Is 250w enough power for modest speed up steep hills

Electrically assisted bikes, trikes, etc. that are legal in the UK
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Jdsk
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Re: Is 250w enough power for modest speed up steep hills

Post by Jdsk »

Nearholmer wrote: 18 Jun 2022, 5:28pm Couldn’t regen be implemented by having the motor drive permanently connected to the wheel, and the pedals connected into the drive via a centrifugal clutch?
As above... it's feasible but it isn't worth it. That follows from the inherent difference in energetics between car-like objects and HPVs, not from the difference in technology.

Jonathan
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Re: Is 250w enough power for modest speed up steep hills

Post by Bonzo Banana »

stodd wrote: 18 Jun 2022, 5:11pm
Nearholmer wrote: 18 Jun 2022, 1:34pm One option you might consider is a “constant effort e-bike”.
Nice idea, I think that could work well for flat and uphills; and probably be easy to engineer with a tweak to torsion controller software.

It doesn't seem worth it for downhill. It seems generally accepted that regenerative breaking is too complex to be worth it on typical crank drive or geared hub motors, and direct drive motors have lots of problems of their own (weight and inefficiency). Of course, just because something is generally accepted doesn't make it true; it would be great if somebody came up with an effective regenerative breaking. I think you will find considerable consumer resistance to the idea of applying the brakes harder on downhill so the rider has to work harder. Maybe even that though; people are willing to pay out for bicycle exercise machines.
The inefficiency of direct drive motors is often over-stated and geared hub motors are no different depending on their torque output. It should also be stated the best regen is on geared hub motors but this means the freewheel clutch is disabled so even more resistance on the flats compared to direct drive hub motors. Some people find this acceptable and you can use a trickle current to restore the freewheel effect easily repaid by applying regen down hills etc. If you use ebike power very sparingly with a regen geared hub or direct drive hub motor you can actually have so called infinite range but this means more effort going up less steep hills without assistance at all. You are literally only applying power for steeper hills only. Not something that could ever be achieved with a mid-drive motor.

The tecnicalities of this is best explained by Grin Technology videos. I think the most efficient motor system I've seen discussed was a geared hub motor with regen, it averaged about 4Wh per kilometer or 6Wh per mile. This was using the ebike normally and a relatively small and light geared hub motor.
Nearholmer
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Re: Is 250w enough power for modest speed up steep hills

Post by Nearholmer »

I never thought it was worth it; the whole thought was a musing to keep myself amused while waiting in the rain.

(I’m used to trains, which have rather more mass, and very low rolling resistance, so are perfect objects for regen.)
Jdsk
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Re: Is 250w enough power for modest speed up steep hills

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: - )

Jonathan
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Re: Is 250w enough power for modest speed up steep hills

Post by Bonzo Banana »

Nearholmer wrote: 18 Jun 2022, 6:15pm I never thought it was worth it; the whole thought was a musing to keep myself amused while waiting in the rain.

(I’m used to trains, which have rather more mass, and very low rolling resistance, so are perfect objects for regen.)
On a direct drive hub motor no reason not to enable regen, you can get up to 20% back under ideal conditions but as low as 5% under bad conditions but also its braking without any brake pad wear at all so if you are the sort of person who brakes early you save a fortune on brake pads too. It gives you a third braking system which helps stop you faster too in combination with the other brakes. There are no negatives to regen on a direct drive hub motor. That 20% figure is for ebikes where the motor is constantly assisting up to 15.5mph but of course if you only use the motor for steep hills regen power could exceed actual used power for assistance. It's harder to have a flat battery with regen and you are often charging in the goldilocks zone where the battery cell takes charge easily and safely to maximise cell lifespan. It also works as a sort of dynamo system that means you'll always have enough power for lights. You'll never be caught out with a completely flat battery you can always get some charge into it.
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Cugel
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Re: Is 250w enough power for modest speed up steep hills

Post by Cugel »

Bonzo Banana wrote: 24 Jun 2022, 10:32am
Nearholmer wrote: 18 Jun 2022, 6:15pm I never thought it was worth it; the whole thought was a musing to keep myself amused while waiting in the rain.

