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amirengineer
10-24-2008, 09:21 PM
hi everybody,
i'm just new here and i found a very intelligence ppl over here whom have a very good knolwge about brushless dc motor...so as i'm going to build my project (acctually it's not a plane,it's a robot)and i'm planing to use a brushless motor but i've a very lettel experient in this field so i'll be greatfull if somebady would halp me here..

i'wont be heavy on u ..so i just need 2 know a few things

*where can i get a good quality brushless dc motor from the ineternet?
*i knew that i should have a ESC & i think they must b sync. ,so how can i know the matching part(what's the interfaces between them) ?does this controller control the speed and the direction or just 1 of them?
*should i use shaft encoder or does the ESC can do it's func.
that's all ,

Fly Time
10-24-2008, 09:38 PM
hi everybody,
i'm just new here and i found a very intelligence ppl over here whom have a very good knolwge about brushless dc motor...so as i'm going to build my project (acctually it's not a plane,it's a robot)and i'm planing to use a brushless motor but i've a very lettel experient in this field so i'll be greatfull if somebady would halp me here..

i'wont be heavy on u ..so i just need 2 know a few things

*where can i get a good quality brushless dc motor from the ineternet?
*i knew that i should have a ESC & i think they must b sync. ,so how can i know the matching part(what's the interfaces between them) ?does this controller control the speed and the direction or just 1 of them?
*should i use shaft encoder or does the ESC can do it's func.
that's all ,
Brushless motors for aircraft are generally designed to run in just one direction, though the direction of rotation is dictated by the ESC, not the motor. You can change the direction by swapping any 2 of the 3 wires between motor and ESC. If you are looking for a bi-directional setup, you might look into RC car power systems, where the motor direction can be reversed by the ESC without manually swapping wires.

If you decide that an aircraft motor is suitable, then I recommend buying an ESC/motor combo from any number of internet sellers. For USA sales, I like headsuprc.com. They have many combos to choose from. There are many different kinds of motors, mostly differentiated by speed (measured in rpm/volt or kv) and power handling (maximum current measured in amps). Also there are two different basic types of brushless motors: inrunners and outrunners. Inrunners are generally for high RPM direct drive applications and gearboxes, whereas outrunners are usually for direct drive applications (usually, but not always).

Not sure what a shaft encoder is, so not sure I can help with that. The ESC controls the motor's speed, and many (not all) also provide regulated voltage to the radio receiver (battery elimination circuit or BEC). Most also have programmable features that prevent the battery from over-discharging, among other things.

Hope that helps get you started. Feel free to ask more questions.

amirengineer
10-24-2008, 09:56 PM
really ur reply was very helpfull,but i wonder ..u know the motor u use for a plain to just rotate the fan (as i think)is not the motor whom gone move a robot u know ,i need to know what exactly the good choice for a robot ..does the inner motor have the power to move a robot with a high rpm or it just do a good performance with the light stuff like fan..etc,or should i use the outer for it's power shaft?
10x alot again

Fly Time
10-24-2008, 10:12 PM
really ur reply was very helpfull,but i wonder ..u know the motor u use for a plain to just rotate the fan (as i think)is not the motor whom gone move a robot u know ,i need to know what exactly the good choice for a robot ..does the inner motor have the power to move a robot with a high rpm or it just do a good performance with the light stuff like fan..etc,or should i use the outer for it's power shaft?
10x alot again
Since I don't know much of anything about robots, it's hard for me to answer that question. What I do know is that for RC planes and helicopters there are a tremendous variety of brushless motors to choose from. Some motors are very small for low power applications, and others are very large requiring very large batteries and high-power ESC's. In terms of power output, I would say they go from 50 watts for very small motors to 5000 watts for large ones. Maybe even more. Large motors are expensive and I have no experience with them. The biggest one I have probably puts out 350 watts.

To select the right motor, you have to know what RPM you need, and how much power you'll need. Having experience with airplanes, I know about how much power I will need to power a given airplane based on it's weight and the speed I want it to fly. I'm assuming that for a robot you will use some type of gear reduction system (gearbox or transmission), and depending on its size, even a very small motor could be made to move it.

LectricPlane
10-24-2008, 10:16 PM
Robots usually use slower rpm applications than planes. you would have to us a reasonable gearbox and probably a low Kv rating motor. The best place for this question, assuming you can not find a specilist robot forum would in a car orientated forum with more members familliar with this type of setup. You would need a seperate encoder to interface to the robots processor (if you are going to have one) for positioning. RC plane speed controllers do only speed and mostly only in one direction, some have a brake to stop...

jdetray
10-28-2008, 04:43 AM
The motors used in robots are most often stepper motors, not brushless motors. Stepper motors are ideal where relatively high precision is required but high speed is not required. Also, controllers for stepper motors are relatively simple and easy to build.

