
Tacocopter Basics - danshapiro
http://www.danshapiro.com/blog/2012/09/tacocopter-basics/
======
lgeek
Long rant incoming...

I'm currently building a quadcopter from parts and I'm writing my own control
software.

I wasn't really familiar with RC components before starting this project, but
I must say I'm impressed with the performance and reliability you get from
very low cost motors, ESCs, propellers, gyroscopes and accelerometers.

However, I think Li-Po batteries are a huge safety issue. There are multiple
factors:

* The battery chemistry is very unforgiving. You overcharge, it gets damaged, you over-discharge, it gets damaged. Same for charge and discharge current. The failure mode? Flammable gasses are released and eventually the whole thing sets itself on fire. And that's a fire you can't extinguish using typical means like water or regular fire extinguishers.

* All RC Li-Po batteries use a soft shell. If your model crashes the batteries can and will get crushed, which leads to an internal short-circuit, which eventually starts a fire.

* No RC Li-Po batteries incorporate Smart Battery controllers (like in laptop batteries) which could prevent overcharge/over-discharge and over-current conditions.

There have been plenty of incidents involving Li-Po fires, including whole
houses burning down.

And still, the batteries don't change. Li-Po makes perfect sense for RC
applications because it has great energy density and allows high discharge
current. But to me it looks like some simple safety features could make this
technology safe enough that you wouldn't have to treat your batteries like
small bombs.

As a side-note, I've initially tried to use laptop Li-Ion batteries for my
quadcopter. Each motor + propeller unit requires almost 12A @ 11V when at
maximum speed - quite typical power requirements for a medium-sized
quadcopter. I couldn't get more than 16A out of an older 6 cell battery
(voltage was abruptly dropping if trying to draw more, so I guess this was the
limit of the cells). I've then tried a new 9 cell battery (which was too heavy
anyway). The controller on this battery considers 20A discharge an over-
current condition and shuts off the output. So I'm stuck with Li-Po batteries
and hoping that they won't set anything on fire.

I certainly wouldn't feel comfortable with current-technology Li-Po powered
vehicles flying around a city without being watched.

~~~
AndrewKemendo
>No RC Li-Po batteries incorporate Smart Battery controllers

What technical impediment is preventing someone from building said controller?

~~~
lgeek
No technical reason really, it's about cost, demand and volume.

Cost is going to be a problem because of the high current involved in normal
operation and even more so in case of a short-circuit.

Let's take a popular battery size, let's say 2200mAh 3S 25C. This battery
should be able to safely support a discharge current up to 55A. For reference,
a 10KW power shower draws less current than this from the mains network. Our
smart battery controller needs to be able to measure the discharge current,
and needs to be able to switch the output on or off.

You can just buy a hall effect based current sensor and a power transistor
that will handle 55A. But these components need to survive in case of a short-
circuit for long enough for a micro-controller to read the current at its
regular polling rate and then turn off the transistor. Expect the short-
circuit current to be a number of times higher than 55A.

So you end up with a parts list that costs you about $10 per unit for small
quantities (500). Have I mentioned the price of the battery I was building
this for? It's $13.

I've thought about building some for myself, but 1) they really should be
mounted inside a hard case together with the battery and 2) I don't have a
space where it would be safe to prototype this, assuming that a failure will
happen.

------
lutusp
Okay HN developers -- when you get done reading the linked article and are
finished laughing at the thought of a little helicopter delivering a taco or a
bottle of beer, start thinking:

* Little helicopters can now lift a substantial weight.

* They aren't very expensive.

* They're easily controlled, more so than a full-sized helicopter (primarily because of computer-aided controls and GPS guidance). So you don't have to be Chuck Yeager to fly one.

* All you need to do is mate the helicopter with a decent camera that can simultaneously beam a picture to the ground for guidance and preview, and take high-resolution pictures on command by way of the radio link.

* Uses: real estate (who desperately need a way to take high-quality pictures of houses from above), surveillance, art, video productions, etc..

This is an opportunity waiting for someone willing to take it on.

~~~
silvestrov
My big fear: when the payload is hand grenades [1], i.e. a "multicopter
bomber".

You can launch the multicopters from places where you're not seen. You can
even do this in nighttime and have them land and wait undetected on some
rooftop until you want them to continue their mission.

A handfull of such multicopters will make more terror than 9/11 ever could do
because 9/11 was (almost) concentrated to a single place. 9/11 had passenger
lists so it was easy to find out who took control of the planes. Multicopter
bombers have no passenger lists, no sender address. You don't know how many
more planes are in the air and when they will strike.

Redundancy and multi-target missions are even cheaper and more efficient with
multicopters than in the 9/11 attacks. Multicopters are so cheap that the
terrorists can launch a bunch of them and not care if half of them fail to get
to their target. Multicopters bombers works for targeting e.g. Disney Parks
and other places with a lot of easily frightened people out in the open.

With 9/11 it was easy to get away from the attacks (i.e. just leave that part
of Manhatten). Multicopter bombers are like a swarm of supersized wasps. You
don't know where to go, you don't know when they'll be back.

1: Homemade "grenades": <http://en.wikipedia.org/wiki/David_Copeland>

~~~
bigiain
When you say "my big fear", I can't help but read "m irrational fear".

