Big Rock Endpoints fail after new servo

SaltyLocal

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I replaced my sons Big Rock servo from the bad stock Spektrum S651 to a new 6s Kraton S652 servo. I set the endpoints and the right seem OK, but the left isn’t turning much and the servo is whining, even when calibration is backed off to only about half travel.

Setting endpoints:


Failed left turn while right seems ok - servo seems to strain either way. Any ideas?


I also physically turned the front wheels left and right and the right definitely turns farther. The left only moves half way or so and seems something is blocking further movement. I did replace the bellcrank with a hot racing part and added their servo saver. I’m lost on what is blocking the full left movement.
image.jpg
image.jpg
image.jpg
 
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Velodromed

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Are you sure you centered the servo properly when you installed the servo saver? Since you replaced several parts at once, probably should back up and start over (that’s what I do). As you disassemble, look close at the HR bell crank and saver, see if something is catching. It may need to be shimmed or adjusted.
 

Tex Koder

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Do a quick test with just the servo , disconnected from the steering linkage.
And see if the servo is able to turn with your input Without any issues/noises.

This will tell you if it's the servo itself is having problems or if it's something with the Ackerman bar & related linkages that's binding..
 

SaltyLocal

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I’ll recheck again tomorrow. Should the servo be mounted using the first two holes seen below?
1CD1A2D1-CF4F-4E50-B9FE-E635C24412A4.jpeg
 

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I’ll recheck again tomorrow. Should the servo be mounted using the first two holes seen below?
View attachment 261836

Those two holes are for the housing that contains the servo and receiver.. and the screws for those are on the underside of the chassis.
 

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The servo is mounted where it belongs. Like stated elsewhere above, start over. Remove and isolate the servo to check for proper function making sure it is OK and not the issue while powered and turning by itself. Then while removed, Move the ST belcrank for proper L-R sweep. Look for anything binding. The servo should be centered, (powered ON) before attaching the servo arm onto the servo spline. Wheels also centered when doing this. Radio ST trim should be at perfect neutral before doing any of this. Steering Endpoint adjustments will not be correct/ done properly if the above doesn't first pan out for you.
 
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SaltyLocal

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I got the front end torn back apart and noticed that the servo arm moves freely and accurately UNTIL I reattach the front diff/shock tower assembly. Once I reattach, the servo arm is slightly hitting the bottom of the chassis when turned to the left. That’s why Im getting half way left turns.

Not sure what to do in this case. Maybe just use the stock servo arm?
 

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I got the front end torn back apart and noticed that the servo arm moves freely and accurately UNTIL I reattach the front diff/shock tower assembly. Once I reattach, the servo arm is slightly hitting the bottom of the chassis when turned to the left. That’s why Im getting half way left turns.

Not sure what to do in this case. Maybe just use the stock servo arm?

Dremel away some of the chassis material that's obstructing the servo movement.
 

Velodromed

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I got the front end torn back apart and noticed that the servo arm moves freely and accurately UNTIL I reattach the front diff/shock tower assembly. Once I reattach, the servo arm is slightly hitting the bottom of the chassis when turned to the left. That’s why Im getting half way left turns.

Not sure what to do in this case. Maybe just use the stock servo arm?
I had that issue when I did the servo on a 3s car for the first time. First make sure the saver is all the way flush with the servo like in the first pic. You can also put a washer or two under each corner of the servo tabs before screwing it down. The second pic is where to put the washers on top of the servo tab to raise the servo up a bit (I don’t have washers on this car, just want to give you a visual).

F6CCE589-6F41-438B-90C8-123A3665D2F3.jpeg


C68ADACD-E0DB-467F-9AA2-38366AA2625F.jpeg
 

SaltyLocal

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I had that issue when I did the servo on a 3s car for the first time. First make sure the saver is all the way flush with the servo like in the first pic. You can also put a washer or two under each corner of the servo tabs before screwing it down. The second pic is where to put the washers on top of the servo tab to raise the servo up a bit (I don’t have washers on this car, just want to give you a visual).

