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4666  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Robotics 101 help on: October 26, 2010, 04:01:08 pm
Can someone please point me in the right direction? Simplest robot I can start with? Is there a HOW TO or ARDUINO ROBOT 101?

Don't know of an "Arduino Robot 101" tutorial, but the simplest robot with a Arduino you could make, would be a desktop-rover style robot.

Get a couple of continuous rotation servos, mount them using double-stick tape to an old CD or similar "throwaway" platform (a piece of foamcore would work great, even a thick piece of cardboard). Put each servo on opposite sides of the base, with the shafts in-line and parallel with the base. Add a couple of wheels (hot glue or more double-stick tape to the control horn of the continuous rotation servo) by using anything lightweight and round (but not too large - maybe a 3-4 cm in diameter). Hot glue halves of a pingpong ball to the underside to act as "sliders" on the front and back. Add the Arduino on top (it can just sit on top, or double-stick tape it). You might want to add a protoboard shield on top of the Arduino, too. Power the whole thing with a 6V battery pack (for the servos) and a 9V (for the Arduino). Simple sensors can be microswitches, or an ultrasonic pinger, or IR distance sensors, etc.

4667  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: How hard would this be for a starter? on: October 29, 2010, 06:10:29 pm
A grid of pressure sensors would really be too much for me. Also because I'm thinking of something simple, just a gadget that I can take with me.

Is there a way to save these logs? Is it possible with just arduino, or I would need another peripheral?

If you wanted to detect random movement, and you wanted it simple and cheap, you could do a "pin-in-spring" detector sensor: Take a piece of small gauge bare wire, and wind a small coil, and put a small drop of solder on the end. Solder the other end to your PCB. In the center (soldered to the PCB as well) put another thicker gauge bare wire, that extends to the end of the coil.

At rest, the coil shouldn't touch the center wire, but when shaken a bit, the mass of the solder will cause the coil to shift and make contact with the center wire. Hook the two contacts (from the coil and the center wire) up to the Arduino via one of the pins which can detect an interrupt, and in your interrupt handler, set a variable to a non-zero value.

In the rest of your code (in a loop, most likely), have a counter or timer running; when the interrupt occurs, store the value of the timer/counter in the EEPROM memory, or better, to an SD card. Alternatively, you could dump it out the serial port and log it on a nearby PC.

If you stick with just the EEPROM or SD card (or micro SD and a Lilypad?), you could make the device really portable. You could do the same thing with an accelerometer, but it won't be as cheap, nor as easy to interface with.

If you did want to go the accelerometer route, though, you could probably make a nice "stack" of Lilypad boards; the Lilypad, then the accelerometer, then a micro SD interface...

4668  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: New sun tracker idea? on: May 20, 2010, 06:13:53 pm
Better answering the question then him thinking he's being ignored, causing him to bump/spam this issue?

I suppose, but its kinda like walking into a library and asking the librarian where the books on how to read are. This is the 21st century; google exists. -boggle-

Also, the actual position of the sun, doesn't always equate to the highest amount of solar activity, cloud cover etc sensing where it is brightest would be better, otherwise you're defeating its purpose.

Very true. Which is why tracking using data of sun position probably wouldn't be optimum.

Tubs and shields are not needed in the hackaday project I linked, I think such things would over-complicate the problem.

In the hack-a-day project, they are using three sensors - one perpendicular to the plane of the solar panels, and one each, left and right, -angled- away from the central sensor. The angles essentially form the "shadow sheild" - but their system is the one that is overly complex.

You can do it with two sensors - both of which point perpendicular to the plane of the solar panels - with either a shadow sheild between, or a couple of small tubes (a couple of chopped pieces of a ball-point pen would work fine). They need to be long enough so that when tilted, one sensor would receive more light and the other less, and you would move in the direction of the one with less light, until both are "equal" (that whole dead-band thing).

Thinking about it, you probably would only need two sensors if you can accurately place them at the front of the device, minus one value from the other, a positive number move to the left, and a negative number move to the right, zero don't move.

Yes, this is what I am saying, but since light from the sun (which, for all intents and purposes, is a point source of light, but is somewhat diffused through the atmosphere - plus there are reflections and such) is "everywhere", you can't just mount the sensors perpendicular and hope that they would work (I suppose you could angle them outward, like the project did - but there would still be the reflections issue) - you need the tubes or a sheild, and place them close together (right next to each other) - for this to work right.

