All back together and 6500W

[safe]

Assuming your efficiency number is correct, the resulting heat will be 4,612 watts X 0.52= 2,398 Watts lost to heat.
(2398/4612 = 0.52)

No, this time you're incorrect.

That simulation is Power(out)... that means that the actual Power(in) is 8812 Watts. (99.9 Volts * 90 amps = 8991 Watts) So the Power(in) is just slightly below full. (10 rpm lower and it would be full)

 

[xyster]

You're right. Brain fart. I missed the "out" part of 'power out'.

 

[Toorbough ULL-Zeveigh]

You, Safe, have a spreadsheet fetish. Simulating other people's machines is erotic for you, isn't it?

Well, I'm pretty confident that I've attained (or nearly attained) mastery over all the aspects of electric bike simulation.

Master of your domain? (a-la Seinfeld, the Contest)

 

[Lowell]

Assuming your efficiency number is correct, the resulting heat will be 4,612 watts X 0.52= 2,398 Watts lost to heat.
(2398/4612 = 0.52)

No, this time you're incorrect.

That simulation is Power(out)... that means that the actual Power(in) is 8812 Watts. (99.9 Volts * 90 amps = 8991 Watts) So the Power(in) is just slightly below full. (10 rpm lower and it would be full)

Again your numbers are way off. 6500W is the input power. No load speed is 77mph as posted in the other thread. Input power tapers off as the speed increases due to back EMF from the hub.

How is your 3hp bike coming along? I'm debating whether to start another vastly more powerful ebike project on a long wheelbase downhill mountain bike, or build up another motorcycle. I was offered a 2001 Kawi 750 project bike, and a CBR900RR... tough choice...

I'm leaning towards waiting on more electric power as the battery availability sucks right now and maybe building a turbocharged or nitrous sport bike. Maybe both

 

[Mathurin]

6500w in, assuming 5606w out is correct, that's 86% overall eff.

 

[Lowell]

6500w in, assuming 5606w out is correct, that's 86% overall eff.

I wish that were true, but the efficiency in the peak current draw range is closer to 75%. Still a healthy 6.5 rear wheel horsepower though. Power draw at 50mph is more like 3600W due to fighting back EMF from the motor, or around 4rwhp. A little voltage boost would pick up the top end quite a bit, but I'm pretty happy with the performance envelope of the bike. Going up hills drops the RPMs down, but due to decreased emf from the motor, power input goes up. I easily pull 45+mph up the steepest hill on my route which keeps pace with traffic nicely.

Next plan is for some aero tweaks, and a windscreen. At 85km/h the wind is worse than this: http://www.triumph.co.uk/uk/788.aspx
The tank fairing makes a big difference on a motorcycle, even without any screen. On the ebike I feel like I'm catching huge amounts of air drag with my stomach and upper body. Safe might have to start a 60mph club. 8)

 

[safe]

50% Heat Savings

By lowering wind resistance you lower your heat because you get a little closer to your efficiency area.

 

[safe]

I hope you've noticed that if you use:

EXTREMELY OPTIMISTIC AERODYNAMIC NUMBERS

...that you can get near the results you want.

Is your bike really that aerodynamic? (currently)

Right now your top speed should be right around 53 mph.

 

[safe]

And I think it's interesting that the simulation is said to be "wrong".

Should we begin to doubt the simulation? (Xyster will get into a panic)

The simulation clearly points to a no load speed of:

Rpm - 1280

Which should translate to:

 

[xyster]

Should we begin to doubt the simulation? (Xyster will get into a panic)

Those RPM and speed numbers are in the ballpark for the 5303 at 100 volts.

1282 rpm X 26" X 3.14 = 104,662 inches per minute

104,662 inches per minute X 60 minutes/hr / 12 inches/ft / 5280 ft/mile =

99mph no load speed. What's to doubt? That agrees with the ebikes hubmotor simulator too, which shows a no-load rpm of about 1300, but cuts off the MPH graph at 65.

No panic from this mechanic!

 

[safe]

The main thing that I see here is that at 100 Volts and with the typical lousy aerodynamics of a mountain bike you run into a "wall" of air at about the same place as the peak power which is right around 53 mph. Peak efficiency doesn't kick in until over 90 mph, so you are "trapped" in an efficiency regime that is bad.

In some ways (with the aerodynamics that are in play) you might actually get better performance at LESS voltage.

