I'd be interested to hear how that feels. I'm kind of guessing it's going to be a fairly rudimentary analogy to a flywheel. Maybe just a minimum rate of accel/decelerate on the motor RPM. If I remember correctly they have asymmetric accelerate and decelerate "flywheel" settings, so riders can set a reasonably snappy accelerate, but a much slower decelerate.
I'd be most interested in these two circumstances:
1. From flat or gentle upslope accelerate hard (ideally wheelie front wheel clear) in to an obstacle perhaps axle height, but ensure the throttle is closed before the back hits. A real flywheel will release lots of torque as the wheel hits and tries to stop. Unless the Stark flywheel has more smarts than I think then I expect it to kind of fall in a heap and not give that big torque surge. This move should also show up if the 'flywheel' response is moderated by the basic throttle smoothing or not. In fact if the throttle settings are set really soft & progressive it should make it easier to feel how the two (flywheel & throttle tuning) interact.
2. a normal splat style clutch dump.
Yeah I have a feeling it's functionally just adjustment to spindown / spin up time, and I doubt it will perform well in either of the situations you describe. No clutch, it's a single speed, so a splat style clutch dumb is totally out. But we'll see when it shows up!
From my perspective what you're doing with clutch & rpm is the gold standard, looking for more snap off the bottom via motor response is a regression that will cause more problems than it solves. But I don't do your style of riding.
I love this quote from an ex-national trials champ rider who now rides hard enduro comps a bit. "Hard enduro is really just trials riding on inappropriate machinery"
Hahaha yes, the issue is that mostly my 250 is a wide ratio transmission (as far from a trials bike as you can get!) so I really need to be in the right gear, or sometimes on a big climb you have to throw in an awkward shift down from 3rd to 2nd because the bike won't lug down low, or you're just absolutely annihilating the clutch for extended periods to keep the bike on the pipe and in the power - pinned to keep the RPMs up, modulating with the clutch, but if you've lost momentum and the tire hooks you can easily end up with it suddenly dropping RPM and you're back out of the power. Amazing when you can ride it the way it should be ridden, a lot of work if you're a little off your game.
I suspect you'll run up against the problem you refer to in the EM. If the flywheel is on the end of the shaft with the output and clutch then you either run out of space for a large diameter flywheel, or you end up with the flywheel hanging far out the end. The EM flywheel is anorexic and spins up/down so fast as to be next to useless. Making a flywheel out of Cu/W helps considerably as Cu/W is roughly 1.5 - 2 x as dense as steel. But it's not cheap.
Adding mass to the clutch basket would be a really, really inefficient way of adding inertia - the basket is spinning so slowly compared to the motor, you'd have to add enormous amounts of weight to make it useful.
Here's a thought for you that I've considered previously. In your QS/ICE crank build you geared the motor to the flywheel (crank) and then out to the drive. What if you drive direct off the motor, but gear the flywheel? So the motor sits where the crank shaft was (with a clutch) and the flywheel sits up above it all running off a gear (belt, chain, gear - whatever works). Now you lose some of the space constraints of hanging a flywheel off the end of the motor and you also gain the possibility of gearing the flywheel up to benefit from the exponential gain in energy with rotational velocity. Those QS motors and even the EM are pretty slow turning, so the flywheel has to be big &/or heavy to be really effective. Throw in a 2:1 step up and now your 4,000 rpm motor is spinning a nice little 8,000 rpm flywheel. Or go 3:1 and have a 12,000 rpm flywheel!
Torquey low rpm motor that makes final drive a bit more manageable combined with a high rpm flywheel. win - win.
Ahh, this is a great point - I was optimizing for _not_ machining out a set of cases, so that's why the location as it sat. The thing about that setup is that the 2 stroke cranks are shockingly heavy (more so when you weld them together), so it did have a lot of good flywheel mass, it was just that the throttle response was really marginal.
I'm really hoping the new EM 4 speed is the answer to all my dreams, I can deal with the flywheel thing if I could just have a bit more flexibility with power vs speed.
Did your EM not have the idle mode? That's a game changer - trying to coordinate picking up revs off zero and clutch just doesn't really work, which is why they have idle on all the better e-trials bikes now.
That's also where you come up against the limitations of controllers that only know about torque without any reference to RPM or load. That horrible characteristic of electric bikes to just spin up madly when there's no load. By the time you start to tame that by limiting the throttle response (really the rate of torque increase) then you can't get any snap out of the system. The control loop has to know about RPM to work the way we want it.
If the "soft start" you mention was a soft rpm rise, but not necessarily a soft torque increase, it would be a completely different feel. You could still get really solid power & acceleration out, but without the crazy runaway that uncontrolled rpm rise gives. At some point you'd hit the limits of the RPM rise rate, and that's when you'd need to be using clutch to step up the snap.
Sorry, I should clarify here - I have done two conversions at this point, one where I did the QS into the ICE motor, and one where I put my EM ePure powertrain into a 300 chassis. The EM does have the idle mode, and is generally pretty great, although I think shortening the gearing will really help, because I've added a lot of weight to the chassis, so while you can clutch up a wheelie relatively easily, it's hard to hold it up with the gas at anything but balance point. I'm hoping that what the EM/300 conversion gives me is a woods weapon to about 30mph that encourages me to have another go at the QS/ICE conversion, because it's enjoyable enough to ride that I want to invest the time and energy to get the extra flexibility of the 6 speed.
The issue I identified with the QS/ICE build was that if I was rolling with the clutch in, I would wing the throttle open to try and get a bunch of power into the flywheel and it'd take about a half second of slow acceleration of the flywheel followed by normal acceleration, and I was assuming that was because it was limiting the change in RPM, as you said.
