Hummina Shadeeba
1 MW
If I have a 55kv motor and an esc that will do 140 amps what torque is possible from the shaft?
Please show ur math. I get lost on the radians part.
Please show ur math. I get lost on the radians part.
https://en.wikipedia.org/wiki/Prony_brakePower output in SI units may be calculated as follows:
Rotary power (in newton-meters per second, N·m/s) = 2π × the distance from the center-line of the drum (the friction device) to the point of measurement (in meters, m) × rotational speed (in revolutions per second) × measured force (in newtons, N).
Or in English units:
Rotary power (in pound-feet per second, lbf·ft/s) = 2π × distance from center-line of the drum (the friction device) to the point of measurement (in feet, ft) × rotational speed (in revolutions per second) × measured force (in pounds, lbf).
A substantial pre-load is then applied to the ends of the band, so that each spring balance has an initial and identical reading. When the engine is running, the frictional force between the drum and the band will increase the force reading on one balance and decrease it on the other. The difference between the two readings multiplied by the radius of the driven drum is equal to the torque. If the engine speed is measured with a tachometer, the brake horsepower is easily calculated.
Ke = back EMF constantK M is the motor ( SIZE) constant
In SI units, the motor constant is expressed in newton metres per square root watt
If:
Kt=(N*M)/A (torque constant)
Ke=V/(rad/sec) (Back EMF)
Then
Kt=Ke=1/Kv
( newton meter per amp) (kT)
.....multiply the product (NM*rad/sec) by 1352.4 to get the equivalent in (inch ounces*rpm). 1352.4 is a conversion factor and is not a magic number that only applies to electric motors. It is made up of the conversion of:
Newtons to ounces
Meters to inches
radians to revolutions
seconds to minutes
In SI units, the motor constant is expressed in newton metres per square root watt
Newton Per Ampere Per Meter (N/A-m) is a unit in the category of Magnetic field strength. It is also known as newton/ampere-meter. Newton Per Ampere Per Meter (N/A-m) has a dimension of MT-2I-1 where M is mass, T is time, and I is electric current. It essentially the same as the corresponding standard SI unit T.
How to calculate torque of motor:
Torque is nothing but a momentary force developed at the time of force is applied to the motor. The unit of torque is N.m (Newton-meter). In other words, Torque T(N.m) is equal to the ratio between the electrical power P(W) in watts to the acceleration.
1RAD = 57.2958 degree.A pound-foot (lbf⋅ft) is a unit of torque representing one pound of force acting at a perpendicular distance of one foot from a pivot point. Conversely one pound-foot is the moment about an axis that applies one pound-force at a radius of one foot.
The value in SI units is given by multiplying the following approximate factors:
One pound (force) = 4.448 222 newtons
One foot = 0.3048 m
This gives the conversion factor:
One pound-foot = 1.35582 newton metres.
SI units for the torque constant are newton metres per ampere (N·m/A).Since 1 N·m = 1 J, and 1 A = 1 C/s, then 1 N·m/A = 1 J·s/C = 1 V·s (same units as back EMF constant).
To translate this model to a rotating motor, one can simply attribute an arbitrary diameter to the motor armature e.g. 2 m and assume for simplicity that all force is applied at the outer perimeter of the rotor, giving 1 m of leverage. "
DogDipstick said:What is the nM/Amp of the motor?
If you do not have this figure, you will have to use a controlled prony dynometer to figure this number. Cannot calculate without.
( newton meter per amp)
mxlemming said:Short answer...
Use SI units
kV to rads-¹/V
Invert it
That's your Nm/A
Multiply by amps
E.g.
55rpm/V is 55x2pi/60 is 5.76rads-¹/V
kT is 1/5.76 is 0.174Nm/A
x140A is 24Nm
That's it.
If your motor saturates, the torque will be lower.
Note... rads-¹/V = radians/(Vs) it just strangely feels more natural to write it in terms of rads-¹ (speed) and Volts
mxlemming said:The ratings in table 48 are fairly close to the level I'm driving my current ebike at, and the belts seem fine (5mhp optibelt and contitech htd5m.
I think they're ratings for a long life expectancy (50k hours from memory is usual for belt ratings), if your willing to accept while service life levels (1k hours would be fairly long life) you can probably substantially overdrive them.
I've found it's very dependent on the stiffness of the rigid link between the pulleys. See my giant trance thread for my updated bracket and the extra bearing and tensioner I've added.
Hummina Shadeeba said:mxlemming said:The ratings in table 48 are fairly close to the level I'm driving my current ebike at, and the belts seem fine (5mhp optibelt and contitech htd5m.
I think they're ratings for a long life expectancy (50k hours from memory is usual for belt ratings), if your willing to accept while service life levels (1k hours would be fairly long life) you can probably substantially overdrive them.
I've found it's very dependent on the stiffness of the rigid link between the pulleys. See my giant trance thread for my updated bracket and the extra bearing and tensioner I've added.
What width belt u use and what torque it does? I’d like to get away with 9mm wide GT2 (5mm pitch) and using a Vesc at 140 amps peak, and with such a huge gear ratio (like 3:1 on first stage and 8:1 total) I’d think I’d be better off with such speed instead of torque and less stress but the calculator shows the opposite
Thanks for ur help.. it is a lot of help
mxlemming said:Hummina Shadeeba said:mxlemming said:I imagine the 9mm belt would suffer a lot at 24Nm. But I'd also be quite surprised if that motor could really supply that torque level.
If you can use 36:105 instead of say 18:52 (not sure what your planning) i expect in practical terms you'd get 3 or 4x the capacity.
Id like to know what torque is possible out of the motor based on its dimensions but whatever it is I think it will be more than I could use at the tire with 8:1 gearing.
36:105 sounds good with the 9mm wide 5mm pitch.