check of the front camber.
In this order, set up. front and rear track to be square, then camber, caster, then toe then Droop. Droop can be done first initially. But droop will affect camber depend on the rigs design geometry, which varies from model to model brand to brand. Sometimes not. If bump steer is obvious, fix it or ignore it , your choice, then set the droop.

 

[Primarrma]

It's hard to set up the toe due to the slop. I agree. I could get a around plus 1 to 1.5 degrees. Give or take. As long as they are close with the battery in place and servo on . Def want toe to be positive. Ever so slight is fine. I tried aligning with wheels off, but it doesn't matter with the slop and all. I leave the 4 wheels on. And constantly compress and settle the suspension between adjustments. These Armas are not track rigs, which I am more acustomed to. But, getting them close to setup really does help and make it drive more predictable. Out the box, camber was extremely negative riding on inner tread knobs, and not even left to right. Puts undo stress at hub and bearings. It will drive out of the box, but until you align it front and rear, you won't realize it's driving potential. And, the front tires will def. wear on the inside. Leave the rear tires with 2 to 3 degrees negative camber. Again the rear camber links are sloppy. So just get it close. The rear toe although fixed is a bit inconsistent left to right. Just my observation. Not tragic. Don't forget to set your Droop after all else is complete.Then take one more final check of the front camber.
In this order, set up. front and rear track to be square, then camber, caster, then toe then Droop. Droop can be done first initially. But droop will affect camber depend on the rigs design geometry, which varies from model to model brand to brand. Sometimes not. If bump steer is obvious, fix it or ignore it , your choice, then set the droop.

This is really great info, thank you, I have always struggled to get good steering with my Kraton. I think if I follow this after my rebuild it will improve dramatically. The Losi 8ight truggy and buggys I've got are so much easier to set up. It's great to hear you got good results for your efforts. The Talion I have was setup really well out of the box, handling is great, though I've bent the chassis now, so I'll re do all the setup when I install the m2c racing chassis. Thank you again.

 

[SrC]

This is really great info, thank you, I have always struggled to get good steering with my Kraton. I think if I follow this after my rebuild it will improve dramatically. The Losi 8ight truggy and buggys I've got are so much easier to set up. It's great to hear you got good results for your efforts. The Talion I have was setup really well out of the box, handling is great, though I've bent the chassis now, so I'll re do all the setup when I install the m2c racing chassis. Thank you again.

TLR and TA are more refined and precise. Designed to better respond to incremental adjustments more accurately. But, the Arma's are the tanks that will take much more abuse. There's a trade off here.