General stuff...what can I expect from an electric motor..
Electric Vehicles, like electric cars, buses, bikes.......
Industrial Applications, pumps, motor spindle drives, hand tools, servos...
Hobbies, model cars, boats, and planes.....
Robotics, powered actuators, lifting and holding systems...
Fans, blowers
Books reference material
General Stuff: How does a motor run?
What controls the speed of a motor?
How many kinds of motor are there?
What's the difference between an AC and a DC motor?
How can I reverse the direction of a motor?
Can I use a three phase motor on my single phase home supply?
What is a PM motor?
Why do magnets attract each other?
Can I make a simple motor?
What is the best book on electric motors?
What motor do I need to convert my car to Electric Drive?
How easy is it to design a motor?
Why are electric cars so slow and heavy?
Why can't you just a put a motor in each wheel?
How do I add electric drive to my bike?
Why does my motor keep burning out?
How about a full size electric plane?
What type of motor shall I use?
What size motor do I need?
What does a high tech motor cost?
Can I use my motor as a generator?
What's the peak output for a motor?
Can I get more out of my motor?
I want to build a GO cart ...help?
Some motor manufacturer's and their URLsMOTORS
WORLDWIDE
Lots of motor goodies at the end of this page...
How does a motor run? An electric motor is a device that can produce a force when electricity is applied. The force is usually the attraction or repulsion between magnets. Usually the magnets are arranged so that the force is tangential to a fixed axis called a shaft. This produces the usual rotary motion, but it can be arranged to work in a straight line hence "linear motors". This force then produces torque, ( a distance times a radius) , measured in ft-lbs, oz-ins, gm-cms., or some other unit like newton-meters.( If your arm were 2 feet long and you held a 6 ounce apple in your hand; the torque your arm muscles would have produce, to cancel the weight of the apple, would be about one newton-meter).
What controls the speed of a motor? The speed at which the motor runs depends on the load that is put on the shaft trying to slow it down, and also on the design and type of motor. There is no lower limit but as the speed increases some motors will not work because of mechanical problems, for example brushed motors are not much use over 15,000 RPM. At very high speeds over 100,000 RPM bearings start to be a problem and air resistance enters the picture. A vacuum is one way to get rid of the friction but then the motor has difficulty in getting rid of it's heat. By using magnetic bearings and a vacuum speeds to 1 million RPM are possible. Each type of motor has a different method of controlling the speed. This can be just varying the voltage for a DC motor or universal AC/DC motor to complex electronic circuits often using micro-controllers for the brushless motor.
How many kinds of motor are there? There are many different kinds( about 20 main types ) of electric motor but nearly all use the attraction or repulsion of magnets. Either one or both of the magnets is an electro-magnet, that is a coil of wire with electric current flowing through it. . To make the effect stronger the coil is usually wound around an iron core. Some motors use the attraction of a piece of steel to a magnet, a "reluctance"motor is this type . For more information on the many different types of motor try your local library, look under Electricity, Motors, Electrical Engineering and Physics,
What's the difference between an AC and a DC motor? All practical motors are really AC in that the magnetic field has to keep changing direction so that the moving part is attracted or repelled by the stationary part. In a DC motor the voltage applied is made into a kind of AC by a device called a commutator in a brushed motor or by electronic switches in a brushless motor.
How can I reverse the direction of a motor? mUnless it is a shaded
pole motor it can probably be reversed. If it's an AC motor then reversing
the wires going to either the start winding OR the main winding will reverse
the direction, if it's a 3 phase motor then reversing any pair of the main
winding will also reverse the rotation. If it's a DC motor reversing either
the field OR the armature windings will reverse it. If it is a permananet
magnet motor then just reversing the wires to the motor will work for a
brushed motor and for a PM brushless motor the controller should have a
reversing switch or jumper. ( Check with the controller manufactuer )
BTW: Some motors have auxialliary windings
and this scheme may not be OK. Always have a fuse in the circuit so it
can blow and NOT your motor!.
Can I use a three phase motor on my single phase home supply? The answer is yes and no! You can but you'll have to make the motor think it's getting a three phase supply. This can be done in several ways, you can read about it in. Phase conversion or using a 3 phase motor on single phase supply
What is a PM motor? Permanent magnets ( PM ) are also used to produce one of the two magnetic fields of the motor, instead of a current carrying coil of wire. These motors have the advantage that once the magnets are made and energized they give free magnetism for life (there are some free things after all ! ) . Using permanent magnets makes the motors more efficient because you save the power that would be used to make an electro-magnet. (This coil is often called a field winding because the magnetic forces produce a field of magnetism).
Why do magnets attract each other? Although it is easy to see the effect of two magnets attracting each other there is no clear understanding of what causes the attraction. A magnet sticks to the fridge door because it produces a magnetic field in the steel door of the opposite polarity, an effect called induction. The force per unit area produced by a magnet is proportional to the square of the flux density and the area of the magnet.
