Granite Granite metal servo arm

[wanderer.77]

hello guys,
do you know if I can use this part:
https://www.amazon.com/Arrma-AR340102-Servo-Metal-Aluminum/dp/B01I5GZQA4
in my granite? I did not find specs for this part..as I already changed stock servo for 20kg/metal/waterproof one, I wanna change this piece of plastic too..
To be honest, It was changed about month ago and I don´t remember exact shape of it..so, will it fit without modifications?
thanks in advance!

 

[jondilly1974]

hello guys,
do you know if I can use this part:
https://www.amazon.com/Arrma-AR340102-Servo-Metal-Aluminum/dp/B01I5GZQA4
in my granite? I did not find specs for this part..as I already changed stock servo for 20kg/metal/waterproof one, I wanna change this piece of plastic too..
To be honest, It was changed about month ago and I don´t remember exact shape of it..so, will it fit without modifications?
thanks in advance!

Not without possible harm to your servo. You need a servo saver, not a metal arm to protect the servo when running. The Kimbrough 124 extra large is what most like. It will need a little bit of trimming, but is usually the best option.

 

[wanderer.77]

Not without possible harm to your servo. You need a servo saver, not a metal arm to protect the servo when running. The Kimbrough 124 extra large is what most like. It will need a little bit of trimming, but is usually the best option.

Thanks, I know Kimbrough 124, but saw some negative reviews and I am still surprised that there is NOTHING available as replacement for this (weak part in my opinion) without trimming / modification..

 

[jondilly1974]

Thanks, I know Kimbrough 124, but saw some negative reviews and I am still surprised that there is NOTHING available as replacement for this (weak part in my opinion) without trimming / modification..

Yeah it’s not perfect, but it’s the best I’ve seen ??‍ I ran a metal arm on mine for about 2 mins until the servo died. Expect to not be able to finish a pack with a solid arm if you jump a tiny bit. If you keep all four planted, you might get away with a solid link.

 

[Arrmature]

There's a few people that have put the Kimbrough 124 spring into the stock servo saver body. I didn't really like the alignment of the 124, so I just transplanted the spring.

 

[wanderer.77]

Yeah it’s not perfect, but it’s the best I’ve seen ??‍ I ran a metal arm on mine for about 2 mins until the servo died. Expect to not be able to finish a pack with a solid arm if you jump a tiny bit. If you keep all four planted, you might get away with a solid link.

good to know - thanks bro

There's a few people that have put the Kimbrough 124 spring into the stock servo saver body. I didn't really like the alignment of the 124, so I just transplanted the spring.

And the results? what I know, Kimbrough is from some vinyl, much durable material than plastic stock, right? thanks.

 

[ptsWolfman]

I could be wrong....
I ended up negating the servo saver altogether. I have the MEGA Granite (modified w/ 3800kv brushless)(so the stock 5kg servo - junk servo IMO). The servo saver died on it (did its job I suppose). But not realizing it was the servo saver that died I replaced the whole servo.
https://www.amazon.com/gp/product/B078WVXP4Y
Came w/ a servo arm that fit nicely (no trimming required). I just went direct, no servo saver.

The servo is not only 25kg, but its pretty zippy 0.09s 60deg, and all metal gears.
Honestly, I've mangled nearly every other part of the Granite.... once I went to that servo and removed the servo saver I've not had to mess with it once.

To each his own and, as I found out, there are plenty of people who absolutely 'must' have a servo saver but there also are those (me) who feels "why?".
So, as they say, "your mileage may vary" (no pun intended on the mileage).

 

[Arrmature]

And the results? what I know, Kimbrough is from some vinyl, much durable material than plastic stock, right? thanks.

I haven't driven very much with it yet, but so far I like it. There are others that did this a few months ago so they would have more experience but as far as I know they haven't had any problems so far.

The Kimbrough does appear to be a harder plastic than the Arrma - the Arrma seems more like vinyl like to me. I was concerned that the Kimbrough spring would be too much for the Arrma body, but it looks fine - the one on the left has the Kimbrough spring and the dirty one on the right, the stock spring:

With the stock servo saver, I was able to turn the front wheels by hand all the way to the end stops without the servo moving at all. With the Kimbrough 124 in my Typhon, I can still turn the wheels by hand a little bit before the servo starts to move. With the Kimbrough 124 spring in the Arrma saver body in my Granite, the servo saver is just a little bit tighter than the 124 in the Typhon. There is enough give to absorb shocks, but not very much more. That's expected as the Arrma servo saver body is slightly smaller in diameter than the Kimbrough, so the spring will be a bit tighter.

The one thing I don't like about the Kimbrough (other than the fit) is that there are some ridges inside the body from the casting process. These can only serve to prevent the spring from moving smoothly inside the body:

I could be wrong....
I ended up negating the servo saver altogether. I have the MEGA Granite (modified w/ 3800kv brushless)(so the stock 5kg servo - junk servo IMO). The servo saver died on it (did its job I suppose). But not realizing it was the servo saver that died I replaced the whole servo.
https://www.amazon.com/gp/product/B078WVXP4Y
Came w/ a servo arm that fit nicely (no trimming required). I just went direct, no servo saver.

