Redbridge Testing - Hubs v Cranks

[10mph]

I took advantage of the Ebike testing day at Redbridge Cycle Track on Sunday, to compare the performance on my crank driven Kalkhoff Agattu with that of some of the bikes with rear hub motors. I was particularly interested to see how the hub motored bikes coped with the short 10.5% hill.

Here is the circuit with plots of the tracks recorded by my GPS.

The underlying map with the 0.5 m interval contours I took from the planning application for the site. They obviously built parts of the track in slightly different positions to that shown in the planning application, but I assume they did not move a lot of hillside so that the contours remain accurate.

The GPS tracks show a lateral scatter of about 5m. I actually rode much tighter set of paths than that were probably located over 1 to 2 m laterally. There is of course drift in the recorded GPS position by up to 5m as the satellite position and the ionosphere vary over timescales of a few minutes, and this accounts for the width of the bike tracks

I rode 8 large laps as follows:

1. My Kalkhoff Agattu -3 speed, in max assist (crank driven)
2. My Kalkhoff Agattu -3 speed, in min assist (crank driven)
3. Easy Motion Volt (folder - crank driven)
4. Kudos Tourer Deore-9 (rear hub motor)
5. Kudos Secret (folder) (rear hub motor)
6. Easy Motion BNeo City (rear hub motor)
7. Wisper 905SE (rear hub motor)
8. My Kalkhoff Agattu -3 speed, in max assist (crank driven)

Except for lap 2 on my Kalkhoff (which was as a result much slower on the hill), I used maximum assistance settings for each bike, and tried to judge the optimum gear setting to provide maximum extra propulsion from my pedalling.

Somewhat to my surprise there was very little difference in performance of the bikes on the steepest part of the hill - all except one managing around 10.5 to 11 mph. Of course I put in quite a bit of pedal power to try and keep the speed up, and this does make it impossible to do an exact comparison of the bikes. I only achieved 8.3 mph on the Kudos Tourer Deore-9. I don't think I was pedalling less hard or in the wrong gear so I suspect that the hill climbing of this bike may be slightly down on the others. I did only a single ride and I would really need further repeats to confirm this conclusion. Here is a plot of the GPS track when riding the Kudos Tourer Deore-9 with my Kalkhoff Agattu track for comparison. The red dots are the GPS position from my Garmin Etrex which I set to record every 2 seconds.

Comments on Folders
This was my first experience perched on folders with tiny 20 inch wheels. I noticed the steering seemed more "twitchy", but perhaps that is something one gets used to. I also noticed that when pedalling hard on the hills, the long front stems on both folders flexed - I wonder how long they would last if ridden hard. The two folders did not seem fast, but perhaps that was because they were set up for a high cadence, which does not suit me. What really surprised me when I went home and calculated their hill speed was that it was also 10.5 to 11 mph. During the ride I had been convinced that the folders felt slower.

The surface of the cycle track is very smooth, so I did not find out how the suspension of the folders would cope with a more normal rough and potholed road. There are off-road tracks at Redbridge, but I did not try them, since I was concentrating on hill climbing.

 

[piotrmacheta]

So do you prefer hub drive or crank drive overall?

 

[flecc]

My experience of owning both is that there's little difference with gradients at around 10%. Below 10% the hub motor bikes mostly tend to be a bit faster climbing, but once gradients get to 14% or more, crank drive through the gears starts to come into it's own, the exact point depending on the rider capabilities of course.

 

[Blew it]

Just to note, two of the hub-motored machines tested have wide differences in the maximum amps demand limited by the motor controllers.

The Wisper 905se has a 16.5 amp motor controller.

If my memory serves correctly, all Kudos machines are fitted with comparatively modest 12 amp motor controllers.

 

[eddieo]

Good stuff! 20 inch wheel folders do indeed feel twitchy and easy to fall off initally util you get used to the steering...but that takes a very short time..

what folders did you try as we are looking for one

 

[NRG]

Just to note, two of the hub-motored machines tested have wide differences in the maximum amps demand limited by the motor controllers.

