Robotics

Using Hobby RC parts in DIY projects

4volt — Sat, 05 Jun 2010 09:29:33 GMT

I’m always happy when I find a new kind of part that is cheap and easy to use with DIY electronics projects or robotics, the more standardized the better.

There’s a whole world of smart electronics and helper things in the hobby and remote control world that are great for robots and other things.

You probably already know that hobby servos are easy to control from any microcontroller like the arduino, but there are a bunch of other things that are just as easy to use. Generic motor controllers, battery systems are also equally as useful, but are sometimes hard to sort out the jargon and acronyms that R/C hobbyists use.

Some of the terms are pretty confusing, and a lot of acronyms and other R/C only rating systems are used. I’ve made this short reference to make it easer to sort out what all those things mean. I've found myself wondering more then once what the difference between an ESC and a BESC, or what a 2S2P 10C battery is.

Power / Voltage Regulation

ESC
(Electronic Speed Controller)

Uses a PWM signal to control the speed of a motor
ECS’s are made for either brushless or brushed motors (See motors)
ESC's are rated in Amps (A) for how large of a load/motor they can control

BEC
(Battery Eliminator Circuit)
Steps a higher voltage down to a lower voltage, a kind of voltage regulator
UBEC
(Ultimate BEC)
Same as a standard BEC, but made for higher voltages
BESC
(Battery eliminator speed controller)
An ESC with BEC
LVC
(Low Voltage Cutoff)
Keeps LIPO batteries from becoming too drained, which can be dangerous, usually a feature of a controller
DVM
(Digital VoltMeter)

Controller Acronyms

RX – receiver

Receives a control signal from the transmitter, output's a PWM signal for servos or speed controllers

TX – transmitter

(The remote you hold in your hand)

Battery Terms

LiPo, LI-PO, Li-Poly
Short for lithium ion polymer battery, the standard type of R/C battery
LiFe - LiFePO4
Lithium Iron Phosphate battery, generally safer then LIPO batteries, better shelf life, faster charging
NiMh
Cheaper, but generally not as good as LiPo or LiFe
S Rating (Like: 1S, 2S, 4S, 6S, etc)
Number of cells in a battery pack
A single LiPo cell is 3.7v
A single LiFe cell is 3.5v
A single NiMh cell is 1.2v
P Rating (Like: 2P, 4P, etc)
Number of parallel lines in the battery, each parallel doubles the mAh the battery can deliver

A 2S2P battery has 4 cells in 2 parallel lines
C Rating (Like: 1C, 10C, 20C, etc)
Amount of current battery can discharge in an hour
1C = Batteries entire capacity

A 10C, 500mAh battery can discharge at 5,000mA (5A) max, and have about a 6 minute life at max discharge

A 20C, 500mAh battery can discharge at 10,000mA (10A) max, and have about a 3 minute life at max discharge
Charging Bag, Charge Pack
A fireproof safety bag for storing batteries
LIPO Monitor
An alarm that goes off if the battery voltage drops too low. Batteries that drop too low can be damaged, or possibly explode.

Motor Terms

Brushless Motor
A motor that runs off of A/C power, and has no "brushes" that transfer current into the rotating spindle. Brushless motors are similar to stepper motors, but only have two coils.
Brushed, Canned, Standard Motor
A traditional DC driven motor
Coreless motor
A motor without the iron core in it's windings
Outrunner motor
Brushless motors where the casing spins and the center stays still

Motor is mounted by the back of the shaft
Low RPM's, high torque
Silent

Inrunner motor
Brushless motors where the center core spins, and the casing is fixed

Motor is mounted by motor casing
High RPM's, low torque
More efficient than outrunners

GB
Gear box, usually for planes
KVM, kv-RPM, KV
A motors' RPM in thousands per volt supplied

Servo Terms

KG Rating (Like: 10kg, 20kg, etc…)
Amount of force the servo can exert in kg/cm
Can also be rated in oz-in (Imperial)
G Rating (Like: 30g, 50g, etc…)
How heavy the servo is
Can also be rated in oz (Imperial)
Sec Rating (Like: 0.20sec, 0.50sec)
How fast the servo can rotate in seconds (usually for 60 degrees)
Digital Servo
Pretty much like a non-digital servo, but uses a microcontroller brain

Testing Jansen Walker Version 3

4volt — Mon, 15 Feb 2010 23:03:04 GMT

Over the last week I’ve been working on the next version of the Jansen Walker, this will be the 3rd release.

