Controlling ESC at a lower speed and using resistors?

Hello, I searched forum about this.

MY esc has slowest angle of 23. ESC wont work below write(23).

I am new to this stuff. 23 is not a slow speed for me. Can I make modifications to ESC? like putting resistors to limit power.

I tried to change voltage to 5 from 12, esc didnt run. Maybe if I lower to 7-8, I can get a little slower speed.

Here is my ESC: Xxd hw30a 30a brushless motor esc for airplane quadcopter Sale - Banggood.com

Here is my brushless: https://www.banggood.com/Racerstar-BR2212-1000KV-2-4S-Brushless-Motor-For-RC-Airplane-p-1083190.html?rmmds=myorder

Here is my code

#include <Servo.h>
Servo esc; 

void initialize_motor()
{
    Serial.print("Arming the motor! \n");
    delay(3000);
    Serial.print("Setting low speed! \n");
    esc.write(5);
    delay(4000);
    Serial.print("Setting high speed! \n");
    esc.write(180);
    delay(4000);
    esc.write(10);
    Serial.print("MOTOR IS READY! \n");
    delay(2000);
}

void setup()
{
Serial.begin(9600);
esc.attach(2); //Specify the esc signal pin,Here as D8
initialize_motor();
}
void loop()
{
int val; //Creating a variable val
val= analogRead(A0); //Read input from analog pin a0 and store in val
val= map(val, 0, 1023,0,100); //mapping val to minimum and maximum(Change if needed) 
Serial.print("Top Motor Angle= ");
Serial.println(val);
esc.write(val); //using val as the signal to esc
}

You've chosen a brushless motor with a maximum speed of around 12,000 rpm on 12V. Motors like that will not run very slowly. What sort of speed are you looking for ?

The best option may be to choose a different motor with a much lower Kv. You can try also a lower voltage, it should run on around 6V which would halve the speed.

Steve

Thanks slipstick.

I want to throw table tennis balls.

I am looking very low speeds.

Is it enough if I change motors? Do I need to change ESC as well?

What maximum and minimum speeds do you need ? In rpm.

And what sort of load are you driving with the motor i.e. what does your ball thrower look like. I would have thought that gearing the motor, maybe something like a belt drive, might be easier but that depends on what you're trying to drive. A small brushless motor like that doesn't have much torque for moving a load (I know the ball doesn't weigh much, but what about the thrower ?)

Steve

Thanks Steve

This is the project I am trying to build. I have no idea how much rpm I need. What I can say is that even lowest speed of my brushless (angle 23) is way too powerful for me.

Can u suggest me a low rpm, low torque small brushless? (can be cheap, chinese. Just for prototyping)

What I can do, I can use 2 brushless motors, going in opposite directions so that I can offset speed. For example, top motor=50, down motor=30, total generated speed is going to be 20 since down motor is spinnig in reverse direction in comparison to top motor.

I can go with brushed dc motor but they have less lifespan.

As far as I understand, ESC doesnt allow low speed since these brushless motors are designed for heli’s or quads, which low speeds can cause heli’s to fall.

Maybe I can modify ESC, or flash some other firmware that allows low speed.

That instructable claimed to be using 700Kv motors on 12V so your 1000Kv motors on 8.4V would be going at the same sort of speed.Using writeMicroseconds() instead of write() would give you finer control of speed but it won't let you get much slower.

If you really need it a lot slower then it doesn't look too difficult to have the motors driving through gears or belt drives instead of direct. OTOH I'm not really sure what I'm looking at. I've never seen or even heard of a "table tennis robot" before.

BTW the low speed limit is because with that sort of motor/ESC the motor has to be turning at a certain minimum speed in order to produce the feedback that the ESC needs to work. There's not really anything you can do about that.

Good luck - Steve

Thanks a lot!

Appreciated.

thelord006: https://www.instructables.com/id/Homemade-table-tennis-robot/

Crazy design. Using RC brushless motors is completely stupid for this, you have way way way more power than is needed (100's of watts!), and as you have discovered only restricted speed control.

A ping-pong ball going at 20m/s (very fast) only has about 0.5 joules of energy, whereas discs of that size would have more, 10's of J, so a 10W motor would be plenty for the most vigorous of smashes.

The energy for launching the ball is nearly all stored in the spinning discs, so a fairly puny pair of motors would be fine for low speed use, the limiting factor being how rapidly the disc spin speed could be changed by the motor.

MarkT: the limiting factor being how rapidly the disc spin speed could be changed by the motor.

One of the main focus of this design is to change the speed of ball in order to throw the ball into various locations in the table. As long as I can do this with a brushed motor, we are fine.

I think the question is how durable brushed dc motors are?

Maybe I should try Brushed DC's.

This is an issue with brushed motors, true, and the cheaper the motor the less durable it will be (and the bearings will be less durable too). In general a motor with ball-bearings is likely to have good brushes with a reasonable lifetime.

Lower power brushless motors are available, but tend to either be industrial/engineering spec (very expensive), or sensorless (and thus no good for slow speed operation - such as gimbal motors which rely on positional feedback to make up for lack of hall sensors). I have occasionally seen some nice brushless auto-commutating motors on eBay, typically they have a control voltage to set the speed and a logic input to select direction, plus power leads.

Would you mind posting links if you see one?

Thanks!