Can I make a simple motor? Yes you CAN, it's easy and will take only half-hour From... Beakmans World
What is the best book on electric motors? Specialized books on every type of motor have been written and I suggest you try a library or technical book store.
I am making a GO CART what should I know? GOCARTS:
I don't know much about building GO carts, but my advice is to use
a 24 or 48 volt motor witha good gear reduction so you have plenty of acceleration
and good grade climbing ability. As to a motor a DC brushed motor $15-120
( my guess ! ) should be fine unless you have more than $5000 to spend;
then go to http://www.Aveox.com www.aveox.com
and tell them you want the best go- cart motor they can build. Surplus
motors can be found at places like C & H Sales in Pasadena CA, and
H & R Surplus, go down to the SURPLUS STORE LIST of URL's . Also you
might want to read NUTS & VOLTS magazine they often have good info
on this kind of topic. If you want to do some calucations look up my calc..
page and use your brains!! EVcalcuation,html
or goto go-cart.html
What motor do I need to convert my car to Electric Drive? Here's
a reply that I gave to one enquirer. EVcalcuation,html
This is about as easy to answer as what gas engine do I need for a gasoline
powered car! The choices are: DC brushed motor, DC Brushless motor, or
Induction Motor. Within each of these main choices are some others for
example under DC brushed you can have a wound field or a permanent field.
This is also true for a brushless motor although wound field motors are
only worth considering if you are trying to do the conversion " on the
cheap". It's possible to get surplus wound field motors like starter motors
from aircraft that will drive a small car.
If you are going to use a new motor then the choice is probably going
to be either of the first two, with the first choice being the DC brushless.
It is the most efficient and trouble free motor and is available in sizes
suitable for electric drive. The induction motor although simple and fairly
efficient needs an expensive controller. The power you need depends on
the application, if it's for flat terrain then a 10 HP motor will be fine,
but if you have some serious grades then 50 HP may be a better choice.
Most electric motors can deliver a lot of power for a short time so a 10
HP continuous rated motor might deliver 25 HP for 1 minute without overheating.
( Whatever motor you select make sure it has
some kind of thermal protection to avoid burning out. It is better to wait
for a hot motor to cool down than to have to replace a burnt out winding
)
The DC brushed motor with a permanent magnet field is a good second
choice and can use a simple controller to adjust speed. It is also available
from "kit car"electric companies who can give you technical support if
you're not an electro-mechanical engineer! If you want the very best select
the DC brushless motor with a rare earth permanent magnet field. Decide
on the performance you need and get a motor matched to your needs. The
motor manufacturer will help you with the final selection. Read the rest
of this FAQ as there questions answered that are directed specifically
to electric vehicles. Keep in mind that
"MOTORS DELIVER TORQUE SO GEARS ARE IMPORTANT"
How easy is it to design a motor? Efficient electric motors are very difficult to design because there are so many interactive parameters that must come together to give the result. Also most of the parameters have a non-linear relationship with each other so to solve the problem requires more than simple algebra. Computer simulations of magnet field equations help with some of the parameter but to get it all together takes a combination of electrical and mechanical engineering, and to control the motor an electronics and feedback control systems specialist will round out the team.
What does an electric motor weigh?
The very best that I can do is 5000 x HP/RPM in pounds. For example, a 20 HP motor at 5000 RPM would weigh 5000 x 20/5000 = 20 pounds, this is a state of the art motor. A good small induction motor will weigh about 5 times this and a brushless with permanent magnet field about 2-3 times.
Why can't you just a put a motor in each wheel? Well you can
and you can't . It depends on what you expect to get from the car and
what you are going to use it for. The highest efficiency will come from
an "in-wheel motor" because you get rid of the gears but the weight and
cost will be higher than a motor on-board the vehicle. Electric motors
produce torque, a given size motor produces so much torque for so much
heat dissipation. This measurement of a motor is called the motor constant
Km. ( I think that the ratio Km/Weight is a more valuable measurement especially
where weight is important such as for electrically powered aircraft.) Power
is the product of torque and speed, so the faster the motor can run the
more power it can produce.
Since the wheels have to go at a speed, decided by how fast you want
to travel, it sounds like a good idea for the motor to drive the wheel
directly. However it takes a certain torque to move the car and this torque
has to come from the motor. If the motor is in the wheel then the motor-torque
must equal the wheel torque. Remember that little tricycle with a pedal
attached to the front wheel that you had when you were a kid. Remember
how you couldn't get up a hill with it. That was because your body couldn't
produce enough force ( torque ) on the pedal. A ten speed bike (or a 24
speed mountain bike) allows you to multiply the pedal force ( torque )
so you can go up steep hills. You trade off speed for torque.
