Mind / Iron
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ERVO FOR THE ROBOT INNOVATOR
6 SERVO 02.2017
I’ve built and flown several quadcopters, including a fiberglass and carbon fiber unit with 4 kg of onboard lithium-ion batteries. However, because the nearest
park is almost always occupied, my go-to quadcopter is a palm-sized unit that I
fly indoors. In my controlled environment, I don’t have to worry about my 6 oz
drone falling from the sky onto a pedestrian, dog, or automobile. However, it
just isn’t as exciting as flying outside with multiple environmental factors to deal
with, from trees and birds to blowing leaves.
While it’s a given that flying drones in some form is here to stay, there’s
clearly an unmet need for robotics enthusiasts who want to break out of their
bedrooms. Enter Underwater Remotely Operated Vehicles (UROVs) — the little
brothers to the massive commercial underwater vehicles used to inspect hulls, ship
wrecks, and pipe lines. In terms of commercial availability, UROVs — sometimes
referred to as Robosubs — are where quadcopters were five years ago. As such,
you’re not going to find a UROV hanging in a bubble pack next to the $39
quadcopters at RadioShack. Parts are relatively expensive, and you’ll likely have to
fabricate a few things from scratch — all great challenges for an experimenter.
I’ve only built one UROV — a bare bones model that survived several
excursions in a nearby pond. Although it might seem counterintuitive, a typical
quadcopter is much simpler to design, build, and operate. Aside from locating
affordable parts, the challenges in building a UROV (in order of importance) are
keeping the electronics dry, power, and heat dissipation.
Starting with the affordable parts issue, I made my first underwater drone
with four used 12V trolling motors that I found on eBay for about $50/motor. A
12” length of 8” diameter PVC pipe with threaded end caps served as the main
chassis. This wasn’t the safest design because the props were exposed.
Another limitation is that all four motors were designed for right handed
rotation. As with quadcopters, you’ll want to use both left and right handed
motors. Camera selection was a no-brainer — I simply mounted my GoPro on the
PVC pipe using an elastic strap to avoid drilling additional holes in the pipe.
For an example of parts designed specifically for UROV use, check out the
CrustCrawler site ( www.crust crawler.com) — my go-to source for aluminum
robot arms and crawlers. CrustCrawler sells 400W and 600W thrusters, with
fully enclosed props, excellent mounting brackets, and waterproof connectors.
They also sell transparent waterproof enclosures that can hold lights, a
camera, and an Arduino or other controller. At nearly $1K for a 600W thruster,
however, these top-end parts are clearly best suited for a robotics club with
multiple members sharing the cost.
The challenge of keeping critical components dry is best met by using
marine connectors designed for this purpose, as well as using grease on the
rubber seals leading to and from the main electronics housing. Obviously, you’ll
have to use motors designed for full immersion.
Power is in some ways less of an issue than with quadcopters. Instead of
dealing with lithium-ion batteries and chargers, you’ll likely use one or two car
batteries or an AC powered supply connected to the UROV via an umbilical
cord. The cord is a bother in that it limits both maneuverability and maximum
Operated Vehicles: The Next
Big Thing in Robotics?