Hummina Shadeeba said:
Maybe it’s due to core losses but so far in papers I’ve read that doesn’t seem the case and why would there be core losses at 0-10 erpm anyway as they would have to be some weird very powerful low speed losses.
Assume a little four pole motor and that's 0-2.5 rpm, which is 0-0.017mph for a 60mm dia. skateboard wheel. Which prompts the question: what problem are you trying to solve exactly?
ok that speed is so slow it may be harder to visualize but if you get a high cogging hub motor and coast down the street at whatever slow speed it will not roll near as far as a regular wheel. what specifically is the lost moment going towards? eddies are exponentially produced and hysteresis at least being linear...maybe hysteresis but would like to see it mapped
Hummina Shadeeba said:
In the paper I posted here core losses as it maps them don’t correlate with cogging in fact it shows greater core losses w less cogging
I skimmed the main section of the paper before and can't get the link to open now, but I believe they set out to produce a motor with less cogging and then characterised it to obtain the normal parameters. It's intuitive that if you change the design of a motor to optimise one characteristic (i.e. reduced cogging) then this may negatively impact other characteristics (i.e. iron losses).
the overall point is the paper shows two motors with only one skewed being the difference between them...the skewed has very little cogging but more iron losses. if iron losses were related to cogging the motor with more cogging should have more iron losses no?
Hummina Shadeeba said:
It’s not net zero or hub motors would roll as far as regular wheels.
But your statement directly contradicts the paper your are otherwise citing to support your argument.
don't know what you mean but im saying, as the paper shows, a greater cogging motor doesn't have more iron losses making it seem cogging is not iron losses.
I do not believe you can, with the information you have, separate out all the other losses (at low speeds) in a motor to conclude only cogging torque can be in play.
no but when all other parameters are the same except one skewed, and then the cogging torque drops substantially that gives a good indication that iron losses aren't causing cogging no?
Hummina Shadeeba said:
I’ve been reading how a magnet can be seen as an endless source of potential energy and opens the possibility there are no losses involved w cogging.
With respect, you need to stop reading that stuff as it's nonsense. Magnets aren't magic and they aren't a source of energy. Any further reasoning or conclusions built on this base are inherently flawed...
not talking about magic. theres a lot of info out there showing how a permanent magnet can be seen as a constant potential energy source in relation to anything ferromagnetic. kinda like a gravity field that's always there and all metal things are already raised and have a potential energy. nothing magical. it could also be used as a permanent damper where a magnetic material is slowed, losing it's kinetic energy yet not due to iron losses only due to the pull of the magnetic field.
Hummina Shadeeba said:
Wouldn’t be too hard to do an experiment to see if the temp increases from just cogging
How about a motor with all North polarity facing up, will it have cogging? Iron losses?
That would be an interesting experiment to try and tease out cogging torque. All magnets facing the right one is an interesting idea, but will you not still get discontinuities in the magnetic field where individual magnets meet? You might need a ring/tube magnet...