Believe me, this is how it is done; look up how solar trackers are built and have been built in the past by experimentors and such - there is a huge wealth of information on the internet about them. Here you can find several, for instance:

One of them uses nothing more complex than relays and CdS cells (LDRs)!


I'd imagine you'd be using move power to run it than you'd be generating from the panels, not sure.

Depends on the panels and the power system being charged.
4669  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: New sun tracker idea? on: May 20, 2010, 05:04:38 pm
Couldn't you just let it sense that more light is coming from east, and it'll turn to it?  I suppose it'd be more efficient to have it reset itself at night, but why not make it easy?

For facing east why not just add a Solid state compass to the mix, similar to the compass' you get in mobile phones/gps etc
You'd need three sensors to know when to stop, otherwise you'll be alternating left and right without knowing when to stop.

The way this king of thing is typically set up (just for east-west tracking) is two sensors separated by a shield (or two sensors, each within a tube). They are oriented so that they are at the correct angle for the sun at the lattitude of the tracker.

The tube/sheild is a "shadow" - you tell the tracker to go left or right until both receive near-equal amount of light (essentially a dead-band, like in a servo). You have to add controls (hardware or software) to deal with clouds and such. You also have other knowledge about the fact that the sun only moves in one direction, plus that in daytime, you are either seeing info from the sensors that is one shaded/one in light - but never both shaded, unless a cloud. If both are under a certain value (ie, in the dark for many cycles/time) - then it is nightime, move back to the east, etc.

All of these functions can be easily done in discreet hardware, as well as program code. If you wanted to change elevation as well, you would use four sensors with independent tubes or a "cross-shaped" shadow shield arranges in a diamond configuration, so you could track "up/down" elevation movement...

What I always find most curious about this discussion, is why it is discussed here at all (outside of the interfacing on the Arduino and possibly code) - the actual hardware, how it works, how you can set things up, etc (including microcontroller-based, discreet electronic hardware based, electro-mechanical, and mechanical based trackers) - can all be found on a ton of web sites out there dealing with solar and other alternative energy subjects.

Solar/Sun trackers have been studied, revised, implemented, experimented with - you name it - in a myriad of forms (including clockwork!) - since at least the late-1700's, if not earlier!


[edit]While that was kinda ranty, I am not upset or angry with anyone, and I don't mean the above as some kind of personal assault on anyone's curiousity; I just find it funny that in an age where you literally have information of an unimaginable amount and magnitude at hand, just a search away, people are still asking others how something is done or how it works. Back in my day, my dad would point at the bookshelf with the Brittanica, and say "look it up!"[/edit]
4670  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: New sun tracker idea? on: May 20, 2010, 03:25:44 pm
The biggest issue with the simple electronics circuit tends to be "how to get it facing east again" for the morning rising of the sun. But yeah, such circuits can be made simply, and not require much in the way of electronics. As I noted, you can build a sun tracker without any electrical work at all; I have seen designs that use heat expansion of a working fluid to drive hydraulic-style actuators (so basically a mechanical form of the simple shaded sensor circuits).
4671  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: New sun tracker idea? on: May 20, 2010, 12:03:07 pm
This should work, provided you have the sun's position data for the general latitude you are at. I don't know if anyone has ever done it, but I wouldn't be surprised if it has.

Something to keep in mind is that while it may be cheaper than the more hardware-based route (you can make a solar tracker without using -any- electronics or other electrical devices, btw), your time and "money" will be spent in the coding. It would seem to be a good learning experience no matter what, though.

Good luck with it!

4672  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: General Sensor/Interfacing question on: October 29, 2010, 06:58:52 pm
That's an expensive bend sensor! You might want to look into this for a cheaper way to make your own bend sensors:

There's also methods using conductive plastic from anti-static bags that you can find via googling...

Unless, of course, you need/must use a comercial solution for some reason (reliability over time, consistency of product, etc).

4673  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: LED Matrix for DiscoRocket on: October 25, 2010, 09:57:30 pm
Is there a weight limit before you need a permit or something?

agooga could probably answer this better, but I think the limit depends on the flight ceiling. IIRC, here in the U.S. you have to get an FAA waiver (or notify them or something) if you intend to go over 20,000 feet. I don't think any model rocket can reach that, but high-power model rockets can easily get that high and much more...

