Help-Me-wi
Going Along a Straight Path No Wind
Top Speed.
Answer
up hill or down
?
wind?
for how long?
wle
up hill or down
?
wind?
for how long?
wle
How can I design a go-kart power system around this electric motor?
M S
http://www.hobbyking.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=5142&aff=54444
This motor takes 48 volts maximum charge. I'm clueless as to what kind of
A) Voltage controller (to control acceleration)
B) Battery setup and connectors
C) Sprockets and how to connect them to the motor and wheels
.would be needed to make this motor work to drive a go kart? Any idea exactly what parts to get (not just the type, but what size, how to connect/assemble...) and where to get them?
Answer
Voltage Range: 20-48v
Non Load Current: 2.0A
Maximum Power: 6500W
Equivalent: 60-80cc Gas Engine
The specification is not all that complete. There is no spec for a critical figure, maximum current. Make an assumption that it is 6500W/48V = 135A. This is according to the "maximum power rating" but that may not be continuous. This motor is for model planes, and very likely is rated to a short time of a few minutes. It needs a copious air flow to keep it cool even so. It is also obvious that the resistance is incorrect, it may be 35 milli-ohms when hot, from the comments of measured 26 milli-ohms when cold. Even this low resistance means it dissipates 640W when at that current (I^2 x R). For comparison it is about the same physical size as a 200W motor continuously rated. A car starter motor rated in seconds may have similar current but only 12V, so this is 4 times the power but smaller.
You can run it from a 24, 36 or 48V battery. The RPM is specified as 130rpm/V so a 24V battery would be a max of 3120rpm up to 3640rpm (no load). User comments suggest as much as 144rpm/V at 24V. The 48V speed is double that (7200 rpm), which is getting to the upper range of some gears and sprockets definitely. I would use a 24V or 36V battery made of 2 or 3 x 12V batteries in series or 10 LiPo cells for 36V. This motor is like a car starter motor in current, so the battery physical size is important as well as its capacity. This reduces overheating. In operation, you will have to manage battery and motor temperature. Consider a fan. Use lithium polymer (LiPo) batteries for the best power to weight. The size (Ah capacity) depends on how long and how hard you run it. These are the trade-offs to win races.
The "esc" mentioned on the page is the matching brushless motor driver and the speed controller for radio control. Get a highest current model to suit this motor. The comments suggest a 100A model esc also works fine, which means the current has to be kept down. The first link is a 130A model. It uses the same drive signal as a radio-control servo. There are plenty of electronics boxes which produce this "throttle control" signal, being an adjustable 1-2ms pulse repeated every 20ms or so, with the width of the pulse proportional to required speed. They are sold as "servo testers", but can be made cheaply too. The speed controller has a maximum and a minimum voltage, and needs cooling at least through the heat-sink to an external heat-sink. I think a voltmeter on the battery and an ammeter on the motor or battery may be a useful thing. The voltmeter ~60V, the ammeter 150 or 200A DC.
The potential starting current with 48V fully charged battery (56V) is up to 2000A. The wiring resistance and the speed controller and the batteries reduce this. The running current is 130A maximum, but I would think less, like 50-80A is a more realistic continuous rating. You need a DC fuse or circuit breaker of 150A or 200A rating at the battery, and wire rated at this current, short run only. It may make sense to have a fan, like a car radiator fan if you use 48V to squeeze the most from it. That would be a separate 12V battery, so the trade off in weight may not make running full power the best way?
Drive reduction.
The speed has to be adjusted from the maximum calculated for rpm/v to the maximum road speed, taking into account the wheel diameter. I don't know whether you will have one wheel drive or a differential. If the road speed is too high, there will not be enough power and the motor will be overloaded, drawing more current than its rating. In theory once cruising the power is less, it is acceleration that needs power. I am not sure how the bearings will go with sideways load. This is too much for a bike chain.
The torque from the motor applies to most speeds and voltages, due to the maximum current:
torque_N.m = (60000 x Power_KW) / (2pi x RPM)
= (60000 x 6.5) / 6.283 x 6240
= 9.9Nm.
Formulas to work stuff out...
Wheel torque
The wheel torque is Efficiency x motor_torque_Nm x drive_ratio. So with 36V and 4:1 gears gives 4680/4 rpm and 39.8Nm reduced to say 75% for losses, so 1170rpm and 30N.m
Force from wheels:
Using the wheel radius and torque
Force_N = Torque_Nm / Radius_m
Acceleration from wheel force and vehicle mass..