- Jeff

CHELLIE
10-28-2008, 05:58 AM
hi everybody,
i'm just new here and i found a very intelligence ppl over here whom have a very good knolwge about brushless dc motor...so as i'm going to build my project (acctually it's not a plane,it's a robot)and i'm planing to use a brushless motor but i've a very lettel experient in this field so i'll be greatfull if somebady would halp me here..

i'wont be heavy on u ..so i just need 2 know a few things

*where can i get a good quality brushless dc motor from the ineternet?
*i knew that i should have a ESC & i think they must b sync. ,so how can i know the matching part(what's the interfaces between them) ?does this controller control the speed and the direction or just 1 of them?
*should i use shaft encoder or does the ESC can do it's func.
that's all ,

Hi, Maybe these links might be of some help, Take Care, Chellie
http://www.robotpower.com/

http://www.robotstore.com/store/default.asp?catid=1532

http://www.robotcombat.com/store.html

http://www.budgetrobotics.com/

http://www.robotstorehk.com/

http://www.societyofrobots.com/robot_parts_list.shtml

amirengineer
10-28-2008, 07:08 AM
thx 2 all of u ...u all r so gental, but i want 2 correct an informationto jdetray that stepper motor r the less preformance & the lowest torq and we only use it for just changing the postion by few steps,.....u know this condition(performance up,cost up,size up,complixcty up & vice versa ) thx to all of u again

slepax
10-31-2008, 03:56 PM
Sorry if this may sound like dumb questions, but could you please explain the basics again, like ..

1. Why are those called brushless motors? If they are brushless, are there any brushed motors?
2. What is this ESC thingy?

It might look like an attack of non-flight related questions. I admit that I am interested in using the motor for something else myself ..

Thanks.

Ronen

Fly Time
10-31-2008, 05:08 PM
Sorry if this may sound like dumb questions, but could you please explain the basics again, like ..

1. Why are those called brushless motors? If they are brushless, are there any brushed motors?
2. What is this ESC thingy?

It might look like an attack of non-flight related questions. I admit that I am interested in using the motor for something else myself ..

Thanks.

Ronen
Yes, there are both brushed and brushless motors. Brushed motors are older technology. There are brushes on the inside of the motor that rub against magnets as the thing spins. Eventually the brushes wear out. Brushless motors obviously have no brushes, and they last much longer. The ESC stands for Electronic Speed Control. It controls the speed of the motor, and many also have built in battery elimination circuits (BEC) to provide regulated power to the radio receiver and servos. This device also monitors the battery voltage to protect the battery and keep it from over-discharging, or dropping below the minimum voltage required to run the receiver and thus control the plane.

The ESC must be matched to the motor and battery combo for the type of motor (brushed or brushless), voltage of the battery pack, and the amount of power a motor is likely to draw.

Oh, and welcome to WattFlyer!

jdetray
10-31-2008, 05:47 PM
One correction. In a brushed motor, the brushes do NOT rub against the magnets.

In a brushed motor, it is the brushes that are connected to the electronic speed controller (ESC). The brushes rub against the commutator, which is a mechanical device on the spinning part of the motor that switches the polarity of the current at the proper time to keep the motor spinning. The switching of the polarity -- which occurs many time per second when the motor is running -- is called commutation. Wikipedia has some diagrams of a this kind of motor, a two-pole DC motor:
http://en.wikipedia.org/wiki/Brushed_DC_electric_motor

In a brushless motor, commutation (the switching of polarity) is performed electronically by the ESC instead of being performed mechanically inside the motor. Thus, a brushless motor does not have a commutator or brushes. That's why it is "brushless."

Comparing brushed and brushless motors, there are some obvious differences. In a brushed motor, the magnets are stationary while the portion with the coils of wire (the armature) is the part that spins.

In a brushless motor, the portion holding the coils of wire (the stator) is stationary while the portion holding the magnets (the rotor) is the part that spins.

In a brushed motor, commutation (current switching) is performed mechanically inside the motor by the brushes and the commutator. So the ESC for a brushed motor can be a relatively simple device while the brushed motor is rather complex.

In a brushless motor, commutation is performed electronically by the ESC. So the ESC for a brushless motor is a relatively complex device while the brushless motor itself is quite simple.