BTW - if you like model rockets, find out when and where your local (if you have one) high-power model rocket organization has their next launch; leave your credit card home.

Its amazing to watch these machines lift off; at a large launch, there will typically be some small vendors set up, selling kits and engines and such (oh - btw, here in the U.S. there are also ATF limits and rules on engine fuel storage and such). The hobby can get very expensive very quickly, and as you watch them fly, it makes you want to buy one, badly. You could max out a few credit cards in no time.

A while back there was a "documentary" on high-power rocketry, where one guy they were following had maxed out every credit card he had to build this large scale behemoth. On the program, you could easily tell his wife was less than thrilled with his "hobby" (oooh boy - you could tell she wasn't happy at all). When it came time for "lift off", it exploded on the pad. Something like $30,000 or so gone in an instant.

They never showed the wife's reaction (I imagine it was a seven-letter word beginning with D)...

4674  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: LED Matrix for DiscoRocket on: October 25, 2010, 09:47:17 pm
Great questions, and I don't mind your skepticism at all-- this is a challenging project!  This rocket is absolutely intended for night flight.  No, I have never heard of any laws prohibiting night flights, in fact there are several perfectly "legal" rockets already built to be flown at night with built in light displays-- the Estes "ASTROBEAM" being one of them.

I could have sworn I read something to that effect; I guess I'm wrong...


This rocket is primarily designed to give a dazzling show on the launch pad for a few minutes before launch-- then to take off normally.  Anyone who has ever seen a model rocket launch already knows that, even a large rocket from a thousand feet away looks small.  That's not the point.

The point is to make a rocket that does something unusual, and to have fun.  Fair enough?


My building partner and I probably have twenty years of scratch-built rocketry between us.  I am VERY familiar with the dynamics of the motors, ejection charges, airframes, balance, center of gravity and design limitations,  and I am already in the process of designing scratch-built payload and airframe components to accommodate my ideas.

I wish I had known this up-front; my response would've been different (likely just asking about the night flying stuff). From my vantage point and your comment, you appeared to be a complete newbie, and that this might have been a "pie in the sky" idea. Glad to hear you have the experience to pull this off!

One idea is to use a smaller diameter tube to carry the ejection gasses through the body of the rocket up to the nosecone for deployment.  This way the electronics can be stored along the main body of the rocket tube.

See what I meant about my lack of "thinking outside the box"? That's actually a great idea!


Anyway-- I appreciate your concerns, but I really just need advice on how to build small electronic components!

Well, you're certain to get it here!

Re: Jeff K's flexible circuit idea...

While not ready for "prime time", something like this might be an interesting "wrap" for your rocket:

Again, good luck with your project - and post a video of the launch!

4675  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: LED Matrix for DiscoRocket on: October 25, 2010, 04:47:06 pm

I'm curious about a few things regarding this plan; my questions might seem a little cranky or gruff, and I don't want to discourage your plan, and perhaps I am not thinking outside the box enough - so bear with me.

First off, I am wondering how many model rockets you have flown in the past? If you have ever flown any, then you will soon see the issues you will face in this project - a few of which I am going to summarize here.

I initially wondered where this light show was going to occur, because so far as I can see it, it can only occur: on a static display, on the pad or in the air. Giving it a little more thought, I realized that the only place where you'd be able to see anything of the light display was -only- on the pad. Once that rocket takes off, you won't be seeing anything. At the apogee, when the chute is deployed, you still won't be able to see much, because it will be so far away - there might be some form of twinkle, but that's about it. Maybe with a pair of binoculars you might be able to see better, but not by much (as anyone who's ever tracked a model rocket can tell you, just keeping the rocket as it descends in-frame is hard enough). Once it is lower, you might see more, you might see less - depending on where it lands, how far away downrange it is, etc.

I also wonder how you intend to even see the light display? AFAIK, night-flying model rockets isn't legal, and can get you in trouble with the FAA (or whatever the equivalent is in your country - you don't say where you are located) pretty quickly. That's not even counting on whether having an on-board light display is legal. I also can't imagine tracking such a rocket at night using binoculars, even with a running light display (and forget it if the light display fails to work for some reason).

What's your thoughts on the above?

