Building a durable 40 MPH bike

[Teh Stork]

So, I'm building a bike for my own school. There are some challenges that needs to be dealt with, I hope you can help me with some input.

1. The bike needs to be unisex.

2. The motor needs to output 100Nm without saturating, up to 45km/h (37mph). I was initially thinking HS3540, but I don't like how the nipples connect to the rim. Maybe the crown?

3. Good front shock. Dampening suitable for city driving, while still fullfilling nr1.

4. Front brakes. V-brakes or disc brakes? I have only bad experiences with disc brakes so far, but then again - I haven't had a proper disc setup.

5. Rear brakes. Disc brakes mounted to the motor.

6. Gear system and pedals. I hope to go for lesser gears, and pedals - any things to think about wrt nr 1?

As for other spesifications:
Battery: 1500Whrs, ~50V. Triangular inframe pack.
Inverter: built by me, maximum of 110Arms phase currents.

I'm somewhat experienced with electronics, battery, inverters and motors - but not so much with bikes. Any tips is therefore appreciated

 

[ian.mich]

So, I'm building a bike for my own school. There are some challenges that needs to be dealt with, I hope you can help me with some input.

1. The bike needs to be unisex.

2. The motor needs to output 100Nm without saturating, up to 45km/h (37mph). I was initially thinking HS3540, but I don't like how the nipples connect to the rim. Maybe the crown?

3. Good front shock. Dampening suitable for city driving, while still fullfilling nr1.

4. Front brakes. V-brakes or disc brakes? I have only bad experiences with disc brakes so far, but then again - I haven't had a proper disc setup.

5. Rear brakes. Disc brakes mounted to the motor.

6. Gear system and pedals. I hope to go for lesser gears, and pedals - any things to think about wrt nr 1?

As for other spesifications:
Battery: 1500Whrs, ~50V. Triangular inframe pack.
Inverter: built by me, maximum of 110Arms phase currents.

I'm somewhat experienced with electronics, battery, inverters and motors - but not so much with bikes. Any tips is therefore appreciated

I would go for the HT35 crystalyte at 20S or 24S, would likely get the speed with better efficiency.

 

[Kingfish]

I like a good bit a math with my morning coffee to kickstart the day

Ready?

I want to know how much Power (W) is required, and with watts, I can calculate Current (I) and running time.

To concert Nm to Watts, I made a couple of presumptions. At 40 mph, I presumed you would use a tire better than standard bike. I've been looking to convert to 2.50-17 Moped, which is I believe 21.75 inches in diameter. We can calculate quickly in a spreadsheet the answer...

d = Diameter = 21.75 inches
r = Radius = 1/2 * d
c = Circumference = 2 * pi * r ->
c = 68.3", or 5.694 ft.

1 mile = 5280 ft
40 mph = 40 * mile / hour = 211200 ft/hr
rpm therefore = 211200 / 5.694 ft / 60 min = 618.2 rpm
f (Hz) = rpm / 60 -> 618.2 / 60 = 10.303

* NOTE: Doesn't matter if the units are Imperial or Metric; we're after Frequency (f) in Hz

P = Power (Watts)
t = Torque (Nm)
P = t * (2π * f), therefore
P = 100 * (2π * 10.303) = 6473.563 W

V = Volts
I = Current (Amps) = P/V ->
6473.563 / 50 = 129.5 A

Running Time = Battery Whr / Motor W
1500 Whr / 6473.563 W = about 23 minutes @ WOT.

That was fun! I might want a bigger battery though, and perhaps run higher voltage :wink:

Empty cup, KF

 

[Drunkskunk]

45kph is 27mph, not 37mph.

45kph/27mph is easily done by a 9C or clone motor, for several hundred $ less that the Clyte. The nipple angle is a non-issue with a single cross lace pattern in most wheel builds.

So the question is, do you want a 45kph bike, or a 40mph bike? Those two things will need radically different bikes.

 

[Tommy L]

I like a good bit a math with my morning coffee to kickstart the day

Ready?

I want to know how much Power (W) is required, and with watts, I can calculate Current (I) and running time.

