Picaxe to control 4 pole brushless motor.

JPU

Senior Member
Hi All

Is there a chip out there that I can connect to a PICAXE chip that will allow me to run a 4 pole brushless motor. I can then use the PICAXE to control various features of the motor eg stop/start,speed, direction and even torque?

I'm sure some of you are thinking "Yes!", go buy a Brushless motor controller and use the picaxe to run the controller.. I have done this.

What I want to do now is build my own controller and I wondered if there was a chip in production that I could hook up to the picaxe to achieve this.

Thanks in advance for any pointers or help...and I am a nube to electronics so please be gentle with the explanation.

JPU
 

Jeremy Harris

Senior Member
I've built a couple of BLDC controllers, but never for a 4 pole BLDC motor and not using a Picaxe to drive the commutation sequence. Don't think I've actually ever seen a 4 pole BLDC motor, TBH, most are three phase, with even multiples of three for the stator windings and number of pole-pair magnets to match the number of startor slots for best efficiency (for example, 3 phase, 12 stator slot, 7 pole-pair motors are quite popular with the RC model crowd).

The Picaxe is too slow to commutate six outputs to drive even a simple trapezoidal drive controller, I believe, and certainly not fast enough to do the required current measurement and on-the-fly pulse width termination needed for effective current limiting. You could perhaps make a very low speed (as in a few rpm) demonstration controller using a Picaxe, perhaps for educational purposes, but it wouldn't be fast enough to do anything very useful, I'm afraid.

There are a few PIC chips with all the hardware internally to make a BLDC controller with good functionality, but not in the Picaxe range, AFAIK.
 

JPU

Senior Member
There are a few PIC chips with all the hardware internally to make a BLDC controller with good functionality, but not in the Picaxe range, AFAIK.
Thank you for your explanation. I don't really know much about brush less motors and I got the information from the spec sheet where it says "winding type, star, 4 poles", perhaps I have interpreted this incorrectly?

I have this motor: BLWR112S-24V-3700 found at

http://www.anaheimautomation.com/products/brushless/brushless-motor-item.php?sID=142&pt=i&tID=96&cID=22

Would it be relatively simple to build a circuit using a pic designed especially for this task? Would you be able to point me at some schematics of simple circuits?

Thanks in advance

JPU
 

Jeremy Harris

Senior Member
Thank you for your explanation. I don't really know much about brush less motors and I got the information from the spec sheet where it says "winding type, star, 4 poles", perhaps I have interpreted this incorrectly?

I have this motor: BLWR112S-24V-3700 found at

http://www.anaheimautomation.com/products/brushless/brushless-motor-item.php?sID=142&pt=i&tID=96&cID=22

Would it be relatively simple to build a circuit using a pic designed especially for this task? Would you be able to point me at some schematics of simple circuits?

Thanks in advance

JPU
That's a three phase BLDC, with four pole pairs, so can be driven by a standard three phase controller. The link that srnet has given is a good one, as there are some very helpful application notes on the Microchip website.

No three phase controller is going to be very simple, as there are some challenges in getting relatively high current six step power stages to work reliably. The simplest BLDC controller I've built is the one described in this thread on the Endless Sphere forum, and may help: http://endless-sphere.com/forums/viewtopic.php?f=30&t=23350 It uses hardware to generate the commutation sequence, directly from three Hall sensor position sensors in the motor (so cannot operate in sensorless mode, but would work OK with the Hall sensors in the motor you've linked to). That thread is a bit of a voyage of discovery for me, as I started off not knowing much about the way these things work, and ended up knowing more than I wanted to about some of the problems!
 

slomo

New Member
This is my first time using this forum. I apologize in advance if I am doing it wrong. I saw that you bought a brushless motor controller and used a Picaxe to run the controller. I need to know how to do this. Did you post it in Finished Projects? Is there a better way to ask questions about how you did this or is this the place?
 

edmunds

Senior Member
I'm a little confused about your requirements.

