Bosch climbing speed

[Danidl]

they may have to deal with other issues - such as abuse of their motors.
If you allow user setting of the multiplier, nothing stops the bike to pull maximum power from standstill or at maximum derestricted speed.

Fair point. , But do hub motors not already allow this? I would not be advocating a full publish of their software parameters. Just a minor mod by which the amount of assistance was increased step by step from the current max of 3 times human effort to let's say 30 times,. But with the proviso that it remains within the safety envelope of the motor. It could be arranged that the bike had to be moving before it would upgrade above the current 2.5. . The hardware is already there in the activia up down switch.

 

[Deleted member 4366]

... I can accept the majority of these figures without question! However the efficiency ones , I have difficulty with. If the hub motors designed speed is 250 rpm, thence it will be rotating at 40% of designed speed and. I would suggest ,that an efficiency of 70% would under those conditions highly optimistic. Whereas the Bosch motor would / should be at optimum rotation speed and therefore higher than the 70% claimed.
If the hub motor was mounted in a small diameter wheel, And was therefore optimised, then it's higher power rating would win out.

The Ezee motor has a very broad efficiency band. All those figures are directly from the simulator, which is based on real data and measurements.

 

[Deleted member 4366]

Fair point. , But do hub motors not already allow this? I would not be advocating a full publish of their software parameters. Just a minor mod by which the amount of assistance was increased step by step from the current max of 3 times human effort to let's say 30 times,. But with the proviso that it remains within the safety envelope of the motor. It could be arranged that the bike had to be moving before it would upgrade above the current 2.5. . The hardware is already there in the activia up down switch.

I keep telling you that motor type has nothing to do with the control system. You can get both hub-motors and crank-drives with torque multiplier systems, and both hub-motors and crank-drives with cadence controls. Some motors have both systems.

 

[footpump]

which ebikes have both ts and cadence sensor and how does one switch between the two?

 

[Danidl]

Torque multiplier systems are not suitable for some people. I can't understand why people on this forum keep recommending them to guys that have arthritis, weak legs or are otherwise not able to pedal hard. You'd be better off with something like a Wisper Torque or a Woosh.

This thread started by comparing an Ezee motor at 48v and 18 amps with a Bosch up a 20% hill. Unless the rider is substantially overweight and assuming the standard 250 rpm version, the Ezee will win hands down.

With a total weight of 100kg and about 100w of rider input, the Ezee bike will climb the hill at 9 mph without overheating, running at an efficiency of 70%. The load is about 600w and the motor will take 864w from the battery

The Bosch motors run at a max current of 18 amps at 36v (AFAWCT). At an optimistic efficiency of 70%, the most power the Bosch would produce 454w, so it only has 75% of the Ezee's power at that climbing speed.

The Ezee would still be able to climb the hill without pedalling. If the rider pedalled harder than 100w, both bikes would climb faster, but the Ezee would become more efficient and the power difference would increase, so the Bosch would never be able to catch it.

Most of what people are saying about how fast they can climb a 20% hill is just dreaming. To climb at 15 mph requires 1141W (100kg all-up weight). The most the Bosch can provide is about 518w, which would mean that the rider would have to provide 623w. That's what a fit person can do sprinting up stairs. I'm sure there are guys on the forum can do that for a short burst, but not the average forum reader will struggle to maintain 200w for any length of time.

Working back the other way, the Bosch at 18 amps, 36v and an efficiency of 80% (very optimistic), can produce 518W. Add 200w rider input, and let's ignore drive-train losses for now. that gives a net power of 718w, which can propel a 100kg all-up weight up a 20% hill at 7.9 mph.

I hope these facts and figures put some of these myths into perspective.

.. thanks that is an excellent factual post, certainly the hub motor driven by the bigger voltage wins in any case.and performs better if the wheel diameter is reduced. The simulator is a very nice piece of software.
Were the Bosch equipped with a 48v battery, and an assurance that the motor and gears robust enough, then it would win.
I am familiar with the differences between cadence ..crank rotate speed sensors and crank torque sensors . For one thing the speed of response of the torque sensor can be much quicker, as nothing has to rotate by 120 or 60 degrees. My previous point was that the major health limitations eg limited leg power could be easily mitigated by increasing the gain of the torque sensor

 

[Woosh]

For one thing the speed of response of the torque sensor can be much quicker, as nothing has to rotate by 120 or 60 degrees. My previous point was that the major health limitations eg limited leg power could be easily mitigated by increasing the gain of the torque sensor

no way a torque sensor can be programmed to be as responsive as a thumb throttle because you have to program in debouncing.

