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OoALEJOoO

SOLVED: Help! M06 randomly steers on-power

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A very strange thing happened today with my trusty M06.

If I accelerate with little throttle, it will go straight but when accelerating mid-throttle to full, the car randomly steers sometimes left, sometimes right. It simply refuses to go straight. It might go straight for a few meters then steer. Once it starts going left or right it will keep going in that direction with significant amount of steering.

I checked for radio interference and there seems to be none. The servo appears to be working well (Futaba S3010 + High-Torque saver). Steering is shimmed with less wobble than a stock M06. Standard toe-in rear, slight toe-out front.

I am thinking maybe there is something going on with the differential (built stock and free). Perhaps it's worn and does not give the same torque to each wheel.

Any thoughts? Thanks for any insights.

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What ESC do you use? This often happened with TEU101 which didn't have BEC to power the receiver. Acceleration caused voltage drop, and analog servos are sensitive to changing voltage.

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@Honza interesting thought. I'm using a TBLE-02S, with its 1.5A BEC. I assume it would be enough for the S3010 servo, especially since I am not giving any steering input, just straight acceleration.

I tested the car in fairly flat concrete and also in a very very flat surface (athelics track extremely clean and even). On both surfaces it had the same behavior with random steering.

I brought along other cars also, all using the same transmitter, and none had issues. Quite confused :blink:

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4 minutes ago, Willy iine said:

This is on a 2.4GHz modern radio?   

Correct, Futaba 3PL + R203GF receiver.

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In that case, we can probably rule out electrical issues. 

50 minutes ago, OoALEJOoO said:

I am thinking maybe there is something going on with the differential (built stock and free). Perhaps it's worn and does not give the same torque to each wheel

Not the differential itself, but it is a good idea to check the drivetrain. Do you use bearings or bushings? Worn out bushings could just bite in shafts randomly. Same with dogbines - check whether they bind during suspension travel. Also check for any play in rear geometry.

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54 minutes ago, OoALEJOoO said:

Correct, Futaba 3PL + R203GF receiver.

Hummm.. should not be getting interference from the motor then.. but if all fails, I would try a differentent motor after checking drive train.

Does your radio have telemetry?  Does the receiver constantly get 6v while accelerating?  

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Thanks for all the comments guys.

@Honza Using bearings. Next step will be a full inspection and tear-down of the drive-train. I'll use the opportunity to also stiffen-up the diff.

@Willy iine No telemetry on the 3PL unfortunately.

@sosidge Tried swapping tires while on the track, no difference :(

If after this the issue is still present, I'll start methodically replacing components one by one: motor, servo, ESC, receiver.

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15 minutes ago, OoALEJOoO said:

Thanks for all the comments guys.

@Honza Using bearings. Next step will be a full inspection and tear-down of the drive-train. I'll use the opportunity to also stiffen-up the diff.

@Willy iine No telemetry on the 3PL unfortunately.

@sosidge Tried swapping tires while on the track, no difference :(

If after this the issue is still present, I'll start methodically replacing components one by one: motor, servo, ESC, receiver.

I think it might be the ESC not providing sufficient power to the servo.  Servo does weird things when under powered.. 

If you have a volt meter you can measure the voltage going to the servo given you have a separate servo wire you can cut and tap into.. while applying throttle. 

This way you won’t have to remove anything physically from the car until you are certain what the culprit is.. 

GL!!

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Could be the ESC, I have an MF01x with an off brand 20kg metal gear servo, and it came with a TBLE-02, I've had that problem a few times and ended up replacing it with a Hobbywing 1060. They're about $12, the motor cords are slighlty shorter so you may have to move it closer to the back.

If you have a regular silver can or Torque Tuned motor you shouldn't be having issues there.

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4 hours ago, OoALEJOoO said:

I'm using a TBLE-02S, with its 1.5A BEC

I have no end of trouble with the TBLEs, slap on a BEC and the troubles go away. 

Broadly speaking, allow 1A per 3 - 4kg, so your servo can be drawing over the 1.5A supplied by the ESC, or borderline. If you have a servo tester (on some BL program cards for example), stick your servo in to confirm. 

If the ESC trips, it will cause the RX to cycle, and depending on models, it could cause the servo to cycle as well. Do note that servos still draw power when in neutral as they need to "hold" neutral, and obviously, the stronger the servo is, the more it will draw. During acceleration, there are forces pushing the steering this and that way, and the servo will be working to keep it straight. 

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Disconnect the servo from the receiver and try again. Check there is no binding at all four wheels. Have you put any aid in the diff to assist drive, or is it stock tamiya grease?

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16 minutes ago, berman said:

Have you put any aid in the diff to assist drive, or is it stock tamiya grease?

