First Test Boats - Paddle 1, 2 and 3



After talking about making autonomous boats for a number of years and finally having all the skills together at the same time, we needed a test boat to program and drive about. Much like Space X, rapid iterations were the best path. For us, that's lots of hot glue and cable ties.

The goal was to keep the test boat as simple, fast, and cheap as possible to build, so we settled on a paddle boat design with an independent drive to each paddle so it would drive like a tank.


Original concept 



Version 1

I threw together a few circles on CAD and sliced them out of a sheet of expanded polystyrene (see CNC Hot-Wire post for details).


Having cut the hull out of foam, we glued a lunch box to it to hold the electronics, then bolted a length of aluminum right-angle to it to hold the motors/paddles.  The paddle wheels were 3D printed and bolted to the motor shafts with little shaft adapters. 

For the electronics, we made a custom PCB with an ESP32, I2C multiplexer, 5v, and 3v3 power regulators, and a dual H-Bridge driver to control the motors. 


 We found a nice lake and threw it in. It performed well under manual control and with that, we definitely had a platform to test software and sensors on. The next stages were to add additional sensors like a compass and GPS to enable automated waypoint missions.


Version 2

Turns out the glue we used for version 1 was not at all waterproof and while the hull shape looks like a boat, the flat back created a lot of unnecessary drag. The next design was pointy at both ends and used polyurethane glue. It also got a longer slimmer waterproof box and a slimmer overall profile to help it go faster. To toughen up the polystyrene hull, it received a coat of black gaffer tape which made it much stronger. 

The electronics were extended with a GPS module, a 9-DOF IMU (3-axis gyroscope, 3-axis accelerometer, and 3-axis compass) module and a 915mhz radio for communication.  The software was also significantly extended to leverage the extra sensor data and perform waypoint missions.

See DroneLink System - Boat Brains article for an overview.



Second boat under construction

The second boat finished


Version 3

Although the gaffer tape made the hull stronger, the water creeps between the tape and the foam and spends days dripping back out again.  The lid of the electronics box only loosely clipped on, with no gaskets or seals to keep the water out which turned out to be a great problem as the paddle wheels flick water everywhere.

The version 3 boat has a water-tight box with a gasket and clips all the way around and improved paddle wheels. The printed ones were OK, but water could flow out sideways around the end of each fin losing efficiency, whereas the new wheels have a wall on the outside to constrain the flow of water. The new wheels were also laser cut from plywood at our local Makerspace and varnished for waterproofness. 

More efficient, lasercut paddle wheels


Version 3 assembled


The boat is now a reliable little workhorse, used for a mix of retrieving other stuck boats and occasionally as a radio relay for other tests, which I will write about in a future post. 



Comments

Post a Comment

Popular posts from this blog

Waypoint Navigation and Sailing Algorithm

Image
This post describes the underlying operation of the Sailing algorithm built into the DroneLink platform.  The functionality is spread across a number of logical modules, allowing for flexible usage in different types of devices, for example, motorboats requiring waypoint navigation, but not sailing logic. Waypoint Navigation All our boats (and other mobile robots) require basic waypoint navigation, implemented in the Waypoint module.  The module loads a list of lon/lat coordinates and associated target radii from a CSV stored in the ESP32 flash filesystem (waypoint.csv).  An example CSV and the resulting visualization is shown below for 4 waypoints: The Waypoint module subscribes to t he current lon/lat location,  from the GPS module, and uses this to calculate once the boat has come within the target distance of the current waypoint (10m radius for the first waypoint in the example above).  Once the target radius is reached, the next waypoint from the file w...
Read more

Volantex Compass Robotic Conversion

Image
Motivated by the desire for a compact, traditional sailing boat that I could easily chuck in the car and launch with minimal prep, I acquired a second-hand Compass Volantex DG65-class RC yacht.  The previous owner had assembled it from a kit, but never quite finished the rigging.  So, having completed that little task I took it out for a sail using the included 2-channel RC transmitter.  This test sail verified it behaved nicely on the water and gave me a sense of how it might behave after conversion to robotic control!  The conversion would involve a few stages: Replace the original RC receiver and battery with a DroneLink motherboard, Power module and LiPo battery Rework the electronics bay to accommodate the electronics Replace the stock hatch with a new 3D printed hatch to house the battery and Compass module Integrate a GPS antenna and 915MHz dipole for the RFM69 radio Create a miniature wind vane using an AS5600 magnetic encoder  Overall layout: New Brains...
Read more

Making the Keel of So Close

Image
Preface this is a blog about making a keel for a model boat. If you haven't read the post about that it won't make a lot of sense - Link to the original So Close post. So Close needs a high-density low heavy keel to keep it the right way up. Sounds easy to make something heavy, but it also needs to be a streamlined shape and have some means of fixing it to the two bits of sheet metal that it will hang between. Still doesn't sound very hard? Just 3D-print a mould of the shape and fill it with concrete, cast in a few bits of threaded rod and job done? Not quite so easy, So Close needs a 6kg keel, but the density of concrete is approximately 2.4kg/L, so 2.5 litres of concrete. Not a small mould to print, but not impossible if done in a few bits. The problem is when put under water it will displace 2.5 litres so now the concrete only weighs 3.5kg and it's huge. Now, of course, I could keep adding more and more concrete, not a very practical strategy, or pick a more dense su...
Read more