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Discussion Starter #1 (Edited)
Had my first weird AT-related behaviour today (it happens to be a DCT-based AT).

Conditions:
  • Dry asphalt. No debris.
  • Air temperature: 25C
  • Straight path.
  • S1
  • Urban Mode
  • Casually approaching a stop sign.
  • Down grade maybe about 3 to 5 degrees.
  • Speed: Less than 40 km/h and decreasing, both brakes applied.
  • I downshifted once, but well before the bucking (maybe 200 feet from the stop sign).
The last 30 feet or so the bike bucked like I was dropping the clutch then releasing (if it was a manual gearbox) and repeat.

The torque was still strong enough to cause both tires to drag rubber.

I would say there were three bucks before coming to a full stop, engine running at idle.

No drama after that, accelerating away from the stop sign position.

I have to say my first instinct was to pull-in the clutch (the whaa?)

55155


= = =

I am going to mark this down as a dangerous stop. There could have been pedestrians crossing with infant strollers ahead of them, regardless if I managed "to muscle" the great AT to the stop line.

FYI.




(2019 AT DCT)
 

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Had my first weird DCT-related behaviour today.

Conditions:
  • Dry asphalt. No debris.
  • Air temperature: 25C
  • Straight path.
  • S1
  • Urban Mode
  • Casually approaching a stop sign.
  • Down grade maybe about 3 to 5 degrees.
  • Speed: Less than 40 km/h and decreasing, both brakes applied.
  • I downshifted once, but well before the bucking (maybe 200 feet from the stop sign).
...

(2019 AT DCT)
Some questions DT:

Were you shifting manually or automatically?

Were you ever braking hard enough to get ABS in the loop?

What do you mean by "torque strong enough to drag tires"? Do you mean engine braking?

Can you reproduce the problem? This is worth trying.
 
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Some questions DT:

Were you shifting manually or automatically?

Were you ever braking hard enough to get ABS in the loop?

What do you mean by "torque strong enough to drag tires"? Do you mean engine braking?

Can you reproduce the problem? This is worth trying.
I was wondering the same kind questions, if it could have been ABS or Traction Control induced rather than DCT

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Also, what was the frequency of the "bucking?" One per second? Two? 1/2? And was it more like surging?

In flight test we would sometimes encounter a problem called roll ratcheting where the pilot's hand and arm inertia would interact with the side stick during aggressive roll maneuvers to cause unwanted roll inputs. The result was a jerky roll maneuver. Could you have caused any of these surges with unwanted or unconscious inputs to brake or throttle?
 

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Discussion Starter #5
Hey WW, good questions ...

Were you shifting manually or automatically?
In S1 [automatic] mode, but asserting a single downshift request using the rider-facing paddle button, and the system obliged.

Were you ever braking hard enough to get ABS in the loop?
No - that is why I took note of the road surface for stones, seeds, etc. and I really was probably in the realm of 20 km/h with both brakes being depressed already.

What do you mean by "torque strong enough to drag tires"? Do you mean engine braking?
Well, that was the best I could describe it. The bucking was brought on by power surging. I could understand the secondary bucking possibly being done due to the throttle position oscillation caused by my wrist response to the initial buck, but the initial buck was a surprise. So, the tires squealed. In replay in my mind, it was hard to distinguish if was due to the surge+braking, or just the surge. There was no hard or aggressive engine braking - just a casual, soft, coming to a rolling halt under a shady tree and let the pedestrians cross my lane with smiles on their faces on a beautiful day sort of stop. Anyway, I hoped to express it this way that it was a wrestle to tame that beast down.

Can you reproduce the problem? This is worth trying.
lol - this is something I am not looking forward to reproducing, however, I do the intersection very often - so I will do what I always do, even with the new trepidation.
 

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Frequency?
 

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Discussion Starter #7
Also, what was the frequency of the "bucking?" One per second? Two? 1/2? And was it more like surging?

In flight test we would sometimes encounter a problem called roll ratcheting where the pilot's hand and arm inertia would interact with the side stick during aggressive roll maneuvers to cause unwanted roll inputs. The result was a jerky roll maneuver. Could you have caused any of these surges with unwanted or unconscious inputs to brake or throttle?
Hmmm, let me replay it ...

Yeah, I would say in the realm of 1 Hz.

Surge - yes, it definitely started like that.

Braking was smooth going in.

Throttle: I am pretty sure I didn't rev it like when downshifting on a manual gearbox. The downshift had already completed. This was definitely, " ... wha da heck? <<insert surge here>> .. oh jeez ... " kind of event. I got nothing else.
 

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Discussion Starter #8 (Edited)
WW: I swear it "felt like" the control system was going open loop.

This is a case where a clutch or a "clutch disengage/override" would have been handy.

= = =

In about 14K kms of DCT riding, this is the first such experience. :oops:
 

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1/2 to 1 Hz is around the frequency where our body inertia can definitely play a roll. In the community, we might call this a RIO (rider-induced oscillation). In aircraft it's called a PIO. I'm not saying you contributed...only that it's a possibility. Usually, a RIO/PIO event requires some kind of initiation to get it going. Yours might have been something like a "brake release with throttle" surge that we've read about recently. Again, just noodling the problem.

