Hill climb

[eP]

It makes a big difference on how much your bike weighs. I've used numbers like:

185 lb rider
100 lb bike

And with numbers like that you get something like this. (see charts and numbers)

I see yours charts and numbers are wrong again

I see you assume 40A limit for controller.
So after conversion to 75A (for 74Nm tork) ( even at no loses ) the motor voltage will drop to less than 40V from 74V . At 400 mohms of winding resistance the heat dissipation will be 2250 W around (30V*75A).
So only less than 10 V could be changed for mechanical power, so you get less than 100 rpm.

For calcs. above i've used crystalyte specs data.
http://www.crystalyte.com/x5specs.htm

So the real eff. will be between 20-24% i'm sure at conditions which you assume.

In the "real world" with that much weight you would not get up to your "peak power" and so you are stuck down at lower speeds. So weight is critical at that steepness. I'm only seeing 1276 Watts at 43% and only a 12 mph top speed. So depending on the ACTUAL weight things could be very different. I doubt that on a 17% slope you will attain anything close to your "peak power"... you will "bog down" at low rpms.... (I'm very suspicious of a real world 17% slope... most roads are not allowed to be built that steep because cars cannot make it up them... Streets of San Francisco maybe?)

You have to keep in mind that your "peak power" at 74 Volts (assuming Lithium pack) happens at 48.7 mph!

Sorry but You are wrong as usual :wink:
48.7 mph it is the highest speed at 74V at no load (idle).
The "peak power" speed is half of that around at 60% eff.
At lower speed and full throttle you get worse eff. especially at 8 mph for 100 rpm around.

My point is: why we try add more input power and use heavy and costly big batteries when we get so bad efficiency ?
Much better solution is add twice more fat motor windings and your eff will be much higher.
At 200 mohms resistance the same work can be done at the same 40A limit but at 48V voltage.
You get much less heat and simple controler with low voltage (60v or 55v) FETs (with better params ) on board.

The one obstacle is :there is no room for more fat wires in that motor's case i'm sure.

So maybe the better idea is start project own more efficient motor (at heavy load) than spending money for big batteries and expensive controlers.

Regards

 

[Lowell]

The Xlyte website specs appear to be wrong.

 

[eP]

The Xlyte website specs appear to be wrong.

How much wrong ?
What is the stall current for x5304 at 36V ?
Is it more than 90 A ?

 

[safe]

Wow, I didn't know they made controllers for the 5304 that allowed more than 40 amps.

My mistake!

Here's the bike at 75 amps... yep, your original numbers look pretty good after all. (I never thought to allow so many amps... oops!)

 

[eP]

Wow, I didn't know they made controllers for the 5304 that allowed more than 40 amps.

My mistake!

Here's the bike at 75 amps... yep, your original numbers look pretty good after all. (I never thought to allow so many amps... oops!)

Where did you found them ?

But i see your calculations are incoherent with X-lyte manufacturer's data again.

 

[safe]

Where did you (find) them? But I see your calculations are incoherent with X-lyte manufacturer's data again.

I was sort of making a half attempt at a joke. They don't make 75 amp controllers to my knowledge, but that's a way to get better performance out of such a bike. The "bottom line" is that we are talking about a theoretical bike and whether it might be able to climb a theoretical 15%+ slope at 70% efficiency. My point is that you can't and will instead get closer to 50% efficiency. (at best) The details of exactly what controller/voltage/motor combinations you use will tweek the results one way or the other, but that's just the "details"... the "big picture" says that a fixed geared bike that has it's performance peak up near 50 mph will have heat and efficiency problems on a really steep slope.

Most hills are designed to be LESS than 5%. A 10% hill is considered a very steep slope and 15% is the kind of steepness that was at the gruesome end of some the Tour De France climbs. When you climb a 15% slope in a normally human powered way you go less than 10 mph.

 

[eP]

I was sort of making a half attempt at a joke. They don't make 75 amp controllers to my knowledge, but that's a way to get better performance out of such a bike. The "bottom line" is that we are talking about a theoretical bike and whether it might be able to climb a theoretical 15%+ slope at 70% efficiency. My point is that you can't and will instead get closer to 50% efficiency. (at best)

For reasonabler amount of power it will be closer to 40% or less (for 40A limit).
For unreasonable power (unlimited) you can get very good eff. if magnets and stator allow. Maybe even more than 50 or 60%.

The details of exactly what controller/voltage/motor combinations you use will tweek the results one way or the other, but that's just the "details"... the "big picture" says that a fixed geared bike that has it's performance peak up near 50 mph will have heat and efficiency problems on a really steep slope.

