Are you sure about that? The motor alone is listed as weighing 4.3kg on the Revolt website.....boisrondevens wrote:I only add 5 pounds to the bike with motor and controller.
boisrondevens wrote:Motor shaft: 11t
Rear wheel: 52t
Here's my back-of-the-envelope calculation (please correct me if I'm full of BS):gwhy! wrote:boisrondevens wrote:Motor shaft: 11t
Rear wheel: 52t
so you are running 100v with a 45kv motor on a 26" wheel with a ratio of 11:52 if im understanding this correct
and the motor is happy is it i.e don't get hot
i just have my doubts about the 80a cont with a kV of 45ARod1993 wrote:Here's my back-of-the-envelope calculation (please correct me if I'm full of BS):gwhy! wrote:boisrondevens wrote:Motor shaft: 11t
Rear wheel: 52t
so you are running 100v with a 45kv motor on a 26" wheel with a ratio of 11:52 if im understanding this correct
and the motor is happy is it i.e don't get hot
According to Wolfram Alpha that would gear the bike up to about 73-74mph unloaded. Using Wolfram Alpha, the standard drag equation (Fd =0.5*Cd*A*p*V^2), and appropriate values for individual terms (effective frontal area (Cd*area) of 0.38m^2 taken from the abstract of this PubMed paper, 1.225 kg/m^3 as the density of air at sea level, and 33.1m/s (a little over 74mph) as the velocity), the drag force on the vehicle at 74mph is about 255N. That force is then acting over a radius of about 13 inches (assumes a 26-inch bike wheel), giving you a back torque on the wheel of 82.88Nm. Feed that through the 11/52 gearing you're using, and you get a back torque of about 17.5N*m on the motor. A motor with a KV of 45 requires about 4.72 amps per N*m of torque you want to put out, so you'll need about 80A or so to actually sustain the torque to overcome drag at that speed. That motor's rated for 60-80A continuous, maybe more, so it should be fine.
That seems fine. I used a loaded speed of 65mph in my spreadsheet and got a torque at the motor shaft of 14.2Nm. The motor weighs 4.3kg so that requires a specific torque of 3.3Nm/kg, which is believable....ARod1993 wrote:Here's my back-of-the-envelope calculation (please correct me if I'm full of BS):
According to Wolfram Alpha that would gear the bike up to about 73-74mph unloaded. Using Wolfram Alpha, the standard drag equation (Fd =0.5*Cd*A*p*V^2), and appropriate values for individual terms (effective frontal area (Cd*area) of 0.38m^2 taken from the abstract of this PubMed paper, 1.225 kg/m^3 as the density of air at sea level, and 33.1m/s (a little over 74mph) as the velocity), the drag force on the vehicle at 74mph is about 255N. That force is then acting over a radius of about 13 inches (assumes a 26-inch bike wheel), giving you a back torque on the wheel of 82.88Nm. Feed that through the 11/52 gearing you're using, and you get a back torque of about 17.5N*m on the motor. A motor with a KV of 45 requires about 4.72 amps per N*m of torque you want to put out, so you'll need about 80A or so to actually sustain the torque to overcome drag at that speed. That motor's rated for 60-80A continuous, maybe more, so it should be fine.
Looks like a 52t chainring bolted to a disc brake rotor? I wonder if you shouldn't flip it around so the rotor spokes are in tension rather than compression. What kind of hub is that with disc rotor mounts on both sides?boisrondevens wrote:I have made the 52t sprocket to fit the rear hub freewheel.