The reasoning is that higher voltage translates to higher rpms which if those higher rpms are not attainable you end up never being able to use them. Instead of getting the "amazing" performance you hope for you instead get a "space heater".

Seems to me that around 80 Volts is about as far as you can practically go...

 

[safe]

This is the problem...

 

[xyster]

The main thing that I see here is that at 100 Volts and with the typical lousy aerodynamics of a mountain bike you run into a "wall" of air at about the same place as the peak power which is right around 53 mph. Peak efficiency doesn't kick in until over 90 mph, so you are "trapped" in an efficiency regime that is bad.

This is why I'd never choose the 5303. The zone of peak efficiency (90+%) begins around 900 rpm -- 200 rpm higher than for the 5304. And torque is lower too. I'm puzzled as to why anybody interested in running voltages > 48V with a 24-28" tire would chose the 5303.
It's place is for use in small, 16 and 20" wheels, and for low voltage systems where the 5303 peak better corresponds with top operating speeds.

 

[safe]

Ideally your peak power, peak efficiency, and top speed potential based on aerodynamics should all be near each other. When you diverge from that a great deal it makes things worse.

There is a "correct" voltage for any aerodynamic regime when you are using a hub motor.

Bikes with gears are "exempt" from this problem because you can simply move the peak power and peak efficiency around as needed for the conditions. So having gearing is an argument for giving greater flexibility and allowing voltages that you otherwise might have trouble using. (but that's another topic)

 

[xyster]

Ideally your peak power, peak efficiency, and top speed potential based on aerodynamics should all be near each other. When you diverge from that a great deal it makes things worse.

Agreed.

There is a "correct" voltage for any aerodynamic regime when you are using a hub motor.

And there is a correctly-wound hubmotor for any voltage/speed combination. I calculated a 5305/24" combo would be my optimal hubmotor configuration. Alas, none was available at that time, so I settled for the 5304/24".

Bikes with gears are "exempt" from this problem because you can simply move the peak power and peak efficiency around as needed for the conditions. So having gearing is an argument for giving greater flexibility and allowing voltages that you otherwise might have trouble using.

Again, I agree. But running 7hp through the chain makes for a very difficult project. Not so with a hubmotor. Gears broaden the powerband, and are an essential complement for low-powered motors (including humans), but gears can't generate power that the motor isn't generating.

 

[safe]

Again, I agree. But running 7hp through the chain makes for a very difficult project. Not so with a hubmotor. Gears broaden the powerband, and are an essential complement for low-powered motors (including humans), but gears can't generate power that the motor isn't generating.

Gears can only help "focus" the powerband to the needs that you might have, they don't increase max power... this is true. As for 7hp and a chain, the last I've heard of motorcycles is that some are pulling 250hp through a chain, so it's obviously "possible" to do. You would need roughly an 80cc motorcycle chain to handle that kind of load. With that kind of horsepower you can skip the pedals and so there's no restriction on the chain type.

The "ideal" chain/motor combination in "my opinion" is the 750 Watt motor combined with pedaling. That way you get roughly equal power from both inputs and everything is legal.

When you go above 1hp to up to 3hp then you are in "Missouri Legal" country and don't need pedals anymore.

Above 3hp and you probably want to make it a hub motor so that you don't attract attention since it's probably illegal if anyone knew what you were really doing.

 

[Lowell]

You guys are forgetting one important detail, and that is the battery pack voltage drops under heavy loads. I have 76 x 18Ah NiMH cells in series which is '91.2' V, but is 105v off the charger, 90 something at cruise depending on load and charge state, and low to mid 80's at full throttle.

The 5304 would be great with a 29 cell A123 pack which can maintain high voltage with low internal resistance, but considering I'm going 46mph up the steepest hill on my commute and the pack is 40-50% discharged by then, I don't think there's a torque problem!

I would like to try the 04 wind sometime though, and Justin told me I could buy just a stator to fit inside my housing.

 

[xyster]

this is true. As for 7hp and a chain, the last I've heard of motorcycles is that some are pulling 250hp through a chain, so it's obviously "possible" to do.

I was speaking of a modified bicycle, obviously. And I didn't say it was impossible, I said it "makes for a very difficult project", presumably including a motorcycle chain, beefier gears, a mount for a big heavy motor, etc. Again, you mischaracterize a statement solely in order to disagree with it.