(I’m used to trains, which have rather more mass, and very low rolling resistance, so are perfect objects for regen.)
On a direct drive hub motor no reason not to enable regen, you can get up to 20% back under ideal conditions but as low as 5% under bad conditions but also its braking without any brake pad wear at all so if you are the sort of person who brakes early you save a fortune on brake pads too. It gives you a third braking system which helps stop you faster too in combination with the other brakes. There are no negatives to regen on a direct drive hub motor. That 20% figure is for ebikes where the motor is constantly assisting up to 15.5mph but of course if you only use the motor for steep hills regen power could exceed actual used power for assistance. It's harder to have a flat battery with regen and you are often charging in the goldilocks zone where the battery cell takes charge easily and safely to maximise cell lifespan. It also works as a sort of dynamo system that means you'll always have enough power for lights. You'll never be caught out with a completely flat battery you can always get some charge into it.
Given that hub dynamos are now well-developed and resilient, I wonder if a braking system could be developed using those, one for each wheel and an integral part of the hubs. They could also be employed as battery chargers, for lighting systems but perhaps also for e-motor batteries ..... ?

There are cycling situations in mountainous terrains where traditional brakes struggle to cope, especially with heavier bikes. Even in West Wales, there are some long and ever-steepening plunges from 3-400m down into a valley bottom at less than 100M. These can require a lot of braking with the risk of brake-fade in some cases. Times 10 that in places like The Alps.

Could hub dynamos be enhanced so that brake levers gradually increased their production of lecky and hence their drag? Would the amounts of lecky produced be significant? Would excess heat be a problem with them too?

Cugel
“Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist”.
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Jdsk
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Re: Is 250w enough power for modest speed up steep hills

Post by Jdsk »

Cugel wrote: 24 Jun 2022, 11:26am
Bonzo Banana wrote: 24 Jun 2022, 10:32am
Nearholmer wrote: 18 Jun 2022, 6:15pm I never thought it was worth it; the whole thought was a musing to keep myself amused while waiting in the rain.

(I’m used to trains, which have rather more mass, and very low rolling resistance, so are perfect objects for regen.)
On a direct drive hub motor no reason not to enable regen, you can get up to 20% back under ideal conditions but as low as 5% under bad conditions but also its braking without any brake pad wear at all so if you are the sort of person who brakes early you save a fortune on brake pads too. It gives you a third braking system which helps stop you faster too in combination with the other brakes. There are no negatives to regen on a direct drive hub motor. That 20% figure is for ebikes where the motor is constantly assisting up to 15.5mph but of course if you only use the motor for steep hills regen power could exceed actual used power for assistance. It's harder to have a flat battery with regen and you are often charging in the goldilocks zone where the battery cell takes charge easily and safely to maximise cell lifespan. It also works as a sort of dynamo system that means you'll always have enough power for lights. You'll never be caught out with a completely flat battery you can always get some charge into it.
Given that hub dynamos are now well-developed and resilient, I wonder if a braking system could be developed using those, one for each wheel and an integral part of the hubs. They could also be employed as battery chargers, for lighting systems but perhaps also for e-motor batteries ..... ?

There are cycling situations in mountainous terrains where traditional brakes struggle to cope, especially with heavier bikes. Even in West Wales, there are some long and ever-steepening plunges from 3-400m down into a valley bottom at less than 100M. These can require a lot of braking with the risk of brake-fade in some cases. Times 10 that in places like The Alps.

Could hub dynamos be enhanced so that brake levers gradually increased their production of lecky and hence their drag? Would the amounts of lecky produced be significant? Would excess heat be a problem with them too?
I think that it would be much easier to deliver regenerative braking by developing the motor rather than a dynamo.

Jonathan
axel_knutt
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Re: Is 250w enough power for modest speed up steep hills

Post by axel_knutt »

I've spent the last 11 years limiting the intensity of my exercise out of necessity, and I've lost all my fitness as a result.
Some, not all, I venture to suggest, because if you’d lost it all then low-medium intensity cycling would be beyond you.
Someone obviously thinks they know more about my exercise than I do.