For years, brushed motors were the only type of electric motor used in electric planes, mainly because brushless motors and brushless ESCs were very expensive. Now that the cost of brushless products has come down, brushless motors are widely used in e-flight.

- Jeff

Fly Time
10-31-2008, 05:51 PM
Good answer Jeff. You get the award for the smartest kid in class today :D

jdetray
10-31-2008, 05:57 PM
Unfortunately, my flying isn't as good as my writing!

- Jeff

ron_van_sommeren
11-01-2008, 11:27 AM
... I admit that I am interested in using the motor for something else myself ...We can give you more specific answers if you tell us your application.

About brushless motors, Jeff also features in that thread:
http://www.rcuniverse.com/forum/m_1558046/tm.htm

Brushless_motors_101
www.gobrushless.com/kb
-> basic overview (5 short chapters)

Prettig weekend ;) Ron

slepax
11-02-2008, 02:46 AM
Thanks for the answers guys. I followed the wikipedia link, it has some general information and also links describing what ESC is.


About brushless motors, Jeff also features in that thread

Brushless_motors_101
-> basic overview (5 short chapters)

Prettig weekend ;) Ron

I read the whole brushless motors thread, some of the info there was a bit confusing but still good and valuable information. For some reason I could not create an account at gobrushless.com, it keeps coming back with "Incorrect or missing confirmation code"

We can give you more specific answers if you tell us your application.

Well, I am trying to build a tennis ball machine. Not sure if you guys know how a tennis ball machine works, but the basic concept is two large wheels (about 6-10" each) rotating in opposite direction. Tennis balls simply drop in between the wheels and thrown out.

I need a fairly fast motor but not as fast as you guys use. Something like 10,000 RPM should be more than enough. On the other hand, the motor needs to have some decent torque to handle rotating the wheel and handling the ball. In terms of torque I guess something like 1/4 HP would be enough.

The motors used for RC airplanes/cars are quite appealing to me. They are fast enough and come with all kinds of shaft adaptors that should help me mount the wheels I need easily. The good thing for me I guess is that motor size is not an issue, the machine itself will be large enough as it is and I will probably use a motorcyle battery to get everything going.

Sorry it came out so long .. still has to read more about this ESC thingy, but any recommendations/ideas will be cheerfully accepted ..

Biffidum
11-02-2008, 04:35 AM
I think you can do better with a starter motor off the same motorcycle you got the battery from. You don't need speed control do you? Just get am RV contactor to control the motor with a switch. The size of brushless motor and ESC you would need would cost quite a bit to get for your project.

slepax
11-02-2008, 01:13 PM
I think you can do better with a starter motor off the same motorcycle you got the battery from. You don't need speed control do you? Just get am RV contactor to control the motor with a switch. The size of brushless motor and ESC you would need would cost quite a bit to get for your project.

Not really, for couple of reasons:
- I need two motors, one to spin the upper wheel and another for the bottom wheel. Also, I don't have a motorcycle to take the battery from, I will simply buy a new one (so no started motor).
- I do need to control the wheels rotation speed so I can adjust the distance of the ball flight.
- In some cases I would also need the wheels to operate at different speeds to produce different ball shots (e.g. top-spin, under-spin)

What did you mean by "cost quite a bit"? The cost of a new balls machine that can actually do what I want is about $2500-3000, so even if I spend a couple of hundreds just for getting a pair of decent motors that's still within my budget (motors and wheels will be my biggest expense I guess).

Couple of more focused questions if that's ok to ask.
- I searched some websites and I could see motors are stated with a voltage range, e.g. 7.4V - 14.8V. What happens if I feed the motor with lower voltage?
- I know what current means, what does it mean for brusheless motor? For some of them the numbers were 10A and higher! Is that for an hour? Or just for normal operation?
- When the specs states power as watts, is that actually torque? Can I just convert that to HP? Or does it mean something else?

Thanks for all the info guys, it really helps!

jdetray
11-02-2008, 08:46 PM
Watts and horsepower are both measures of power. 1 HP = 746 W.

Torque is not the same as power. Therefore, torque is not the same as watts. It is possible for a motor to consume a great deal of power without producing much torque.

The voltage ratings for model aircraft motors are based on the nominal voltage of a lithium-polymer (lipo) battery, the type of battery most commonly used in electric flight. Each lipo cell has a nominal voltage of 3.7V. Therefore, a 2-cell-lipo is 7.4V, a 3-cell is 11.1V, and a 4-cell is 14.8V. Many of the electronic speed controllers (ESCs) used with brushless motors are designed specifically to work with lipo battery packs.

