robot lawnmower

Changes to the Robot’s drive system

I was going to use DC Brushed Planetary Geared Motor, because of the noise I have now bought new motors. I have already started designing the new drive system (that will also functions as a support frame for the rear parts). The new system will be CNC milled in Aluminum for better strength. To reduce noises I will switch over to use a belt-drive. This way I can also change pulleys quite easy and allowing me to change the gear ratio quite easy.

So the New motors are 6355 Sensored Brushless (BLDC) motors 190kv. Brushless DC motors have many advantages over brushed DC motor counterparts. The most obvious advantage of a brushless motor is its lack of brushes and physical commutator. This difference means that there are many fewer parts that can wear out or break and need to be replaced than in a brushed motor. A BLDC motors tend to be more reliable, last longer, and be more efficient. In fact, BLDC motors have life expectancies of over 10,000 hours.

When changes are made, usually others parts needed to be changed or redone. When switching to the Brushless motors I need to add bearings for the drive shaft and redesign the first motors mounts. When you touch something usually many parts follow. So its always good to think ones or twice before changing from the original design (causing a lot of extra work).

With the new design I will use a 10mm drive shaft instead of directly mounting wheels on the motor-shaft (that could have a negative impact on the motors in the long run) I will use timing pulleys and belt drive. A small pulley on the motor (6-15T) and a big pulley on the drive shaft with (50-100T) The exact gearing I will need to be calculated and tested). The lawnmower speed should be around 2-5km/h (normal use) and it should not be 100% throttle on this speeds. The high speeds on 100% throttle my aim is around 10-15km/h (NOT FOR CUTTING). The brushless motors also have fewer parts = meaning more silent.

So here is my first sketch of the new drive-system.

Belt-drive Brushless motors
Belt-drive Brushless motors (first sketch)

 

New motors specs:

Model: Outrunner 6355
Type: Sensored
KV (rpm per volt): 190KV (high torque)
Max. Power: 2600W (eq. 3.5HP)
Max. Amps: 71A Max.
Volt: 10S LiPo (42V)
No-Load Current: 1.9A
Size (without shaft): 63mm*55mm
Weight: 560g
Shaft: 10mm with 3mm keyway
Internal PCB with 120 degree hall effect sensors

 

I also bought new motor controllers, VESC 4.12 PCB R-SNAKE/ FLIER equipped  with heatsink to avoid overheating of the Mosfets on long runnings or in extreme conditions of use requiring a lot of  the motor and consequently of the VESC

VESC 4.12 w/ Heatsink + 6355 Outrunner Brushless Motor
VESC 4.12 w/ Heatsink + 6355 Outrunner Brushless Motor

Here is the specs for the VESC:

  • Built-in BEC: 5V
  • Connetctors (male and female): XT90 to battery and 5.5mm Bullet to motor
  • Battery (Lipo): 3-12Cells
  • Current: up to 240A for a few seconds or 50A continous
  • Version equipped w/ heatsink cooler
  • Compatible with Sensorless and Sensored Brushless Motors
  • Hardware/ PCB by Benjamim Vedder: 4.12
  • Updated Firmware version from factory: 2.54
  • Dimension of VESC board: 60x40mm
  • Power wire: Silicon wire
  • Weight: 73g
  • Brand: Flier (and distributed by R-Snake High Voltage Speed Controllers)
  • Strong, Reliable and Progressive Electric Brakes
  • Start from a stop with Unsensored Motors as if it was Sensored
  • Many Safety Features such as Current Control and Temperature Control Features
  • Sensored and Unsensored (FOC) allows your electric skateboard to run with barely any motor noise
  • Regenerative Braking
  • Sensored or Sensorless operation
  • Great start-up torque also with sensorless motors

 

So here are some great link when working with gearing brushless motors:

https://sdp-si.com/eStore/CenterDistanceDesigner

http://www.electric-skateboard.builders/t/beginners-guide-to-building-your-own-electric-skateboard-drivetrain/53

Calculating speed

 

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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