 

[Deleted member 4366]

which ebikes have both ts and cadence sensor and how does one switch between the two?

Wisper Torque. It has a setting in the LCD. That gives two completely different modes of control.

Most premium brands, including Bosch, have a cadence sensor in their system, but they don't give you the option of getting selectable fixed power when you pedal. I guess they're pandering to all the people that want their bike to be like a normal bike, i.e. you have to pedal hard to get a lot of power.

Some bikes that use torque multiplier systems have a climb mode, where they increase the base power so that your legs don't get so tired when you climb hills. That was on the Kalkhoff Impulse 2, but I'm not sure if they back-pedalled on that since the reliability problems came to light.

 

[Mal69]

... That figure presumably is the peak efficiency, when the motor is running at its designed speed, if the motor were stalled , for instance, it will still be consuming the same (or more ) electrical power but its mechanical power out is zero and all the electrical power appears as heat. If the motor is running at 50% of peak speed, it's efficiency is much less than optimum, .. but after what value depends on the type of technology employed

I looked into this, I think peak efficiency is 576watts for the Oxygen e-bike motor, I presume it will be working at peak on the hills, what I am not so sure about is whether it will get me up those hills.

I think crank drives are more for really fit people, the motor will
give u three times the power you give via pedal power. I don't know how hub drives work and how much I will have to pedal to get up those hills, I hope it's less pedal power than if I had bought a crank driven bike.

 

[Woosh]

I think peak efficiency is 576watts for the Oxygen e-bike

the mechanical output is less than that, because of electrical to mechanical conversion loss. If the motor is crawling up a steep hill, the efficiency of a hub motor can drop below 50%, most of your battery's output will be converted to heat.
With a crank drive, you can select the right gear to keep the motor running at better efficiency, you can increase the efficiency a fair bit (about 10%-15% on a 15% gradient to give you an idea) when climbing very steep hills.

 

[Mal69]

the mechanical output is less than that, because of electrical to mechanical conversion loss. If the motor is crawling up a steep hill, the efficiency of a hub motor can drop below 50%, most of your battery's output will be converted to heat.
With a crank drive, you can select the right gear to keep the motor running at better efficiency, you can increase the efficiency a fair bit (about 10%-15% on a 15% gradient to give you an idea) when climbing very steep hills.

Well that could be a worry on a sizzling hot day if a battery is also getting hot from the hills, I would still think for people like myself the hub motor requires less pedalling power on the hills, even if I am going up them slow, and crank drive is better suited for the fit people who can peddle more, is this thinking wrong? Will I feel the heat of the battery?

My hope is I will get fitter, i am not overweight but my legs are weaker than they used to be, I will cycle as best I can on the hilly sections but motor support hopefully helps me and I really don't want to be walking up the hills.

 

[Woosh]

if I am going up them slow, and crank drive is better suited for the fit people who can peddle more, is this thinking wrong? Will I feel the heat of the battery?

Bosch bikes don't have throttle, most Chinese crank drive bikes do, with the latter, you pedal as much (or as little) as you like. The benefit of gearing is still the same.
This is my best selling CD bike:
http://wooshbikes.co.uk/?santana-cd

 

[Danidl]

Well that could be a worry on a sizzling hot day if a battery is also getting hot from the hills, I would still think for people like myself the hub motor requires less pedalling power on the hills, even if I am going up them slow, and crank drive is better suited for the fit people who can peddle more, is this thinking wrong? Will I feel the heat of the battery?

My hope is I will get fitter, i am not overweight but my legs are weaker than they used to be, I will cycle as best I can on the hilly sections but motor support hopefully helps me and I really don't want to be walking up the hills.

... What Woosh was saying is that the majority of the energy from the battery is converted into heat, if the motor is struggling at low revs. But that e heat is being generated in the motor not the battery. The battery don't know whether the current it's producing is going into motion or thermal.

If the bike has a central drive helping to power the crank then it has the advantage of using the bikes gears to keep it in the higher efficiency sweet spot for that motor and it's efficiency can remain high. Now the maximum efficiency of the motors used in hubs is around 80% , and there is no reason why a crank motor is significantly better or worse than that... there is no magic sauce. but if the motor is going at half the designed speed it's efficiency could drop to 50%., Whereas the crank motor might be 15% to 20% more efficient as it is potentially still at its sweet spot.
In the Bosch active the maximum assistance given by the motor is 2.5 times the cyclists effort , so the total power going to the wheel is 3.5 times the cyclists effort. If you select the lowest gear and go at the lowest speed without wobbling, then the cyclists input is very very low.
As my much earlier posting and the calculator website shows going up a hill requires some effort going up a steep hill fast requires a lot of effort. Any motor including a high efficiency lower powered motor as in the Bosch or a lower efficiency much higher powered motor as in the hub unit will both get the job done

 

[Deleted member 4366]

I looked into this, I think peak efficiency is 576watts for the Oxygen e-bike motor, I presume it will be working at peak on the hills, what I am not so sure about is whether it will get me up those hills.