The current rating for a motor is usually given as the maximum continuous current the motor can draw without overheating. Current is related to the load placed on the motor. The greater the load, the more current the motor will draw. If the load causes the motor to draw too much current, the motor will overheat. This may result in the breakdown of the insulation on the motor windings, causing a short-curcuit and ruining the motor.

In addition to specifying the continuous current rating, a motor manufacturer may also specify a higher "burst" rating. A motor can be used at its burst current only for short periods of time (20-30 seconds).

- Jeff

dar
11-06-2008, 05:18 AM
Slepax,

I think Biffidum is on the right track... but starter motors are designed for short duration operation and might die more quickly that you'd like if run continuous. I'm not so sure about motorcycle starters, but automotive ones consume ALOT of current because they use a current coil to set up the magnetic field rather that permanent magnets like a lot of other brushed and brushless DC motors.

I think you might be best to buy yourself something like a couple of brushed DC motors like bower motors from an auto wrecker (the motors used to power the interior heating /cooling air vents). These type of motors are very easy to control compared to brushless motors. For a controller, just do a web search on "LOW SIDE PWM DRIVE DC MOTOR CONTROL FETS"... you can buy simple kits to do this, or the parts to do it yourself if you can find a schematic on the web of a controller that does what you want to achieve (I bet you could do a controller for under 10 bucks if you keep it simple!).

Also, these motors are very robust and you can side-load or misalign a bit the output shaft without too much worry about damaging the motor. Model airplane motors are design to take mostly thrust load from the shaft and using them to drive wheels might cause damage to the shaft or bearings if the load is too much.

Another thing to consider is you have to bring the wheels (that "grab" the ball) up to speed and this means you have to build up quite a bit of inertia... airplane motors don't have to deal with this type of intertia (the propeller does not weigh much!) so you may exceed the peak currents for a brushless motor unless you carefully control the start-up.

As an alternative, there are lots of industrial 12V motors and controllers out there and I'm sure you could get some used gear at a reasonable price if you snoop around.

Best of luck: And don't you go launching tennis balls at any R/C airplanes!

-dar

groundrushesup
11-06-2008, 05:53 AM
This is such great info, guys. Glad you took the time to write it down for us.

Time to crack open the DigiKey catalog, huh? :p>

Cheers,
GRU

Biffidum
11-06-2008, 02:57 PM
Just to clarify. Most modern gear reduced starters are brushed and incorporate permanent magnets (sort of explains why they cost way more than in the past). I have made go-karts out of Honda Civic starters. All you need to do is drill cooling holes in the brush housing to keep it cool. These things have as much power and speed as my 5.5HP Honda gas engine powered go-kart (yes I have multiple hobbies, this one involves all the kids on the street).

I would guess that the intermittent spike in current (as a tennis ball passes through) will not overheat the starter motor.

I am familiar with the blower motors DAR is suggesting and I am not sure they would have the necessary torque to spin up the wheels needed for a tennis ball launcher. The wheels on these things are usually 8-12" in diameter and are made of a solid polymer of some sort. They need to be a decent size to track the ball consistently straight. You would need a fair amount of momentum in the wheels to deal with a tennis ball squeezing through and achieving a usable velocity. I would guess the wheels would weigh at least 5lbs each.

DC motor speed controls are more cost-effective than AC ones, but either way, I have a feeling that a speed control capable of controlling a started motor similar to that of the Honda Civic in this type of application (not starting a car) is not going to be cheap. Definitely a pulse width modulation type is the way to go as DAR suggests.

http://www.coleparmer.ca/catalog/product_view.asp?sku=7010010

dar
11-06-2008, 08:26 PM
Biffidum... right on that, I was refering to the commonly available direct drive starters. Last I heard on PM starters is they were not in widespread use, guess I'm still living in the past on starters (time to buy a newer car?). I recently got a starter for a '03 Toyota Corolla for a project but I thought it was direct drive, so I assumed it had a field coil (could be a PMGR? Dang, I should go check!). I wonder what precentage of the auto market is now using PMGR starters???

Using a gear drive PM starter for a Go-cart... Hmmmm, now I like the thought of that...

Agreed, most of the energy needed to propel the ball will come from the inertia of the wheels, I would not worry either about a short duration current spike rasing the temperature enough to cause overheating.

A lot of those blower motors are puney, but you can get some pretty massive ones (depending on the vehicle they came from) and I've used some for driving other things with much success... but an 8 to 12" wheel at 5lbs, well, that is pretty big.