According to the first post. 

6 hours ago, OoALEJOoO said:

(built stock and free)

 

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I was having the same issue with the Savox 1251 in my TT02. I took apart the servo and cleaned the potentiometer with some electronics cleaner and haven’t had a problem since.

I’d gone through the whole car several times, making sure that the steering wasn’t binding, replaced a few bearings, found a cracked knuckle, solid servo horn, everything I could think of. It was driving me nuts, because the car was essentially impossible to drive with any precision, and I’d never had a problem like this before. I’m guessing that a tiny bit of trash had gotten in there somehow. On the positive, my TT has never been this good!

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Thanks guys!

Did a quick inspection of the drive train without disassembly and everything seems in good condition. Before I try to dismantle, I'll first switch the TBLE-02S ESC to a HW1060. If that solves it then, the TBLE could not handle the servo. To further validate this theory, I'll then put back the TBLE but put a Futaba S3004 servo instead of the S3010. If the TBLE can handle this lower-draw servo then it would be further proof that the TBLE is getting overwhelmed. Motor is a Torque Tuned.

This would be bad news though. I have a few TBLE-02S and 04S on my yet-to-be-built kits that I was hoping would serve me well...

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32 minutes ago, OoALEJOoO said:

I have a few TBLE-02S and 04S on my yet-to-be-built kits that

This is why I usually select "Remove Tamiya ESC" to save £10 when I order my kits in the UK. However that can be risky as some of the kits comes with 1060 these days, and I could be saving £10 to spend £20 to get a 1060 to replace the one removed! 🤷

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@OoALEJOoO Sounds like a plan!  I run 1060 on most of my newer cars including those that run SuperStock motors with either a Savox 1251 or 1252 servos (or those Amazon 25kg servo’s) with no issue so it should be able to handle most servos out there.  

 

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Interesting that only one person suggested looking into tyres.

Any RWD car will "randomly" veer off it's path when grip is less than perfect. I observed that first hand on all my RWD chassis from the F1's to the M-06 to the TT conversions. When you mentioned that partial throttle was fine I thought there was probably a grip issue here.

I would hold the car off the ground and try going full throttle a second or so (don't unglued you're tires of the rims 😅) and watch the steering servo for random glitches. You'll know immediately if there's something wrong with the ESC and servo.

Again looks like a grip issue. These threads usually diverge into "it's the diff" "it's the servo" "it's the tyres" "did you check your bearings" kind of cacophony so I will stop there and not add any more!

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8 hours ago, OoALEJOoO said:

Thanks guys!

Did a quick inspection of the drive train without disassembly and everything seems in good condition. Before I try to dismantle, I'll first switch the TBLE-02S ESC to a HW1060. If that solves it then, the TBLE could not handle the servo. To further validate this theory, I'll then put back the TBLE but put a Futaba S3004 servo instead of the S3010. If the TBLE can handle this lower-draw servo then it would be further proof that the TBLE is getting overwhelmed. Motor is a Torque Tuned.

This would be bad news though. I have a few TBLE-02S and 04S on my yet-to-be-built kits that I was hoping would serve me well...

If it helps any I threw my TBLE-02S into my Grasshopper and it works fine there, but I only run a 380 motor in it and an old Futaba servo.

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Thanks for the feedback. Lots of possible root causes indeed. I'll try to summarize each option, along with supporting/unsporting evidence as much as possible (and within my limited understanding). I haven't had a chance to replace anything, but I did a lot of testing and troubleshooting last week when the problem was present. Since I have no time to work on the car but currently have a lot of time to type, here goes some recapping:

2.jpg

Condition of the car:

  • Chassis: Tamiya M-06 in good condition with limited wear. Full ball-bearings.
  • Wheelbase: 239mm
  • Settings: loose diff (just a little bit of AW grease). Stock rear toe-in, a little bit of front toe-in (later set to little toe-out to troubleshoot). Super-mini CVA shocks, using kit stock springs & oil.
  • Tires: Front 60D Radials (50683) perhaps 3/4 of their thread remains, Left/Right even wear. Rear 60D Radials M-Grip (50684), around 1/2 of their thread remains, left/right even wear.
  • Steering shimmed, little slop.
  • Servo: Futaba S3010 with Tamiya High-Torque saver (51000)
  • ESC: Tamiya TBLE-02S (1.5A rated BEC)
  • Motor: Tamiya Torque Tuned
  • Pinion: 20T
  • Other load on the ESC: x4 LEDS, loading about 0.018A each, total 0.072A. One raspberri-pi fan rated at 0.20A.
  • RC: Futaba R203GF receiver + Futaba 3PL transmitter

Symptom:

  • Car would randomly steer left or right when throttle is around above half. If throttle is below half, car would tend to go straight.
  • Car would usually go straight for a few seconds, then either veer left or right.
  • Once it would veer, it would stay on that direction with significant steering, perhaps the equivalent of 25% steering input.
  • If you would stop the car and repeat, the same random behavior happened.