Anybody ever seen a bicycle with 5+hp run through the gears? Even the insane-a-cycle uses a separate, single-geared sprocket.
http://www.electricrider.com/custom/index.htm
"The chain appears to be the weak link in the drive system, requiring a change every 500 miles, and that's fine with me."

 

[xyster]

I would like to try the 04 wind sometime though, and Justin told me I could buy just a stator to fit inside my housing.

You should try that. More torque per amp should make life a bit easier for your batteries, less voltage droop too. At 80 kph (50mph) and 90 volts, the efficiency of the 5304 looks from the sim to be about 8% greater than the 5303 at 80kph and 90 volts.

 

[safe]

I have 76 x 18Ah NiMH cells in series which is '91.2' V, but is 105v off the charger, 90 something at cruise depending on load and charge state, and low to mid 80's at full throttle.

Okay, that's more like it. Less volts actually "helps" you because it brings down the rpms. I'm seeing 43 mph up a steep (5%) hill as being pretty realistic...

 

[Lowell]

this is true. As for 7hp and a chain, the last I've heard of motorcycles is that some are pulling 250hp through a chain, so it's obviously "possible" to do.

I was speaking of a modified bicycle, obviously. And I didn't say it was impossible, I said it "makes for a very difficult project", presumably including a motorcycle chain, beefier gears, a mount for a big heavy motor, etc. Again, you mischaracterize a statement solely in order to disagree with it.

Anybody ever seen a bicycle with 5+hp run through the gears? Even the insane-a-cycle uses a separate, single-geared sprocket.
http://www.electricrider.com/custom/index.htm
"The chain appears to be the weak link in the drive system, requiring a change every 500 miles, and that's fine with me."

That bike looks like it would be very ill handling at speed, as well as creating a lot of extra aero drag. I'd like to see a design that uses an Etek or PMG style motor but still looks like an ebike.

Something along these lines, but with a narrower, higher mounted battery pack plus pedals to look legal.

http://www.austinev.org/evalbum/615

 

[safe]

Anybody ever seen a bicycle with 5+hp run through the gears?

There's no reason to even have pedals or gears above about 2 hp. Aerodynamically you are far better off simply getting out of the wind and letting the bike do all the work. If the goal is to create an electric transportation vehicle then "big horsepower + pedal power" makes little sense intellectually.

It makes more sense to think in terms of SMALL MOTOR (like 750 Watt) with pedals OR big motor and no pedals.

At least it seems more logical to me...

 

[Lowell]

Anybody ever seen a bicycle with 5+hp run through the gears?

There's no reason to even have pedals above about 2 hp. Aerodynamically you are far better off simply getting out of the wind and letting the bike do all the work. If the goal is to create an electric transportation vehicle then "big horsepower + pedal power" makes little sense intellectually.

It makes more sense to think in terms of SMALL MOTOR (like 750 Watt) with pedals OR big motor and no pedals.

At least it seems more logical to me...

My pedals aren't even connected to the back wheel, although if I put a chain and rear cog on they would be functional. Their only purpose right now is footrests and to keep the ebike look for the police. I thought about adding some nice footpegs, but it really changes the look in a non bicycle way. At least with cranks on the bike I can move my feet in circles if need be....

 

[xyster]

There's no reason to even have pedals above about 2 hp.

I understand what you're saying so far as pedaling adding so little to the power and the aerodynamics being more important to range....but there's still good reason to have pedals. I like pedaling along with my 3hp bike for the exercise, and if something electrical breaks down I can still pedal home. I also enjoy taking the bike out twice per week for 8 mile, one hour, pedal-only treks around the local park. And of course by pedaling, it's identifiable as a bicycle. If it wasn't, I'd eventually be booted off the bike trails.

 

[Lowell]

There's no reason to even have pedals above about 2 hp.

I understand what you're saying so far as pedaling adding so little to the power and the aerodynamics being more important to range....but there's still good reason to have pedals. I like pedaling along with my 3hp bike for the exercise, and if something electrical breaks down I can still pedal home. I also enjoy taking the bike out twice per week for 8 mile, one hour, pedal-only treks around the local park. And of course by pedaling, it's identifiable as a bicycle. If it wasn't, I'd eventually be booted off the bike trails.

Exactly. My bike is right at home at low speeds in 'bike only' areas. (unless nobody is looking of course) 8)