To concert Nm to Watts, I made a couple of presumptions. At 40 mph, I presumed you would use a tire better than standard bike. I've been looking to convert to 2.50-17 Moped, which is I believe 21.75 inches in diameter. We can calculate quickly in a spreadsheet the answer...

d = Diameter = 21.75 inches
r = Radius = 1/2 * d
c = Circumference = 2 * pi * r ->
c = 68.3", or 5.694 ft.

1 mile = 5280 ft
40 mph = 40 * mile / hour = 211200 ft/hr
rpm therefore = 211200 / 5.694 ft / 60 min = 618.2 rpm
f (Hz) = rpm / 60 -> 618.2 / 60 = 10.303

* NOTE: Doesn't matter if the units are Imperial or Metric; we're after Frequency (f) in Hz

P = Power (Watts)
t = Torque (Nm)
P = t * (2π * f), therefore
P = 100 * (2π * 10.303) = 6473.563 W

V = Volts
I = Current (Amps) = P/V ->
6473.563 / 50 = 129.5 A

Running Time = Battery Whr / Motor W
1500 Whr / 6473.563 W = about 23 minutes @ WOT.

That was fun! I might want a bigger battery though, and perhaps run higher voltage :wink:

Empty cup, KF

Hi KF!

At WOT at full RPM there usually isn't much wattage. I can pull 5-7,000 watts off the line, but once
up to speed that drops to 2,000 to 2,500 watts at WOT 78kph and 600-1200 watts at 54kph(wind/hill dependent) and pulling 6,473.563 watts from a 1500whr pack will only yield .23 of an hour, and .23
of 60min is 13 or 14 min at 100% DOD. (I didn't check all of the math. I'm good at estimating and
I quickly noticed that 1500 whrs is 3,000 in 1/2 hour and 6,000 for 15min)
But you are still my Hero KF! I admire your work!

Also 45kph is only 27.96mph not 37mph.

Tommy L sends.....

 

[LSBW]

Building a durable 40 MPH bike

Don't we all?

 

[Dauntless]

Dang, but where's the formula? I wanted to turn my C in Trigonometry loose on it.

 

[Teh Stork]

Thank you for all the answers.

I've already got a spreadsheet for estimating rotational force given torque and speed. Much of the same you've calculated there KF. Nice calculations, but you forgot system efficiency going from rotational power to battery power. I expect my system to be about 75% efficient at "WOT" giving a load that is about 5,3kW for 4kW mechanical.

To clarify (as i messed up in first post), I want a motor that is capable of producing 100Nm up to 45km/h - is a 9C capable of this? I want the bike to be able to do 60km/h (~40mph). I do have access to Field weakening and other stuff, so hitting 60 km/h in ebike.ca's simulator is no must.

For safety, voltage will not be upped to 20-24s - and so it is a maximum of 50V that is avatible. Higher phase amps will need to make up for it. I'm hesitant to leave 26" wheels, but maybe I have to.

The voltage limitation is what limits motor choices. I have a 2,7kW HS3540 setup at 75V now, ideally I'd clone this

 

[Kingfish]

@ Tommy L - awe shucks <blush, kick pebble> :wink:

Well, the thing is that - yes you need a lot of power on Start, but you also need it to reach speed, and the power required is roughly inversely proportional to the speed... sort of like the equation

E = mc^2

As it is, I was hooked when the OP suggested he wanted 100 Nm for Torque - which is quite a bit of raw power. On my present 2WD (9C 2806 x 2) I am running about 3.5 hp (total) to reach 40 mph, but I can't hold that speed for any length of time on the Commuter pack (15S6P @ 1912Wh).

I've been using 100 Nm (per wheel) as the design benchmark for my next ride, a 2WD eMoto - so I had the numbers partly in my tiny head from doing the calcs.

Using my present system to extrapolate the weight of batteries:
Given 1500 Whr,
5S1P LiPo weighs 1.27 lbs./578 g. = 106.25 Whr
For the 15S6P Commuter, that's 22.86 lb.s/10.4 kg -> not that bad.

To run for one hour:
6473.563 W / 106.26 = about 61 batteries (however arranged). Probably 18, 20 or 24S would make sense from a voltage perspective.
=> 61 * 1.27 = 77.5 lb.s/35.3 kg

That's about 4/5ths of the entire pack I used for my road trip to California.
I think 100 Nm is overkill - unless we're hill climbing Pike's Peak @ 40 mph

Even then, I'd want a bigger battery. KF

 

[Tommy L]

Also, look at JOHN IN CR. He has 6 phase hubs with twin controllers. Just might
be the ticket! :wink:


Tommy L Sends.....

