Understanding the real world considerations and implications of Speed VS Torque models

[RagingGrandpa]

I'll join the team: You should not care about the announced wattage on the different EUC.

Advertised watts are a continuous power rating. Think: sustaining a high torque for more than 5 minutes, without melting or damaging anything. If you need to climb a long steep mountain road while riding 50kph+, maybe you care... but it's a very rare situation for an EUC rider to be running into these thermal limits of the motor itself. More often, powerful riding in hot climates reaches the controller cooling limits; not the motor.
 

On 7/3/2024 at 11:25 AM, on one said:

I am curious about Voltage as relates to electric unicycles, is that gimmicky too?

Voltage is not a gimmick! 

Voltage defines the maximum speed a BLDC motor can reach (assuming all other things remain constant). 
You can see this effect easily yourself: notice the difference in lift-spin speed with your own EUC, comparing lift speed at a full-battery voltage vs the lift speed at 0% voltage. It will be about 25% less. That's the voltage effect.

Higher system voltages give us higher speeds, or let us use higher-torque motors within the same speed range.
 

5 hours ago, on one said:

is it sensible to formulate a ratio between volts/watts to derive a number that would correlate to a given wheel's 0-50km time?

Not quite. 
Acceleration is a function of force. For a spinning motor, that means torque. 
Best possible acceleration from 0-to-50 is revealed by a motor torque curve (graphed vs speed). But we have almost no such data for EUC's. 

 

Edited July 24 by RagingGrandpa

[Mono]

Let's put it slightly differently: there are strict physical limits on the wattage that is absolutely necessary to reach a certain speed or get a certain acceleration. There is no such thing for voltage, at least not for the voltage ranges that we are talking about here (like 50-200V).

As a specific example: if we want to accelerate 100kg with 0.5g (0-80km/h in 4.5s), we need (if I am not mistaken) the power of ≈0.13kW per km/h speed,^1 which the motor and all other components have to deliver (the chain is as strong as its weakest element). For example at 50km/h, we need 0.13kW x 50 ≈ 6.7kW just for the 0.5g acceleration plus another 1kW-or-so to overcome wind resistance. At 25km/h, we need ≈ 3.4kW for the 0.5g acceleration plus some ≈200W to overcome wind resistance. If there is less wattage, there is less acceleration, period.

Just to be sure we are on the same page: a 7kW motor can deliver 7kW (usually) only at a single speed point, namely around half of the spinout speed, and less everywhere else, like in the red graph here.

^1 Power [kW] ≈ speed [km/h] x acceleration [g] / 3.7

Edited July 24 by Mono

[RagingGrandpa]

@Mono is talking about instantaneous power.
Meaning: sustained for only the brief amount of time necessary to accelerate.

But the label rating for the EUC motor is the continuous-duty power. Sustained for long durations. Very different.

[Mono]

46 minutes ago, RagingGrandpa said:

@Mono is talking about instantaneous power.

I am talking about power, period. Riding conditions that need the most notable amounts of power are 

• wind resistant
• acceleration
• climbing

46 minutes ago, RagingGrandpa said:

Meaning: sustained for only the brief amount of time necessary to accelerate.

But the label rating for the EUC motor is the continuous-duty power. Sustained for long durations. Very different.

To all I can see, the graphs shown here determine the limits of acceleration power too. After all, there is no energy source that can increase the shown nominal power even for one second. The motor could sustain the power, sure, probably, but the motor is not the power source, it's just the converter.

Correct me if I am wrong, but wheels do not have an up-voltage converter for overpowering the motor, right? And motors don't have a down-resistance converter to boost their amperage for a second or two, right? If we can agree on these two, we have another simple universal law which limits the power = voltage * voltage / resistance.

Edited July 24 by Mono

[RagingGrandpa]

18 minutes ago, Mono said:

the graphs shown here determine the limits of acceleration power

Yes!

18 minutes ago, Mono said:

there is no energy source that can increase the shown nominal power even for one second

Correct!

18 minutes ago, Mono said:

wheels do not have an up-voltage converter for overpowering the motor

Correct!

