New lightweight ebike project

Hi all,

I am looking for some advice for yourselves on an ebike project I’m looking to create. It’s for speeding up my 24mile cross country commute to work.

I am a fairly fit road cyclist, and have reached the limit of what I can do without significant extra effort / training. My commute currently takes me ~1.5hr on my road bike, but would like to bring that to ~1hr with some ‘assistance’.

I have run some simulations both on Steve Gribbles excellent site (https://www.gribble.org/cycling/power_v_speed.html) and through spreadsheets, and it looks achievable. I need to triple my mean power output to take 20-30 minutes off, while keeping total system efficiency as high as possible (aero drag, rolling resistance, weight). I want this to be stealth, and not be a massive power sink like many ebikes I see.

With a sensible road bike + Aero bars, I should be able to maintain 30mph on 0% with 540w wheel power (180w legs, 360w motor). With 80% efficiency from battery to wheel, rising power requirements to 450w.

The bike requires significantly higher power draw on the uphills (>720w at wheel) and 0w on downhills to keep within energy budget. Wasting energy on excessive high speed turbulence is not an option, but spending on potential energy is. I live in the UK with lots of smaller hills, so overheating shouldn’t be a problem.

John Wessels bike https://www.electricbike.com/kepler-super-commuter/ is what I almost exactly envision. It’s very nicely engineered, with the core principles that I aim for, and so I have stolen many ideas from this (Thanks John)

Overall plan:

Budget - £500 donor bike + £300 for: motor+controller+control panel

Donor bike - Will be the best road bike I can get on eBay for the price, definitely with discs, ally frame and Tri bars added on.

Hub motor - I have eventually decided on a geared hub motor, such as in Johns bike. I was originally CADing up a belt driven 90mm outrunner (with sprag clutch pressed over machined down ISO disc mounts on rear wheel), but have decided the loss in efficiency going to a pre assembled epicyclic drive is worth the savings in time and cost - not to mention looking more stealth.

Torque sensor - BB system is elegant and means the bike responds naturally. Seeing the Thun didn’t last (and I really don’t want a square taper!) is there a better modern alternative? Or a PAS system?

Control panel / Controller - Cycle analyst seems the most popular control panel, even if it is quite bulky and not the best looking (sorry!). Also, is there any update on the best controller to use in this instance, or is modifying the Lyens 6 FET or Vesc the best option? I am an engineer by trade, and am happy to modify electronics / code / generally tamper to get it to work!

Battery - I have access to high performance (VTC6) 18650 cells and was going to build them into an 80mm bottle in a very tightly packed 18s2p configuration with 30A Aliexpress BMS. This would go on a bottle holder and provide the 400Wh I think I’ll get away with.


Final questions:

Does this all generally sound like a sensible plan?
Whats the best geared motor? Nylon & sintered gears concern me, are there any with POM or better? Decent clutches?
Best controller / torque sensor / control panel combo?

Many thanks in advance everybody.

A Couple of Threads to Read
Here ... https://endless-sphere.com/forums/viewtopic.php?f=3&t=49691
and
Here ... https://endless-sphere.com/forums/viewtopic.php?f=3&t=76519

30 Mph is going to be hard to reach unless you are using 16s - 20s battery packs.
Every other item you want is doable , except for the higher speed.
If you could be happy with the motor and your legs together to get to about 25-27 mph it is
Quite within reach. ( I only get up to 20-24 mph using both the motor and as much as my legs/cardiovascular system can put into it )( 201 RPM Q100c CST Motor in a 700c wheel )

Check out what Chas58 has done:

https://endless-sphere.com/forums/viewtopic.php?f=3&t=49691

You have to be very careful using a small hub-motor for high speed because there's a much higher chance of damaging it at low speed. My feeling is that for 30 mph, you need to go up to a Q128C. The 36v 328 rpm one run at 48v would give you what you want, which makes a very simple installation, and it means that you can use a small 17A KT controller that has a very nice PAS system, so no need for heavy torque sensors and CAs.

https://bmsbattery.com/ebike-kit/768-q128c-135mm-500w-rear-driving-ebike-hub-motor-ebike-kit.html?search_query=q128c&results=2#/214-rpm-328/42-voltage-36v

http://www.pswpower.com/peng/iview.asp?KeyID=dtpic-2016-3F-39N8.50CQE

You need the LCD with the controller, so don't think it's optional.

