My esk8 build plan/BOM:
I’m planning to build a single motor belt driven board to get me up steep hills and go thrillingly fast. I weigh around 85 kg but I want to support some extra heavy users or luggage. This is going to be a sort of stream-of-consciousness type writing down my thoughts post and I need some advice telling me if I’m doing it right, if my math is off, etc.Here goes!
I found a few 4000W motors that seem appropriately powerful without breaking the bank:
motor: aps 6384s £90 (I want sensored motors so I can use FOC to start from standstill and increase efficiency) 130kv: 200kv:
I want to use a 12 cell LiPo pack (12S) to have a lot of power, so I’m operating at 44.4v nominal:
Since I want to use the ABEC11 107mm flywheel, it was recommended to use a 44T wheel pulley (can’t find the source for this statement). I am definitely not decided on gear ratio.
Pulleys: HTD3, 15mm belt, 16T/44T gear ratio 1:2.75 https://www.beltingonline.com/16-tooth-htd3-pulley-16-3m-15f-7737?zenid=089bs39h0ps2hqt2jdo4d4cc24 https://www.beltingonline.com/44-tooth-htd3-pulley-44-3m-15f-7749?zenid=089bs39h0ps2hqt2jdo4d4cc24
Driven rpm at this ratio: 5772rpm/2.75 = 2099 8880rpm/2.75 = 3229
Circumference of 107mm wheel: 336.15mm
Speed calculations: 130kv: 2099 rpm * 336.15mm = 705578,85mm/min v/60000 = 11,76 m/s = 42kph
200kv: 3229 rpm * 336.15 mm = 1085461,965mm/min v/60000 = 18,1 m/s = 65kph
How much torque do I need from the motor ?? Torque T = Fr, F = ma Worst case scenario mass 120 kg Desired acceleration 0-10 m/s in 5s (arbitrary numbers here) F = 120 kg * 2 m/s^2 = 240N r = 107/2 = 53 mm = 0.053 m T = Fr = 240N * 0.053m = 12.72Nm
For the 130kv motor, max torque = 5.8Nm (according to sales page). Does this mean I need a gear ratio such that: 13Nm/5.8Nm = 2,24 ? If that is the case I should have enough wheel torque with this motor given a ratio of 2.75 which should give me a max wheel torque of 15,95 Nm.
For the 200kv motor, max torque is listed as 3.8Nm. 13/3.8 = 3,42: Seems like I’d need more of an unconventional gear ratio to make it work with this motor.
Is my math completely bonkers? What haven’t I thought of that is absolutely critical? I’ll probably make another post later in the electrical category for the rest of the stuff, with ESC, battery &c.