I recently had a question about putting one of our standard hub motors on a small wheel (16"). Perhaps I opened the Pandora's box myself when I stated that our hub motor selection is not optimized for that size but will work. The follow up question was predictable, "Whadda' mean?" and the essay on brushless motor design had begun.This is the short version.
When I said "optimized" I was splitting hairs a bit, any of Luna's motors sold today that will physically lace into a 16" rim will work just fine. There are motors designed with a specific wheel size in mind, and here is why.
Motors have 2 main parts , magnets and electro magnets. The electro magnets are the part of the motor with all the windings, by adjusting the size of the wire and the number of times it is wound around you can tune the characteristics of a motor. Motors with heavy wire and fewer turns can have the same amount of material inside as a motor with very thin wire and a lot of turns. If given the same voltage and amperage, the heavy wire design will spin faster than the light wire one but have less pulling power (torque). The thin wire design will spin slower but pull harder.
Luna's current selection of motors are designed with the 26" to 29" wheels in mind, the manufacturers found a balance by using the correct wire size and the right number of turns to make these perform well. The reality is if you are looking for perfect optimization on a small wheel bike ( folding bikes come to mind) then ,maybe its worth looking into. The other 99.5% of us, don't worry about it.
When I said "optimized" I was splitting hairs a bit, any of Luna's motors sold today that will physically lace into a 16" rim will work just fine. There are motors designed with a specific wheel size in mind, and here is why.
Motors have 2 main parts , magnets and electro magnets. The electro magnets are the part of the motor with all the windings, by adjusting the size of the wire and the number of times it is wound around you can tune the characteristics of a motor. Motors with heavy wire and fewer turns can have the same amount of material inside as a motor with very thin wire and a lot of turns. If given the same voltage and amperage, the heavy wire design will spin faster than the light wire one but have less pulling power (torque). The thin wire design will spin slower but pull harder.
Luna's current selection of motors are designed with the 26" to 29" wheels in mind, the manufacturers found a balance by using the correct wire size and the right number of turns to make these perform well. The reality is if you are looking for perfect optimization on a small wheel bike ( folding bikes come to mind) then ,maybe its worth looking into. The other 99.5% of us, don't worry about it.