If you want to do it without an intelligent chip connected to picaxe, as already pointed out it is probably unlikely going to be very useful.

If you want/can use an IC designed for the task, I have found ST (STMicroelectronics) and TI (Texas Instruments) to have some of the best motor driver ICs that contain a fast, dedicated processor and some other necessary hardware. Both have loads of options for driving BLCD motors, so a specific choice will depend on what your other requirements are. ST product group landing page is this, I think.


Good luck,

Edmunds
 

Jeremy Harris

Senior Member
This is my first time using this forum. I apologize in advance if I am doing it wrong. I saw that you bought a brushless motor controller and used a Picaxe to run the controller. I need to know how to do this. Did you post it in Finished Projects? Is there a better way to ask questions about how you did this or is this the place?
If you want to drive a hobby-type brushless motor using a Picaxe, then the easy way is to use a standard hobby motor Electronic Speed Controller (ESC) and feed it with a standard servo signal from a Picaxe. This will work fine, and allow the speed of the brushless motor to be controlled over its whole range. If you want to change direction, too, then use an electric car type ESC, as they have motor stop in the centre of the PPM servo output range, full reverse at one end and full forward at the other end, so again a standard Picaxe servo output signal can control it OK
 

macrobeak

New Member
bidirectional ESC

If you want to drive a hobby-type brushless motor using a Picaxe, then the easy way is to use a standard hobby motor Electronic Speed Controller (ESC) and feed it with a standard servo signal from a Picaxe. This will work fine, and allow the speed of the brushless motor to be controlled over its whole range. If you want to change direction, too, then use an electric car type ESC, as they have motor stop in the centre of the PPM servo output range, full reverse at one end and full forward at the other end, so again a standard Picaxe servo output signal can control it OK
Jeremy, there are ESC's now which van be programmed to be bi-directional.
I have used the EMAX BLHeli series of ESC with their programmer quite successfully.
Apart from bi-directional, there are many parameters which can be programmed including brake, timing, start force, curve mode, control frequency, low voltage protection and cutoff mode.
 

premelec

Senior Member
@Bill.b Is there a table of torque and horsepower for larger RC motors - i don't understand their KV notation in this context... thanks...
 

Bill.b

Senior Member
The Kv notation refers to the revs per volt. i.e if rated at 1000Kv the motor will rev at 1000RPM per each volt. at 6v = 6000rpm .
other numbers quoted are the dimension of the motor.

Bill
 

Bill.b

Senior Member
Understanding R/C Brushless Motor Ratings



kV Ratings
Ok, lets start with kV ratings. The letters kV stand for the the RPM of your motor per volt with no load. For example if you own a brushless motor with a kV rating of 4600 and 12V. Take the 4600, multiply by 12 to get 55,200 RPMs. This is the max RPMs that this motor can reach under no load. Once you get it inside your vehicle, this will come down due to friction.
Almost all brushless motors will have the kV ratings stamped somewhere on them. Some motors will have kV ratings on the motor can, others on the motor leads, but some you will only see on the motor�s spec sheet.
Ok. now you are this far, so what does this mean to you really?
 A motor with a higher kV will have more top end speed, but not as much acceleration/torque.  A motor with a lower kV will not be as fast, but will accelerate faster.
So, now you can decide which one works best for your kind of racing. You have the room to really crank it up and reach top speeds? A higher kV will get you there. But maybe you are on a shorter track, and what you want is acceleration out of the corners, then look for a lower kV number. Still not sure which way to go? Try something in the middle!
Note: If motor heat is an issue then a lower kV rating with a higher voltage battery will give you the same effect.
The big thing to remember when using kV for your Brushless Motor Ratings is that your Brushless Motor and ESC will each have a maximum input voltage (battery cell count) that is allowed. So if either your motor or ESC has a lower maximum voltage then you must use this to calculate your top RPMs. If you go over the recommended voltage then you have a high chance that something will fry in your setup.