I think crank drives are more for really fit people, the motor will
give u three times the power you give via pedal power. I don't know how hub drives work and how much I will have to pedal to get up those hills, I hope it's less pedal power than if I had bought a crank driven bike.

Your Oxygen will be fine. You should set the power setting to the highest (sport?) using the "set" button on the LCD. Then use level 6 pedal assistance, which will give you the full power from the motor regardless of how hard you pedal.

 

[GLJoe]

I would still think for people like myself the hub motor requires less pedalling power on the hills, even if I am going up them slow, and crank drive is better suited for the fit people who can peddle more, is this thinking wrong?

Probably. You have to define what you consider 'peddling more' to be. Because it makes a difference whether you mean peddling hard (as in riding slow but putting in lots of leg muscle power), or peddling fast (just keeping a fairly high cadence up).
As long as a person can turn the pedals at a reasonable cadence, then doing this on a crank drive bike will usually be 'easier' on the rider (and more suitable for unfit people) than a similar powered hub drive when climbing steep hills.

 

[Mal69]

Probably. You have to define what you consider 'peddling more' to be. Because it makes a difference whether you mean peddling hard (as in riding slow but putting in lots of leg muscle power), or peddling fast (just keeping a fairly high cadence up).
As long as a person can turn the pedals at a reasonable cadence, then doing this on a crank drive bike will usually be 'easier' on the rider (and more suitable for unfit people) than a similar powered hub drive when climbing steep hills.

My definition is putting in less leg muscle power because I have not got it to give, so pedalling slow on hills and with much less effort, from everything I have read a crank drive would be a very difficult bike for me to get up hills.

Pedalling more and harder on hills is something I generally regard a much fitter person to do and surely a much fitter person will be able to cycle a crank drive better than I can, do I have this wrong, are crank drives without a throttle easier to ride up hills when you have weak legs?

I did consider the Wisper 905 Torque before deciding on the Oxygen, I see two posts above yours and they help explain things a little more.

 

[Mal69]

Bosch bikes don't have throttle, most Chinese crank drive bikes do, with the latter, you pedal as much (or as little) as you like. The benefit of gearing is still the same.
This is my best selling CD bike:
http://wooshbikes.co.uk/?santana-cd

The Woosh Zephyr looks very nice but would be better if you could change to a higher battery, 13Ah or higher would be nice, the Rio FB is nice too but I would personally change the tyres on it, good value for money.

 

[Woosh]

are crank drives without a throttle easier to ride up hills when you have weak legs?

no, bikes with throttle are easier to ride uphill. The Woosh Santana CD and Krieger are like that, you don't have to pedal if your legs are tired and they can still climb pretty steep hills (up to 15%) on throttle alone, albeit slowly.

The Woosh Zephyr looks very nice but would be better if you could change to a higher battery, 13Ah or higher would be nice, the Rio FB is nice too but I would personally change the tyres on it, good value for money.

The Zephyr is supplied with 12.5AH battery, that's about as much I can squeeze inside that frame this year. We'll get 14.5AH next year.

 

[lohr500]

Lots of interesting discussion in this post. As a 17 stone overweight 50+ newbie to this game, I have to say that I am absolutely delighted with my Bosch CX drive equipped Cube. I live in the Yorkshire Dales and believe me, there are some pretty steep hills. At no time have I been defeated in getting up any hill so far. Will it fly up at 15MPH if I pedal hard enough ? Probably. But most of the time I just pedal at a cadence that I am comfortable with, using the gears that Cube took the trouble to fit for me and trying to keep to the lowest power level to maximise range. In Sport or Turbo mode, even the steepest climbs do not take a lot of effort to get to the top of. Surely if anyone wants to climb hills at speed without any pedal input, then they should be looking at a motorbike or scooter.

 

[Woosh]

lohr500, you don't need the throttle but some of my customers need the rack to carry their oxygen bottle. Some have had recent heart, knee or hip operations.
They still want to enjoy riding their bikes, the throttle is the equalizer.

 

[lohr500]

Fair comment Woosh and I'm not knocking the no pedal/throttle option.
I was just responding to the original post which talked about hill climbing at speed with the Bosch system. If I wasn't fit enough to at least maintain some degree of cadence on the steep hills to keep the Bosch system providing assistance, then a throttle based alternative could be a solution.