The Wisper 905se has a 16.5 amp motor controller.

If my memory serves correctly, all Kudos machines are fitted with comparatively modest 12 amp motor controllers.

Yes, I think David alluded to that a while back, 12amps is about the maximum you can draw from a 36v system to get within the 250w +10% mark...

 

[10mph]

Thanks all for interesting comments and questions.

So do you prefer hub drive or crank drive overall?

I am still a fan of my Kalkhoff with the 24V Panasonic crank motor. I know it is efficient and I get good range. I would like to see an efficiency/range comparison done between hubs and cranks - but that would need a lot of testing.

I am not a fan of having one hand clasped to a throttle as seemed needed on some of the hub motor systems without a proportional torque sensing control - but that is a criticism of the control system rather than the hub motor as such. I like to be able to give prolonged signals with either arm. Also I did not like the way some of the hub control system carried on pushing for about a second after the the throttle was released- but I suppose you might learn to live with that.

But overall I must say that I was impressed by the hill speed of the hub bikes, but I am sure Flecc hits the nail on the head when he says,

My experience of owning both is that there's little difference with gradients at around 10%. Below 10% the hub motor bikes mostly tend to be a bit faster climbing, but once gradients get to 14% or more, crank drive through the gears starts to come into it's own, the exact point depending on the rider capabilities of course.

Blewit and NRG:
You are right that peak input power from the battery will be important. Most of these systems were 36V. I note that 16amps at 36V is 576W, a long way above the 250W motor rating. Does the Wisper eat battery Wh when used on maximum assist, or does it just get you up the 10% hills with reasonable efficiency? I don't know without measuring consumption.

I heard a salesman using the 36V system on his bike as a selling point to a customer. I refrained from pointing out that with thicker wires a 24V and the appropriate number of turns on the winding a 24 V system can also be made efficient. The other thing is that I regard 36V systems as being well over half-lethal if with wet hands on the handle bars one were to get a shock from hand to hand

The usual safe working voltage threshold for working on batteries is 50 volts DC.

from Shocking Batteries - Electric Shocks from Batteries

Eddieo: I was interested to try out a folder for use when visiting central London, thinking it could easily be transported by train then stored securely inside certain destinations. However, the weight around 20kg would be a struggle with a lot of manhandling on steps etc. Perhaps I will try a much lighter, non-electric one. After all central London is pretty flat - perhaps I would not need electric assist for occasional rides through parks etc avoiding the tube.

 

[flecc]

I note that 16amps at 36V is 576W, a long way above the 250W motor rating.

Of course this is gross power, the law refers to motor power output which will probably be around 75 to 85% of that gross figure. Still well above the limit though, but the eZee controller is currently 20 amp on bikes marketed as 250 watt. My early eZee controllers were claimed to be 30 amp, and they certainly deliver a little over 27 amps with nominal 37 volt lithium batteries, totalling just over 1000 watts gross.

 

[NRG]

Yes, as flecc says thats gross, the motor in the case of the Wisper is probably close to 350w after losses, the Kudos just over 250w...at 20amps the motor will be closer to 450w, at 27amps around 590w!!!

48vDC is the considered safe maximum, its mentioned in the EN document as is a voltage used by many telcos for instance with battery operated equipment...

In theory 36v is better than 24v, the losses are less and you don't need a bigger more powerful controller or a higher Ah battery...at the powers we use though the losses aren't that great its just the size of battery that probably works against it...

 

[Wisper Bikes]

Hi 10MPH,

I didn't think we were represented at Redbridge this year? I wish you could also have tested the new SEL which in tests will pull the same rider twice as far up a steep incline as the SE.

The Wisper SE bikes are "Rated" at 250W and have been certified as so in the EN15194 tests conducted by Swiss based SGS laboratories. However when the demand is there the max power is indeed just short of 600W.