So my point is: if you really care about eff. the best way is rewind the stator windings for lower resistance or to do better - bigger stator with room for more Cu.
Lets look at Aurora project.
There is very high eff. motor - and very powerfull.

Most hills are designed to be LESS than 5%. A 10% hill is considered a very steep slope and 15% is the kind of steepness that was at the gruesome end of some the Tour De France climbs. When you climb a 15% slope in a normally human powered way you go less than 10 mph.

I very often riding at 3-4 mph at my steppest local roads, so i'm sure they are over 10% slope.

So i have 2 ideas for bike:
1) economic with 2 motors: one geared for rear , and fast hub for front.
2) powerfull with high power end high eff. hub for front.

Regards.

 

[TylerDurden]

So my point is: if you really care about eff. the best way is rewind the stator windings for lower resistance or to do better - bigger stator with room for more Cu.

Randy (EbikeMaui) says he has designed an affordable high-efficiency pancake motor using a stator from a junkyard and high-quality magnets. He cannot show the motor design, because he is still seeking a partner ($$) for development.

 

[safe]

So i have 2 ideas for bike:
1) economic with 2 motors: one geared for rear , and fast hub for front.
2) powerfull with high power end high eff. hub for front.

I've thought of that, but the hub motor that is geared for hill climbing will provide a high back emf while the front motor that is for speed is going at high rpms. You would need the rear hub motor to somehow "disengage" (freewheel) once you passed it's no load speed. It would be easier to use one of those two speed hub motors.

 

[eP]

I've thought of that, but the hub motor that is geared for hill climbing will provide a high back emf while the front motor that is for speed is going at high rpms.

Not at high rpms but at relatively high.
As that motor will be relatively weak (for assistance purpose ) so the peak speed will be relatively low - not very high in fact.

You would need the rear hub motor to somehow "disengage" (freewheel) once you passed it's no load speed.

Yes, freewheel i need for rear hub and driving by chain.

It would be easier to use one of those two speed hub motors.

I've hope You are wrong again :wink:
Two speed motor (hub) using the same magnets so you can't get much more tork at first speed (gear) than you can get at second (when you want get the max from motor's magnets).
Two motors solution could be much more flexible.
At rear freewheel is possible to get huge tork for low speed assistance (at low power) and at front hub you could get relativly low tork at reasonable speed ( for assistance at low power too ).So you dont need massive magnets at your front motor hub as it will needn't work below speed you assume (10 mph for example).
So you dont need reserve high B (induction) for high stall current as this motor will never must work at stall.
So you can use almost 100% magnets power (B) at higest current at your lowest speed limit.
Such mutor will need inteligent controller which will keep up motor current below safe limit.

This way you can use cheap weaker magnets (neo of course). Crystaylyte motors at peak power point using only B = 50% Bmax (which is still safe for magnets) from peak power current, so the magnets have to be relatively strong to withstand B generated from stall current.

What you think about that ?

 

[safe]

Two motors solution could be much more flexible.
At rear freewheel is possible to get huge tork for low speed assistance (at low power) and at front hub you could get relativly low tork at reasonable speed ( for assistance at low power too ).

What you think about that ?

Well, I'm very biased towards gearing. With a chain and an internally geared multispeed rear hub you can choose whatever gear is necessary to do what you want. You can choose to run at near full efficiency all the time if you have a wide enough gear range for it.

I use gears and love them...

And after a lot of calculations comparing "fixed" verses "geared" bikes we've "more or less" (some might complain) agreed that it takes TWICE as much power for a "fixed" bike to achieve the same range of performance as a "geared" bike.

It depends on the LAWS of your area. If your laws allow higher power then you are better off with a hub motor and big voltage and big amps. If your laws limit your power then you get "more bang for the buck" with a geared bike.

What you propose (the chain on the rear and the hub motor on the front) does achieve much of what is desired and would likely work well, but it means you have to double the amount of motor weight... with a geared solution the motor weight is less and the gearing range is more... but you lose an extra 5% in friction losses. This is easily made up in efficiency advantages over the hub motor.

My answer is... I don't know.... maybe you might try it...

 

[eP]

Well, I'm very biased towards gearing. With a chain and an internally geared multispeed rear hub you can choose whatever gear is necessary to do what you want. You can choose to run at near full efficiency all the time if you have a wide enough gear range for it.

I use gears and love them...

OK, so tell me what is the cost of internal gear hub and what can do it.
Is it possible to get the range from 1:6 ratio to 1:1 ratio for example ?

I need such wide range as i project 3 mph for climbing assistance peak power speed, and maybe 18 mph for speed riding assistance (peak power).

And after a lot of calculations comparing "fixed" verses "geared" bikes we've "more or less" (some might complain) agreed that it takes TWICE as much power for a "fixed" bike to achieve the same range of performance as a "geared" bike.