As an example a motor that could drive a small car needs to produce
about 5 hp at 1000 RPM if mounted in the wheel, such a motor will weigh
about 25 pounds. Now at 10,000 RPM a brushless PM motor that produces 5
hp will weigh only about 8 pounds. The difference ( 30-8 =22 ) pounds is
not all gained because you have to reduce the speed of the motor to the
wheel speed of 1000 rpm using a gear box that will weigh about 8 pounds.
This still makes the high-speed motor plus a gearbox lighter and usually
less expensive than the in-wheel motor. It also gives more flexibility
because a variable gearbox allows the driver to adjust for the load and
grades.It also dramatically improves the efficiency when starting from
a standstill. Imagine trying to drive a gasoline car if you only had top
gear, or better still think about your tricycle...! For some applications
the extra weight may be OK. and an in-wheel motor makes sense, the overall
efficiency can be very high, as much as 98%, the vehicle will be very quiet
since no parts are moving faster than the wheels. (It will sound as though
you are coasting). Also goto EVcalcuation,html
If you go to This is what you get from an IN-WHEEL motor and if you go to special in-wheel for Solar Race Cars you'll get a good idea of what an in-wheel motor looks like.
How do I add electric drive to my bike? This can be easy if you keep two things in mind, don't expect to make long trips , and use the motor as an assist. A small motor with a continuous output of 500 watts will provide plenty of power. You can put out about 1/8 HP or 746/8=93 watts. so you would have five times your usual power. However for a short time you might be able to put out 2 HP ( only for 10 seconds or so !) so the 500 watts might come in handy when you're trying to get away from the traffic lights. Also you'll need to gear down the motor to the wheel speed. Unless you want a very heavy motor the motor will be running at 5,000-15,000 RPM . Some motors are available with built in gearboxes but they usually will only give you a 3 or 4:1 reduction . The cranks on your bike will be usually at 50-100 RPM, that's a long way from the motor speed. Some builders use a small tire or roller on the motor and rest it on the outside of the wheel tire; this is simple, but the friction eats away a lot of power. A chain reduction ( if kept clean ) works well , and it will be really helpful if you can use the built in reduction on the bike. A couple of 12 volt small car batteries or a lighter NiCad pack will give you a good range 30-40 miles. You'll also need a speed controller. Since the power is similar to that used with model planes and cars, check out what they use. ( Cruise the www under hobby cars electric) also check out AVEOX who make the worlds leading hobby electrics http:/www.aveox.com/~motors. A brushless DCPM motor will be the best, followed by the PM brushed motors. Cost for motor and controller, gears etc. will run from $2000 down to $50 for an all surplus DIY project . You can also use an in-wheel motor see This is what you get from an IN-WHEEL motor
Another ebike question..".I
am interested in building an ebike for personal use. I visited your
website and have a few questions. I am very interested in
purchasing a 12 volt electric motor/controller combination that
could be used on a modified bicycle frame. I envision a motor
in the 5 HP
ballpark. Does this sound about right? How much would
such a motor with controller weigh? What would be the approximate
current flow of a
5 HP motor at an RPM that would move an ebike at around 35 mph?
How long would this motor operate on a deep-discharge type lead-acid
battery? Are there other types of batteries that you recommend
that provide better power/weight ratios? Lots of questions,
but you seem to
be very knowlegeable in this area and I am just starting to put
some figures/designs together. Basically, I am asking for your help
to steer
me in the right direction. I am a mechanical/electrical
engineer, currently working as a helicopter pilot. Has anyone used
one of your
motors in a successful ebike? Thanks for your help. "
The 5 HP power is far to high. You can
assume that for each HP you will need 1000 watts of energy. A 70 pound
lead acid battery will
provide only about 1000 watt-hours. This translates
into 1 Hp-hr so a 1 HP motor on the bike could run for an hour.
The motors I design are all custom and cost
from $5,000-$35,000 for 2 prototypes. To get a feel for the ebike I would
start with a 1/2 HP motor
and use a good gear or chain reduction. The
higher the reduction the better as the emotor will work best at high speeds
for efficient use. You
can get surplus motors for 24 volt use in
the aircraft industry.. may be you can find an old actuator motor? A couple
of small car batteries will do to
get a feel for the project you can then run
either in series or parallel to make a simple speed controller. The car
batteries ONLY useful
properties for EV use are low cost and availability.
If this all works well spend some time on the EVlistserver and you will
get losts of
support. ( GO
Back to: main page for info on the EVlistserver:
MAIN PAGE )
Why does my motor keep burning out? This is probably due to incorrect match between the load and the motor. Read the nameplate ratings and check that the use matches the motor's output. Most often running the motor at a faster RPM if a variable speed and using a simple reduction will change the position dramatically. Some single phase induction motors use capacitors to start the motor and also to assist with torque while running. These capacitors do fail and should be checked out. Low line voltage or running an induction motor on an incorrect voltage is bad news. The current will be much higher than the rating even under light loads and starting may impose a very hard burden on the motor. It could also be the control system is defective or that there are loads that you are unaware of. Monitoring the current with a recorder might be a useful way to check this. Installing a circuit breaker to limit the current will also work , but take care that no danger is possible when the motor suddenly stops working. Get some help from your motor supplier they are usually very knowledgeable and will offer solutions from their own experience.
