Ianhill
1 MW
- Joined
- Sep 25, 2015
- Messages
- 2,918
Motors are rated in KV (rpm per volt applied)
The torque output is the current applied
Torque × rpm = power
Output power is measured in Hp
Current × voltage = input power measuered in watts
The watts being applied will rise as the torque demand is increased so half throttle at stall speed may equal the same or less watts with full throttle and a little momentum, so the watts applied can not give a clear indication of the speed your at.
Brushless motors are synchronous so they spin at the same speed as the magnetic field rotates with no slippage, The controller increase's it's frequency with hall feedback to detect rotor position and increase the rotor speed, The current applied is the amount of torque
Bldc motor's tend to produce all their torque at zero rpm, max power at midrange and max efficency at high rpm, There's graphs on Google to see the typical characteristics but typically you don't want to load the motor to much and try keep the rpm high like a drill making a hole keep the motor singing and it will reward you with low running costs or increased battery range.
If your wheel spins at 80kph and your ride speed is 50kph when loaded then there's a high demand on torque and efficency will be crap you need to look at the graph to get geared decent and with a midrive it's easy with a dd hub it can be more tricky but they can still be torquey enough when in small rims.
This graph shows how the torque and efficency plots change as the volts and amps are both increased, (a mildly overvolted motor)
See how there's more torque available but the efficency zone has gone further up the scale and there's more overall power usage so with out careful gear selection it could lead to a motor that is using peak power constantly again a bad situation.
It's also possible to see from the graph that overvoltIng the motor and gearing it lightly so it can spin to max rpm easily can give an efficency of 75% at 250rpm and still be producing torque with the higher rpm over the stock motor that was all out of torque at that point.
The overall power will still be usable if the torque demand is low enough for the motor to have no issues in reaching the rpm even when climbing it's efficency will be higher than stock and the gearing back a bit and overvoltIng can actual give better climbing torque with simular speeds but much better range.
Running low volts is not a problem it can actually help in some situations like hubs with no gearing, as the efficency drops down the chart, I find with my mxus 3k dd hub i run it at 10s with 80amps phase so the rpm I need to reach for efficiency is lower and i still have good launch and climbing torque to maintain 20mph.
I can not reach as high as efficency as if I was at higher volts 20s etc but there's no lesser gearing option left so this was the way of making the hub work for my usage on bike paths and need to keep the original legality of my bike, on the plus side I get less wind resistance at 20mph rather than the 40mph I'd need to maintain at 20s, so I've made 20mph my sweet spot with the voltage used, gearing of the hub in the wheel and my self peddling along after lots of math and contemplating.
I can get upto 30 miles off 350wh so lowering the volts to the hub lowered my efficency a bit but being a hub Its hard to gear down, the only option was to use the smallest rim i could and lower the voltage to make efficency in the small wheel at slower speeds and then the lack of wind helped me gain overall with a steady 20mph easily achievable with my help, the overall power usage spikes up and down so I'm helping a lot and some points completely off the thumb throttle and I maintain the 20 mph.
Where a geared down mid drive could take that 350wh past 50 miles at a slower pace and geared lighter, it needs gears and to put it's power down through the chain to do it, I'm well happy with my ride no gears just simplistic and robust all over can deliver max torque off the line along with my peddling it shoots me upto 20 mph with very little issue and will be reliable over time, the electrical side and the push bike side, single speed is a must with decent power I leave bikes for dust at the lights if it had 20s and the tallest gearing I could find for myself to peddle at 40 mph then it would really rocket and the torque output would spread further over the speed range but then I'd be defeating the rides purpose of being a bike in legality eyes, at the moment a quick Bluetooth tune and I still get decent efficency that would not be possible at 20s range would suffer and only gearing could change it something hubs don't have easy access to.
The torque output is the current applied
Torque × rpm = power
Output power is measured in Hp
Current × voltage = input power measuered in watts
The watts being applied will rise as the torque demand is increased so half throttle at stall speed may equal the same or less watts with full throttle and a little momentum, so the watts applied can not give a clear indication of the speed your at.
Brushless motors are synchronous so they spin at the same speed as the magnetic field rotates with no slippage, The controller increase's it's frequency with hall feedback to detect rotor position and increase the rotor speed, The current applied is the amount of torque
Bldc motor's tend to produce all their torque at zero rpm, max power at midrange and max efficency at high rpm, There's graphs on Google to see the typical characteristics but typically you don't want to load the motor to much and try keep the rpm high like a drill making a hole keep the motor singing and it will reward you with low running costs or increased battery range.
If your wheel spins at 80kph and your ride speed is 50kph when loaded then there's a high demand on torque and efficency will be crap you need to look at the graph to get geared decent and with a midrive it's easy with a dd hub it can be more tricky but they can still be torquey enough when in small rims.
This graph shows how the torque and efficency plots change as the volts and amps are both increased, (a mildly overvolted motor)
See how there's more torque available but the efficency zone has gone further up the scale and there's more overall power usage so with out careful gear selection it could lead to a motor that is using peak power constantly again a bad situation.
It's also possible to see from the graph that overvoltIng the motor and gearing it lightly so it can spin to max rpm easily can give an efficency of 75% at 250rpm and still be producing torque with the higher rpm over the stock motor that was all out of torque at that point.
The overall power will still be usable if the torque demand is low enough for the motor to have no issues in reaching the rpm even when climbing it's efficency will be higher than stock and the gearing back a bit and overvoltIng can actual give better climbing torque with simular speeds but much better range.
Running low volts is not a problem it can actually help in some situations like hubs with no gearing, as the efficency drops down the chart, I find with my mxus 3k dd hub i run it at 10s with 80amps phase so the rpm I need to reach for efficiency is lower and i still have good launch and climbing torque to maintain 20mph.
I can not reach as high as efficency as if I was at higher volts 20s etc but there's no lesser gearing option left so this was the way of making the hub work for my usage on bike paths and need to keep the original legality of my bike, on the plus side I get less wind resistance at 20mph rather than the 40mph I'd need to maintain at 20s, so I've made 20mph my sweet spot with the voltage used, gearing of the hub in the wheel and my self peddling along after lots of math and contemplating.
I can get upto 30 miles off 350wh so lowering the volts to the hub lowered my efficency a bit but being a hub Its hard to gear down, the only option was to use the smallest rim i could and lower the voltage to make efficency in the small wheel at slower speeds and then the lack of wind helped me gain overall with a steady 20mph easily achievable with my help, the overall power usage spikes up and down so I'm helping a lot and some points completely off the thumb throttle and I maintain the 20 mph.
Where a geared down mid drive could take that 350wh past 50 miles at a slower pace and geared lighter, it needs gears and to put it's power down through the chain to do it, I'm well happy with my ride no gears just simplistic and robust all over can deliver max torque off the line along with my peddling it shoots me upto 20 mph with very little issue and will be reliable over time, the electrical side and the push bike side, single speed is a must with decent power I leave bikes for dust at the lights if it had 20s and the tallest gearing I could find for myself to peddle at 40 mph then it would really rocket and the torque output would spread further over the speed range but then I'd be defeating the rides purpose of being a bike in legality eyes, at the moment a quick Bluetooth tune and I still get decent efficency that would not be possible at 20s range would suffer and only gearing could change it something hubs don't have easy access to.
, My English is crap along with a long winded explination, it could be condensed a lot but it's there it's the very basic thing to start considering along with getting a grip on cell chemistry and it's favoured conditions etc.