I was under the impression that I hadn't been able to exercise at much above about 100bpm for over a decade, with no cycling at all for over two years. Cardiologists used to keep telling me that atrial fibrillation was no reason to stop exercise (and it isn't, for some patients) but every time I resumed I ended up back on an ambulance. You would have thought that after 10 such trips they would have got the message, but apparently not. The sudden cessation of cycling altogether occurred because I got frustrated at 8 years of losing fitness, and tried to return to training nearer to the way I used to. Just prior to this I was still able to walk 12-15 miles a day on the Oxfordshire Way provided I kept to a gentle pace, now my limit is about 2 hours gentle walking a week at 80-85bpm, which just enough to fetch groceries from Tesco.

The simple bottom line is that the maximum level of exercise I can tolerate is lower than what it takes to maintain my fitness, and I think that the reason for the fitness loss is that it takes intensity not duration to maintain fitness.
the advice I received from a cardiologist was that the overall health benefits of cycling, including age-appropriate spells of intense effort, so vastly outweigh any specific cardio risk that comes with it
What are you trying to do, contradict me with my own argument?

The Schnohr study I quoted says that mortality rate is reduced more by increasing intensity than by increasing duration. The large volumes of exercise that come with chronic endurance training are a risk for developing arrhythmia. ACSM Guidelines for Exercise Testing and Prescription recommend just 500-1000 METminutes a week for optimum health, a lot less than a typical cycling enthusiast. At my most enthusiastic I was averaging 6000-8000 METmins/wk.
cardio risk isn’t worth worrying about except in the case of a person with specific health conditions.
Specific health conditions like atrial fibrillation and a history of chronic overtraining, you mean?
The chap was a keen cyclist himself
John Mandrola is a keen cyclist, and an atrial fibrillation patient. He's also a consultant electrophysiologist (a cardiologist who specialises in treating heart arrhythmias).
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hemo
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Re: Is 250w enough power for modest speed up steep hills

Post by hemo »

Problem with DD hubs in the UK and most of the world is they are illegal to use on the road as I have never seen a 250w version except for the illegal cyclotricity ones that claim to have this mode on there 1000w kits one can't simply have a dual rating motor just to try an sneek inside the law.. 500w rating is the lowest I have seen.
axel_knutt
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Re: Is 250w enough power for modest speed up steep hills

Post by axel_knutt »

Jdsk wrote: 24 Jun 2022, 11:42am I think that it would be much easier to deliver regenerative braking by developing the motor rather than a dynamo.

Jonathan
Indeed. Nobody's going to incur the weight of a motor and a dynamo, when a motor already is essentially a dynamo.
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Cugel
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Re: Is 250w enough power for modest speed up steep hills

Post by Cugel »

axel_knutt wrote: 24 Jun 2022, 1:02pm
Jdsk wrote: 24 Jun 2022, 11:42am I think that it would be much easier to deliver regenerative braking by developing the motor rather than a dynamo.

Jonathan
Indeed. Nobody's going to incur the weight of a motor and a dynamo, when a motor already is essentially a dynamo.
The weight of some dynamo hubs configured to also act as brakes is unlikely to be an issue on an e-bike, especially if the more conventional brake gubbins can also be dispensed with.

Having a brake in only one hub motor would not be enough; and perhaps having separate brakes from the motor would simplify things, no bad design principle albeit contradicted by the principle of integrating things with similar functions.

Cugel
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Nearholmer
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Re: Is 250w enough power for modest speed up steep hills

Post by Nearholmer »

No other type of vehicle that I know of has a separate traction motor and regen generator, they all use the one machine to do both jobs, and they always have since the principle was first understood in the 1870s, because it is so obviously weight-efficient to do so. Even lifts and escalators, where the mass of the machine doesn’t have to be lugged about, are like that for simplicity.

The one case I can see for having two rotating machines on a bike would be if mechanical transmission (cranks, chain, gears typically) between “human engine” and wheel was to be replaced with electrical transmission, by using a pedal-powered generator to supply electricity to the traction motor, with “gear change” by power electronics. This is how most large diesel-electric locomotives, gas turbine-electric ships, and some heavy land vehicles are configured, but for low power applications mechanical transmissions can still usually be made lighter than electrical ones, so it may be a while yet before we see the all electric transmission bike become popular, although some hobbyist is bound to put one together for fun, if they haven’t already.

