Dealing with the Clunk

[FreepZ]

I'm finding the "transmission slop", which we're all calling "the clunk" on this forum, to be quite distracting, and even somewhat risky in some situations.

Slow Circles
I was practicing some slow circles and figure eights in the street in front of my house last night, and had to stomp my foot down pretty hard a couple of times to keep from dropping the bike. The problem is that when keeping he throttle open just enough to maintain a slow speed, the gears are bouncing between push and pull. If I'm slowing down too much and I have to blip the throttle, there is a relatively long delay before the motor starts pushing the wheels again, and then I get a heck of a kick in the pants.

The obvious solution, which I'm sure you've all figured out, is to aggressively drag the rear brake. This keeps the motor pushing and avoids and delay when some acceleration is needed.

Deceleration to acceleration
The transition from deceleration to acceleration can be jarring. I've been trying to get the most battery regeneration that I can by using a lot of engine braking to slow down, but the drawback is that when I open the throttle again, I get the clunk.

The solution here is to get better at throttle control, but I have found that I've been concentrating way too much on trying to lessen the clunk at the cost of paying attention to the road. Hopefully over time this will become second nature.

Starting from a stop
Shinysideup has already found a solution for this issue:

Yeah, the "clunk" is noticeable, but ,,,

The clunk really bothered me for the first few days. But I've learned how to minimize it to the point of elimination most of the time. Either it's gone completely, or it's no more jarring than shoving my BMW into first from neutral at a light.

The trick is really easy and has become automatic. If I'm stopped on any surface other than a very steep downhill, I put my feet on the pavement and push the bike back a bit, maybe 6 inches to a foot. This takes the slack out of the drive train, so that when I next roll on the throttle, the bike just goes, smoothly. If I can't roll the bike back (steep hill or car too close behind me) I just very slowly nudge the throttle, while waiting for the light to change, which takes the slack out with just a very faint sound.

That solution has been working pretty well for me and others on this forum.

Alternative solution 1
It should be possible to set the gears up for acceleration (i.e. push rather than pull) by dragging the rear brake and giving some throttle just as the bike is about to stop. In theory this will work, but in practice, this may be too much fuss when you've already got to remember to down shift, keep level, brake, and left foot down like they taught us in MSF class.

Alternative solution 2
I wonder if adding some creep to the bike would solve the starting clunk issue. That would mimic what a gas bike is doing -- i.e. always keeping the motor pushing the gears. However, doing that would mean that you would have to start the bike in neutral, or have your hand on the brake, else the bike would start to creep forwards.

Disclaimer
I haven't ridden all that many motorcycles in my life, mostly a couple of Kawasaki Ninjas, and both of those were well past their break in period, so I cannot speak to how bad the transmission slop is compared to many other bikes. All that I can say for sure is that it's significantly more than my Ninja 500.

[Virtually Yours]

I Just out of curiosity does the clunk get an better after the break in period?

Also regarding your slow manuvers, when starting off in first from a dead stop we don't need to use the clutch but if we did would that also help the clunk and the gears bouncing between push and pull mimicking our ICE brothers?

[FreepZ]

Also regarding your slow manuvers, when starting off in first from a dead stop we don't need to use the clutch but if we did would that also help the clunk and the gears bouncing between push and pull mimicking our ICE brothers?

1. The manual recommends not using the clutch from a dead stop.
2. The reason for 1 is that it's very difficult to not over-rev the motor when there's no load (i.e. it's not trying to push the bike).

If you over-rev too much, the bike will shutdown (according to the dealer guys who tested out the bikes). I've been cautious, so I haven't experienced that yet, but that sounds plausible.

[Richard230]

Perhaps modifying the throttle or programming to reduce the initial throttle response, like Zero has done on the 2012 models, would help.

Or maybe Brammo might want to consider installing some sort of damping device in the drive-train (which many IC motorcycle use) to absorb the initial slack shock.

Or perhaps the new transmission needs some more development.  Drive-train slack is something that has been around on motorcycles for many years, to one extent or another, and it can take a lot of work to get it under control. 

Having owned 40 motorcycles, I would say that what you are experiencing sounds like a lot more drive-line slack than I have ever experienced from my motorcycles (and some have been kind of irritating, but not to that extent).  I had no "slack" issues with my two chain-drive EMS GPR-S bikes that used a direct-drive system, so my guess is that the problem lies with the transmission and not excessive slack in the chain.