Do you _really_ fear "multicopter bombers" with a fleet "like a swarm of
supersized wasps"?

To me, that's in the same class as people wo are afraid of flying, yet happily
drive their car to the airport.

Realistically, terrorists don't skill up with brand new technologies to try
carrying hand grenades around, they use cars/trucks/airplanes. If _I_ had a
budget set to get explosives in amongst people, I'd be buying or renting
cars/pickups/small trucks which can carry thousands of pounds of explosives
around a city relatively inconspicuously. I wouldn't be training up teams of
rc-pilots/hobby-UVA-geeks to be able to deliver a pound or three of explosive
at a time.

~~~
silvestrov
What's the easiest and cheapest:

a) _buying a few hand grenades and premade multicopters?_ Hobbyists in Germany
have already multicopters which are GPS pre-programmed so you don't need any
pilots to control them during the mission.

b) _creating thousands of pounds of explosives?_ Try read the detailed diary
from the 2011 Norwegian terrorist to see how much time and trouble it took
produce his bomb: way more time and effort than most would think.

The next 10 years will make multicopters much more accessible to non-geeks,
but "thousands of pounds of explosives" won't be any easier than today. New
tech gets old very quickly.

~~~
learc83
Why do you need multicopters? Terrorists already can (and some have) plant
small timed bombs in crowded areas. I don't really see much difference other
than that they can target more secure areas. This would be useful if they
wanted to attack military targets, but since their usual goal is civilian
casualties, they can by definition already get to places civilians congregate.

~~~
klochner
When planting a bomb you have to visit the scene of the crime and risk being
seen.

With multicopters there's virtually no risk of getting caught.

~~~
wtracy
A multicopter is going to be a lot more conspicuous than a person with a
briefcase. I don't buy it.

------
alexandros
Fun stuff. How about a RC plane dropping off quadcopters loaded with the
payload for the last mile? (the copters can meet the plane on the way back or
fly home alone. You get the range + efficiency of the plane with the agility
of the copter.

~~~
tehwebguy
This can probably be solved easily, but my first thought is under-tested
quadcopters being dropped from planes like spinning taco bombs.

------
noonespecial
I'd really like to see a "you can fly anything commercially that weighs less
than 5 pounds and has a terminal velocity below 30mph in freefall" rule.
Bigger loads and speeds would be subject to some regulation and licensing.

This would cause a Cambrian explosion in development. It would be wild.

~~~
throwawaay
Imagine one of these payloads landing on someone's head. Wolfram Alpha offers
up "2.4x impulse force acting on a baseball being hit by a bat" as a
comparison when you plug in "5 lbs * 30 mph".

I like the idea, but there probably needs to be more development in safety
systems before anyone could reasonably consider allowing that.

~~~
mbell
> Imagine one of these payloads landing on someone's head. Wolfram Alpha
> offers up "2.4x impulse force acting on a baseball being hit by a bat" as a
> comparison when you plug in "5 lbs * 30 mph".

I'm not sure what value this comparison has. Impulse force doesn't tell you
much of anything about how much damage would be done to a persons head.

~~~
elteto
You are working with the wrong concept, m * v is momentum, not impulse.
Impulse would be equivalent to the change in momentum over time [1]. Actually
5 lbs falling at 30 mph would probably crush a human skull or at least crack
it open. It is easy to see why from the equations:

F * delta t = m * delta V, therefore F = m * delta V / delta t

This means that the force generated in the impact is inversely proportional to
the time of the impact. Since the skull is pretty hard, we can say that the
impact time will be very short, probably in the order of 1e-2 seconds. Such a
sudden change in velocity, from 30mph to 0mph in 1e-2 seconds, generates a big
force, and therefore a big impulse.

[1] <http://en.wikipedia.org/wiki/Impulse_%28physics%29>

~~~
mbell
Indeed, however to say anything about damage you need to know the area where
the force is applied and more about the materials. If the bottom of the copter
is padded the duration of the impact coud be much longer and spread over a
larger area.

Also, F = m * delta V / delta t is only valid if force is constant in this
context. I would expect acceleration to vary during the course of the impact
so this relation would likely not hold [EDIT] in terms of determining damage I
mean.

~~~
elteto
Yes, in this case the equation refers to the average force over an interval of
time: if at time instant A we had a speed v1 and at a later instant B we have
some speed v2 then a force with a magnitude of _at least_ m * (v2 - v1) / (tB
- tA) must have acted, therefore the analysis should hold.

As you point out the area is very important in the analysis, since Pressure =
F / A. For large areas the force "spreads out" and the damage is less.

