Brushless motor
robot lawnmower ROS

Brushless vs. Brushed DC Motors

I bothered quite a bit about how much my motors sounds. When the lawn mower is working the ultimate goal is that is should be as silent as possible. When you sit in the garden and sip on a glass of wine you do not want to be disturbed by annoyed sounds. I want it Silent.

Reading around on the internet my path came across Brushless Motors. They are silent, smaller and powerful.

My current DC Planetary Geared Motor 24 Volt:

 

For the Cutting motors I have ordered T-motor P60. From the start, I intend to use their T-motors ESC AIR 40A. But after some investigations, they will maybe not will be able to work as expected. For the cutting system I need to be able to monitor the current of each motor so I can know how hard they are working. If they work to hard the cutting system should go up to pre-cut that section and in next run it will be able to cut it without any problems. I also need blockage detections. Anyways. this led me to the VESC (a open source ESC with alot of features)

Which include:

  • The hardware and software is open source. Since there are plenty of CPU-resources left, the customization possibilities are almost endless.
  • STM32F4 microcontroller.
  • DRV8302 MOSFET driver / buck converter / current shunt amplifier.
  • IRFS7530 MOEFETs (other FETs in the same package also fit).
  • 5V 1A output for external electronics from the buck converter integrated on the DRV8302.
  • Voltage: 8V – 60V (Safe for 3S to 12S LiPo).
  • Current: Up to 240A for a couple of seconds or about 50A continuous depending on the temperature and air circulation around the PCB.
  • Sensored and sensorless FOC wich auto-detection of all motor parameters is implemented since FW 2.3.
  • Firmware based on ChibiOS/RT.
  • PCB size: slightly less than 40mm x 60mm.
  • Current and voltage measurement on all phases.
  • Regenerative braking.
  • DC motors are also supported.
  • Sensored or sensorless operation.
  • A GUI with lots of configuration parameters
  • Adaptive PWM frequency to get as good ADC measurements as possible.
  • RPM-based phase advance (or timing/field weakening).
  • Good start-up torque in the sensorless mode (and obviously in the sensored mode as well).
  • The motor is used as a tachometer, which is good for odometry on modified RC cars.
  • Duty-cycle control, speed control or current control.
  • Seamless 4-quadrant operation.
  • Interface to control the motor: PPM signal (RC servo), analog, UART, I2C, USB  or CAN-bus.
  • Wireless wii nunchuk (Nyko Kama) control through the I2C port. This is convenient for electric skateboards.
  • Consumed and regenerated amp-hour and watt-hour counting.
  • Optional PPM signal output. Useful when e.g. controlling an RC car from a raspberry pi or an android device.
  • The USB port uses the modem profile, so an Android device can be connected to the motor controller without rooting. Because of the servo output, the odometry and the extra ADC inputs (that can be used for sensors), this is perfect for modifying an RC car to be controlled from Android (or raspberry pi).
  • Adjustable protection against
    • Low input voltage
    • High input voltage
    • High motor current
    • High input current
    • High regenerative braking current (separate limits for the motor and the input)
    • Rapid duty cycle changes (ramping)
    • High RPM (separate limits for each direction).
  • When the current limits are hit, a soft back-off strategy is used while the motor keeps running. If the current becomes way too high, the motor is switched off completely.
  • The RPM limit also has a soft back-off strategy.
  • Commutation works perfectly even when the speed of the motor changes rapidly. This is due to the fact that the magnetic flux is integrated after the zero crossing instead of adding a delay based on the previous speed.
  • When the motor is rotating while the controller is off, the commutations and the direction are tracked. The duty-cycle to get the same speed is also calculated. This is to get a smooth start when the motor is already spinning.
  • All of the hardware is ready for sensorless field-oriented control (FOC). Writing the software is the remaining part. However, I’m not sure if FOC will have many benefits for low inductance high-speed motors besides running a bit quieter. Sensored and sensorless FOC is fully implemented since FW 2.3.

With that list of goodies, it’s a pretty obvious choice. You can find the ROS drivers here

Each VESC costs around $ 100 and upwards and each motor needs one VESC. So That will set me back 300 USD for the motor controllers for the cutting system. The T-motors P60 cost me 300 USD.

VESC
VESC

So when this said I also might change the DC Brushed Planetary Geared Motor that´s being used today. Mostly because they are to loud for in my option and second because they are a bit slow.

I am thinking of using VESC and Geared BLDC Motor Planetary Gearbox Ratio 15~50:1 with NEMA 23 180W 24V Brushless DC Motor (Ratio 50:1) instead (this will be later on) now focus in on trying to complete a first test prototype.

 

here is a sweet robot running VESC, ROS and brushless motors (I love the sounds of the motors).

 

 

What are the Advantages of Brushed and Brushless DC Motors?

Brushed

  • Low overall construction costs;
  • Can often be rebuilt to extend life;
  • Simple and inexpensive controller;
  • Controller not needed for fixed speed;
  • Ideal for extreme operating environments.

Brushless

  • Less overall maintenance due to lack of brushes;
  • Operates effectively at all speeds with rated load;
  • High efficiency and high output power to size ratio;
  • Reduced size with far superior thermal characteristics;
  • Higher speed range and lower electric noise generation.

 

raess

Chief Technology Officer with a demonstrated history of working in the internet industry. Skilled in Business Planning, Computer-Aided Design (CAD), Quality Process Development, and SolidWorks. Strong business development professional with a Higher Education Diploma with specialization in Mechanical Engineering focused in Product development from Blekinge Institute of Technology.

http://valify.se

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