In answer to the question about eating up the power when on max assist, yes it certainly does drain the battery, hence us using good 16Ah cells. Any bigger we find we start to lose reliability and any smaller means the length of time the battery/motor combination performs at or about peak performance during each discharge is too short.

Recently we have limited the maximum power setting in the LED handle bar controller to about 80% of actual max power, to obtain 100% a rider also needs to open the throttle fully. This way the extra 20% is on demand only through the throttle so when the bike is cruising in Pedelec mode only the battery charge life is extended. The difference in range between pedelec only at max power and riding with the throttle constantly open fully is about 30%.

All the best

David

 

[Davanti]

Recently we have limited the maximum power setting in the LED handle bar controller to about 80% of actual max power, to obtain 100% a rider also needs to open the throttle fully. This way the extra 20% is on demand only through the throttle so when the bike is cruising in Pedelec mode only the battery charge life is extended. The difference in range between pedelec only at max power and riding with the throttle constantly open fully is about 30%.

All the best

David

Hi David ... I'm still getting my head around this (but I think I'm getting there!). When is 'recently'? What I'm really asking is, is my SEL pre or post this change to max power setting in the LED handle bar controller?

Best Wishes

Don

 

[eddieo]

"The difference in range between pedelec only at max power and riding with the throttle constantly open fully is about 30%"

And why I dont use throttle at all on the DaaHub what with the smaller battery.....

 

[Wisper Bikes]

Hi David ... I'm still getting my head around this (but I think I'm getting there!). When is 'recently'? What I'm really asking is, is my SEL pre or post this change to max power setting in the LED handle bar controller?

Best Wishes

Don

Hi Don, without knowing your frame number I couldn't be certain, however if you ride along the road on full assist and then open the throttle wide, you will certainly notice a difference if the bike is set up this way. I would imagine it would be though.

All the best

David

 

[Wisper Bikes]

"The difference in range between pedelec only at max power and riding with the throttle constantly open fully is about 30%"

And why I dont use throttle at all on the DaaHub what with the smaller battery.....

Very wise Eddie, it would reduce range significantly on the 36V 9Ah DaaHub battery.

 

[10mph]

Hi 10MPH,
I didn't think we were represented at Redbridge this year? I wish you could also have tested the new SEL which in tests will pull the same rider twice as far up a steep incline as the SE.

e-bikes direct of Bodiam, Sussex had a range of bikes of different makes on show. I wanted to experience riding a Wisper which is always seems to have a good reputation on this forum. I did ask about the SEL and was told about more gadgets but not about the extra power which you mention.Twice as far on a steep hill does sound that it would need extraordinary amount of power.

As I mentioned in my OP all the bikes except one lifted me through 5 m in 10 seconds. Taking the weight of bike plus me as 115Kg, once can calculate the power to be
115 x 9.81 x 5 / 10 = 564 watts.
This is output power from the bike's motor which reaches the road. It is just the gravitational potential increase, I have not bothered to estimate and add the few watts which will be needed to overcome air resistance at 5 m/s, or indeed the tyre's rolling resistance. So this power which I calculate from my ride matches very well what you say,

The Wisper SE bikes are "Rated" at 250W and have been certified as so in the EN15194 tests conducted by Swiss based SGS laboratories. However when the demand is there the max power is indeed just short of 600W.

So what does the SEL output if it goes twice as far on steep hills? 1200 watts? In the EN15194 tests conducted by Swiss based SGS laboratories is it also rated as a 250 watt motor for continuous operation and therefore legal in the UK.

Or did you mean range rather than power? So is it just a bigger battery on the SEL?

 

[eddieo]

I'm exactly the same weight as you so will watch your reviews with interest!lol

SEL has 16.5 Ah battery, same as other top spec Wisper bikes. I would have one except to heavy for my camper rack. My Daahub has a similar Dapush system, but lighter bike. It used to do 23 mph (derestricted by me) before controller change, now 20-21 mph. So I can fully understand where David is coming from.....