That would work with a 13S3P battery if you use high discharge cells. Those controllers use current control, so you can use level 4 if you find the current a bit to high for your battery. They still give maximum speed on all levels, so you can adjust the power to what you want on the fly.

Very good advice above. Also, the builds of crossbreak and sunder can be looked at.
And of course, for inspiration, the fantastic builds of Nadar;

https://www.electricbike.com/mini-hub-motors/

Because of aero, and inefficiencies of electric stuff, you will be needing closer to 1000w to maintain a 30 mph cruise.

This will make your bike heavier than you planned, because the battery just doubled in size from what you expected. And it won't be all that stealth, generally.

I don't mean to dis your strength, Its just that keeping up 30 mph without a peloton to hide in is harder than you may realize. Its hard for the motor too is the catch 22.

Doing some simple math, if you put out 300w continuous yourself, which is outstanding, you still need another 700w to get there. So you will need about a 700-800 watt hour battery, to run at 700w for one hour. On a bad weather day, it will take more power, or you will need to slow down. So to have enough each day, I'd suggest a 48v 20 ah, 1000wh battery for your commute. Your battery will under deliver that much, on cold winter days.

If you lower your expectations to a 25 mph cruise, which is still pretty quick, you can carry a smaller battery, and would need only a motor able to cruise 25 mph. A much much easier goal, and more in line with your desire to have a bike that is more inconspicuous, and lighter. A simple 500w rated geared motor and 48v 15 ah battery would do then.

That's right. I just looked through the sums again. 80% efficiency is too optimistic. You won't get that, especially if you include say 5% for controller efficiency. When the motor drops to 50% of its max speed, efficiency would be about 60%, so I think that even 70% average might be optimistic, but using that, you get 514W needs to be provided by the battery for 1 hour, so you'd need at least 600Wh to avoid running out, which would mean 13S4P as a minimum using Samsung/Panasonic GA cells. If it were my project, I'd go up to 13S5P to be sure of having enough and to allow for a bit of battery degradation.

Another point to note is that the battery capacities quoted are at low currents. As the current goes up, the capacity goes down. My Panasonic 13S4P batteries (I have 3 the same) are nominally 556Wh, but my wattmeter says I get about 400Wh from them.

motomech said:

Very good advice above. Also, the builds of crossbreak and sunder can be looked at.
And of course, for inspiration, the fantastic builds of Nadar;

https://www.electricbike.com/mini-hub-motors/

Click to expand...

that stuff is just awesome. It inspired me! He would have a lot of fun with the light and powerful batteries of today!

For reference,
For a 24 mile commute,
I average about 15-16 mph pedaling (probably 18mph cruising speed) and that takes me about 93 minutes.
On the ebike, I average about 21mph (about 24-25 mph cruising speed) and that take me about 67 minutes.

At low power and high speed, a road bike makes a big difference. At 25mph, a road bike needs 450 watts, where a mountain bike needs 600 watts. That is just air resistance. My road tires save me about and additional 30 watts in rolling resistance.

Interesting thing about electric motors is that the power falls off as it goes faster (after it hits a current peak).

So, for my Q100, going from 24mph to 25mph requires an increase in 50 watts (air resistance) while the motor power falls off by 100 watts. So, I have to add 150 watts leg power to make that jump of just 1 mph. Food for thought.

As a comparison this is my ride



This is currently running a 36V 500W Bafang CST in the rear with 10S5P battery pack of about 16Ah. My commute is 14 miles each way with a good proportion being off road, forest tracks, fields, riverbanks ect, if the ground is dry I can do around 18MPH off road as it is very bumpy, in thick mud I average about 4MPH with unbroken wheel spin (awesome fun on the way to work), on road I cruise at about 22 MPH depending on gradient and wind direction, According to the computer I average between 17 and 19MPH, the 14 miles takes about 45 minutes, I seem to average 6 - 8Ah of battery consumption per leg of journey dependent on wind speed, this is with quite hard pedalling, about the same as you might do without the motor but the assistance gives about another 10MPH on top of what you would normally achieve.

