From an electrical point of view 4 motors should be more efficient as heat-loss is caused by amperage and voltage drop. The voltage drop increases linearly with current therefore the heat-loss rises exponentially with higher current.
For example:
Rmotor = 0.1Ω
Imotor = 30A
Ploss motor = Uvoltage drop * Imotor
Uvoltage drop = Rmotor * Imotor
=> Ploss motor = Rmotor * Imotor2
1 Motor:
0.1Ω * 30A2 = 90W
4 Motor:
4 * 0.1Ω * 7.5A2 = 22.5W
Mind you the values are just guesses and the “gain” in efficiency from more motors will likely be eaten up by the mechanical resistances, but for direct drives this may be a net gain.
So by your example I would end up using the same 90w but the heat will be reduced by 75%? @pakue meaning cool running motors at all times and ample power to be tapped at any time being my 3.2 torque would become 12.8 and my motors would be able to achieve a higher weighted rpm while staying cooler than a single drive
In that example I was just calculating with the heat loss (90W for the single setup). The actual power you pump in is obviously higher, maybe 500-1000W, but that is what gets you moving (TotalPower = HeatLoss + MechanicalPower).
The total torque in my example would stay the same as you are still giving a total of 30A (thats what determines the torque of the motor), which are just spread over more motors. If you would want the 12.8 Nm in total each motor needs 30A and the heat output is again 90W per motor.
Under the same conditions a 1WD will always generate more total (electrical) heat than a 4WD.
Yes, that is what I thought, this build will enable 60 amps to each motor as 4 batteries are 10s 10ah each @pakue motors are rated to 2450w and 65amp each but i figure a limit of 60 amp through vesc should be safe. Battery total is 1480w/h and each pack has a 200-300amp ability
@pakue as you’ve been the only one to show you know the science involved, do you concur with my estimation that this build will be able to travel up to and over 100km/70m range on a single charge whilst overcoming hills and hitting speeds in excess of 40km/25mph
Yes, that was my hope because a 10ah battery would probably only give me 30km range with a single motor, my hope is using 4 I will increase the range 400%
I am not sure If I get you correctly. You do not get double the range with 2 motors instead of 1 or 4x the range with 4. It’s just that using 1 motor for the same amount of work instead of 4 will be less efficient. By some percents, several, maybe even 10+.
not really but you really need to know your stuff to be able to calculate what the differences are. Longer cables mean more heat, connectors mean more heat… 2 motors are more efficient than one… Yep… But unless someone like pakue shows you the real calculations and specific examples you have no clue how important that difference between having 2 feet of wires vs 1 foot and having 3 plugs vs 5 will make. In most cases it doesn’t matter. But to know for sure you need to understand everything there is about it.
It’s not complicated. :::::: I^2R ::::::losses (current squared x motor resistance) are by far the biggest loss and four motors will allow a much lower squared current number in what would be then four equations reducing ultimate losses. So other than friction increasing from multiple belts and pulleys (which could vary greatly) having more motors is going to be more efficient.
Cables and plugs will have the same I^2R losses and the more motors and wiring and escs you have the less current they individually have to transfer so more efficient for the same power output compared to a single motor, wiring, and esc.