The fatality of the accident can vary due to many circumstances however I
think we can safely assume that for the purposes of our initial analysis, 5
lbs traveling at 30mph and crashing into my head is not something I am looking
forward to ;)

------
lazyjones
I'd prefer something like this:

[http://www.engadget.com/2009/08/01/urban-mole-robot-could-
de...](http://www.engadget.com/2009/08/01/urban-mole-robot-could-deliver-your-
mail-via-insane-network-of-u/)

\- no noise \- no accidents involving people \- less energy needed \- much
simpler / robust construction

------
wheaties
Is this for real or is it the most cleverly disguised viral advertising
campaign for Doritos? I don't see any mention of any other taco brand plus the
use of a Doritos branded image...

~~~
danshapiro
OP here. I just find Doritos Locos inherently amazing.

------
jaredstenquist
I hope you are right. If so my domains will become more valuable...

\- pizzacopter.com \- burgercopter.com \- foodcopter.com

------
primitur
I really like the idea of multirotors taking off, literally, to be part of a
delivery team.

Incidentally, I'd really like to be able to use those rotors to recycle things
- literally to shred, perhaps, my plastic trash - such that the remaining
processed materials can be used in .. say .. a 3d printer.

Also, lets get the 3d printer and quadrocopters pretty much working smoothly
together so that one provides resources to the other. Oh, no wait, lets just
make the 3d printer print quadrocopters, and the quadro's feed the 3dprinters
.. and .. well now lets just make a flying recycling 3d printer robot, and be
done with it.

On Mars. Because if we do it here, the damn thing _will_ take over our planet.

------
ArekDymalski
That could be useful for delivering mail in skyscrapers. But The biggest
challenge to solve would be finding the way to prevent interceptions/stealing.

~~~
chime
If the cost of copter + payload is low enough, there is little incentive to
steal. It should be similar to shopping cart theft or most probably less. The
system can be built to go up, travel horizontally above the reach of most
people, and then drop down at destination.

You could buy a perch like they show here:
[http://www.youtube.com/watch?v=E7X0_6o9J10&feature=playe...](http://www.youtube.com/watch?v=E7X0_6o9J10&feature=player_detailpage#t=68s)
\- the perch has a GUID, knows its GPS location, and carries insurance. When
you order from any vendor, you just give them your perch ID along with your
credit card. If the order is lost before it reaches your perch, it's the
vendor's problem. Once the copter touches down on your perch (and informs the
vendor of the safe delivery), you press 'Go Home' to launch it back. If it
doesn't reach the vendor, your perch insurance takes over. Too many lost
copters in your neighborhood and vendors will be able to deny service based on
risk.

I think if the copters are no louder than a car pulling up the driveway, this
can work very well.

~~~
ArekDymalski
I actually thought about stealing the delivered goods not the copter itself :)

------
jahewson
Things that fly are really, really dangerous, and the benefits really need to
be worth the risks. I don't think a Taco is worth the risk that one of these
things goes out of control over the freeway and causes a 100-car pileup. The
idea of cheap and plentiful multi copters would make this sort of event
inevitable.

Of course there may be a much simpler problem: hungry seagulls.

~~~
dsr_
If it goes out of control over the freeway, it won't cause a 100-car pileup.

The first car to hit it will probably notice the crunching noise. A quadcopter
with a 2lb payload weighs about 5lbs total.

The owner is going to be in more danger when he comes to pick up the pieces
than any of the cars.

~~~
jahewson
The article suggests a "modest" speed of 40mph for the quadrocopter, which
seems pretty fast to me. Let's call it 30mph. Our car on the freeway is doing
say 60mph. Presuming they're travelling in opposite directions, that's 5lbs
travelling at 100mph.

So what you're saying is that if I fire a MacBook Pro at car at 100mph then
nothing will happen. Unlikely...

And one of these smacking a pedestrian in the head at 40mph isn't going to be
much better.

~~~
base698
Depending on the design of the frame. Some are made of plastic and break apart
really easy on impact. None of them, even the the aluminum frames, are even
close to as dense as a MacBook.

------
genwin
When the drones come to US cities, and it seems they will within a decade,
I'll be moving to a smaller town, however small or remote it takes to escape
the noise. I'll accept that I'm an old fogey who can't handle "progress".

------
rubyrescue
One nitpick - Bernoulli's principle is NOT why airplanes fly... it's angle of
attack. Spirited debate at <http://en.wikipedia.org/wiki/Lift_(force)>

------
brador
Called it: [http://nerdr.com/3-ridiculously-slow-systems-for-startup-
dis...](http://nerdr.com/3-ridiculously-slow-systems-for-startup-disruption-
idea-dump-monday/) (Amazon delivery copters)

------
abecedarius
How about ornithopters? Naively I'd guess they'd come in between planes and
quadcopters in both efficiency and agility. Since seagulls can land without a
runway, a tacothopter ought to be able to, too.

------
Tichy
Why not use zeppelins? Could they be energy efficient? Just not sure how to
deal with wind. But it has been done, so I guess it is possible.

~~~
andrewflnr
I don't think they're very fast. On HN we've kicked around the idea of
attaching a balloon to a quadcopter or similar to extend its range.

------
orangethirty
Fun read. Though we should first perfect the dark art of pizza deliveries
before attempting to fly a taco over our heads.

------
draggnar
How about one that works like the osprey?

~~~
philwelch
The Osprey is _incredibly_ complicated to design and operate. The only reason
the Marine Corps even bothers with it anymore is because it makes the
impossible possible in terms of long range vertical insertion. The cost-
benefit just isn't there for tacos.