How about a full size electric plane? It would be OK if electricity could be stored as efficiently as fossil fuels like kerosene and gasoline. Even with the poor performance of batteries an ultralight or glider electric drive is practical and attractive because of the ease of use and almost zero maintenance. Also the shape of electric motor means you can put them anywhere, even buried in a wing. Solar powered planes are possible and a hybrid system with inboard turbines and electric drive has some devotees.The hobbyists are constantly pushing what electric planes can do and the hobby pylon races are now won by electrics...so look out for the future! A solar powered plane flying at 70,000 feet could keep in sync with the sun and provide a cheap "satellite" . See my comments on FUEL-CELLS above, a fuel-celled powered plane with electric drive looks a good bet very soon... you read it here first!
When the motor manufacturer knows these critical answers then you can get practical help. The end application is often important because of safety, weatherproofing and reliability. Give the motor manufacturer every bit of information you have. They will be able to help you much better.If you give me the information I'll try and direct you to an appropriate motor manufacturer. See the list of motor manufacturers below...
What size motor do I need? First you need to know the final speed and then decide if you can put any speed reduction between the motor and the application, if you can, the motor will be smaller and lighter. Induction motors can run at a variable speed with a special controller but remember that motor size for a given job will be smaller if you can use a higher RPM. Also don't get an oversize motor they will consume more power and the running cost may be a significant factor especially when the motor runs continuously. A small improvement in efficiency even at the higher initial cost will usually pay for itself in a few years. Get the motor supplier to calculate the payback period, you will be favorably surprised.
Where can I find a simple AC line operated geared motor? I usually suggest VanWeise Gear company for production designs but there are other companies like Bodine that make excellent geared motors. See the list of motor manufacturers below...
Band Saw motor?
Hi, do you have any suggestions as to how to control the motor speed
of a band saw... 115V single phase 1725RPM type of motor... Is this a "line
frequency = speed design?
The kind of motor used on most band-saws is a an induction motor. You can control the speed by using an expensive variable frequency and voltage converter or SCR speed controller that simply reduces the on time for each cycle, this does reduce speed but also the power available so at low speeds the power will be very low and the motor will stall easily, The simplest and best way is with a variable speed drive using a belt-pulley system. Alternately you can get a DC motor and controller. The cheapest way is just to use stepped belts as they so in most drill presses. This has the advantage of increasing torque as the speed goes down.
Here's a list of motors manufacturers
WORLDWIDE !!!! MOTORS
WORLDWIDE
Curtis PMC Controllers for EV's Curtis
PMC
Aveox controllers for Brushless motors, hobby and industrial,
also servo systems AVEOX
H&R good source for a wide variety of surplus H
&R
C & H SALES http://www.candhsales.com
Alltronics Lots of great surplus Alltronics
Please let me have any good surplus companies
I'll add them in.
Roger Arrick asks: Can I get Arrick Robotics listed as a "manufacture
of PC-based stepper motor control systems and XY positioning tables"
at http://www.robotics.com" ? Sure Roger...here it is Arrick
Robotics
This is a technical article about Universal
Motors that David Evans
published this year ( 1998 ). http://www.gselectric.com/electric/universl.htm
ROBOT WARS:
Just check this out: these machines use a lot of high tech skills and
servo systems;http://www.customforum.com/robotwars/
What's the peak output for a motor?
For most motors the peak output is limited by the design. Induction motors have a peak output torque of from 10 times running torque to just more than the running torque. Permanent magnet motors are limited by the type of magnet, some will demagnetize permanently if the motor current is too high. For those brushless rare earth magnet motors the peak may be 100 times the running torque. For a brushed motor the peak is usually the current limit of the brush commutator system. The thermal time constant of the motor may be important if the motor is expected to produce higher than rated torque for extended periods.
Can I get more out of my motor?
It depends why the motor is not giving you what you need. If the motor is simply getting too hot then a fan may be the answer. If the speed is too low then may be you can change the gearing between the motor and the load. A motor controller may allow you to change the speed range. If your motor is an induction motor increasing the voltage will give you more power, at the expense of increased heat. Increasing the capacitance value in a single phase capacitor run motor may help. Most DC motors will give you more power ( same torque but higher RPM ) as you increase the voltage; as the speed will increase you will have to increase the reduction in a gear box or belt drive so your final load speed is the same.
Here's some useful motorconstants and conversions
You can reach me by e-mail at: EMAIL