 

[Chalo]

1. The bike needs to be unisex.

What do you mean by this? Bikes are inherently unisex. Do you mean you need a step-through or deep step-through frame? If so, don't make it a 40mph e-bike. Step-through frames are just not that strong.

If you want rear suspension to accommodate routine 40mph speeds, you may not have a choice of any step-through frames. If the usual speeds are below 30mph, then suspension isn't necessary for riding on graded surfaces.

I suggest a mountain bike frame with a strongly sloping top tube, for generous standover clearance with good frame integrity.

 

[bobc]

my bike is a cheap, old, no- suspension mountain bike. It does 20mph and uses about 25Wh per mile. It is hanging together because it only does 20, any more & I would need full suspension. If your local roads are all billiard table smooth you might be OK ;^)
At these speeds power use on the bike is pretty much all aero. If I geared my bike for 40mph I would use 8x as much power, and 4x as much energy per mile (100Wh/mile)
The best basis for high speed ebikes like this are the "downhill bikes", they are tough enough & have full suspension. Quite dear though. Cheap full sus bikes are typically not damped at all &, well, cheap - expect a fair amount of maintenance. The damping is arguably not a big deal on an e-bike (bike damping is tricky because of "bobbing" when pedalling - not an issue when electric....)
Should be a fun project. Chalo is right about the step-though frames - remember 40mph is serious speed - you reach that speed falling 53ft off a cliff....
Oh yeah - back brakes are less important on a bike, really just there as backup; max braking on a bike, you are on the verge of doing a stoppy & there is no weight on the back wheel - touch the back brake & you're off! So I wouldn't worry overmuch about rear disc being an absolute necessity.

 

[Teh Stork]

As it is, I was hooked when the OP suggested he wanted 100 Nm for Torque - which is quite a bit of raw power. On my present 2WD (9C 2806 x 2) I am running about 3.5 hp (total) to reach 40 mph, but I can't hold that speed for any length of time on the Commuter pack (15S6P @ 1912Wh).

I've been using 100 Nm (per wheel) as the design benchmark for my next ride, a 2WD eMoto - so I had the numbers partly in my tiny head from doing the calcs.

I think 100 Nm is overkill - unless we're hill climbing Pike's Peak @ 40 mph
KF

Overkill is just the thing I'm aiming for, crazy hill climbing abillity is one of the focus areas. Acceleration from zero to 45 should be a bit over 4 seconds, that's very fast.

1. The bike needs to be unisex.

What do you mean by this? Bikes are inherently unisex. Do you mean you need a step-through or deep step-through frame? If so, don't make it a 40mph e-bike. Step-through frames are just not that strong.

If you want rear suspension to accommodate routine 40mph speeds, you may not have a choice of any step-through frames. If the usual speeds are below 30mph, then suspension isn't necessary for riding on graded surfaces.

I suggest a mountain bike frame with a strongly sloping top tube, for generous standover clearance with good frame integrity.

I've had trouble with women and low males (I'm quite average myself at 177cm) not being able to ride my current bike since it has a high top tube. I will not go with a step through frame no, probably something along the lines of this:

Enough room for the battery pack will need to be balanced with top tube "aggressiveness".

 

[cal3thousand]

Full suspension frames often have a Y shape with a sloped top tube, which is easier to mount/dismount. I would look into that option since you are building a 40MPH bike.

 

[leffex]

1. The bike needs to be unisex.

As for other spesifications:
Battery: 1500Whrs, ~50V. Triangular inframe pack.
Inverter: built by me, maximum of 110Arms phase currents.

School stuff you need to free some time. Go get a complete DH bike, stable at 40 no problem. Then 3-6 and 1 is fixed as a motorcycle is unisex, as a motorcross - so a dh bike. Then you can focus on electric, performance and stability stuff.