A few members on here have the bike.

 

[Davanti]

Hi Don, without knowing your frame number I couldn't be certain, however if you ride along the road on full assist and then open the throttle wide, you will certainly notice a difference if the bike is set up this way. I would imagine it would be though.

All the best

David

Thanks David ... I'll will test this out tomorrow after I return from my First Service appointment slot with You Know Who ...

Best Wishes

Don

 

[10mph]

Correcting a bad mistake

In my post yesterday evening I wrote

....all the bikes except one lifted me through 5 m in 10 seconds. Taking the weight of bike plus me as 115Kg, once can calculate the power to be
115 x 9.81 x 5 / 10 = 564 watts.
This is output power from the bike's motor which reaches the road. .....

I should have said 564 Watts is the power reaching the road from the combined power of the motor and my own legs which were pedalling hard on the hill. I only realised this bad mistake reading it over before bed last night.

Measuring or estimating the rider input is a major problem. For measuring motor power, it would have been much more informative to have done additional hill climbs under throttle only for those bikes such as the Wisper which can be driven solely with the throttle with the pedals stationary or tuning lightly without force.

On the Redbridge test day I was preoccupied with comparing hill climbing performance of a range of bikes with my Kalkhoff which uses the Panasonic motor control system based on a proportional torque sensor. The motor output is governed by the rider torque and you can't get any motor output without providing some of your own pedal power. I attempted a fair comparison with my Kalkhoff, but I should have done additional circuits with throttle only to provide exact data on the hill climbing power of the motor alone.

Can we have another Redbridge test day - or an event on a similar hill course where we can do an improved set of tests?

I can make a rough estimate of my rider pedalling power on the steep section of the hill as follows:

My first ride of the hill was with my Kalkhoff Agattu in maximum assist and it took 10s to climb 5m as shown in the diagram in my first post. The corresponds to 564 Watts motor + rider into the road.
My second hill ride was with my Kalkhoff Agattu in minimum assist. I have just checked my GPS track - I took exactly 20 seconds for the same 5m climb. so that is a total power into the road of 282 Watts.

In minimum assist Kalkhoff Panasonic (2010/11 model) is said to provide a motor power of 50% of the rider power. This would make the rider power 188 Watts and motor power 94 Watts in order to give 282 Watts total.

In maximum assist Kalkhoff Panasonic (2010/11 model) is said to provide a motor power of 200% of the rider power. This would make the rider power 188 watts and motor power 376 watts in order to give 564 Watts total.

188 watts from me is rather more than I can provide into an unassisted bike over two or three minutes on a long steep hill. However the steep part of Redbridge hill was very short -only around 48 m long for the 5m rise. So I think I might reasonably be expected to be capable of a 10 to 20 s burst of 188 Watts.

My revised conclusion is that all the bike motors except the one which was slower are capable of providing about 376 Watts into the road on a 10.5% hill.

 

[flecc]

.
I think I might reasonably be expected to be capable of a 10 to 20 s burst of 188 Watts.

I'm sure that is true, my own similar tests in my seventies using a Panasonic system on a 14% hill showed that for very short bursts of a few seconds I could exceed 300 watts, but that quickly collapsed when attempting to sustain it. My comfortable sustained power was nearer a third of that.

 

[Wisper Bikes]

I will be pleased to give you all a little more information later today or tomorrow morning, I have my tech team in Kunshan working on afull answer. At the moment Dapu are being a little secretive, but they say it is a combination of higher revs and lower gearing which gives more torque at lower speeds which is when you need the extra "umph" for hill climbing.

Being of "simple mind" I simply understand that when I pedal up a hill on the sel it feels more powerful than any other 250W rated bike I have ever ridden. Yes it does have higher specs on the bike equipment such as hollow tech crank axle and hydraulic brakes etc but the main difference is the motor and the weight of the cables and connectors delivering the power to the motor. (Sorry for the plug! I can't help it sometimes)

All the best

David