Motor Turns
Motor Turns is the same for brushed motors and brushless motors. The word turns stands for the amount of wire windings around each of the motor's rotor poles.
 The higher the number of wirings/turns means less top speed, but higher acceleration/torque.  The lower the number of turns equals higher top end speed and lower torque/acceleration.  A motor with a turn rating of 5.5 will have less acceleration/torque but higher top speed than a motor with a 12 turn rating.
Current Rating - Amps
It is a great idea to find an ESC that has a current rating that is higher than your motor�s by at least 20%. It will be a good safety cushion to make sure that you don�t burn up your brushless power plant.
Here's why: the max current rating is the maximum amount of current that a motor is able to handle safely. This current is measured in Amps. The continuous current rating of a motor is the Amps that a motor can handle safely over a long period of time.
The estimated current rating of a motor is usually on the factory specs sheet. However other factors affect the actual current that a Brushless motor will draw. Things like the kV rating, battery voltage, how heavy the RC vehicle is, and gear ratio or prop size. The harder a motor needs to work to reach it's top speed, the higher the Amp draw is.

Watts Watts are the power rating or the horsepower equivalent of your brushless RC Motor. The math here is Amps x Volts = Watts. You will see a watt rating in the brushless motor specs. Your brushless motor should have a watt rating on its spec sheet, something like "180W". This is the amount of "horse power" that it should produce safely. Running anything over this rating could damage your motor, especially over a long period of time.

Motor Efficiency
The efficiency of a motor determines its quality. Higher efficiency means better design and high quality components. The higher the efficiency of the motor the more power it can produce before it overheats. A 70% efficient motor produces 70% power and 30% heat. A 85% efficient motor produces 85% power and 15% heat. If your battery is sending the ESC 180 watts, your motor will produce 153 watts (85%), the rest is gold ole heat. 27 Watts of heat will melt solder with some soldering irons, so, that is a lot of wasted watts!
A cooler running motor will give you much less trouble. To reduce heat you can change your gearing or prop size, use a more efficient motor, reduce your voltage or amps, or try a motor heat sink and motor fan. Keeping the heat down on your motor allows it to run longer, and give you the power it needs.. Efficiency matters folks.
 

The bear

Senior Member
@ premelec,

If its any help, scroll down Bill.b's link. https://www.banggood.com/Racerstar-2...category<br />
All will be revealed.

Regards, bear..
 

premelec

Senior Member
@Bill.b - thanks for that detail - gives me a lot to cogitate on... i understand watts and efficiency and such and back emf at particular RPM and am still uncertain about available torque at various RPM with _current limited_ to a rated maximum input number - perhaps power is more or less linear with with RPM since at stall the power output is zero [and something is beginning to smell bad ;-0 ] and full RPM watts out = watts input times efficiency. [Disregarding windup inertias and sticking with steady state RPM] - anyhow I'll look into it further.

@bear - thanks for suggestion also..
 

Jeremy Harris

Senior Member
In general, torque varies more or less linearly with current, rpm varies more or less linearly with voltage. Efficiency varies with winding resistance, motor core loss, windage and a tiny bit due to friction. Maximum power pretty much always comes down to the physical motor size, and its ability to shed heat.

There are sets of motor characteristics you can calculate and plot to look at all the compromises and select the best wind, voltage and current for a particular operating point. As an example, I have a 16ft electric river launch, driven by an old, rewound, TowerPro 5330 motor (it has a stator that's 53mm diameter, 30mm long). That will theoretically peak at at a couple of kW, but will get warm at that sort of power after a few minutes. I've wound it to get best efficiency with a modest reduction ratio drive, delivering around 100 W, where the motor doesn't even get warm. I also fitted this motor with internal Hall sensors, so I could run it from a high efficiency ebike speed controller (easier to interface to boat controls than an RC-type ESC). Efficiency was key for the way I did things, as the boat is powered by four 100W solar panels on a canopy and a small battery. The motor efficiency curve is pretty flat (over 90%) from a torque output of around 0.4 Nm to around 1.1 Nm, but drops off rapidly below 0.2 Nm.
 
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