* * * MOTOR UNIVERSITY (Lab 101) * * *

[xyster]

Man... I woulda lost a bet that you made that name up. :?

I lied. Just testing your "power" of insight and intuition. :wink:

 

[TylerDurden]

Man... I woulda lost a bet that you made that name up. :?

I lied. Just testing your "power" of insight and intuition. :wink:

See... I had you figured right: a fightin', lyin' sack of rural sheep.

Not some cheese-eatin' surrender-monkey.



Now if we could get this torque/voltage thing cleared up, we could continue with *****Moron University*****.

 

[safe]

Wow...

I step away for a few hours and come back and the thread has added something like 3-4 pages.

The root of the problem seems to go back a long ways with TylerDurden and it has to do with a complete inability to understand the relationship between torque, rpm and power. He seems to have somehow invented a way of understanding those three ideas without incorporating them into a unified whole. It's fascinating really... it's like watching someone practically swimming in the relationships in all the formulas we use and yet he never "gets it". The relationship that is at the core of his problem is:

Power = Torque * Rpm

One day he will look back and say "what was I thinking?" but so far it hasn't happened.

I had a similiar mental block when I was facing "current multiplication". I simply could not accept that such a thing could happen. It defied my mental picture of how things were supposed to be working. At some point it took something akin to a "leap of faith" to simply start thinking that "god" or "current multiplication" is a real thing and then eventually it starts to make some sense. Mental blocks are tough... the mind ends up defeating itself... :?

Everything that I've come to realize about playing around with controller logic comes down to understanding power. So the formula is central to what I've been presenting...

 

[xyster]

:lol: You're a master-debater in your own right, TD.

The way I see it, the crux of your disagreement with reality is nicely summed up in this quote below, the debate boiled down to a simple yes/no.

One more Socratic query: if 100 volts 10 amps accelerates your bike at the same rate as 10 volts 10 amps (as you said you thought it would), what happens to all the extra power (90 volts X 10 amps = 900 watts had to go somewhere!)? I'm saying the extra wattage (power) goes to faster acceleration.

....
Ja, I'll contend that if 10V gets you to max 100rpm in 10sec, 100V will too... but the 100V test will continue to rise in RPM to 1000rpm or whatever.

 

[safe]

I'm going to throw the formulas back out for review. Power Input is very straight forward, but the Power Output is a little more complex. Power is what it's all about... torque needs rpms to produce power... so torque is not time dependent. And that might be at the root of TylerDurdens problem, that "time" is represented with power, but not with torque. Manipulation of how time relates to torque is how you manipulate the result. Time and gears are related because you change relationships with different gears.

Volts = ( Duty Cycle ) * ( Battery Voltage )

Amps = ( ( Volts ) - ( BackEmf ) ) / Resistance

Power(In) = Volts * Amps

Power(Out) = ( Volts - ( Resistance * Amps ) ) * ( Amps - NoLoad )

Efficiency = Power(Out) / Power(In)

Heat = ( ( Amps ) ^ 2 ) * ( Resistance )

 

[eP]

Another question:
Look at where peak torque is on every motor in every configuration on the hubmotor simulator:
http://www.ebikes.ca/simulator/

It's at zero speed, right?

And torque decreases between zero speed and top speed, right?

What does your intuition tell you:
Is peak acceleration near the point of peak torque (at 0kph)?

Or is peak acceleration nearer the point of peak power (the redline)?

Acceleration depends on torque not the power out.
In other case you will be unable to leave out the stall point for the sake of power_out = 0 at stall point, so in your false theory the acceleration should be equal to zero also.

 

[TylerDurden]

The way I see it, the crux of your disagreement with reality is nicely summed up in this quote below, the debate boiled down to a simple yes/no.

And yet...

you have not provided any third-party confirmation that raising voltage raises acceleration.

 

[fechter]

Guys, guys, ... you're making my head hurt.
Just for simplicity, consider brushed motors.

OK, if you put 10 amps @ 10v into a motor it will develop a certain amount of torque. If you put 100v to the SAME motor, it will try to draw 100 amps, because the resistance is the same. It will go like hell until it burns up.

If you've ever played with a motor and a big pile of batteries, you would know this.

If you have a *controller* that limits the current to 10 amps on the MOTOR, it will make no difference what the battery voltage is as long as it's over 10v. It would, however, allow the motor to reach a much higher rpm with 100v input. Since the torque will be nearly the same until it reaches max rpm, the power output will be much greater, but the torque will always be the same (or less).

Of course these cases are exaggerated, but good for illustrating the point.

For a given motor construction, the torque is a linear function of current (minus a small correction for other losses).

Acceleration is another matter. Force/mass=acceleration. Force will be porportional to motor current, minus the force needed to overcome wind resistance, rolling resistance, and grade. Generally speaking, acceleration will be the greatest at near zero speed.

Safe: your formulas look good. They make sense to me.


I want to 'condense' all this stuff into one of my newbie guides at some point, but it is extremely challenging to write things in a way that's easy for ordinary people to understand and at the same time is complete.