A_m/s/s = F_N / M_kg
Velocity after period of acceleration..
With constant acceleration.
Change_in_Velocity_km/h = Acceleration_m/s/s x time_seconds x (3600/1000)
Fun project.
Voltage Range: 20-48v
Non Load Current: 2.0A
Maximum Power: 6500W
Equivalent: 60-80cc Gas Engine
The specification is not all that complete. There is no spec for a critical figure, maximum current. Make an assumption that it is 6500W/48V = 135A. This is according to the "maximum power rating" but that may not be continuous. This motor is for model planes, and very likely is rated to a short time of a few minutes. It needs a copious air flow to keep it cool even so. It is also obvious that the resistance is incorrect, it may be 35 milli-ohms when hot, from the comments of measured 26 milli-ohms when cold. Even this low resistance means it dissipates 640W when at that current (I^2 x R). For comparison it is about the same physical size as a 200W motor continuously rated. A car starter motor rated in seconds may have similar current but only 12V, so this is 4 times the power but smaller.
You can run it from a 24, 36 or 48V battery. The RPM is specified as 130rpm/V so a 24V battery would be a max of 3120rpm up to 3640rpm (no load). User comments suggest as much as 144rpm/V at 24V. The 48V speed is double that (7200 rpm), which is getting to the upper range of some gears and sprockets definitely. I would use a 24V or 36V battery made of 2 or 3 x 12V batteries in series or 10 LiPo cells for 36V. This motor is like a car starter motor in current, so the battery physical size is important as well as its capacity. This reduces overheating. In operation, you will have to manage battery and motor temperature. Consider a fan. Use lithium polymer (LiPo) batteries for the best power to weight. The size (Ah capacity) depends on how long and how hard you run it. These are the trade-offs to win races.
The "esc" mentioned on the page is the matching brushless motor driver and the speed controller for radio control. Get a highest current model to suit this motor. The comments suggest a 100A model esc also works fine, which means the current has to be kept down. The first link is a 130A model. It uses the same drive signal as a radio-control servo. There are plenty of electronics boxes which produce this "throttle control" signal, being an adjustable 1-2ms pulse repeated every 20ms or so, with the width of the pulse proportional to required speed. They are sold as "servo testers", but can be made cheaply too. The speed controller has a maximum and a minimum voltage, and needs cooling at least through the heat-sink to an external heat-sink. I think a voltmeter on the battery and an ammeter on the motor or battery may be a useful thing. The voltmeter ~60V, the ammeter 150 or 200A DC.
The potential starting current with 48V fully charged battery (56V) is up to 2000A. The wiring resistance and the speed controller and the batteries reduce this. The running current is 130A maximum, but I would think less, like 50-80A is a more realistic continuous rating. You need a DC fuse or circuit breaker of 150A or 200A rating at the battery, and wire rated at this current, short run only. It may make sense to have a fan, like a car radiator fan if you use 48V to squeeze the most from it. That would be a separate 12V battery, so the trade off in weight may not make running full power the best way?
Drive reduction.
The speed has to be adjusted from the maximum calculated for rpm/v to the maximum road speed, taking into account the wheel diameter. I don't know whether you will have one wheel drive or a differential. If the road speed is too high, there will not be enough power and the motor will be overloaded, drawing more current than its rating. In theory once cruising the power is less, it is acceleration that needs power. I am not sure how the bearings will go with sideways load. This is too much for a bike chain.
The torque from the motor applies to most speeds and voltages, due to the maximum current:
torque_N.m = (60000 x Power_KW) / (2pi x RPM)
= (60000 x 6.5) / 6.283 x 6240
= 9.9Nm.
Formulas to work stuff out...
Wheel torque
The wheel torque is Efficiency x motor_torque_Nm x drive_ratio. So with 36V and 4:1 gears gives 4680/4 rpm and 39.8Nm reduced to say 75% for losses, so 1170rpm and 30N.m
Force from wheels:
Using the wheel radius and torque
Force_N = Torque_Nm / Radius_m
Acceleration from wheel force and vehicle mass..
A_m/s/s = F_N / M_kg
Velocity after period of acceleration..
With constant acceleration.
Change_in_Velocity_km/h = Acceleration_m/s/s x time_seconds x (3600/1000)
Fun project.
Powered by Yahoo! Answers
Tidak ada komentar:
Posting Komentar