But it's missing the point: EUC's advertise their motors by "rated power" - which isn't the maximum that the system can produce. 
So when we see things like "2000W motor" advertised, it's practically meaningless. So we just ignore it 

[Mono]

43 minutes ago, RagingGrandpa said:

But it's missing the point: EUC's advertise their motors by "rated power" - which isn't the maximum that the system can produce. 
So when we see things like "2000W motor" advertised, it's practically meaningless. So we just ignore it 

I see, right, motor wattage specifications are shaky numbers which was the point I made in my first post (yet I would not consider the computation of the actual power requirements missing a point). Yet, you seem to suggest that EUCs are under-advertised with their rated motor power? Behaviorally speaking, this is surprising to me, I would have expected over-advertisement. I just checked the first I could grab:

delivers 7500W and is advertised with rated 4000W

Looks like you're right 

Edited July 24 by Mono

[timmytool]

The wattage number quoted by manufacturers is just that a number, it needs context behind it to mean something. Most times the number is pulled out by marketing or rounded up from the engineers.

The sherman L for example 3200/8000 watts, the 3200 is implied as a nominal power and 8000 watts peak instantaneous power. But even then those numbers need more context is that a 1 hour nominal or 24 hour, is it just based on heat load, to what temp. Is the instantaneous power just based on max amperage at full or nominal voltage, is that at one second five seconds thirty? Sherman L is quoted at 840amps peak with its mosfets but it there another weak link as 8kw / 130 volts nominal = 62 amps even worse with max charge volts 53 amps. The 2 batteries (left right) are fused at 40 amps each but should be able to peak higher for short loads. I'm assuming the 840 amps is a single phase so phase to battery is usually half of phase, but even if that's all mosfets / 3 phases / 2 to get battery amps thats still closer to 140 ampa not 60amps.

Now the Sherman L is quoted as having a higher torque to the lynx(same voltage wheel same manufacturer) but same top speed and motor power ratings. So one can only assume it's the same motor with the same kv but they can throw more amps lower on its touque curve but is still limited by the same thermal limits so why is the peak watts not higher?

We used to know the free spin speed of euc's but now even that info is hidden behind artificial free spin limits. From a true free spin speed we could estimate a motors kv (speed / circumference = rpm, rpm/voltage= kv), kv lets us calculate the motors kt or torque coefficient thats gives us the torque per amp. If we assume the motor wattage is in the ballpark wattage/voltage gives amps at nominal and peak (times/divided by 2 is a reasonable estimate when only one nominal/peak figure is given). From that we can use it with kt to get motor torque, times it out by motor dimensions to get wheel torque to the ground.

If someone does the maths and compared it to the wheel pull force values from the diy tests we might get a better picture of facts vs marketing. 

https://forum.electricunicycle.org/topic/28025-💪-euc-pull-force-test-results-reviewers-please-do-this/#comment-418391

[RagingGrandpa]

Advertised power is only a distraction.
Better that we ignore that number totally, and make our buying decisions based on other criteria. 

[EUCzero]

Does not help having a 10000000W motor if the controller only output 1000W.
That is what we are trying to tell you. So don't put any weight on the rated power of the motor as it does NOT tell what power the EUC has.

[on one]

My intuition is that once the volts are equal to or greater than 100 and the watts are equal to or greater than 2500 then the benefit of higher and higher numbers provides less and less benefit.

[EUCzero]

Now when top speeds are above 50-60 miles per hour, main hurdle will be air resistance.
You get 4 times more air resistance but 2 times speed. So you need 4 times more power to double the speed. It is not linear.
And I am NOT talking about rated motor power, but FULL SYSTEM OUTPUT power. So even if freespin will increase but upping the voltage, the riding speed will not increase the same amount of %. 
Sitting down, good riding position, clothing and so on will soon become important to set new speed records.

[on one]

That's a great point, I really need to account for wind resistance and weight in my formula, but I feel like setting it aside for now. I have a working concept of power now, but I don't understand what is meant by FULL SYSTEM OUTPUT. Could you explain?

[EUCzero]

As most have tried to tell you. Forget about motor power in wattage, as it is NOT the power the EUC will have available for it's forward acceleration. That is just the power the MOTOR is rated for. Not the EUC.... only the motor. So as I wrote above, an EUC motor can have a rating for 10.000 watt. I will still be a weak and slow EUC if the controller only feed the motor with 300Watt.
And THAT is what you do not seem to understand. The manufacturers only tell you the motor wattage. They are not telling you the wattage from the whole system. What actually moves the EUC forward. That power they do not tell you. And without knowing that, your formula will not tell you anything.

What yopu should ask for is not the motor wattage, but the controller wattage. And that again change with firmware. Begode have done this many times by upping the amperage on certain controllers just by changes in the firmware. Motor wattage the same. But FULL SYSTEM OUTPUT wattage increased.

 

So by FULL SYSTEM OUPUT POWER (watt) I mean the power the EUC actually have available for forward acceleration. Not single components like the motor alone, but every component together as a whole system.

