speedmd wrote: ↑
Apr 26 2022 7:41am
6 phase windings and dual controllers could be a suitable setup to gain on both issues. Bigger motors also.
Not sure how the sevcon is setup to run the 2012 Polaris Ranger EV, but the "low" setting on the stock three speed switch acts just like a low gear. Need to dig into this a bit deeper.
I know I've got a bee in my bonnet about this, but I very strongly believe that trying to throw more electrical power at the problem is completely counterproductive. More power without the proper delivery characteristics is just going to make things worse and worse, not even considering the extra weight of motor, controller & batteries as you make it all more powerful.
Unless and until someone develops a controller specifically capable of providing the characteristics required for trials. Actually by extension for many other motorcycle activities - it's no coincidence virtually all the top hard enduro riders come from a trials background.
Personally I think we're a very long way away from doing without a mechanical clutch except for basic entry level riding.
Trials bikes are universally completely gutless compared to similar sized "dirt bikes", probably half the power or less. It's telling that most trials riders have no clue how much power their bikes make, and nor do they care. It's also telling that there are youngsters on 125's who are capable of challenging riders on 300's right up to the Expert class. The 125's are positively anaemic in their power output! Yet they can still be competitive simply because they can rev high and so store energy in the flywheel.
Power isn't a substitute for finesse in this sport.
This lack of power isn't totally by accident either. Yes, with 2-strokes it can be thought of as the engine can produce a total sum of power beneath the output graph (the area), by tuning the exhaust etc it's possible to shift power from one part of the graph to another. This is why the most powerful 2-strokes are "peaky", developing nearly all their power in a very small band. Having a peaky motor would be a disaster for trials! So 2-stroke trials bikes have to sacrifice peak power for smooth delivery right from idle.
However there's also the simple fact that too much power just makes it far too easy to spin the wheel. Having a heavy flywheel helps mitigate that, and this could similarly be done in the controller by limiting the rpm rate rise.
I'll deviate for a moment to explain my understanding of rpm vs torque in trials. If we look at the more advanced splatters and zaps it's easier to see one of the difficulties for a controller to overcome. In either of these moves, where the bike is sent more or less vertically airborne, the key mechanism is rotating the whole bike really rapidly around the rear axle so the centre of gravity accelerates upwards. Once that is headed skywards it's relatively easy to bring the rest of the bike along with it. The key here is that the back wheel has to be accelerated from usually close to 0 rpm to pretty much flat out (for that gear) in a fraction of a second. We're talking around 1/30th - 1/15th of a second from what I can see on video of the guns. If the acceleration is too slow the bike isn't going to rotate fast enough and will get going forward, not up. Given the light weight of the bikes, the rear position of the pegs and the fact the rider is trying to help the bike to rotate, there isn't actually a lot of torque required to get this rotation going. So RPM is often more critical than torque.
It's absolutely common that at the completion of a splat or zap there are still way more rpm available than needed, so you pull the clutch and control the drive with that, adding throttle as needed. This reinforces that RPM is often more critical than torque.
So now you need a controller/motor that can go from 0 to full rpm in say 1/30th second. Probably doable but perhaps needs an oversize controller to achieve it? Not my field of knowledge. There's also the impact on the bike of that sort of starting torque applied by the motor, it could be beneficial or it could be an added complication, I don't know.
If rpm rise is limited by controller then how do you get the massive instant torque & rpm when required, and also the ability to chop that torque totally when needed? The answer is by having a separate control regime operated by the clutch lever. So that the rpm ramp is 0-full over just a few mm of lever travel (as it is on current bikes - the engagement travel is really very short). That still doesn't go anywhere near to solving the problem of how that instant power is applied. Nor does it actually totally cut drive - there's still the inertia in the motor rotor etc. - that's when trials bikes get away from people, when they can't chop power with the clutch fast enough. Your clutch is your get out of jail free card!
A flywheel supplies power that decays as power is drawn down. So now the controller needs to supply big rpm that rapidly drops, but critical is that it drops in response to the load
. There's no use punching up into a big splatter across a gap only to find that rpm has dropped to zero by the time the rear wheel hits the rock face! That will end badly indeed. So now our controller needs to see the load applied to the drive and adjust the decay rate accordingly.
Keep in mind that during all of this the throttle can only be used for really coarse control - I defy anyone to be able to finely control a throttle tube while they are simultaneously launching into a big jump, pulling the bars hard to their hips and then dropping their hips down to the rear tyre.
Consider this also - with a mechanical clutch in slipping state the amount of power delivered to the rear wheel effectively does not vary if the motor rpm are varied. This allows all sorts of stuff to happen, but one key one is that it's possible to dial up the power rather approximately with that coarse control throttle and apply it smoothly to the rear wheel via the clutch. This too can be done electronically I expect, but I don't know of any controller really setup to do it?
I could go on - I've spent a lot of time considering this! There's lots of other situations where these same factors are blended in different ways, but always it comes down to decaying power in response to load, ability to instantly cut all torque to the rear wheel and the ability to use throttle to dial the "available power" and use the clutch lever to finely manage the delivery of that available power.
These last two often seem to be totally disregarded in these discussions, but I think they're critical.
A throttle tube is slow, coarse and impossible to keep accurate as the bike and rider leap about. It's great for the basic power control but complete rubbish for the fine & rapid stuff.
A clutch lever is operated by one finger with the rest of the hand stabilised on the grip. The operating range is over just few mm. It's amazing how accurate and consistent riders become. I've reviewed videos where it's gone from fully slipping to fully engaged to partly slipping then out to full engaged in 1/15th of a second - 4 frames of a 60fps video while the rider was gapping to splatter! Absolutely not possible by throttle.
So I ask, why not just put in a flywheel and clutch?
Sorry for the totally excessively long rant.