Hi!
I am unsure about the right KV value for my application (custom eBike/Pedelec) and I started to wonder, how important it really is.
My understanding is that I need to align the KV value together with the battery voltage so that I can reach my maximum desired speed. (If the motor runs to slow, it wouldn't support the cyclist anymore of course.)
For simplicity and focus, let's keep gear/pulley ratio out of the way and assume direct drive.
Let's assume these values:
- d_wheel=70cm
- V_max=30km/h
- U_bat_min=30V (10S battery)
That would mean:
- RPM_Vmax = 30 km/h * 1000 / (0.7m * 3.14) / 60 = 228 RPM
- KV = 228 RPM / 30V = 7.6 -> roughly 8
Until now, I thought in this hypothetic scenario would have to be roughly 8, but then I started to wonder if that is really true when using current (torque) but not RPM/duty control? Is that calculated KV value only the minimum in this case and any other value > 8 would work?
Reading a bit more on that topic I found out about motor characteristic curves and got some for different KV values (same motor) from two manufacturers (Flipsky, Maytech).
They seem to confirm that lower KV motors provide higher torque at lower current but higher voltage (due to more windings).
So for the hypothetic case described earlier, does that mean, while I could use any motor with KV > 8 in general, it makes most sense to use roughly 8 due to higher torque?