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Tank Robot Build Tutorial

This is a live video streaming tank robot and how it came together. The robot streams live on LetsRobot.tv

Build Progression

Version 7 of the tank uses a night vision camera and a USB microphone
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Version 7 top view
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A gripper tilt servo was added to the front of the tank so it can grab more things.

This uses an MG-996 servo. The servo brackets, screws, and bearings all came from a 6-DOF arm kit.

The Camera mounts and gripper were from a 6DOF arm kit
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Version 6 of the tank used a logitech C920 for camera and microphone. V6 added current monitoring
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After 50,000 battery measurements from one session I captured the full LIPO discharge curve. The BMS cuts out at 6v.
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Arduino in font, Raspberry pi in the rear
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The robot can unflip itself using the camera tilt servo:

I added an arduino to read the hall sensors on the motors. The arduino reads a GPIO pin to find edge transitions and calculate motor RPM based on the 75:1 gear ratio

Here you can see blue tape on the magnetic encoder which spins past the hall sensor.

Download Motor Specs Here

This is a 9V DC 150 RPM motor. Model GM25 370 75:1 geared motor with 2 hall sensors
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Headlights are connect from GPIO to an NPN transistor and the 3v lines on the pi
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V3 robot obtained a gripper
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V4 top - 2x 5v regulator for RC Battery Style 2
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V4 underside - Battery "Style 2" - 78Wh / 2x 5,200mah RC Batteries in Parallel
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V3 underside - Battery "Style 1" - USB 99 Wh / 26,800 mAh battery
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V3 battery pack connections
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I bought another RavPower battery pack, but it did not work the same and it did not stay powered on. The over current protection circuit cut off the power output.

So I broke open the battery pack and rewired it from an 8P setup to 4P2S to provide 7.4v just like the RC battery setup.

V6 Battery with 4A BMS Protection and voltage & current mononitoring via INA219 sensor
99 Wh / 26,800 mAh via 8x 18650 cells
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V3 gripper with neoprene pads
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Battery Style Runtime Comparison

Style 1 - USB Battery
26,800 mAh @ 5v = 99.2 Wh
15 Hours 12 Minutes

Style 2 - 2x RC Car Batteries
2x 5200 mAh @ 7.4v = 77.6 Wh
11 Hours 29 Minutes
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V2 got everything screwed in
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V2 top close up
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V2 Components
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The LED headlights are connected via a 100 ohm resistor and NPN transistor. This connects to the 3v power rail on the raspberry pi and a GPIO pin for control.

V2 Underside Single Battery Config
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V1 was pretty rough
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V1 had had night vision for a bit
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Scissors were fun
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Controls on Lets Robot
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Gripper Modifications

The end of the gripper kept getting caught on things. Removing the screws on the end helped significantly.

gripper screws 1
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gripper screws 2
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I was attaching neoprene pads cut off from a mouse pad to allow more grip, but they needed to be replaced every day or two. Covering with heat shrink eliminated that problem

gripper covers heat shrink 1
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gripper covers heat shrink 2
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gripper covers heat shrink 3
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Maintenance Items

The tank was pulling to the left pretty hard. Swapping the 75:1 gearbox from a similar wild thumper motor fixed the issue.
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The treads are wearing down froms spinning against the concrete floor constantly


Tank Trouble

The internet drivers get the tank into lots of shenanigans

Doll Hair doesn't play well with spinning things
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Doll Hair Untangling
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V5 the weak 3d printed camera braket broke after a few days of abuse by random internet drivers

V5 the new aluminum bracket uses a proper ball bearing so should last a while

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The gripper servo horn came unscrewed from the constant vibration. I didn't use thread locker and it hasn't happened again, but if it does, threadlocker is the answer.

Stuck in a fan

This chair leg is wide enough to get the gripper around but you cannot get back out!

