Motor stutters when steering

[Deerhurst]

My go to crawler is a highly modified Tamiya Hilift. Went out crawling today and noticed that sometimes when steering and on the throttle in 1st gear it would momentarily cut the throttle. Seems to be fine in 2nd and 3rd. Problem seems to only happen in 1st gear.

The steering servo is an old Savox. ESC is a BRXL. No external BEC but the BRXL BEC should be fine and has been fine for years.

I'm wondering if the steering servo is dying.

Any suggestions?

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[23drumerboy]

Originally Posted by Deerhurst

My go to crawler is a highly modified Tamiya Hilift. Went out crawling today and noticed that sometimes when steering and on the throttle in 1st gear it would momentarily cut the throttle. Seems to be fine in 2nd and 3rd. Problem seems to only happen in 1st gear.

The steering servo is an old Savox. ESC is a BRXL. No external BEC but the BRXL BEC should be fine and has been fine for years.

I'm wondering if the steering servo is dying.

Any suggestions?

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Is there a "roasty"/seized bearing on the shaft holding the "1st" drive gear?

Also, sometimes depending on your torque output, power, gearing/FDR, when in "low" gear so to speak, tons of torque can cause the driveline to "buckle"/twist/flex in weird ways, but most common would be both axles wrapping-under (in towards center of truck, stressing the physical limitations of Universal joints THROUGHT the driveline. Not only is this VERY hard on bearings, and u joints, etc, but will load the already bad/on their way out bearings in ways that can amplify the sound/stutter/etc, to an audible, usually pin-pointable area/part/bearing. I recommend trying to duplicate the issue on a stand all 4 tires off the ground, (make sure driveshafts clear the stand), put her in first and try to hold the truck with throttle/TX hand, and manipulate the axles/cycle suspension to vary loading and see if u cant trace and issue, could possibly be a simple EPA issue with servo settings



Read-Up! Mod-On! Crawl EXCESSIVELY!

[Deerhurst]

Good plan! It was occasionally stuttering upside down too. I'm have to play with it.

It happens sometimes when the wheels are being turned from center and sometimes on return to center. It started just after I had a light controller die. One of the controllers that goes between the receiver and the ESC/servos. I also lubed all the bearings and bushings I could get to a few crawls ago, around the same time the light controller died. I would expect my motor to have plenty of torque to push through failed bearings being a Holmes Torque master with a BRXL on 3s and that it's blown up diffs and mangled driveshafts without pausing in the past.

Adjusting the sub trim for the shift servo seemed to help a little. I adjust the shift servo usually to push against 1st or 3rd a little. When I let off of that, and got a poor gear mesh, it seemed to help some which is what lead me to think it's an electrical issue.

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[Deerhurst]

It's not a mechanical issue. I can slowly move everything around, flex the axles and leafs, turn the wheels but when I quickly steer full lock left and right the ESC lights go out and the motor stutters. Light on the ESC stays bright.

Still thinking steering servo.

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[ferp420]

sounds like you might have 2 issues my guess on issue one is the steering servo is glitching and my guess on issue 2 is the shifter servo end points adjustment
if im right just adjust the endpoints on the shift servo to solve the issue

my guess as to why its happening only in first gear
the savok servo is a power hungry little B and under normal driving its fine but if the shift servo isent set right and its fighting to shift in to first gear its gona use more power than normal causing the reciver to momentairly loose power and signal so the esc and steering servo stop for a second till it gets its signal back

i think drummerboy waz spot on with the end.point adjustments for the shift servo
but if the epa dosent solve the issue you can try a glitch buster or a bec to get more smoother power to the servo

[Deerhurst]

I've done some more fine tuning for the shift servo which reduced the issue but not eliminated. The issue there was the mount had come loose over time and I had adjusted the H and L end points and throw to compensate.

Rapid movements of the steering servo still freaks the system out. I have some spare servos on order, need them for my Erevo anyways and I'm out of spares, so I might drop one in and see how it does.

The truck has been flawless until now and run heavily for 5+ years. It's a pig too so between hard use, some water baths and the weight I wouldn't be suprised if a servo was dying.

A good high power BEC is always a good idea!

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[Druxus]

Well if it only happens in 1st gear you can rule out your steering servo. I would get it in 1st gear and unplug the shift servo and then run it. If it runs fine you have isolated your problem. Could be the servo at this point or something in the transmission not letting the servo move as far as it should drawing a bunch of amps. While a bec isn't a bad idea, the fact that it ran for 5 years without it points to a problem.

[Deerhurst]

Replaced the steering servo and havnt been able to replicate the problem. Going to try to hit the rocks later today and see if it is gone.

I was able to put the truck on the table, with the old servo, and wiggle the steering and watch the ESC lights go out without the truck moving. Replaced the steering servo and good to go so far.

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[Druxus]

Yeah steering servos have caused some weird things for me when they are going out. Just seems weird that it would only do it in 1st gear tho.

[Deerhurst]

Originally Posted by Druxus

Yeah steering servos have caused some weird things for me when they are going out. Just seems weird that it would only do it in 1st gear tho.

Totally agree it's weird in just 1st. I'm wondering if in 2nd and 3rd the wheel speed is enough where it mostly coasts through the stutter. No idea.

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[ferp420]

it sounds like the shift servo took out the steering servo a bec or a glitch buster could stop the problem from coming back if that was the problem
a bec will also help keep the esc cooler so its not a bad idea

[Deerhurst]

Originally Posted by ferp420

it sounds like the shift servo took out the steering servo a bec or a glitch buster could stop the problem from coming back if that was the problem
a bec will also help keep the esc cooler so its not a bad idea

I should probably pull the 10A BEC from my unused chassis.

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