wiki/content/project/pipoint.md

+++
date = "2017-03-15T20:40:46+01:00"
title = "pipoint"
summary = "A rover tracking camera"
+++
<michaelh@juju.net.nz>  2017-03-15  <https://juju.net.nz/michaelh/project/pipoint/>

## Overview
An automatic camera pointer that keeps a rover like a model aircraft
in the center of the frame.

## Background
Some time ago I set up a camera, pointed it at the sky, and recorded
as I flew my model plane about.  It was quite cool, but the plane
covers so much area that most of the video was of blue sky.

## Requirements
The system shall be able to keep the following rovers in frame:

* A 1 m wingspan model aircraft flying at 100 km/h at 50 m to 200 m
  range
* A 1/10th scale model car driving at 40 km/h at 20 m to 100 m range

The system shall support a standard field configuration, where the
rover says to the left, in front, or to the right of the operator but
never goes behind.

The pointer shall support point a GoPro-class camera, especially a
~60 g Turnigy HD ActionCam with a 170" lens.

To minimise development time, prefer re-using existing hardware and
software platforms.

To minimise hardware integration time, prefer a system with fewer
parts.

Doing a round trip to test the system takes some time.  To minimise
the round trips:

* In-field setup shall be minimised
* The hardware, software, and parameters shall be readily modifable
* The system shall support near real time debugging and tuning

The system shall use my standard tooling which is Go, Git, Ansible,
Prometheus, and Buildbot for CI.

## Implementation
The system shall consist of:

* A PixFalcon Micro and GPS on the rover
* A 433 MHz telemetry link
* A Rasperry Pi 3 based base station
* A Lynx B servo based Pan and Tilt Kit 
* A Linux laptop for display and control

![Overview](overview.svg)

The components are:

* A Wifi accesspoint used as link when in the field
* A Wifi client used as link at home
* mavlink as the protocol
* mavproxy to bridge between serial and UDP
* gobot as the framework

The modes are:

* Locate.  The base station uses the rover's GPS and compass to locate
  the base station itself.
* Run.  The base station receives the rover's location, calculates the
  camera angle, and sends commands to the servos.
  
The support systems are:

* Fast runtime configuration.  The settings can be edited without
  interrupting the app.  Idea: use `spf13/viper`
* Commands (like to switch modes) are sent over REST.

The core abstraction is a parameters.  These have an age and fire
events when updated.  A set of parameters may be updated as a group
and events will fire at the end.  Parameters have the same basic API
as `spf13/viper`.

Servo control is via PWM.  The PWM pins are:

* PWM0: GPIO18 / pin 12
* PWM1: GPIO19 / pin 35

Instructions on enabling these via DTB are [here](http://www.jumpnowtek.com/rpi/Using-the-Raspberry-Pi-Hardware-PWM-timers.html).

## Test plan

The inital at-base checks are:

* Check that the battery packs can run the electronics and servos
* Check connectivity via the access point
* Check the rover manual control
* Check the remote battery
* Check that rover telemetry is received by the base
* Check that the GPS can lock and is received by the base
* Check the camera battery and storage

The in-field checks are:

* Repeat at-base
* With the rover at the base, mark the base location
* Save this location as default
* Manually drive the rover ~10 m away at 0 deg to the base
* Adjust the pan offset to point

## Deliverables
The deliverables are:

* TODO

## Milestones
TODO

Milestone | Week | Result
--------- | ---- | ------
M1 | W1 | All foos have bars barred
M2 | W3 | All bazs are frobbed

## Risks and mitigations
TODO

## Alternatives considered
Do nothing...

## Appendix
Issues

* GPS seems to be sampled at 2.5 Hz, and sometimes arrives earlier or
  later.