I think even a large PM gear-motor like the starter you suggested could still be open-loop PWM controlled by something built from scratch for a reasonable cost... it just comes down to getting the right FET (heart of the control device) that can do the work. Controlling 100Amps+ is not unusual for some of these components and you can connect them in parallel if you have to (Digikey ROCKS!).

I bought a (new) Leeson motor and controller drive a few years back for a project where I had to spin a tire on a car to the same rpm as 80km/hr on the road (while the car was on a lift in our lab)... it was DC drive and had a gear-head; nice off the shelf solution but cost a good few bucks. You could have sent a tennis ball in orbit with that.


Fun stuff... great to share these ideas and experiences.

-Dar

slepax
11-10-2008, 12:58 PM
Thanks heaps for all the replies guys. I know this thread is far from being RC related, but it seems some guys here have sound knowledge about motors. Apologies for dragging this so long.

Starter motors from what I understand will probably have plenty power to rotate the ball machine wheels, but what about speed? From what I gathered to produce balls flying fast enough the motor would need to run at ~5000 RPM, even more if possible. The limited amount of starter motor specs I could found on the web quoted roughly 3000 RPM as the upper limit. Do you know if they can run at higher speeds?

I could find some brand new starter motors on eBay for about $70 (Aussie dollar), so in terms of price they fit my budget perfectly.

Biffidum
11-10-2008, 02:05 PM
Don't forget to factor in the radius of the launch wheels. There is also the possibility of gearing.

slepax
11-10-2008, 03:22 PM
Don't forget to factor in the radius of the launch wheels.

Yes, you are absolutely right!

If I calculate this right, so with an 8" wheel I can theoretically get 115 km/h at the top end. Obviously I will have the subtract friction, wind and other factors, but this is a good start.


Just one last question ... from the same limited number of specs I could find, it seemed starter motors consume quite a lot of power. You mentioned building a go-kart using a Honda starter motor, how did you handle the power requirements of the motor? I would need a huge battery to support a motor consuming so much power even in idle.

Biffidum
11-10-2008, 03:39 PM
I used a typical marine deep cycle lead acid battery ($90) and it would provide power (under high amperage conditions) for about 15 minutes of driving.

For your setup I would think that it would run for at least half an hour. Remember the current the motor draws is a reflection of the work it has to do. Once spinning, the fly wheels would draw little current to keep them spinning. You could use a couple of pneumatic wheel barrow wheels to drive the tennis balls ($20/piece). The curvature of the tires could pose a problem though...

Other than a battery, I would think that a decent 10AMP battery charger would provide the necessary umpf to get the wheels spinning.

As for speed control and curves etc... couldn't you just play with the wheel setup. For example, if you could pivot one wheel on the vertical axis, this would change where the wheel contacts the ball relative to the other wheel causing an off axis spin (curve the ball). Or just change the air pressure in one of the tires. Sorry, it just seems that there is a simpler and cheaper way to achieve what you want.

Simplest design would be pulley driven wheels that are connected by a twisted fan belt (causes opposite spin). The wheels would be in a flat configuration on a flat sheet of steel. The balls are fed between the spinning wheels along a trough in the flat sheet. The entire assembly would pivot. To create top spins or whatever you could have a shute that the ball exits through which has a friction surface on one side only. Then set up the shute so that it can rotate, permitting the curve to angle in 360 degrees. As the ball travels along the exit shute it will drag on the friction side causing a bias spin as it exits the shute. As for a friction surface it could be a piece of rug or whatever...

I'm wasting too much time here better go...

dar
11-13-2008, 06:23 AM
Slepax,

Don't rely too much on the spec'd current for the starter motor, because you're not turning over a 1.7 or 2litre engine! That takes quite a bit of juice. One way to think of it is, if you lock the output shaft stationary, you will get a huge current draw (and kill the motor very quickly)... and when you don't put anything on the shaft you get the least amount of current draw. For this type motor it needs to operate somewhere in the middle by design (for starter in engine), and I suspect you'll be on the low end.

You'll consume most of the power at start-up as you load energy into the wheels, once you're up to speed the current will stabilize and be lower than at start-up. This current is determined by the back-emf at the stable speed, resistive loss, brush-drag, bearing-drag and even air resistance on the wheel! The current will spike when the ball passes through and then it'll drop again as the speed gets back up.

I expect the start-up to be the highest current draw (but no where near for an engine cranking!)... you can start-up slower if you have a PWM controller. That will greatly limit the current draw. So a decent lead-acid car battery should do the trick.

I like using CRYDOM solid state relays for switch elements, very durable... I think you can PWM some types of those if you keep the frequency low (100-200Hz).

hope this helps...