After 1 day the USB microphone got caught on something and wrapped around the treads and shredded

This was probably a good thing - after the repair it had a nice short cable



Motor Control Wiring Diagram

Note: I'm powering the servos through the H bridge

Bigger
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Code

Controller Code (using old lets robot controller still):
github.com/RyAndrew/runmyrobot

Video Stats Overlay
github.com/RyAndrew/letsrobot_pygame_overlay



Build Instructions

1. Download and install Raspbian Stretch Lite. Use Rufus or Etcher to burn the .img to an SD card

2. Find the IP address of your pi and SSH into it or use the HDMI port to login and find the IP. We will assume the rest of the steps you have a terminal (ssh) access and can run commands.

3. Run: sudo raspi-config. Connect to the wifi, enable i2c

4. Install i2c-tools and make sure you detect your motor hat. to learn more read about raspberry pi GPIO here and Adafruit motor hat here.

4.1 Run: sudo apt install i2c-tools

4.2 Run: i2cdetect -y 1

You should see your devices detected at address 60 and 70:

pi@raspberrypi:~ $ i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: 60 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: 70 -- -- -- -- -- -- --

5. Install git, python, pip

5.1 Run: sudo apt install git python3 python3-pip

6. Clone the runmyrobot repo

7. Install Adafruit Motor Hat Library

7.1 Run: cd /usr/local/src && sudo git clone https://github.com/adafruit/Adafruit-Motor-HAT-Python-Library.git

7.2 Run: cd /usr/local/src/Adafruit-Motor-HAT-Python-Library && sudo python setup.py install

8. Sign up for LetsRobot.tv account, get your robot id and camera id

9. Enter your robot and camera ids into the start scripts

10. Launch start_robot!



Parts List

Total Cost ~ $370

Base

Tank Chassis $106 Amazon.com B077HMY3YK

Battery - pick 1

Battery Style 1 - RavPower 26,800 mAh USB Battery $90 Amazon.com B01LRQDAEI
Battery Style 2 - 2x Pcs Floureon 2S 7.4V 5200mAh 30C LiPo RC Battery $27 Amazon.com B06ZZ8TCNV

Electronics

Raspberry Pi 3 B+ $40 Amazon.com B07BDR5PDW
Logitech C920 Webcam $60 Amazon.com B006JH8T3S
Adafruit DC & Stepper Motor Hat $26 Amazon.com B00TIY5JM8
PAM8403 3W+3W DC 5V Mini Stereo Audio Amplifier $7 Amazon.com B078VTYQMT
2x Pcs LM2596 DC to DC High Efficiency Voltage Regulator 3.0-40V to 1.5-35V Buck Converter $10 Amazon.com B076H3XHXP
Arduino Pro Micro 5v 16mhz (price for 3) $21 Amazon.com B01MTU9GOB
INA219 INA219 I2C Current/Power Monitor Sensor (price for 2) $10 Amazon.com B07L69L3J9

Servos

2x Pcs MG995 Metal Gear High Speed Torque 12kg Servo $26 Amazon.com B00M8TXSBO
Gripper from 6DOF arm kit - no servos included! $41 Amazon.com B01NBBBE21
Gripper from 6DOF arm kit - WITH servos included! $60 Ebay.com 112923829325

Connectors and Hardware

20 Gauge Silicone JST Connector, SIM&NAT 5.9 inch $8 Amazon.com B071XN7C43
Generic 4.0mm 4mm RC Model Battery Male Banana Gold Plated Bullet Connector Plug For RC Lipo Battery $8 Amazon.com B01CJMVY74
100Packs 3.9mm Brass Bullet Male & Female Wire Terminals Connector $9 Amazon.com B075T13MTM
#2-56 UNC Stainless Steel Phillips Pan Head Machine Screws Nuts Assortment Kit (#2-56UNC) $13 Amazon.com B07BWBPV5G

Misc Parts

3 watt Speaker pulled from an old pair of computer speakers

Wires, Cable Shink Tube, Headers, Resistors, Bare PCBs



Page Revision History

2019-01-20 Tank Bot V7 Photos

2019-01-16 Tank Bot V6 Photos

2018-12-18 Motor Fritzing Diagram

2018-12-17 V5 18650 Battery Pack

2018-12-10 Aluminum Camera Bracket

2018-12-04 Video Overlay Info

2018-11-30 Published