[CAT in HAWAII]

Perhaps modifying the throttle or programming to reduce the initial throttle response, like Zero has done on the 2012 models, would help.

Or maybe Brammo might want to consider installing some sort of damping device in the drive-train (which many IC motorcycle use) to absorb the initial slack shock.

Or perhaps the new transmission needs some more development.  Drive-train slack is something that has been around on motorcycles for many years, to one extent or another, and it can take a lot of work to get it under control. 

Having owned 40 motorcycles, I would say that what you are experiencing sounds like a lot more drive-line slack than I have ever experienced from my motorcycles (and some have been kind of irritating, but not to that extent).  I had no "slack" issues with my two chain-drive EMS GPR-S bikes that used a direct-drive system, so my guess is that the problem lies with the transmission and not excessive slack in the chain.

I think it has more to do with the computer telling the transmission to go backwards (pull) to start the rege station of power,,, which maybe at xxx miles an hour (5 maybe?) it should just be in "neutral" or SLight push mode (for safety or maneuvers like parking or ) so you don't tip the bike,,,

Just an observation,, seems logical to me,,,

[AJ Nin]

That sounds more reasonable. I have owned 18 motorcycles and never have I experienced a clunk on take off. Only when you actually shift especially into first can there be a clunking sound. This Empulse clunk is something new related to the electronics. If someone from Brammo would be so kind as to explain exactly what it is and assure us that it will not lead to problems down the road, that would be good enough for me. I could live with it.

[7racer]

Hey Freepz,

do you notice this less when you start in 2nd or 3rd?  Just curious.  I think I do, but still don't have that much mileage on the bike yet.

[FreepZ]

I haven't tried starting in 2nd or 3rd. I'll give it a try the next time I'm on the bike. Shinysideup's trick of moving backwards a few inches works so well that I've been doing that most of the time. Also, since range is always a concern for me, I'm always trying to keep the revs as near to 5,000 as I can, which means staying in 1st until about 30 mph.

I did notice that shifting seems to be getting smoother. Out of the crate, the shifter felt very rough.

[frodus]

From talking to Brian, and another rider friend of mine (a mechanical engineer that has ridden the bike), It's just normal transmission slop. All transmissions have it to a degree, and it doesn't sound like it's got more or less than any other transmission.

I think the issue here, is that there's normally an engine spinning the primary gear reduction. This puts constant pressure in circular motion in one direction, constantly taking the slack out of the transmission for you. Then when you're off throttle, and you're going from accelerating to engine braking, that engine still keeps that pressure in that one direction and it's reduced, but not eliminated. It still has a bit of a clunk when going from accel to engine braking as the transmission goes from being driven by the engine, to driving the engine.

My SV650 has some bit of this when I engine brake. Some of this is softened by dampers in the rear wheel (not sure if the Empulse has them or not).


So essentially when you back the bike up, you're taking out the slack, just like an engine+clutch would.



My thinking:
Maybe Brammo could have the motor creep a little bit. Just a tiny bit such that when engaged, the vehicle won't move, but it'll just put pressure on the gears. Also, if you're driving, I'm not sure if the VCU knows which gear you're in, but it could look at throttle position and when you clutch and go up, decrease RPM to just above the gear you're going to, and if you shift up, increase RPM to just below the gear you're going to. This may help keep the slack optimized.

[flar]

Also, if you're driving, I'm not sure if the VCU knows which gear you're in, but it could look at throttle position and when you clutch and go up, decrease RPM to just above the gear you're going to, and if you shift up, increase RPM to just below the gear you're going to. This may help keep the slack optimized.

The main cause behind this is that an electric motor spins so unbelievably quickly with just a mild throttle input.  It has very little resistance to RPM changes and if you twist the throttle in neutral or with the clutch pulled in then it will redline in a very tiny fraction of a second.  That kind of readiness amounts to a sudden engagement of the drive train that is orders of magnitude greater than anything with a pair of clutch plates engaging or a chemical (explosion) reaction being indirectly fed by a change in air pressure could ever hope to achieve.  As the Tesla salesman kept pointing out when I test drove a Roadster, the connection to the pavement is so much more immediate than any chemical linkage (i.e. modifying the ingredients to the C of an ICE) could ever hope to accomplish.

This isn't a gear change issue.  It is a "starting from a dead stop" and "switching back and forth between engine braking and acceleration" issue.

Any time you have the clutch pulled it will gently "creep" the slack back out when you release it because the clutch engages more gradually (unless you dump it) than twisting the throttle with the drive train connected.