But if you get enough range of performance from very powerfull hub you will not care for extra range.
Especially for the cost of reliability.

It depends on the LAWS of your area. If your laws allow higher power then you are better off with a hub motor and big voltage and big amps. If your laws limit your power then you get "more bang for the buck" with a geared bike.

I dont care about LAWS
I'm not sure what bang i can get with gears.
And what gears you taking about ?
Internal hub gears ?, motor hub gears ? or chain gears ?
Each of them have weak and strog sides.
Maybe i'm wrong but weaks i suppose are"
1) high price and low range between opposite gears (top and bottom).
2) low range as above - low flexibility
3) low reliability, change problems

What you propose (the chain on the rear and the hub motor on the front) does achieve much of what is desired and would likely work well, but it means you have to double the amount of motor weight... with a geared solution the motor weight is less and the gearing range is more... but you lose an extra 5% in friction losses. This is easily made up in efficiency advantages over the hub motor.

My answer is... I don't know.... maybe you might try it...

Rear motor weight could be very low as it could be high rpm motor.
It could be relatively ineficient motor an gearbox (eff.=60-70%) (as it will work for short period of time) but it is still much higher than 40% or 20%.

Two motors advantage is very efficient hub which can work without gears and gears loses.

 

[safe]

Right now I'm using a typical 6-speed derailler freewheel. I bought one of these, but I haven't created the new bike to test it yet. At only $122 it's a good deal I think. The 6-speed derailler gives me a gearing range of 200%, but this hub will give me 305%.

http://aebike.com/page.cfm?action=details&PageID=30&SKU=HU2206

Plus.... deraillers are 95% efficient and these hubs are usually about 90% or better, so the relative losses that you get from being in the "bad place" of the motors powerband are easily made up with gearing. Heat losses drop to next to nothing on a hillclimb with the right gear. It really is nice... you can use a small motor to climb a steep hill and not even get the motor hot.

 

[eP]

Right now I'm using a typical 6-speed derailler freewheel. I bought one of these, but I haven't created the new bike to test it yet. At only $122 it's a good deal I think. The 6-speed derailler gives me a gearing range of 200%, but this hub will give me 305%.

http://aebike.com/page.cfm?action=details&PageID=30&SKU=HU2206

Plus.... deraillers are 95% efficient and these hubs are usually about 90% or better, so the relative losses that you get from being in the "bad place" of the motors powerband are easily made up with gearing. Heat losses drop to next to nothing on a hillclimb with the right gear. It really is nice... you can use a small motor to climb a steep hill and not even get the motor hot.

But this way you lose regen capability.
At hilly area it is very valuable as you can get back 20% or more power you spend for climbing.

Lets assume we riding 2 hours at 150W average rider power at hilly area. If we want double the range and time at the same rider work so we need 300 Wh of energy.
But if we could regen 20% of that energy so we would need only 180 Wh at the same case.

Lets assume we use DeWalt packs at $90 per pack.
Witout regen we need 5 packs, with regen only 3 packs.
If pack's life is 4 years, so every 4 years we can save $180 if we use them for riding at hilly areas.

Your 8 speed hub is pretty expensive. At lower money you can get motor hub at goldenmotor : http://www.goldenmotor.com/

So 2 motors solution is more convenient for assistance as you don't need gear change when the fast slope change occur.
And it is really cheaper when you include needed battery cost.

But you keep in mind that it is idea for assistance only - not for scooter like vehicle. When you dont care about economy, and dont care for pedaling - you dont need biker derailers so the 2 derailers for 1 motor could be good for you. Especially if your bike has your own frame ( when it is not typical MTB ).

For converting MTB it is hard task add extra derailer for motor when you have one for biker.
So 2 motors is more easy to project for that case also. The one weak point of my 2-motors idea is how to add freewheel to rear hub - maybe instead rear disk brake (6-bolt mounting).

 

[scottclarke]

The one weak point of my 2-motors idea is how to add freewheel to rear hub - maybe instead rear disk brake (6-bolt mounting).

As a rule, you can't 'bolt on' a freewheel since it adds another 25mm to the wheel width - it is a problem when using a 5+ speed block on the right side.

A narrow internal hub with a thread both sides would be the ticket.

Scott

 

[safe]

Here's a problem...

With the two motor solution you will have two situations:

1. Slow speeds- Here you want the rear hub on full and the front hub on low or off so as to not overheat it.

2. Fast speeds - Here you want the rear hub to be off and freewheeling and the front hub to be on full.

How do you control this?

Do you use two throttles?

