Sometimes a horse is just a horse

No there is no fundamental error. A brushless motor is pulsed with a short pulse, which pulses are slowly increased until the maximum speed is reached. While the magnet is permanent on giving full magnetism, thus the axis turns a fraction due to the torque. If measured at that particular moment all the time, you will get a graph like above. Unfortunately I suggest you make a brushless motor, you will learn a lot. bert

 

I understand how brushless motors work. It has no relation to what torque and moment are. Only a stalled motor can be said to have a moment. Once it moves, if the is acceleration or an opposing force, there is torque. Equating both is a fundamental error since one is static and the other dynamic.

 

Both are dynamic. You have miss read "moment" You measure every time the torque is applied by having a pulsed current going through the winding's. That is dynamic. Bert

 

Torque is the rate of change of an angular momentum; also the moment of a force.

 

< The Dutch-language comment which was reported as sexist and subsequent comments relating to that have been removed; life is too short to waste a day being irritated so it has been removed as it was not important to the thread. Let's please try and respect one another and keep the threads productive and enjoyable to everyone. Thanks very much for your understanding. >

 

Good morning Gonzo, I meant moment as time interval, you took the moment as in a toque formula. Unfortunately I cannot use my electrical torque calculation due to the fact that I cannot measure my magnetic flux phi. However I meant time interval. I am using and converting outrunner brushless motors. I have 14 magnets in the moving part and 12 ancre’s and copper coils statically. If the PWM kicks in (Pulse Width Modulation), there will be a short current pulse and then for a long time nothing until another next pulse is induced in the coils. During this pulse it creates a torque refer

N * mu * current

mag field = -----------------

2 * radius

where N is the number of turns of wire in the loop. The torque stops when the PWM is closing, and it has a small waiting time and then again a high current pulse which makes the magnets turning a little more. Etc.etc.

However because at very low revolutions the time interval is longer than measuring the torque and you therefore one get a graph as drawn on the right hand side. Trust that this explains it. Bert

 

BertKu - how are you accounting for the induced EMF? Are you controlling the current rather than voltage of the pulses?

 

Always a pleasure to argue with you

 

DCockey, very good question. I do not control the voltage, that is constant 24 Volt and 36 Volt. I am controlling my speed with the length of the PWM (Pulse Width Modulation.) The current is controlled by the very low Ohmic resistance of the coils and at low speed lower inductance, as the wires are very fat and thick bundled. The controllers I make myself with the help with Microchip info. The 3 sensors for positioning, were proposed by Jeremy Harris some 5 years ago. The current at low speed are extremely short and high and the graph is actual slightly different (higher at lower speed lower at higher speed) But I did not wanted to confuse too many people. The reason is, that at low speed with control by sensors the inductance is not build up, that is what I only could figure out.

My electronic over current sensor and temperature sensing I have build, trips at 150 Ampere at low speed, while the average current is about 6 Ampere, with the propeller in the water. My N type MOSfets can handle 350 Ampere each at 1 Micro second, thus 150 Ampere is well within the safety spec. The core frequency I use is 10 Khz. If I place a second motor parallel to the first motor, with one controller. The induced EMF is powering the second motor. By swapping 2 wires, the motor turns in the opposite direction. I originally wanted to do that with the 2 motors I am now preparing for my new rudder I have build. But I have decided to give them each its own controller. Reason is, if one motor stalls, due to weeds, both motors stop and that would be a disaster. However due to very slight differences from the two motors, the average current is higher. Trust that this is what you liked to know. I remembered that some years ago I placed the software written in the electronic section. Bert

 

It is a pleasure. As long you don't call me rude and allow me to use sometimes capital characters, we allow each other to have a different views. Bert

 

now that the drama is past us, how about the 4 questions...

 

1. Why does the Ferrari accelerate in the max power revs and not at the max torque revs?
I haven't a clue, you must ask Ferrari
2. Do you think high school level mechanics such as F=mA, P=VF etc. Are matter of opinion?
I only think in electrical torque
3. The tractor in the earlier example. If the higher revving one is geared so output shaft speed is identical with the lower revving one. Which output shaft can output higher torque? I took it for NO mechanical reductions , straight 400nM at 1000 rpm and 400nM at 2000 rpm. Just had 2 different sized wheels = the same
4. If we assume a boat has a propeller operating from 0 to 1000 rpm. At what rpm is the shaft torque highest? (Bonus what does this shaft torque demand curve look like?)Again, I work with electronics. Absolute no clue. But for an electrical e-motor, whereby the starting current could be made extremely high for a fraction of a second= answer at low rpm. Bert

 

Hi Bert,

Gonzo's post #38 you are replying to here was a response with a wink to the substantive but questionable on topic post #36 of yours, and had nothing to do with any of the previous thread issues that you mentioned in the above quote. So why trying to drag this back to the forum ?

Different views and opinions never have been a problem, however when these are presented as the truth while contradicting with the facts, then these will be discussed like happens here on this excellent thread about a fine technical topic.

Opinion​

Fact​

Whenever myself reads a thread of interest and someone is shouting in my face with capital characters then these are at chance to be addressed by me like in post #19, since in general this is considered to be a rude way of internet posting, and so I don't like to be confronted with this on a open forum where I'm a member.

For me this is especially so when the capital characters shouting sentence is defending the mix up and interchange of facts and untrue opinions such as in post #6, which opinions are allowed to have of course, and as such are subject of the fine discussion here.

So please answer the question I've asked you in post #19:

Regards,
Angélique

 

Or maybe it's the physics that say that POWER equals work done in given time. More work in given time means more acceleration, more force on the wheels = more power.

I see. You did claim earlier that it depends on the professor... Also you quote random drivel that claims power being irrelevant number and push the idea that gasoline engine's power would be inferior to electrically created (horsepower being equal).

Tire size IS a mechanical reduction in itself. So yes the shaft torque will be the same but force on the tire's contact patch will be double on the small diameter tractor (ie. able to pull a bigger plough at same speed). Or if we used gearing (and equal tire sizes) the shaft speeds made equal the 2000rpm/400Nm tractor would output double the torque from shaft, ie. able to pull a bigger plough at the same speed or if placed in a boat able to push faster.

Yes e-motor can produce high torque at low rpm. Boat propeller's torque demand goes up with revs and at low revs is minimal. The advantage of very broad power band doesn't get to shine on a boating application.

 

My experience is that with smaller wheels and higher revs, the wheel starts spinning. I can in an e-motor produce high torque and lower torque at where ever point it is needed by shifting the need for high currents or low currents when it is needed. That is not easy to do with a mechanical means, except if something gets added like a
electric motor to help boosting the needs. Bert