Edited July 26 by EUCzero

[on one]

The lack of transparency and consistency from the manufacturers and the dealerships certainly creates problems with working on my formula, that's for sure.

20 minutes ago, EUCzero said:

So by FULL SYSTEM OUPUT POWER (watt) I mean the power the EUC actually have available for forward acceleration. Not single components like the motor alone, but every component together as a whole system.

I love that you made this point, yet this also creates a new problem set.

 

23 minutes ago, EUCzero said:

What yopu should ask for is not the motor wattage, but the controller wattage. And that again change with firmware.

I hadn't thought about controller wattage. I will investigate this matter. Believe me, I'm keenly aware of the problems associated with published numbers on watts and volts. I love that @alcatraz seems to focus on the battery, because that's an exact representation of potential power. Perhaps I will include a variable for battery as well, but I thought that's what volts was.

[timmytool]

58 minutes ago, on one said:

The lack of transparency and consistency from the manufacturers and the dealerships certainly creates problems with working on my formula, that's for sure.

I love that you made this point, yet this also creates a new problem set.

 

I hadn't thought about controller wattage. I will investigate this matter. Believe me, I'm keenly aware of the problems associated with published numbers on watts and volts. I love that @alcatraz seems to focus on the battery, because that's an exact representation of potential power. Perhaps I will include a variable for battery as well, but I thought that's what volts was.

Voltage * amps = watts, you can get 100kw from a 10 volt system if you can throw 10,000 amps at it. Just like a 1000 volt system giving 100 amps also gets 100kw. Volts has some advantages but by it self is not a indication of ability.

Samsung 50e cells vs 50s cells for example both "buckets" hold 5 litters (5 ah) but the 50e has a garden hose(10-15 amps) to get the water out while the 50s has a fire hose (25-45 amps).

But as said the weak link in the system could be anything and specs dont always match reality. In euc's: Lean, Software > controller, battery + wires, phase wires, motor, each having a absolute amp limit then a thermal limit. After that you have physical limits like rider ability, velcro for the lean pads, the euc's physical properties, motor then the tyre and ground surface. Then at speed you have wind resistants and all that entails like more lean, better posture/position to reduce drag, countering the pushback from the wind, countering side gusts to stay on track etc etc.

Dont get stuck in the weeds a few metics that gauge potential and real world test or two to gauge reality, you dont need to model the euc in a computer to calculate its drag coefficient.

[on one]

I'm going to keep watts in my formula and add a variable for wheel weight. I'm aware that watts is a problematic variable but it's the only one I have available to account for the variables of which you speak:

59 minutes ago, timmytool said:

Software > controller,

and

59 minutes ago, timmytool said:

wires, phase wires, motor,

I'm not stuck in the weeds at all. I just don't have published data for control board output. If I did then I would choose to use that as a variable instead of watts.

[rcgldr]

On 7/26/2024 at 1:37 PM, EUCzero said:

Does not help having a 10000000W motor if the controller only output 1000W.

An actual example of this is the V10F. It has a 2000 w motor, but uses a modified controller from V8F (which has 1000 w motor, 2000 w peak, 30 amp fuse). Comparing it to 18L, both have 20S4P battery packs, but V10F has 40 amp fuse, while 18L has two 30 amp fuses for a total of 60 amps. Peak power on V10F is about 2650 w, while it's about 4000 w for 18L (nominal power is a bit higher on recent versions of 18L, 2200 w). V10F is only 3 mph faster than V8F 23 mph GPS versus 20 mph GPS. 18L top speed is around 28 mph GPS (maybe a bit more, claim is 31 mph, but i don't know correction factor).

[alcatraz]

This stuff is confusing to me too. I think we need real world testing to figure out where the limits are for each wheel.

Remember that the manufacturers have an incentive to protect their wheels within the warranty period. They can brag about wattages but then tweak the output limits in software between firmware versions.

So even if you put a wheel on a dyno and measure it, it's only valid for that firmware version and controller version. 

[UniVehje]

On 7/23/2024 at 11:18 PM, on one said:

For my next wheel, I am particularly interested in the capability of an EUC to accelerate between 8mph to 35mph.

This thread offers good discussion on why nominal wattage number isn't that important. Especially for your quest here. Most common mistake seems to be thinking EUC motors in terms of gas engines where horse power (or wattage) number actually means something and is produced by the engine. It is understandable to think like that. This has been well commented here already...