Hey, even us "experts" get screwed up on the math sometimes..

 

[TylerDurden]

HA!

I stand corrected.

But, I'm not alone...

:lol:

p.s. Thanx Fechter, that makes sense.

 

[Malcolm]

Ohhh, you spoiled the show Fechter. I thought this was a warm-up for Wimbledon

New balls please!

 

[safe]

Guys, guys, ... you're making my head hurt.
Just for simplicity, consider brushed motors.

...

Acceleration is another matter. Force/mass=acceleration. Force will be porportional to motor current, minus the force needed to overcome wind resistance, rolling resistance, and grade. Generally speaking, acceleration will be the greatest at near zero speed.

Safe: your formulas look good. They make sense to me.

I'm glad you commented because people here respect your opinion.

But let me add that when it comes to acceleration it's true that Force/mass=acceleration... but the force (torque) coming from a motor has to go through the gears before it actually accelerates the bike. So let's make an example:

If motor "A" has a 1:1 gear ratio and 100 Nm of torque it will provide a torque of 100 Nm at the rear wheel. If bike "A" weighs 100 kg then with a = F/m we get an instantanous acceleration of 1 m/s. (these are easy and round numbers)

If motor "B" has a 1:10 gear ratio and 100 Nm of torque it will provide a torque of 1000 Nm at the rear wheel. If bike "B" weighs 100 kg then with a = F/m we get an instantanous acceleration of 10 m/s.

So when you lower the gear ratio by 10 times you either increase the steepness of a hill you could climb or increase the rate of acceleration.

Of course if your gear is really low then you might accelerate from 0 - 5 mph and need to shift already because you are sliding into the no load area.

The better way to comprehend how the power meets the road is the concept of "power" as being the product of torque and rpm. "Power" is a time dependent concept whereas torque is not bound to time. I'm pretty sure that at the root of all the misunderstandings here is the fact that people are trying to figure things out using torque when in a world of gears torque is not a constant. Hub motors have really easy math because the motors current and it's torque and it's acceleration are all linearly related, which is not so in a geared bike. (as demonstrated above)

Thanks for the support again Fechter...

 

[safe]

Acceleration depends on torque not the power out.

Read the posting above.

 

[safe]

Axiom:

A motor that is geared down to apply half it's speed at the rear wheel will appear to be twice as strong and half as fast.

 

[fechter]

When analyzing complex systems, it's good practice to change only one variable at a time to see what effect it has on the system.

In the case of gearing, it should be intuitive that having the gearing very low will give you stump-pulling torque and a really fast zero to 5mph time.

Looking at the power balance in a system is another way to calculate things based on conservation of energy. There is almost always more than one way to get the same answer to a physics problem. While both approaches may be valid, sometimes it is easier to visualize one over the other.

 

[eP]

I'm glad you commented because people here respect your opinion.

But let me add that when it comes to acceleration it's true that Force/mass=acceleration... but the force (torque) coming from a motor has to go through the gears before it actually accelerates the bike. So let's make an example:

If motor "A" has a 1:1 gear ratio and 100 Nm of torque it will provide a torque of 100 Nm at the rear wheel. If bike "A" weighs 100 kg then with a = F/m we get an instantanous acceleration of 1 m/s. (these are easy and round numbers)

If motor "B" has a 1:10 gear ratio and 100 Nm of torque it will provide a torque of 1000 Nm at the rear wheel. If bike "B" weighs 100 kg then with a = F/m we get an instantanous acceleration of 10 m/s.

...
Thanks for the support again Fechter...

Wrong units mr Teacher

m/s is speed unit - speed is not the same as acceleration

And what about rim diameter - is it important for acceleration or not ?

 

[safe]

Looking at the power balance in a system is another way to calculate things based on conservation of energy. There is almost always more than one way to get the same answer to a physics problem. While both approaches may be valid, sometimes it is easier to visualize one over the other.

The hub motor makes the math so much easier.

With the fixed gear you can pretty much associate current to torque and indirectly to power. Gears screw with the powerband and can either place torque into areas that are good to have or into places that are very bad. Everyone is happy when a hill comes up and they can downshift and hum up the hill with ease. Where it's screwing with peoples heads is the effect of upshifting too much. You can effectively "create a hill" where there is none with gears because you can try to pull a gear into the wind that is so tall that the motor is struggling below it's peak power and far below it's peak efficiency. The math does prove my point about all of this, but it's just far enough away from easy comprehension using "fixed gear math" for some of the folks here to put two and two together and see it.

Gears make everything much more complex... but as long as the laws around the world use power restriction as their primary criteria for legality the geared bike with have a place. Top speed is a real question mark as far as legality, but power is not.