The servo is not only 25kg, but its pretty zippy 0.09s 60deg, and all metal gears.
Honestly, I've mangled nearly every other part of the Granite.... once I went to that servo and removed the servo saver I've not had to mess with it once.

To each his own and, as I found out, there are plenty of people who absolutely 'must' have a servo saver but there also are those (me) who feels "why?".
So, as they say, "your mileage may vary" (no pun intended on the mileage).

I have a couple of 2WD trucks where I have no servo saver. I have strong metal gear servos in them and the tie rods have enough flex that they serve as servo savers. What I've found is that the tie rods will pop off the balls before the servo gears strip. The tie rods in the Mega may also have enough flex, but not the ones in the 3S BLX.

 

[ptsWolfman]

I haven't driven very much with it yet, but so far I like it. There are others that did this a few months ago so they would have more experience but as far as I know they haven't had any problems so far.

The Kimbrough does appear to be a harder plastic than the Arrma - the Arrma seems more like vinyl like to me. I was concerned that the Kimbrough spring would be too much for the Arrma body, but it looks fine - the one on the left has the Kimbrough spring and the dirty one on the right, the stock spring:

View attachment 95431

With the stock servo saver, I was able to turn the front wheels by hand all the way to the end stops without the servo moving at all. With the Kimbrough 124 in my Typhon, I can still turn the wheels by hand a little bit before the servo starts to move. With the Kimbrough 124 spring in the Arrma saver body in my Granite, the servo saver is just a little bit tighter than the 124 in the Typhon. There is enough give to absorb shocks, but not very much more. That's expected as the Arrma servo saver body is slightly smaller in diameter than the Kimbrough, so the spring will be a bit tighter.

The one thing I don't like about the Kimbrough (other than the fit) is that there are some ridges inside the body from the casting process. These can only serve to prevent the spring from moving smoothly inside the body:

View attachment 95434


I have a couple of 2WD trucks where I have no servo saver. I have strong metal gear servos in them and the tie rods have enough flex that they serve as servo savers. What I've found is that the tie rods will pop off the balls before the servo gears strip. The tie rods in the Mega may also have enough flex, but not the ones in the 3S BLX.

I've also done this to my Senton BLX ... so far no issues.
Again, for me, I don't want to try to advocate that everyone does this. I just hear a lot about Servo Savers blowing out or people having to make adjustments to the K 124 etc..... I get the idea of a SS, but so far its not been an issue.
(Senton has a $16 20kg servo on it -- smaller tires so I didn't worry about 'needing' heavier duty 25+ kg)... but $16 for a servo vs a $15-$20 servo saver. The financial math didn't add up.
Popping a ball joint could be a concern -- but, again, so far I've not had any issues. (and I'm realllllly not gentle with my rigs).
(as my nickname amongst my friends is "Tumble-ina".... something about cliffs, large drops, and me having a tendency to go "whoops, didn't think I was that close")

 

[Arrmature]

(Senton has a $16 20kg servo on it -- smaller tires so I didn't worry about 'needing' heavier duty 25+ kg)... but $16 for a servo vs a $15-$20 servo saver. The financial math didn't add up.

There's one other consideration missing in your equation, the cost of a new ESC. If the servo gears jam and the servo is in a position other than the position being commanded, the servo will be in a stall condition. A 20kg servo will draw somewhere between 4 and 6 amps when stalled, but the BEC is only rated for 3 amps continuous. A servo saver greatly reduces the likelihood of jammed servo gears. It is an unlikely scenario for sure, but it did happen to me once. I had to replace the servo and the ESC. My 2WD trucks have cheap brushed ESCs in them, so I'm OK to take the risk there.

There is no right or wrong answer when it comes to servo savers. It's just a question of understanding the risks and deciding which risks you're comfortable taking and which ones you want to mitigate.

 

[ptsWolfman]

There's one other consideration missing in your equation, the cost of a new ESC. If the servo gears jam and the servo is in a position other than the position being commanded, the servo will be in a stall condition. A 20kg servo will draw somewhere between 4 and 6 amps when stalled, but the BEC is only rated for 3 amps continuous. A servo saver greatly reduces the likelihood of jammed servo gears. It is an unlikely scenario for sure, but it did happen to me once. I had to replace the servo and the ESC. My 2WD trucks have cheap brushed ESCs in them, so I'm OK to take the risk there.

There is no right or wrong answer when it comes to servo savers. It's just a question of understanding the risks and deciding which risks you're comfortable taking and which ones you want to mitigate.

