Sometimes a horse is just a horse

Sorry Kerosene, I pompously posted without reading quite a few of the previous posts.

 

Thank you that you quoted me. I have already corrected my thread. It was quoted by that person not by me. You did not mention whether the wheels on the tractors are the same. If the 400 nM and 1000 rpm has double the size wheels, the job gets done in principle the same time as 400 nM and 2000 revs and 1/2 size wheels. The latter will probably more spin in ploughing than the bigger wheels. What I like to say, if you have a large propeller at 1000 revs, you probably will have less cavity than smaller and faster props. I love my high torque right from lower revs to high revs on a eMotor. You cannot say that on a petrol/gas or diesel motor. Bert

 

I understood that you were quoting someone else and meant to be clear about that.
Exactly the same tractor, plenty of gears to choose from and the only difference is the engine. The tire doesn't care at all whether it is diesel, petrol, LNG, electric motor or steam engine.
Two motors both peak at 400Nm one at 1000rpm and the other at 2000rpm. The latter has double the hp and double the pull - regardless of the motor type.

 

Bert, in most parts of the world everyone is free to post both right and wrong on the internet, and Google will find right and wrong alike without giving qualifications to the finds.

So, what did you do to verify for the truth of what you quoted from the internet ?

And, whenever you quote from the internet, please be so kind to provide also a link to the source, so whoever is interested has the option to read it all in it's original context, and this way you also give the due credits to your source.

And please behave yourself, stop shouting in my face with capitals, since it's just rude, and therefore it detracts from your arguments.

Then about what you shouted in my face with the capitals, the matter at hand is about facts, not about opinions.

 

That is not correct. Cavitation is a function of propeller tip speed. A propeller of twice the diameter at half the rotational speed, has the same tip speed as the smaller faster one.

 

A propeller needs very little torque and power at low rpm, thus it is not at all usefull to have high torque at low rpm with a propeller (different story for a wheel drive). If you can get the same (maximum) power at a lower propller shaf rpm, you can use a higher diameter propeller. There is an optimum diameter for each application. Bigger diameter does not always mean better. Outboard propeller diameters are close to the optimum diameter, if they are used for the speeds they are designed for.

The very high efficiency propellers used in some elecrical or human powered vessels work only for a very small power. With "normal" power they would be unusable due to cavitation.

 

Now that is some sensible information. Thank you for that. Look guys, I love e-motors, very soon Lithium batteries will have reached double capacity. I have 2 diesel engines, the Mitsubishi Colt, 2.8 litre motor car and the KIA Sportage 4x4 at 2.2 litre. They are doing a marvellous job for me, but I find them smelly, special the one I have already done 268.000 km in. But I like 2 bearings, a lot of people could make an e-motor in the workshop with limited tools, maintenance is low, wear and tear is also low for an electric motor. And above all, I like the high torque from low revs to high revs, so I can find the best position for my propeller. I may be wrong, but we all have preferences. Once again thanks for your nice reply . Bert

 

Bertku, if you think that two tractors, one half the power, can do work at equal rate (by changing gearing - just think that for a sec!)
OR that high school level mechanics are matter of opinion I see no point in crafting explanations. None of them clearly stop you to think - and why would you if you think that this is matter of opinion.

 

You see Kerosene, I had a tractor on my farm before I retired and moved to my present place. I did some ploughing and the tractor did not even knew that I was ploughing. Thus my philosophy was, a tractor with large wheels need only 1000 revs and a tractor with 1/2 size wheels at 2000 revs, to do the same job in the same time. Just to point out to you, that something was not specified and that was the wheel size and that the tractor had a torque meter on board. But it was interesting reading. Bert

 

You do realize that 400Nm / 2000 rpm engine with half size tires can push on the tire contact with exactly double the force compared to bigger tired 400Nm/1000rpm counterpart.

If your tractor didn't feel the plough then it wasn't working very hard. What you are saying is essentially that farmers world wide could just shift into higher gear.

I didn't specify the tire size or color of paintjob of the tractor as when trying to compare apples to apples it makes sense to keep variables to minimum. In addition I thought that it's kind of given that aspects not mentioned would stay the same for sake of clarity. This exact issues is the probkem with e-motor marketing.

Oh, I do have 3 tractors, forrestry tractor, a combine, telescopic loader. I know the hp of each pretty well, no idea of the torque numbers on any of them.

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I can prove that the torque from a e-motor has not from 1 rpm to full speed the same torque and is a curve from zero to maximum and I can prove that the curve is max at 1 rpm and maximum at full speed. Let me qualify this. The magnets has constant magnetic power. If I have a torque meter, which reads the average at a time period, I can prove that at 1 rpm the torque is nearly zero, even if the current is maximum. If I measure the torque at 1 millisecond interval, I will read maximum at 1 rpm with the high current and maximum at full speed with practise the same high current. Thus the curve is horizontal high. refer to my scanned drawings. However that said, I just love e-motors. I am now building up 2 more e-motors and I could not care, whether my propeller is perfect and is not at maximum efficiency. I just love 2 bearings and not a handful of them in a diesel engine. That is just me. I see you also love tractors, mine was from 1958 a Ford, strong as hell. Bert

 

I was struggling to get the fax going here is the graph. Bert

 

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But besides that, you have fully bypassed all the relevant points.
Can you comment on the following:
1. Why does the Ferrari accelerate in the max power revs and not at the max torque revs?
2. Do you think high school level mechanics such as F=mA, P=VF etc. Are matter of opinion?
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?
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?)

 

I can read the graphs and see a fundamental error. First, there is no such thing as a moment torque. It is either one or the other. A moment is a force around an axis that is not turning, while a torque is measured around an axis that is turning. The first is a force which generates a reaction force and is therefore static. The second is generating work and there is motion.