However, there's something to add to your quest. EUCs are not the best machines for extreme accelerations. I think they accelerate really well and it's thrilling to feel it. But we should always remember that hard acceleration on a self balancing vehicle is the most dangerous thing to do. On any modern wheel normal and even rapid acceleration is safe and ok. But your quest seems to find out what wheel will give you the best acceleration and what specs are needed for certain level. The thing is that to reach the given top specs you will have to accelerate at the very edge of the ability. EUC cannot (in any safe scenario) put down the max power. Acceleration is a side product of the wheel keeping you upright. EUC only cares about balancing you and sometimes it has to accelerate really fast if you try to lean forward too much. But if you lean so much that the wheel runs out of torque, you will face plant. Acceleration is more about skill and pad setup than watts and volts. Of course you need enough torque to not over lean. Most modern wheels have more torque than you can lean. The bottle neck is usually not the wheel specs. 

Here's a thought experiment for you. Let's imagine a motorcycle track race. You probably know already that the biggest horse power bike might not win as the bottle neck is in tire traction and front wheel coming up. But let's add a rule that the motorcycles have to accelerate the whole way with front wheel up, doing a wheelie all the way. How many hp is needed to win a wheelie race? You need enough to lift the front wheel but after that it's other features and especially skill. EUC riding is essentially like riding a constant wheelie except the balancing part doesn't require any skill as it's done by computer. 

Let's also assume you have two wheels. One gives full system power of 10 000 W and the other 15 000 W. Then you ride both and lean as hard as you can (let's imagine same setup otherwise and the lean is the same). The more powerful EUC will not accelerate faster. If it did, you would fall on your butt. Both EUCs will only give as much power as is needed to keep you upright. If keeping you upright required 8 000 W, both wheels would give you exactly that. If you are not able to lean more, bigger specs will not give you any benefits except more confidence in leaning as there would be bigger headroom in torque. So just buy any modern EUC and then practice your leaning and you will accelerate faster. Smaller diameter wheel is easier to lean and you need good pads to make that superman position. But I still recommend being content in normal acceleration to be safer. Remember that hard acceleration is same as trying to fall on your face and trusting the wheel to keep you up. 

[on one]

 

3 hours ago, UniVehje said:

Remember that hard acceleration is same as trying to fall on your face and trusting the wheel to keep you up. 

Shouldn't this be addressed with firmware? On my wheels, KS14D and Ninebot Z10 I am learning to feel when my wheel is getting taxed by my acceleration input. My firmware is actually quite good at giving me feed back on my acceleration inputs: both wheels start to nose lean before they tilt back and/or provide an audible danger warning.

[Rawnei]

31 minutes ago, on one said:

 

Shouldn't this be addressed with firmware? On my wheels, KS14D and Ninebot Z10 I am learning to feel when my wheel is getting taxed by my acceleration input. My firmware is actually quite good at giving me feed back on my acceleration inputs: both wheels start to nose lean before they tilt back and/or provide an audible danger warning.

KS14D is absolutely not a good example of wheel with good safety features and I'm guessing Ninebot Z10 isn't either.

A lot of modern wheels have dynamic tiltback based on PWM which is a very good feature (plus alarms), but with enough intent a rider can push through that if they want to, rider has to be aware of limitations and be responsible too.

[rcgldr]

3 hours ago, on one said:

nose lean

 

2 hours ago, Rawnei said:

tiltback

on one is referring to pedal dip, not tilt back. It's possible that he's using soft mode, and it's not a true pedal dip, but just a soft mode forward tilt. Pedal dip is just barely exceeding the limits, which is not good. Some youtube reviewers will deliberately overlean and get pedal dips, but only by doing jerky movements below 5 mph. In a few cases, this has blown fuses on smaller EUCs, so it's not a good idea.

[on one]

4 hours ago, Rawnei said:

KS14D is absolutely not a good example of wheel with good safety features and I'm guessing Ninebot Z10 isn't either.

Why not? If you say that without good reasons then it's a meaningless opinion that is potentially dangerous.

[Rawnei]

20 minutes ago, on one said:

Why not? If you say that without good reasons then it's a meaningless opinion that is potentially dangerous.

It's a weak wheel with speed based tiltback.

If your only experience is a Z10 and a King Song 14D why are you doing all these mental gymnastics? What is the endgame here?

[on one]

@Rawnei, I don't want to be your flying monkey, not fall victim to your narcissistic comment,

1 hour ago, Rawnei said:

If your only experience is a Z10 and a King Song 14D why are you doing all these mental gymnastics? What is the endgame here?

If it's a low power, weak, wheel, then can you help me understand why that makes the King Song 14D unsafe?