Burnt my old motor, looking for something a bit more capable, intending on building my own.

[jasonbay13]

Hi all! i'm new here. below i have several questions and plenty random bits of info.

i'd been using a 36v deck motor from an electric mower but even short distances it would get hot. just a few minutes in the yard would make it hot. gearing had top speed ~30, downhill - no-load wattage was 200w. flat ground 20-25mph was 800-1000w. dont even bother uphill, it turns into a little oven.
being 2 pole, wouldnt that mean the motor would be most efficient at ~3600rpm depending on steel lamination thickness? i believe it was wired in lap winding with 28 comm bars and 28 slots 6 turn 1mm wire. the gap between rotor and magnet seems pretty big IMO and the thickness of the magnet puts even more distance from the rotor field to the back-metal, which if i read correctly reduces efficiency. but also brings me to the question as to how drone motors spin up to such high speeds and retain efficiency; is it the use of aircraft steel (even smaller laminations)?
i want to re-wind the motor and have the wire to do it but i'm unsure as to what actual differences there are of how i wire it. one book from the 20's i was reading said wave winding was impossible on a 2 pole motor but the internet now doesnt know from a quick google search.



i got a 350w rated hub motor from a friend that i put new wires on after coming loose and ripping them to shreds. it now resides on the front of my transport and i have it hooked to a sensorless amazon controller. it works well enough to get me to the dentist with only a warm hub and nearly cold controller. it has 6w no-load draw and the most i can get out of the controller is ~1kw peak. what would cause the efficiency difference to be so big between a big heavy motor that doesnt have the oomph to get me up a hill without melting and a light hub motor rated at 350w able to power me up about as well?
weird thing happens with it though, if i give it too much load it will cut out entirely then start up again and if it hits the load too hard it cuts over and over. is that normal? sensorless operation? it also cuts out at 49v though it has written on it 36/48/72v clearly set for 72v range...
isnt the most efficient rpm the one that is equal to a formula that accounts the poles per phase and rpm to frequency that corresponds with the steel laminations?
and then isnt the air-core motors completely free of the burden on frequency-related inefficiencies? but if the tesla force provided by one watt is less in an air-core than a steel core, i'm confused.
about the speed of the hub motor, it seems to be 3600erpm relating to a rpm ~270. the controller has a speed selector switch and low does limit the speed some. i find that when on high i am unable to notice a difference except in the consumed wattage. flipping while on flat ground the wattage drops by as much as 200w. is that extra 200w actually being used to propel me and i just cant tell the extra 30% of power due to the part where it takes 4x as much power to go twice the speed? or is it decreasing the efficiency and turning into heat more than work?


on the topic of building my own motor i had bought 18 20x40 cylindrical neodymium magnets and was hoping they could be used in an axial-flux prototype, but i think i would need a lot more of them to make anything usable.



hopefully i've posted in the right place, and not to be too coherent-writing-nazi on me thanks!

p.s.
also looking for good sources of motor and electronics information. almost everything i can find is from india or bulgeria and not in english and filled with wrong or bad info as found out by personal failures and doing thorough research on the specifics. the two books i found from the 20's and 40's have so much information in one place it's almost like i've discovered the internet! except the info in these books isnt readily available anywhere in a coherent manner on the internet that i've found.

 

[amberwolf]

Brushed motors can't be oversped by too much from their original designs in many cases, as the commutator bars can fly off (grenade) and destroy the motor (and things outside the motor if they are flung off hard enough to go thru the casing).

If a motor is designed for the power you need but it's overheating in actual use at that power or below, then it is probably not being spun fast enough to work as it was designed. Mower motors are intended to spin very fast, so if yours is not spinning fast while under load then you would need to re-gear the system to allow the motor to spin at it's design speed but still drive the wheel at the required speed.

You can see how this can work with the ebikes.ca motor simulator, using any of the motors that are thermally modelled there (that produce an "overheat in" result when pushed too hard), and the middrive option so you can change the gearing.

If you want to stick with brushed, you might instead consider a powerchair motor with gearbox.

 

[jasonbay13]

i have no idea what the actual rating for the motor was. it came from a GE: My Elec-Traks - Lawn Care Attachments

at 36v it gave a little under 3600rpm iirc. as i said i had the gearing where it tops out ~30, where i need it and aside from modifying a dirt bike transmission i have no way to change gears. its weird that the much smaller less-rated hub motor on the front is just as capable of getting me going. what would be the cause for that? i have a wheelchair but wasnt going to use those tiny motors for a commuter. the reduction is low enough i could put 29" wheels to get the speed i want, but then the motors are too small to get me going that fast anyway.

i was going to leave the front brushless and the rear brushed. that way i can make it home if something awry happens. i hate pushing home.

 

[neptronix]

Yeah brushed motors tend to have low efficiency also.
You can rewind it but it won't improve it substantially.

If you want to run dual motors and don't have high power requirements, there exist 4-5lbs dual reduction geared hub motors.. a pair in a 29er would be pretty zippy.

 

[jasonbay13]

from my research, brushed motors are around 60-70% efficient and bldc around 75-85% efficient.
i could wind it in wave for more efficiency at reduced torque but it already didnt have enough torque.

my total budget atm is as near $0 as possible. i have tons of ac motors and alternators i can use wire from, and the alternator can be used as a bldc with 4 amps applied to the field windings. but havent finished that project yet (a mountain bike with a double-rim in the back with a serpentine belt to the alternator. 3600rpm on the alternator equates to 30mph or so).
but being a 12v alternator i would think it'd be best run at 12v the internet thinks 36v is good for them. wouldnt the best determination of that be to find out the max amp draw (stall current) at whatever voltage i want to use and make sure my controller is rated for that load?

my goal is a commuter, back and forth to peoples houses and stores. usually have some tools in my crate and a backpack full. so total weight is around 500lb.