You want to build something that generates alot of heat, hub motor will not like the amps that youll put into it. 50v and hs3525 wont do it ....or maybe but not so good speed. I use hs3540 but it can get hot using it at high wattage. Ok at 2000 continues and 2-5 minute 4.5kw input but not more than 15 minutes continues at max(85v 45a)

Good luck

 

[Drunkskunk]

You are looking at several major problems to get what you want.

First of all, 50volts peak means a 44.4v battery at the most. There are no hub motors that will hit 60kph at that voltage. That would be an extremely low wind motor. Like, a 1 turn motor perhaps. That would fry most controllers in existence. You are simply going to need more voltage. the now extinct 5302 could hit 55kph at that power level, but they did eat controllers when put into 26" wheels.

Second, 100NM at 40KPH isn't going to happen with a bike hub motor. An HS3540 on a 44.4v battery and a 100 amp controller will make around 100nm at start up, but Electric motors drop torque as the rpm increases. At 40kph, it's only producing 25nm. You would need a motor capable of roughly over 400NM at the start to get your target, and that kind of power would wad up a bicycle frame into a pretzel shaped pocket sized object.

 

[voicecoils]

If you want rear suspension to accommodate routine 40mph speeds, you may not have a choice of any step-through frames. If the usual speeds are below 30mph, then suspension isn't necessary for riding on graded surfaces.

I suggest a mountain bike frame with a strongly sloping top tube, for generous standover clearance with good frame integrity.

At the risk of beating a dead horse (repeatedly), here's 2 examples of bikes that meet the criteria of "durable". They were actually designed to travel in the 40MPH speed range. Both go higher (50-55mph) and will comfortably sit on 40mph with brakes, suspension and frame strength to suit. One has new world tech, one old world tech. Both are reliable and bicycle proportioned with low stand over height and approximately step through frames. Trouble is they're mopeds, not bicycles.

Honda CT110

Sachs Madass 125

I'll take the one with disk brakes, Chalo can have the drum brake'd bike. Both work fine though

 

[Chalo]

Trouble is they're mopeds, not bicycles.

As a result, they weigh three times as much as bicycles of comparable structural soundness. It is an engineering choice that can be made, but it's generally contrary to our energy-efficient methods and ethics.

 

[DAND214]

I read all the post and I still don't know if you want 45kph or 40mph.

Climbing hills and doing 40mph is not normal for any E-bike.

So is it 40 MPH or 45 KPM?

My MAC 8t on 15s lipo is short of 40MPH but does climb hills well. Not long ones just stp shot ones or long overpasses.

Dan

 

[Teh Stork]

You are looking at several major problems to get what you want.

First of all, 50volts peak means a 44.4v battery at the most. There are no hub motors that will hit 60kph at that voltage. That would be an extremely low wind motor. Like, a 1 turn motor perhaps. That would fry most controllers in existence. You are simply going to need more voltage. the now extinct 5302 could hit 55kph at that power level, but they did eat controllers when put into 26" wheels.

Second, 100NM at 40KPH isn't going to happen with a bike hub motor. An HS3540 on a 44.4v battery and a 100 amp controller will make around 100nm at start up, but Electric motors drop torque as the rpm increases. At 40kph, it's only producing 25nm. You would need a motor capable of roughly over 400NM at the start to get your target, and that kind of power would wad up a bicycle frame into a pretzel shaped pocket sized object.

I realize this. Just to clarify, I was going with a 58,8V peak battery. With field weakening, motor speed can be increased - be it at a efficiency loss. I want the bike to be built for 60kph, so it will stand up to endless abuse at 45 kph.

I do not need a motor capable of 400Nm. I think Justins simulator has got you fooled here. My controller regulate phase amps and don't work the same way as cheap chinese controllers. Electric motors are mainly limited by saturation point (phase amps). Torque doesn't drop until bEMF+voltage drop caused by phase amps = supply voltage.

Students will use this bike as a research platform for energy storage systems, advanced motor systems and embedded microcontroller systems. I'm sorry for all the confusion, it's definitely not a normal bike project.

 

[hjns]

To clarify (as i messed up in first post), I want a motor that is capable of producing 100Nm up to 45km/h - is a 9C capable of this? I want the bike to be able to do 60km/h (~40mph). I do have access to Field weakening and other stuff, so hitting 60 km/h in ebike.ca's simulator is no must.