Checks done on-site:

  • Drive train seemed free, no binding.
  • Tested on two running surfaces: Hard tennis court in fairly good condition. Athletics running track (made of super smooth hard-rubber-like surface) extremely flat & even. Car exhibited the same issue on both surfaces.
  • Tested with and without body, same issue. This ruled-out effects of body interference with the tires and the additional loading of the LEDs (0.072A) on the BEC.
  • Swapped front tires left-to-right. Same issue.
  • Swapped rear tires left-to-right. Same issue.
  • Checked propping the car with a base, body removed, and hit full-throttle to see if the servo will glitch. No glitches, it remained steady. Tried steering a few times while full-throttle. No glitches, remained steady as well. The ESC would be not very loaded though, as the motor would be free-spinning.
  • Checked servo holding power by forcing tires to steer by hand. The servo held its position with the saver springs yielding to the torque, per normal.
  • I also brought two other cars on that outing (DT-02 and T3-01), both bound to the same transmitter. None of them had any issues.
  • *EDIT: The car had a slight toe-in when I first spotted the issue. I tweaked it to a small toe-out and the issue persisted.

Gathering possible root causes & troubleshooting from all the posts above:

  • BEC on the TBLE-02S is too weak. It certainly is possible, although it would mean there is some deterioration either of the servo or the ESC. I have run this car before with the same configuration and no issues. The fact that the servo remained steady when propping it and going full-throttle, would mean that the BEC can keep-up when there is little motor load, but cannot under hard acceleration. This is also supported by the fact that the issue was not present when accelerating less than mid-throttle.
    • Troubleshooting: Swap the ESC or swap to a less powerful motor. Add an external BEC (will have to research how to do this given this ESC already has a BEC). Run the car with the servo disconnected and see if it goes straight (not sure a disconnected servo can hold netural, it might still veer but for other reasons). Disconnect fan.
  • Faulty servo. My thought is that a faulty servo would have shown the issue on the propped test and also when running less than mid-throttle, which did not. My though is that the servo is OK, unless the fault is sensitive to motor load.
    • Troubleshooting: Swap the servo, ideally to one with lower power (Futaba S3004). Dismantle and inspect the existing servo.
  • Tires & Grip. Tests were done on two different surfaces and swapping tires left/right, with the issue still present. I've ran my RWD TT-01, RWD TT-02 cars and RWD DT-03 on these same surfaces with no grip issues. My thought is that the issue is probably not related to grip.
    • Troubleshooting: Not sure what further can be done to check for grip. Maybe switch to new tires. Will check the shock oil.
  • Binding drive train. The fact that it veers sometimes left and sometimes right would mean binding is shifting sides, which would be quite odd/unlikely.
    • Troubleshooting: Dismantle, check, clean & lube the drive train.
  • RC interference. The other two cars brought on the same outing, bound to the same transmitter, had no issues.

Based on the above what I would probably do now is put a HW-1060 ESC or swap the servo to a low-power one. I don't think I have a HW-1060 with soldered deans star-plugs handy, so I'll probably swap the servo first.

Many thanks for all your help so far :)

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Front toe-out might be the issue. Try setting the toe to 0, or just a whisker of toe-in. It will be less aggressive on turn-in, but should track a lot better. I accidentally set up my 1:1 Mazda Miata with a degree or two of toe-out once, and it was undrivable. Also, if memory serves, the M06 has pretty sloppy steering out of the box, but allows for four 850 bearings to be installed in place of the plastic bushings. Might be worth a try, bearings are cheap.

It just sounds to me more like a mechanical problem than an electronic one.

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@markbt73 Thanks for the reminder about another tweak I did while on-site. When the issue appeared, the car had a slight toe-in. I then tweaked it to a slight toe-out but the issue persisted :(. I'll add that to my recap post above.

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5 hours ago, OoALEJOoO said:

The fact that the servo remained steady when propping it and going full-throttle, would mean that the BEC can keep-up when there is little motor load, but cannot under hard acceleration.

Not sure if I understand correctly, so please correct me I'm wrong. You tested the servo while the wheels are freely spinning in the air? Or do you keep it slightly to the ground so that the motor and ESC gets some load like under real acceleration?

If the first one I would try it again with wheels touching slightly the ground to simulate the driving conditions. So you can see if the servo do anything strange under acceleration.

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