I don't use the clutch for up-shifts, it's a recipe for redlining the motor because it spins so quickly and the transmission is actually very smooth doing power-up-shifts.  Nor do I rev match for downshifts - I only downshift while in regen and then I do use the clutch and there is no clunk.

[FreepZ]

Hey Freepz,

do you notice this less when you start in 2nd or 3rd?  Just curious.  I think I do, but still don't have that much mileage on the bike yet.

Starting in 2nd didn't seem to improve much. Starting in 3rd was a lot smoother. There was still a clunk, but it wasn't as harsh. In fact, keeping the bike in 3rd gear all the time makes the bike quite easy to use. Minor clunk, easy acceleration, limited top speed, and gentle engine braking. It's great if you want to trust a beginner with your bike.

[BrammoBrian]

Travis (Frodus) is correct, this is typical motorcycle transmission backlash that is being felt.  It is amplified to some extent because:

1. The electric motor does not idle like a gasoline engine. 
2. We instruct riders not to slip the clutch during launches for the best performance.
2. There is no engine vibration damping the feel of the lash being taken up. 

Here's some videos we did today for more information and hopefully will make everyone understand that this isn't a problem or sign of impending problem with the bike.  I think you'll find the last video particularly helpful for those less familiar with how a motorcycle transmission operates.  I apologize for the poor quality, but I wanted to get these up as fast as possible to address your collective concerns.







The idea of adding a "creep" or "idle" speed is a good one and one that was investigated by the Brammo engineering team.  In the end, it was determined that the rider could compensate for this issue better than we could design software "band-aids" for it. 

I would urge Richard (FreepZ) to at least live with the bike until the break-in period is through and then see if it's still a problem.  I believe that you'll enjoy the feeling of "mastering" the bike.   Out of curiousity, were you riding the bike in Normal or Sport mode? 

We COULD reduce torque to reduce the feel of the lash, but our assumption has always been to provide the highest level of performance.  I think you'll find that "Normal" mode is also less aggressive as we reduce the peak torque of the motor to about 75% and also reduce the regen. 

I'm off to go ride in circles in the parking lot - I'll let you know how that goes. 

[FreepZ]

@Brian - Thanks for those videos. That's a very good explanation of what's going on.

I agree that the backlash is not something that I should be too worried about, as long as it's not going to damage the bike. The only danger with the lashing is when using the first gear and going slow, but I could get exactly the same issue with a regular gas bike. Dragging the brake smooths out the ride and eliminates that danger. (Heck, I should use that rear brake some times. Most of the time I'm using the regen to slow down and don't hardly touch the brakes. )

If I was really that bothered by the backlash, I could always just keep the bike in 3rd gear, since doing that really softens the lashing. A more interesting proposition is to, as you said, master the bike. I'm getting better and finding the correct throttle position to get the motor to barely push the wheels.

As for modes: I'm still only using Normal mode as I haven't passed the 600 mile break in period.

[BrammoBrian]

@Brian - Thanks for those videos. That's a very good explanation of what's going on.

I agree that the backlash is not something that I should be too worried about, as long as it's not going to damage the bike. The only danger with the lashing is when using the first gear and going slow, but I could get exactly the same issue with a regular gas bike. Dragging the brake smooths out the ride and eliminates that danger. (Heck, I should use that rear brake some times. Most of the time I'm using the regen to slow down and don't hardly touch the brakes. )

If I was really that bothered by the backlash, I could always just keep the bike in 3rd gear, since doing that really softens the lashing. A more interesting proposition is to, as you said, master the bike. I'm getting better and finding the correct throttle position to get the motor to barely push the wheels.

As for modes: I'm still only using Normal mode as I haven't passed the 600 mile break in period.

Richard, sound like a good plan.  I agree that dragging a little rear brake can help.  I also want to point out that I am not implying that you're riding the bike "wrong".  Just that I hope you'll learn (and come to love) it's quirks by the time the break-in point is through. 

Fair warning - you'll probably find Sport mode is even more jarring as the torque delivery is even more aggressive.  By then, you'll be comfortable with the bike, so hopefully you'll be able to enjoy the performance benefit. 

Flar makes some good points as well.  The shifting technique can also lessen the "impact" (ha!) of this backlash.  I'll try to get a video of a proper upshift to show how smooth and gearbox friendly it can be.  I'll have to get creative with the GoPro cameras...

[Gavin]

Can't wait to see the video on proper up shift...I've put so many miles on an Enertia that I have forgotten how to shift

Gavin