View attachment 262222

View attachment 262223
Sweet! I didnt think of that! This forum rocks because members like you! Thank you @Velodromed
 

SaltyLocal

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There is absolutely no way that this 23 tooth servo saver plastic nub will sit completely flush on the Spektrum S652. I’ve pushed it down as hard as I could, tried screwing it in to make it flush and it was just about bending the servo. Anyone know 100% that this S652 is definitely a 23 tooth servo? Maybe a try a different nub??

671675B7-4E96-40F7-860F-C3954EDCF060.jpeg
 

SaltyLocal

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Since I can’t find a HR manual for the bellcrank, servo saver, etc… does anyone know which hole works best for the BR? Stock front suspension except for the RPM arms and HR pivot balls.
5FC9E43E-99A6-4419-B61C-C62355999272.jpeg
 

Velodromed

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I can guarantee you that it is a 23t servo. Maybe you got a poorly made servo saver. Are you in the states? Send me a direct message if you are.
 

SaltyLocal

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Since I can’t find a HR manual for the bellcrank, servo saver, etc… does anyone know which hole works best for the BR? Stock front suspension except for the RPM arms and HR pivot balls.
F44FD2C3-184D-4938-B444-94CA141EAA06.jpeg

I can guarantee you that it is a 23t servo. Maybe you got a poorly made servo saver. Are you in the states? Send me a direct message if you are.
Yes, I’m FL. I was able to get the 23 nub to sit flush on the servo THEN mount the arm. I was initially putting the nub on the arm then trying to get onto servo. It seems better now.

Once I got the diff cover and bellcrank installed, the servo arm was still rubbing the chassis. 🤬 I ended up taking it out for the third time and filing down some of the chassis were it was rubbing. About to test now. TBC…
 

Velodromed

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  7. Typhon 3s
  8. Vorteks
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Since I can’t find a HR manual for the bellcrank, servo saver, etc… does anyone know which hole works best for the BR? Stock front suspension except for the RPM arms and HR pivot balls. View attachment 262540

Yes, I’m FL. I was able to get the 23 nub to sit flush on the servo THEN mount the arm. I was initially putting the nub on the arm then trying to get onto servo. It seems better now.

Once I got the diff cover and bellcrank installed, the servo arm was still rubbing the chassis. 🤬 I ended up taking it out for the third time and filing down some of the chassis were it was rubbing. About to test now. TBC…
Oh right, I just noticed/realized you’re using the HR servo saver. Yeah I had a lot of trouble when I tried one. It didn’t last very long either before the spring broke. Hopefully, you have better luck with yours…
 

SaltyLocal

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8855CD4F-242B-4B30-8899-D06649B0141C.jpeg
After filing down the chassis a millimeter or so, the servo saver and bellcrank can now fully move. Filing down wasn’t desired but at least it’s hidden. I’ll calibrate and hope all remains positive.

Now on to getting this 40mm fan mounted to the motor. 🤞🏽 Not sure why only one mount was included when there is four screws to mount the fan. 🤷🏽‍♂️
 
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Velodromed

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  10. Infraction 4x4
View attachment 262581 After filing down the chassis a millimeter or so, the servo saver and bellcrank can now fully move. Filing down wasn’t desired but at least it’s hidden. I’ll calibrate and hope all remains positive.

Now on to getting this 40mm fan mounted to the motor. 🤞🏽 Not sure why only one mount was included when there is four screws to mount the fan. 🤷🏽‍♂️
That mount is made for double fans, only need two screws for each fan. I have several in my 3/4/6s cars. You can put one fan on each side. It’s also set up so that you can fit 30 mm or 40 mm fans. It’s a very solid mount. I like to replace the button head screw with a cap head and use a little bit of Loctite. Be careful not to crank it down too tight or you can strip the threads.
 
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SaltyLocal

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That mount is made for double fans, only need two screws for each fan. I have several in my 3/4/6s cars. You can put one fan on each side. It’s also set up so that you can fit 30 mm or 40 mm fans. It’s a very solid mount. I like to replace the button head screw with a cup head and use a little bit of Loctite. Be careful not to crank it down too tight or you can strip the threads.
Thanks man! You’ve been MORE THAN helpful! So a 40mm fan can be mounted with just two bolts? Will it hold the fan sufficiently? On my K6s, I purchased one of @Camaroboy383 fan mounts which are phenomenal, unfortunately I cannot find a similar mount for the BR’s 38mm can.
 
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