The goal is to make it much easier to assemble, faster, and 1/3rd larger using 3mm (1/8in) material.

The biggest change is that instead of using modified servos, which seem to scare a lot of people off, use geared motors which are about the same price. That will make the electronics side easier, perhaps slightly more expensive depending on your controls.

The new version will use the Tamiya Twin-Motor Gearbox, that has a good 203:1 ratio that is ideal for a medium to low RPM walker. It’s $10.95 at SparkFun.

I see three obvious ways to control the walker electronically:

Very simple: switches and batteries
Direct wired buttons to the motor and battery would work well, but have no speed control
A generic R/C setup with a remote, receiver, and two small speed controllers. I think this would be fun.
An arduino or any microcontroller with a motor shield

I’m also playing around with ideas to make assembly easier and faster. Currently it takes about 4-6 hours to assemble, mainly because of all the legs and joints. There are 5 joints per leg, and there are 12 legs.

The next thing I'll be trying is nylon tubing and compression using bolts, that should allow for secure joints that still still rotate freely. As soon as my parts arrive I’ll be testing this method, I think it will shorten assembly time by as much as half.

Power required to emulate a human brain

4volt — Sat, 06 Feb 2010 07:27:47 GMT

Recently, I posted a article about how much computational power it would take to emulate the human brain, and my calculations were off by a factor of 10. I've corrected my estimates and here are the updated sections:

Emulating the Human Brain

The Blue Brain Project has successfully simulated 1 cordical column on the Magerit super computer (100 TeraFLOPS), and human brain has an estimated 1,000,000 columns.

So with 5.2 ExaFlops, one could emulate 52,000 cordial columns. And that’s 1/20th of enough power to emulate a human brain.

To emulate the entire human brain you would need approximately 100 ExaFLOPs

That's a lot of FLOPS!

I chose the above estimation because many others rely on calculating how many operations per second the brain can processes, not how many computer calculations to emulate the brain. I.E. It takes many more computer computations to emulate a brain computation.

Fore some more notes see: http://www.smartcomputing.com/articles/2002/s1302/39s02/39s02.pdf

Conclusion

Henry Markham in his recent TED talk, thinks that a human brain could be emulated in 10 years.

I agree with his estimate, using Moore's law 10 years seems like an achievable goal.

If you are interested in the subject you may also like Ray Kurzweil's research and books.

Total Processing Power of the Internet

4volt — Mon, 18 Jan 2010 23:38:03 GMT

As a brain exercise I decided to try and estimate the total processing power of all the computers on the entire internet, and see if that is enough processing power to emulate the human brain.

Since this is an estimate, I will try my best to figure it out with public data.

Here was my process:

Total Number of Computers

No one knows exactly how many people (computers) are connected to the internet since a single IP address can be shared with any number of pc’s, but the best estimate I was able to find was here: Internet World Stats

They use population statistics and penetration data to estimate this. This does not include extraneous connected devices like gaming consoles, or other devices.

Total Computers: 1,733,993,741 (1.7 Billion)

Effective Processing Power per Node

Since all the computers are separated by the internet, I chose to use SETI@home as a benchmark for the effective benchmark of how much processing on average a node can handle

According to BOINC stats, Seti has 186,250 active computers (more inactive ones), and the peak processing speed is 704.507 TeraFLOPS (tF). (As of 01/17/2010)

That’s 3.782 GigaFLOPS (gF) per node.

Also, on average computers running SETI are probably faster then the average computer online, especially considering poorer countries. So lets round down the average to 3gF.

3 GigaFLOPS is much lower then the peak processing power of a modern computer, a (Intel Core i7 965 XE), can process about 70, while some of the newest GPU cards can process upwards of 1,000 GigaFLOPS.

This leaves me to believe that tele-processing is very inefficient compared to traditional supercomputers, though it is not without advantage.