Hadn't given that a thought..... though the other day my Senton did get a rock stuck where it always gets stuck (anyone who runs a Senton knows... 'that spot').
Totally jammed up the steering. Servo was twitching (on its own) because it didn't know what to do. Not sure, maybe I just got it in time but the ESC still kicking fine. .. I hear ya though, doesn't seem to be a right/wrong (black/white) condition. That's why I totally put my stuff as IMO or YMMV, because while it has worked for me so far that isn't to say it won't fail horribly for someone else.

 

[wanderer.77]

I could be wrong....
I ended up negating the servo saver altogether. I have the MEGA Granite (modified w/ 3800kv brushless)(so the stock 5kg servo - junk servo IMO). The servo saver died on it (did its job I suppose). But not realizing it was the servo saver that died I replaced the whole servo.
https://www.amazon.com/gp/product/B078WVXP4Y
Came w/ a servo arm that fit nicely (no trimming required). I just went direct, no servo saver.

The servo is not only 25kg, but its pretty zippy 0.09s 60deg, and all metal gears.
Honestly, I've mangled nearly every other part of the Granite.... once I went to that servo and removed the servo saver I've not had to mess with it once.

To each his own and, as I found out, there are plenty of people who absolutely 'must' have a servo saver but there also are those (me) who feels "why?".
So, as they say, "your mileage may vary" (no pun intended on the mileage).

hmmm, that´s interesting..it seems that is about not to worry to try it without servo saver.

 

[Arrmature]

And the results? what I know, Kimbrough is from some vinyl, much durable material than plastic stock, right? thanks.

I've now done a bit of driving with the Granite (Arrma saver body with 124 spring) and my Typhon (124 servo saver) and I do like the steering response in the Granite better.

I finally got around to measuring the torque required to deflect the stock Arrma stock SS, the KIM 123 SS, KIM 124 SS, KIM 125 SS and Arrma SS body with 124 spring and here what I measured for 10, 20 and 30 degree servo saver deflections:

You have to take the Kimbrough measurements with a grain of salt. All three of the Kimbrough savers don't turn smoothly, so the torque jumps around a lot while turning. The Arrma body whether with the stock spring or the 124 spring turns very smoothly, which is probably why I find my Granite centers more consistently than my Typhon.

I was a little concerned about using the stronger spring, but based on my measurements I'm comfortable. My steering endpoints are a little under 30 degrees from center, so unless the servo itself jams, the servo will never need to push any harder than 7.2 kg-cm, which will draw about 2 A from the BEC. I would not use the stronger spring with the stock servo however - it's far too tight to offer sufficient protection.

The Typhon now has an Arrma servo saver body with a 124 spring. The first spring transplant took a couple of days and the second about a minute.

 

[bemenaker]

So are you saying stock SS is better than the km? And not to bother with stronger spring?

 

[GRC]

How do you open up the servo savers to get the spring out/in. Just pry them open?

 

[Arrmature]

So are you saying stock SS is better than the km? And not to bother with stronger spring?

Not at all. The stock servo saver is really weak. Surprisingly, even though the Kimbrough feels much stronger it isn't quite twice as strong, but the extra spring force makes a big difference. My preference of the 5 was the stock servo saver body with the Kimbrough spring - it gives the strength of the Kimbrough with the smoothness of the stock saver. Also, the dual horn design of the stock saver takes some play out where the servo link connects and the splines of the stock saver fit much more tightly.

How do you open up the servo savers to get the spring out/in. Just pry them open?

They just pry open. Getting them reassembled is a whole other challenge. I found a method that worked well for me - I really should have taken some pictures.

 

[Arrmature]

If anyone else wants to try transplanting the spring, I took a few pictures of an Arrma spring going into a KIM124 servo saver body. The process is the same if you want to put a 124 spring into an Arrma body.

First, open the saver by carefully prying it open. It does take some coaxing as the top cap clips quite strongly into the bottom of the servo saver. Do it in a confined space so you can find the spring when it flies out (and wear eye protection):

You'll have these parts:

The Arrma servo saver parts are more or less the same. The Kimbrough spring is a bit shorter, but is made of a heavier gauge wire.

Next you'll need a couple of finishing nails that fit snugly in the holes in the main body and bottom cap. The ones I used were 1.44mm in diameter and were a good fit in the Arrma and a little loose in the Kimbrough. I used some 3/4 inch nails I had lying around, but I would suggest going longer to reduce the chance of pushing one through your thumb later. Use the nails to align the bottom and main body of the servo saver and insert the ends of the spring into the body:

The Arrma spring is quite happy to sit like that, but the Kimbrough spring will want to jump out. You'll have to hold it and keep downward pressure on it, keeping the bottom cap on an angle to the keep the spring ends inside the body. Then you need to push the spring into the body while pressing down with your thumb (this is where longer nails would have been better). I used a 7mm socket on a screwdriver handle, but anything wide will do. Once the spring drops in, keep pressure on it:

Carefully pick it up, put it on the top cap and push down hard - you'll hear a loud snap:

Remove the nails and you're done:

 

[bemenaker]

Nice write up.