An issue for regen braking on a bike would be, I think, that the battery is unlikely to be able to soak-up energy at the rate needed to provide full braking at all times, so either resistor grids to create and waste heat, or mechanical brakes, to create and waste heat, would be necessary too. In winter, of course, the rider could wear a suit containing fine wire heating elements, and be warmed while braking, or they could be provided with a brake-powered coffee percolator mounted on the handlebars.

The ultimate, of course, would be to get rid of the batteries, and have a system of overhead wires, from which these two-wheeled hybrid (human-electric) vehicles would draw energy, and through which braking energy from descending bicycles would be passed to provide traction energy for ascending bicyles, the riders nodding in appreciation as they passed partway up/down each hill. Railways have been doing that for nearly 150 years in places.
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Cugel
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Re: Is 250w enough power for modest speed up steep hills

Post by Cugel »

Nearholmer wrote: 24 Jun 2022, 2:06pm (snip) In winter, of course, the rider could wear a suit containing fine wire heating elements, and be warmed while braking, or they could be provided with a brake-powered coffee percolator mounted on the handlebars.

The ultimate, of course, would be to get rid of the batteries, and have a system of overhead wires, from which these two-wheeled hybrid (human-electric) vehicles would draw energy, and through which braking energy from descending bicycles would be passed to provide traction energy for ascending bicyles, the riders nodding in appreciation as they passed partway up/down each hill. Railways have been doing that for nearly 150 years in places.
I would very much like a coffee percolator on the bike, although I'd have mine behind me bum, so as not to cool the coffee to quickly in the breeze. (My glutes provide a rather large shelter).

But what really appeals is the notion of trolley-bicycles! When I wus a little boy child, 391 years ago, there were trolley buses everywhere. (Mrs Thatcher was just a small bad fairy then, so we still had proper buses). I rode on them just because I liked them, all over South Shields and, sometimes - after a diesel bus trip to Newcastle (No. 86) - around The Big City 'cos they had 6-wheel trolley buses there.

A trolley bicycle could have a much thinner whippy pole up to the wires; and a gubbins to remote-control the wire points ahead. The trolley bus points required the conductor of the bus to leap off and run ahead to pull a ball on a rod, which changed the points. We naughty boys would sit on the roadside railings, indicating to the conductor that he could continue to collect the fares since we would pull the points. Of course we only pretended to, so the bus went one way and the trolleys another. They never caught us, those conductors. They were too busy putting the trolleys back on with a big hook on a pole.

But I digress.

What were we talking about again ....... ?

Cugel
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Dingdong
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Re: Is 250w enough power for modest speed up steep hills

Post by Dingdong »

'Motor Shame!' We are no longer in Kansas :lol:
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Cugel
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Re: Is 250w enough power for modest speed up steep hills

Post by Cugel »

As you'll have gathered by now, I like them Fazua motor systems in an e-bike. Not for moi the geet big Bosch & similar, with massive battery, lumpy motor and the potential to topple you back down the stair going up to your bike shed before landing on you to give you a nasty crush! No.

This Fazua article paints a good picture of many of the reasons I prefer a Fazua-equipped e-bike to alternatives. But many of its observations could be applied to the lightweight hub-motored bikes, especially if they have tweakable motors that allow different power profiles to be set by their riders.

https://fazua.com/en/support/help-cente ... al-assist/

I know that even in this forum of often purist cycling traditions, some of those who fancy the e-bike have a yen for more power, speed and the like - an e-motorbike, perhaps with a throttle and an enjin that makes a macho-noise. :-) But if you want to stay a cyclist as you grow decrepit, so need to be able to continue up the hills, perhaps even at the pace of younger or fitter companions, the light weight minimal-assist e-bike style may be what you really seek, rather than a brutish Bosch-motored behemoth.

Cugel, not a Fazua salesman, honest.
“Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist”.
John Maynard Keynes
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