Total Processing Power

Now, assume all 1.7B computers were all running this hypothetical peer to peer processing application, and bandwidth was not a bottle neck.

1,733,993,741 * 3 = (5,201,981.223 TeraFLOPS, or 5.2 ExaFLOPS)

In case your wondering:

1 Peta = 1,000 Tera

1 Exa = 1,000 Peta

Currently the fastest supercomputer is “Jaguar” with 2,331 TeraFLOPS. (Top 500 November 2009)

Emulating the Human Brain

The Blue Brain Project has successfully simulated 1 cordical column on the Magerit super computer (100 TeraFLOPS), and human brain has an estimated 1,000,000 columns.

So with 5.2 ExaFlops, one could emulate 52,000 cordial columns. And that’s 1/20th of enough to emulate a human brain.

To emulate the entire human brain you would need approximately 100 ExaFLOPs

That's a lot of FLOPS!

Fore some more notes see: http://www.smartcomputing.com/articles/2002/s1302/39s02/39s02.pdf

Wrap-up

After reading more about the Blue Brain Project, they are emulating a cordial column, as well as analyzing and visualizing that data, which is not necessary for a independent AI.That coupled with the inefficiencies in communication with tele-processing, I suspect that there is a lot of improvement that can be made.

Henry Markham in his recent TED talk, thinks that a human brain could be emulated in 10 years.

I agree with his estimate, using moore's law 10 years seems like an achievable goal.

If you are interested in the subject you may also like Ray Kurzweil's research and books.

Alternatives

More likely a successful AI would be a efficient Emergent-type hive AI. Where independent nodes contribute to a beneficial goal with independent actions. This would not look like a traditional AI to us, the patterns would probably to numerous and vague to track accurately.

This was meant as a thought experiment, if you have any comments please leave them. I will revise this article as I see fit.

Using the Minimal Arduino

4volt — Wed, 27 May 2009 15:47:48 GMT

Todbot has posted an excellent tutorial on how to setup and use the minimal Arduino, which is the bare minimum you need to run a ATmega chip and the Arduino bootloader.

Todd goes into detail about how to get the bootloader onto the chip as well as how to setup the Arduino environment to use it.

Even if your not interested in building an Arduino from scratch, It’s a good read if you are interested in the technical aspects of what makes the Arduino work.

http://todbot.com/blog/2009/05/26/minimal-arduino-with-atmega8/

Stripping a Scanner for Parts (in 10 minutes)

4volt — Thu, 21 May 2009 04:35:12 GMT

I’m starting on a project that I’ll be using stepping motors and belts, and after looking for cheap parts online, I thought I could do better by stripping down some old scanners.

People are excited to get rid of there old computer stuff, the great thing is it doesn't matter if the old scanner works. Even if it doesn't turn on likely the motor and mechanical parts are still good for salvage. I posted a ad on Portland’s craigslist in the wanted section and got several responses, in a week I had a bunch of scanners for free, I only had to pick them up. I found that putting in the ad that you would be reusing the parts for a robotics project people were very interested.

Scanners are easy to take apart, they are pretty simple machines and generally there are some catches, and a screw or two around the edges of the top cover.

Once the cover is off, you can start stripping parts, the valuable and easy to use parts are the stepper motor, linear slide, belt and gears. There may also be an optical end-stop sensor, and some buttons that are easy to re-use. You can get more hardcore and try to salvage parts on the actual circuit board, but that takes a bit of research to figure out what is useful.

Here are the parts from two example scanners, both have similar parts and took about 10 minutes to gut.

From all my scanners I salvaged at least:

1 Stepper Motor
1 Linear slide bar
1 Timing belt
1 Set of gears for the belt
A few buttons and LED’s

If I were to buy those parts I would be spending at least $20-30, and they are all in good usable condition, just for the stepper motors alone it was worth my time. Also most of not all of those scanners would have went to the landfill. I was able to recycle most of the electronics, and I put the plastic shells in the city recycle bin, that’s something you can’t do while the electronics are still inside. That’s a net win anyway you look at it.