The bike weighs in at about 29Kg (63Ib). The extra weight of the motor does course issues off road as it is difficult to keep the extra mass in contact with the ground at high speed over the very rough stuff, otherwise the set up works very well indeed. Make sure all wires are secure as the vibrations will course the wires to fracture otherwise. I have good suspension seat post so have the controller mounted to the seat to limit the vibrations, the battery cells are wrapped in quite a thick layer of foam again to limit vibration. If like me you will come off a few times if it gets really muddy so best arrange the kit in such a way that it cant get damaged when the bike is sliding along on its side including when the handlebars spin around 180 degrees. I use urban type tyres on a mountain bike frame, these are good on road but not so good off road.

I'm not sure where you are in the UK but certainly where I live the road surfaces are shocking, 30MPH on a hardtail will shake your teeth out, remember your bike will be quite a bit heavier with the motor and batteries and you will possibly have more of your body weight on the seat so potholes will be worse and its more difficult to 'bunny hop' over them, I can freewheel down some of the hills were I live at between 35 and 40MPH, much over 30 everything becomes a blur from the battering, the roads down south seem to be much better.

Another thing I have found worthwhile is to use down hill tubes in the tyres, these cut down substantially on the number of punctures, any thing that saves removing the back wheel/motor on a pitch black cold winters evening out in the sticks is very much worthwhile.

Up to fairy recently I have been using a 250W controller with the 500W motor, this didn't limit the top speed too much as by then the current consumption starts to drop off however hill climbing power was limited but not by that much. I found that this controller would work perfectly with the PAS sensor (also it is MUCH smaller and easier to hide), as soon as the pedals start to turn the controller would give full power. The pas just didn't seem to work with the 500W controller so I use a thumb throttle and a cruise control switch. Realistically 99% of the time I'm running on full throttle on road, off road you will definitely need the throttle else you will be cycling the motor on and off with the brakes to try to keep the speed down otherwise things can get a bit hairy!

I tend not to have too many controls as there is generally way too much going on to take my eyes off the road so have a couple of switches that I can operate with my thumbs without looking or taking my hands off the bars, on a pitch black winters evening I wouldn't be able to see them anyway. Left side is a high/low power switch, on the right is a cruise control switch which used to be a PAS on/off switch so the PAS wouldn't kick in if I was doing a slow tricky manoeuvre (negotiating bollards ect).

Having a battery on board also allows some decent lighting to match the increased speed.

Its certainly well worth doing, I use my bike every day rain or shine and love it!

RustyKipper said:

As a comparison this is my ride

Up to fairy recently I have been using a 250W controller with the 500W motor, this didn't limit the top speed too much as by then the current consumption starts to drop off however hill climbing power was limited but not by that much. I found that this controller would work perfectly with the PAS sensor (also it is MUCH smaller and easier to hide), as soon as the pedals start to turn the controller would give full power. The pas just didn't seem to work with the 500W controller so I use a thumb throttle and a cruise control switch. Realistically 99% of the time I'm running on full throttle on road, off road you will definitely need the throttle else you will be cycling the motor on and off with the brakes to try to keep the speed down otherwise things can get a bit hairy!

I tend not to have too many controls as there is generally way too much going on to take my eyes off the road so have a couple of switches that I can operate with my thumbs without looking or taking my hands off the bars, on a pitch black winters evening I wouldn't be able to see them anyway. Left side is a high/low power switch, on the right is a cruise control switch which used to be a PAS on/off switch so the PAS wouldn't kick in if I was doing a slow tricky manoeuvre (negotiating bollards ect).

Click to expand...

Put one of these on your Xmas list. I guarantee that you'll love it:

http://www.pswpower.com/peng/iview.asp?KeyID=dtpic-2016-3F-39N8.50CQE

or this one for a bit more power:

http://www.pswpower.com/peng/iview.asp?KeyID=dtpic-2016-3F-33C0.50CGS

30mph takes a massive increase in power. This calculator lets you figure it out. I punched in some numbers for a 30lb bike and a 175lb rider on level ground, and it's not pretty: Going 20mph already requires 215 W, but it's not linear so getting to 30mph costs you 500W!
The main reason is aerodynamics, so my inclination is to consider recumbents. And since you'll be on the bike a lot you'll appreciate the better comfort and lower fatigue.