 

[eP]

A narrow internal hub with a thread both sides would be the ticket.
Scott

Good advice Scott.
But i see internal hub too much expensive for me at this moment. (this project - it should be as cheap as possible but still reliable)

The other option is BMX flip-flop hub. ( One gear at rear it is enough for me when i will be assisted for low and high speeds.)
But i'm not sure what the problems will be at this case.
We need an adapter (for opposite side as both freewheels need to work at the same direction) at that case i suppose.
At short series such adapter will be much cheaper than internal hub i hope.

Regards

 

[eP]

...
How do you control this?

Do you use two throttles?

As motors will never work at the same moment (for the sake of eff. ) both can be control by the same throttle.
I dont see any obstacle at that point.

We have very smart uP, uC etc. now , and very very cheap .
So we need cheap board wich will co-work with one BLDC controller and two BLDC motors , or one BLDC and one brushed DC motor simple PWM part of that board is really inexpensive.

For now i see serious mechanical problems not electrical.

I would like ask you for small simulation for now (if you like that idea ).
How much we could gain from regen for different slopes etc. for economy assisted riding.

Over half year ago i've done some estimations at the my local forum but nobody could understand my idea
So i'm curious what you could get at the same area.

 

[TylerDurden]

Currie makes wheels with freewheels on both sides. (no flip)

IMO: A better solution is Randy Draper's (ebikemaui) stacked freewheel adaptation; using a transmission one-way bearing and go-kart sprocket.

http://endless-sphere.com/forums/viewtopic.php?p=10689&highlight=#10689

 

[safe]

How much we could gain from regen for different slopes etc. for economy assisted riding.

The reason that regen is not as effective as you might think is that most of the energy you put into a bicycle goes into the wind. You can't "recapture" the wind resistance losses, so all you can recover is the relatively small gains you save up from hills.

Regen is mostly a waste of time in my opinion...

If you really want to save energy the answer is lowered wind resistance.

 

[TylerDurden]

The reason that regen is not as effective as you might think is that most of the energy you put into a bicycle goes into the wind. You can't "recapture" the wind resistance losses, so all you can recover is the relatively small gains you save up from hills.

Is that smoke I smell??

:wink:

 

[eP]

Currie makes wheels with freewheels on both sides. (no flip)

IMO: A better solution is Randy Draper's (ebikemaui) stacked freewheel adaptation; using a transmission one-way bearing and go-kart sprocket.

Is possibe to buy currie hub only ?
How much they cost ?

Would you like shortly explain why Randys solution is better than Currie ?

Thanks TD

 

[eP]

The reason that regen is not as effective as you might think is that most of the energy you put into a bicycle goes into the wind. You can't "recapture" the wind resistance losses, so all you can recover is the relatively small gains you save up from hills.

I must totally disagree with You.

I usually riding up to 30mph down my hilly street, and i'm sure i could riding much faster if i didn't use all the time front brake.
So im sure i could save a lof of energy if i could ride down at 15 mph or even less.
Try to calculate potential savings for -10% slope for different speeds.
As a bonus you get a safe speed - it is also very important for me as we (PL) have local streets at very bad condition

Regen is mostly a waste of time in my opinion...

If you really want to save energy the answer is lowered wind resistance.

Assisted cycling is a form of wasting of time as you can waste more time than at case when you ride unasisted.
So it is matter of point of view.
I assume the time is not important, much more important is the range and price.
If you care about time you have many others options much more efective at this point.

If yours bateries are fully discharged you have a lot of time to charge them again. Much more than slow speed time losing.

At lowered wind resistance you get higher spped, so you cannot save energy this way (downhill).

 

[TylerDurden]

Is possibe to buy currie hub only ? How much they cost ?

The hubs are probably available from currie parts department. Unfortunately, the currie parts department sucks... very undependable.

Would you like shortly explain why Randys solution is better than Currie ?

The currie setup requires a left-threaded hub and left-threaded/left-pulling freewheel. (Did I mention the currie parts department sucks?)

Randy's setup permits a wide variety of hubs, including geared hubs. It also supports a wide variety of sprockets, to optimize motor/hub gearing.





Other options:

The Cyclone parts can also be used for the crank-freewheel:
http://endless-sphere.com/forums/viewtopic.php?t=395

A freewheel can be added to the motor:
http://endless-sphere.com/forums/viewtopic.php?p=2390&highlight=#2390

 

[eP]

The currie setup requires a left-threaded hub and left-threaded/left-pulling freewheel. (Did I mention the currie parts department sucks?)

Randy's setup permits a wide variety of hubs, including geared hubs. It also supports a wide variety of sprockets, to optimize motor/hub gearing.

I'm not sure: Is Randy's setup permits for work pedaling ?
Are any pictures or drawings available with more details how it work ?

Many Thanks