Update: While it's outside the scope of this article (10 minutes or less) to get into the details of salvaging more electronics, read the comments below for some more interesting comments and uses or other parts found in scanners.

Jansen Walker Beta 2

4volt — Mon, 04 May 2009 08:00:31 GMT

I’m releasing the plans for the beta 2 of the Jansen Walker,

Improvements include:

3 pairs of leg on each side instead of 2
A drop-in platform for the center
Several other small improvements
Improved building plans.

Check out the Jansen Walker project page for all the files and plans.

Theo Jansen on "Robots Podcast"

4volt — Mon, 27 Apr 2009 07:09:15 GMT

It’s no secret that I’m a fan of Theo Jansen’s work, he is the inventor of the Jansen Mechanism that I used as the basis of my recent Jansen Walker project.

Jansen was recently interviewed on the generically named "Robots Podcast" where he spoke about his thoughts on if he was a artist or scientist, if the Strandbeest have thoughts, his building materials, the design of the legs, how he would like the Strandbeest to outlive him, also microcontrollers and commercialism.

Check out the podcast over at Robots Podcast.

Jansen Walker Beta 1 Official Release

4volt — Sun, 19 Apr 2009 09:24:21 GMT

I’m officially releasing my Jansen Walker as a beta with the source files and a video!

4volt Jansen Walker Beta 1 Video

Jansen Walker: An openly designed Creative Commons licensed robot.

What you see here is the Beta 1 version of the walker, a laser-cut robot, based on the Jansen Mechanism. It has 8 legs and scuttles similar to a crab walking sideways. The brain is a Arduino, and the legs are powered by 2 micro-servos modified for continuous rotation.

If you would like to buy a kit of just the plastic in its current state, check out the donate page, or take the plans to any of the many laser cutting services.

For the full write up and source files check out 4volt.com/Projects/Jansen/

Modifying Micro Servos for Continuous Rotation

4volt — Sun, 19 Apr 2009 04:29:43 GMT

There are many ways to power your next project but I’m quite partial to the continuous rotation servo because it’s very easy to hook up to your micro controller, you don’t need to build or buy a separate controller or h-bridge to power the motor. In a servo all that is built in. All you need to do is connect the power directly to your battery and send a low-voltage control signal to tell it what you want it to do.

Servos out of the box are meant to rotate in a fixed range of 180 degrees, but modifying them for continuous rotation is easy, my first servo took about 30 minutes, and now I can do them in about 15 with no problems.

Take the back cover off
You’ll need a small jewelers screw driver. There is one long screw in each corner.
Take out the gears
The gears will slip out easily from the casing, you may need a small pliers for the main (largest) gear.
Make sure that the largest gear has teeth all around the outside of large part of the gear. I've recently come across some micro servos that do not have teeth all the way around and are impossible to modify for continuous rotation.
Cut the mechanical stops off
Usually there is a small tab on the inside of the gear cover, easily removed
There may also be a stop inside the potentiometer, since the pot is essentially also the axel you’ll have to leave it in, but make sure that it can rotate all the way around. You may need to snip off some small metal tabs on the inside of the pot.
Add some resistors
There are three wires coming off of the pot, snip all three off and solder two resistors starting from the middle wire, connecting one to each of the other wires. In these photos the wires are Green Red and Yellow.

I used 1.75k resistors, but your servo may be different, use a multimeter to determine what is best for you.

Note: I hoped to take to pot off the axle and glue it into it’s center point, but that’s impossible with most micro servos since the axle is part of the pot.
Re-assemble
Center

The one thing about modifying servos for continuous rotation is that when you use the resistor method it's likely that they are not perfectly balanced. You can tell if you have that problem when the center PWM value sent to the servo and it starts rotating, when it should be stopped. I use the SoftwareServo.h library that lets you adjust the center PWM value to compensate in software

If your using the Arduino, here is a script that uses the SoftwareServo library and a loop to continually adjust the “setMaximumPulse” property on the servo object.

Upload the sketch, open your serial monitor pane, and wait for the servo to stop spinning, when it does write down the last number shown in the serial monitor and use it in the setup of your servo. For more details see the script source:

Continuous_Rotation_Servo_Test.pde