Once you transcend the laws for electric bikes you effectively step into the motorcycle world. You would then need a motorcycle license, motorcycle training classes, registration, money, money, money, etc... So the goal of staying "under the radar" is a high priority for me personally because I don't want to be creating stuff that could never be sold legally as an electric bike. (even if it has to be sold in a slightly restricted manner)

750 Watts with Gears... it might be the future... ???

 

[xyster]

Once you transcend the laws for electric bikes you effectively step into the motorcycle world. You would then need a motorcycle license, motorcycle training classes, registration, money, money, money, etc... So the goal of staying "under the radar" is a high priority for me personally because I don't want to be creating stuff that could never be sold legally as an electric bike. (even if it has to be sold in a slightly restricted manner)

Just wire in a simple series/parallel switch on a 36v/72v system and voila', you've got on-road legality and off-road thrill.

 

[safe]

Just wire in a simple series/parallel switch on a 36v/72v system and voila', you've got on-road legality and off-road thrill.

How would you configure the controller?

I suppose you could run a 72 Volt and 40 Amp controller and then when the switch is set to 36 Volts the controller will just accept the lowered voltage base and still allow the 40 Amps current. The only thing is that you would have to use a controller with no low voltage cutoff because you would obviously have some troubles with that. Which also means you ought to have a separate voltage meter to show what the battery status is.

But somehow I doubt that you could sell that legally... after all... the motor is mandated by law to be restricted to a rated load of 750 watts. But I guess that since heat is a result of current and not voltage you could indeed get more power without burning up the motor.

Here's a thought...

Has anyone ever taken a Unite Motor of 36 Volts and boosted the voltage up to 72 volts?

Does it survive?

I was going to take it slow and try first to see what happens when you take a 36 Volt Unite and go up to 48 Volts, but I don't see why you couldn't go even further...

Heat = ( ( Amps ) ^ 2 ) * ( Resistance )

Also, the doubling of the voltage also doubles the rpms, so gearing becomes more difficult.

You would pretty much have to start with a hub motor and go from there or stay in the hub motor world completely. (I just have a suspicion that these 25 lb hub motors will be banned eventually and the future motor will be more like 5 lbs, like the Unite motor)

We're living in the "Wild West" days of electric bikes right now, but eventually the law will tighten and I'm guessing what the future will look like...

 

[Lowell]

I don't think any motors will be banned. The responsibility will come down to the manufacturers and retail outlets which sell legal ebikes.

 

[safe]

I don't think any motors will be banned. The responsibility will come down to the manufacturers and retail outlets which sell legal ebikes.

My understanding of the law is that it provides lawsuit protect to the manufacturer and retailer of any bike that passes the three rules for ebikes which are:

1. 750 Watt motor.
2. Pedals that work.
3. Maximum motor driven speed on the flat is 20 mph. (as sold)

If you can pass those three rules then you have lawsuit protection. If not, then you take your chances and if Johnny crashes his ebike then the lawyers can sue you any way they damn well please. If you are a small company you simply go bankrupt and disappear. If you are a big company then the jury is instructed that they need to "stick it to the big guy" and so the jury tends to allow verdicts in proportion to the size of the company. So if your company is huge (millions of dollars) then they can sue for 10% of the value of the company... which is why they get verdicts in the millions of dollars. Any company that is worth millions will comply with the law. The small time shop will still be around to "risk it" until they get sued and die.

 

[xyster]

If you can pass those three rules then you have lawsuit protection.

Huh? Do you remember off-road three-wheelers? Though the vehicles were legal and safe when operated properly, lawsuits forced three wheeler manufacturers to stop making them.
My ol' Yamaha 225 DX -- just like the one I had when I was thirteen:

 

[safe]

...Though the vehicles were legal and safe when operated properly, lawsuits forced three wheeler manufacturers to stop making them.

There's no such thing as "complete" protection from lawsuits. But having a law that protects the manufacturer in that the government is basically labelling an ebike "safe" if it passes the three rules. If it does not pass the three rules then someone can argue:

"Well, the bike you sold my son was not backed by the government as a 'safe' electric vehicle. So you are some kind of irresponsible monster that deserves to lose everything... after all my son Johhny was innocently riding down the road and ran into the ice cream truck and it was because your bikes hub motor had so much power and weight that he lost control... blah, blah, blah.... sob.... gasp... cough... etc"

 

[safe]

Dirty D

You might read this extremely long thread.

The formulas I use are below. Notice that I've isolated the duty cycle (percentage %) and solved the formulas in terms of duty cycle. By doing it this way you can substitute different controllers and see the results without changing the rest of the equations.

Duty Cycle (BCL) = ( ( BackEmfVoltage ) + ( SQRT ( ( BackEmfVoltage ^ 2 ) + 4 * ( BatteryVoltage ) * ( CurrentLimit * Resistance ) ) ) ) / ( 2 * BatteryVoltage )

Duty Cycle (MCL) = ( BackEmfVoltage + ( CurrentLimit * Resistance ) ) / BatteryVoltage

Volts = ( Duty Cycle ) * ( Battery Voltage )

Amps = ( ( Volts ) - ( BackEmfVoltage ) ) / Resistance

Power(In) = Volts * Amps

Power(Out) = ( Volts - ( Resistance * Amps ) ) * ( Amps - NoLoad )

Efficiency = Power(Out) / Power(In)

Heat = ( ( Amps ) ^ 2 ) * ( Resistance )