HamRover: Part 1
The parts to our Amateur Radio Robot, the HamRover, have arrived. To help us mock up the layout, we got out the good ol' scotch tape. The final rover will go in a water resistant case that we will mount on top of the chassis.
We will be making use of:
- Arduino Uno with HamShield: LoRa Edition, right angle SMA adapter, and SignalStick antenna
- 2.5W Solar Panel
- 900mA Solar Lithium Charger + 5V Booster
- 2x 18650 LiPo batteries wired in parallel (~4000mAh)
- Tank tractor kit with dual motors
- L298N motor controller
- TTL serial JPEG camera
- MPU-9250 9 DoF sensor (Accelerometer + Gyro + Magnetometer)
- UBlox 6M GPS
My 7 year old son, who has now several robot builds under his belt, is assisting with the assembly.
Our HamRover will:
- Use the Cape May, NJ LARPS coverage area at ground level
- Provide periodic telemetry information:
- GPS location, heading, speed and quality
- Output from our IMU sensor (MPU-9250) to determine compass heading and orientation of our HamRover
- Battery voltage level from a voltage divider
- Transmit digital pictures using the reliable data transport function of LARPS
- Receive command and control messages for movement
- Keep batteries indefinitely charged using our 2.5W solar panel
- Make use of its tractor belt drive to navigate over a variety of terrain
Most importantly, all source code, plans, and potential circuit boards will be released open source and made available on our github. If there is enough interest, there's a possibly we will sell a dedicated controller board or even a kit.
HamRover Build, Attempt 1
First, we connected up the various components to mock up how the circuit would work on top of our rover chassis. We found that while the collection of prototyping and breakout boards assembled pretty quickly, the tank chassis was not easy.
The tractors were the incorrect length, which required us to take out difficult to remove pins and shorten the tractor.
We loaded a simple sketch that cycled between the 4 directions: forward, backwards, turn left, and turn right. We uploaded it to the Arduino, expecting our robot to move around.
However, it didn't do that very well. The motors rotated while the rover was off the ground, but placing it on the ground caused it to halt.
Even though our high "C" rated batteries could source a lot of current, there simply was not enough voltage to move the motors with any amount of strength. Later we discovered they were 12V motors -- even though the kit comes with a lithium battery holder.
Since our solar battery charger + 5V power booster board could potentially put out ample current for the motors, we tried controlling the motors at 5V. However, the voltage still was not high enough move our HamRover.
Modifying our Design
With now the requirement for so many voltages to operate our rover, we are forced to do one of two things:
1. Obtain a high current booster for 12V, and plug it into the L298N board
2. Build a 11.1V Lithium Ion battery pack (3 cell) and regulate downwards for our Arduino and HamShield: LoRa Edition
Option 1 requires a circuit board that may or may not exist, but it might be an easy fix. We could still retain our charging circuit with this design with no modifications. The L298N can accept some relatively high voltages, and since controlled via logic level, would need no modification.
Option 2 would allow us to use a simple regulator (or buck regulator) to step down the voltage for our Arduino, which operates at 5V. The problem lies with how we would charge the multi cell battery pack. It would probably require a custom charger.
There is a third option .... we may be forced to design our own rover board. This would reduce complexity of assembling various breakout boards and reduce size and weight. It would be a lot easier for us to provide a kit that way.
Do you have any ideas? Mention them in the comments. We will let you know what we finally decide on next week.