Here's a rather famous event where one of my favorite test pilots suffered a pitch PIO in the YF-22 at Edwards Air Force Base back in '92. Check out the video. Tommy suffered a 55 G crash load and walked away. He told me once he was pissing blood for a week after this crash.:oops:


This was caused by a mode change in the flight control laws when Tommy put the gear up and went to full afterburner. Note in the first pass he is gear up - no AB. In the 2nd pass he adds AB and pulls the nose up. The aggressive response of the aircraft surprised him and the fun began. Those conditions together signify an up and away mode - the thing is a fighter plane with very sensitive controls - not a bird tuned down for landing.

Here's a PIO in the Saab Grippen. Note the pitch bobble that gets the party started:


Here are some thoughts: We've read here on the forum about riders experiencing a surge caused by a throttle input while releasing brakes. The surge occurs with brake(s) release. Know that there has to be some allowance for a deadband in the brake pressure sensor so it isn't continually signalling inappropriate mode changes to the ECU. This means the ECU might see the brakes "turn off" even while you might have a very slight input.

But all of this is supposition DT. If this were my bike I would spend some test time at that location trying to carefully reproduce the problem so I could better understand the cause & response. Try doing some brake on/off changes with throttle to see if you can cause a surge.
 

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Discussion Starter #11
WW: I don't doubt the possibility rider weight and/or input "timing" could have been factors. However, the situation was so tame, yet sudden, nothing made sense.

dallas: I could have titled the thread "Bucking AT" instead of "Bucking DCT", however, this happened on a DCT-based AT. In regards to your tire screeching question, I am speculating it was a part of the power surge and possibly the fact that I was still applying brakes while landing the routine and slow stop. The control system is going to respond with the brake inputs as well - as WW outlined.
 

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WW: I don't doubt the possibility rider weight and/or input "timing" could have been factors. However, the situation was so tame, yet sudden, nothing made sense.

...
That could have been the throttle/brake release event. Remember this discussion?


Anyway, that kind of surprise is enough to get a party like you attended underway.
 

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Discussion Starter #13
That could have been the throttle/brake release event. Remember this discussion?


Anyway, that kind of surprise is enough to get the party started.
Yup, I read that thread intently. Good discussion for sure.
 

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One read of the DCT section in the shop manual and threads on the forum convinced me to go manual. These type of faults and undocumented features sadly sooner or later come with the DCT. I apologise that this isn't helpful DT but may just help future buyers stop and think for a moment when the hungry salesman is doing his best to sell his wares. If when informed, you really feel DCT is the way to go, be mindful of the potential for situations like yours.

Will be interesting to see how this thread develops and what finally unfolds.

Good luck
 

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Discussion Starter #15
Hey Ray, thanks.

I am sold on the spirit of the DCT given its maturity, in general. Implementations will vary across brands, however I thought it would be prudent to share the experience with Forum members, even if it turns out to be a "one of" occurrence, or some sort of freak combo of user input, although I still believe that would still be an issue.

With well over 10000 clicks using Honda DCT technology, I am not concerned, yet.
 

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As WeeWIlly mentioned, a rear-brake/huge surge incident happened to me twice (listed on the DCT Doubts thread). @DoubleThumper, might you have temporarily released/eased the rear brake at some point? As I mentioned on the DCT thread I've heard a few folks say that Honda's software reduces power to the throttle significantly when rear brake is applied. Logically, then, releasing the rear brake should cause a power surge to the throttle unless it has been programmed to feed the power back progressively.
 

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Discussion Starter #17
As WeeWIlly mentioned, a rear-brake/huge surge incident happened to me twice (listed on the DCT Doubts thread). @DoubleThumper, might you have temporarily released/eased the rear brake at some point? As I mentioned on the DCT thread I've heard a few folks say that Honda's software reduces power to the throttle significantly when rear brake is applied. Logically, then, releasing the rear brake should cause a power surge to the throttle unless it has been programmed to feed the power back progressively.
Maybe a possibility - hard to recall. However, the front brake would have been still applied. Both brakes were asserted during a routine slow speed stop.

Even if that were an attributing issue, it would remain an issue and possibly a use-case gap in Honda's control management algorithm - speculation-wise.

= = =

Hmm, now thinking about it, if the front brake wasn't asserted, the suspect the machine would have run away. The bucking could have started on the first recoil of the front brake/suspension on the initial surge. This makes sense to me. I reckon everything after the initial surge is a consequence.
 

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As WeeWIlly mentioned, a rear-brake/huge surge incident happened to me twice (listed on the DCT Doubts thread). @DoubleThumper, might you have temporarily released/eased the rear brake at some point? As I mentioned on the DCT thread I've heard a few folks say that Honda's software reduces power to the throttle significantly when rear brake is applied. Logically, then, releasing the rear brake should cause a power surge to the throttle unless it has been programmed to feed the power back progressively.
That's an interesting idea. I can't say I have ever used the rear brake all the way to a stop. It would be an interesting experiment to see if it would surge a little.





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Discussion Starter #19
That's an interesting idea. I can't say I have ever used the rear brake all the way to a stop. It would be an interesting experiment to see if it would surge a little.
Yes. I do use the rear brake to the final stop, but usually in stop-n-go traffic (super slow moves). Regular stops depends on the situation in front of me and varies the order of brake/clutch/release management (traditionally speaking). Nevertheless, more often than not the rear brake is used to at least very near the end of the stop.
 

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... But by the end of the stop you'll have rolled right off the gas anyway, so there would be no open throttle to accept the surge. Can you recall if the throttle was fully closed while you were braking? Bucking would, I assume, only be generated by the front brake/wheel.
 
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