For safety, voltage will not be upped to 20-24s - and so it is a maximum of 50V that is avatible. Higher phase amps will need to make up for it. I'm hesitant to leave 26" wheels, but maybe I have to.

The voltage limitation is what limits motor choices. I have a 2,7kW HS3540 setup at 75V now, ideally I'd clone this

I read and re-read this thread, and it is still not clear to me what you want. You say a max of 50V for safety reasons, and you building a controller with 100Amp phase current max. To me, that sounds like a really weak motor - controller combi. With my "cheap chinese controller" which is an 18FET from Lyen, I run 84V (20S Lipo) with 100A battery current (210A phase current), resulting in max power of 8kW. I run this on my Cromotor, and my Cromotor will give me 250Nm at start and 100Nm at 40kmh. Max speed is 75kmh / 45mph.

In summer (25oC ambient) I will get the motor to 120oC within 15 minutes of hard driving, and the only thing that saves me from burning it is the CA turning down the current automatically.

I really doubt that you will get to those deliverables with any 50V configuration, even if you up the current to 300A. Apart from 50V 300A being quite deadly (so much for the safety aspect), assuming your controller survives, you will just burn up the motor under load...

 

[Dauntless]

Trouble is they're mopeds, not bicycles.

As a result, they weigh three times as much as bicycles of comparable structural soundness. It is an engineering choice that can be made, but it's generally contrary to our energy-efficient methods and ethics.

So now what bikes do you suggest in that category? All expensive, or are there cheaper that would hold up. Those Honda CT's and the Madass as solid and not so heavy really. Bikes will mostly have trouble matching that.

 

[full-throttle]

At the risk of beating a dead horse (repeatedly), here's 2 examples of bikes that meet the criteria of "durable"

Beating anti-anything-that-looks-like-fun troll wearing a dead cat on his head would be more appropriate :lol: although he seems to enjoy being beaten up..

Voicecoils, your opinion is one of most valuable on this forum. There are only a handful of people that can claim to be: a full time e-bike mechanic, an engineer, both road and Mt bike enthusiast, motorbike rider and have: completed multi-day e-bike tours and supported e-moto race bike. I prob missed a few. So pay attention kids.

 

[Chalo]

...they [mopeds] weigh three times as much as bicycles of comparable structural soundness. It is an engineering choice that can be made, but it's generally contrary to our energy-efficient methods and ethics.

So now what bikes do you suggest in that category? All expensive, or are there cheaper that would hold up. Those Honda CT's and the Madass as solid and not so heavy really. Bikes will mostly have trouble matching that.

My essential point is that the diamond frame is a truss that's very efficient and self-reinforcing. When you build a bike with other than a diamond frame, you have to use a lot more material to provide the same strength. A large diameter boom frame like the MadAss is probably the next best thing to a diamond, though. It forsakes the efficiency of a truss, but exploits the efficiency of a large diameter tube.

For structural integrity, the more basic the bike, the better. Large diameter straight tubes in a totally boring triangulated format are what you want. Here's one example. Simple bikes like this should be cheap, and they should be the default type. But buyers have been addled by marketing-driven gimmicks, visual branding,and unhelpful features, so good uncompromised basic bikes are getting scarcer.

You can't go far wrong with a Surly Troll or Long Haul Trucker frame, but I think there should be cheaper, stronger, and more basic frames along similar lines. It seems like all the really no-nonsense and inexpensive frames I see these days are for fixed gear bikes, with no provisions for derailleurs or luggage, and inadequate tire clearance. That's better than nothing, but it's not really suitable to become a good e-bike or utility bike. For that, you need more than just a strong, stiff frame. You need room for big tires, and adequate places to bolt things on-- like racks, linear-pull brakes, and rear derailleurs. Ideally, the frame is made of steel so you can easily attach your own enhancements as desired.

 

[Lebowski]

About the unisex: how about something like:
http://www.cube.eu/en/tour/travel/delhi-rf-lady/
Kind of a cross between step-through and a top tube

How about one of these:
http://www.bemoto.ch/vespaverde/video.html
A Vespa will definitively be safe and have the brakes to run at the speeds you want. They are unisex.
Standard they have a 2-stroke integrated with the swingarm. What this guy does is he replaces
the swingarm for one that has an (agni ?) electric motor.