Finally - I am wondering how you intend to connect the LEDs to the Arduino? Your LEDs will be on the outer tube of the rocket (so far, so good - though you are going to want to run several wind tunnel and other tests to verify that the rocket won't go off-course due to the extra drag caused by the LEDs, etc - on the outside). Since the ejection charge from the engine has to travel up through the tube to push the nosecone and chute out, your Arduino would have to be in the nosecone (at first glance). The data lines would then need to be connected (in some manner?) to the data lines on the tube via some kind of specially made "friction" contacts around the inner top edge of the tube (and bottom outer edge of the nosecone)...

Alternatively, you could invert the workings of the rocket, and have the ejection charge blow out the engine pod (which would consist of the engine and fins, mainly - you see this on simple two-stage rockets for the first stage), draging the chute out. This way the Arduino could be directly connected to the LEDs, with no nosecone separation.

Another method might be to forgo an ejection charge entirely, and have the Arduino trigger something to cause the ejection, rather than using an engine with an ejection charge (this is how many high-power model rockets eject their chutes - although you have to make a black-power ejection charge, and have a source of kevlar cloth).

The first method is problematic in that the light show, at apogee, would stop when the ejection charge occured (making downrange tracking - especially at night - difficult to impossible). The other two methods would require a custom rocket to be built; not an impossibility, but not easy, either (and they would require a lot of testing before first flight to ensure that they don't go "horizontal" on takeoff).

Finally, you don't mention what kind of "model rocket" you intend to use? Do you have a specific model picked out? Do you know what engine size/impulse you will be using (this is very necessary data just to know whether it will even get off the pad - of course, you won't know anything until you can calculate the final weight of the payload and display)?

There's a lot more to this project than simply sticking an Arduino (well, its equivalent) and driver circuitry into a tube arrayed with a bunch of SMD LEDs - if you want to have a chance at succeeding, while not endangering spectators, and not running afoul of the authorities...

Good luck!

4676  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Component Placement in a circuit on: October 26, 2010, 04:07:38 pm
But just in general... should the resistor go before or after the LED, in the above circuits? i.e. which is best practice and why

My take on this is 1 or 3 - here's why:

It is common "sense" to envision current as flowing from high potential (voltage) to ground (ie, from positive to negative). In reality, this isn't true at all (and nothing really "flows" anyhow), but the visualization is easy to see.

Resistors are used to decrease current in a circuit (thus lowering the current through the LED in this case), so from the "flow" perspective above, it makes more sense that the current flows out the pin, goes thru the resistor (and lowering current), then thru the LED, then to ground.

Once again, in reality this isn't how it actually works, and it ultimately doesn't matter which side the resistor is on, as RuggedCircuits has already noted...

4677  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: How to Calculate weight motor can handle on: October 22, 2010, 06:24:02 pm
I agree kids electric riding toys might be the easiest to start with. Generally built to withstand some abuse. Most of the larger ones are 12v powered.

I think it is worth trying, if you can find such a toy cheap enough (or free). I have a PowerWheels H2 for my robot project that has no problem carrying my fat butt (240 lbs) on level concrete, but I don't know how well it would work on say, carpet.

Also, it might take some work modding the drive system to get it to fit the requirements of the project, while maintaining the structural stability. You might try removing the plastic wheels used by the toy, and attaching smaller rubber-tired wheels (like for lawnmowers or dollies); note that this will require some custom work to match the wheels up with the output hubs on the gearboxes (PowerWheels gearboxes are weird in this regard).

If you plan to pursue using a toy ride-on like a PowerWheels vehicle, check out the following resources:

4678  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: How to Calculate weight motor can handle on: October 22, 2010, 04:25:33 pm
If you go with the "wheelchair" or "mobility chair" motor route (and as already suggested, for this application, I would) - you're going to find a couple of things:

1) The motors are expensive
2) The motors are expensive to interface with

First off is finding the motors. Your best bet is Ebay or Craigslist. On Ebay, for the motors only, look up keywords like "mobility", "chair", "wheelchair", "motor(s)", "scooter" and of course combinations thereof. Another good word to use is "transaxle", but be careful that you are getting a dual-motor differential drive transaxle that has two motors in it, and not a single motor transaxle with a differential (the first is used for chairs like the Hoveround, the second for chairs/scooters like the 3-wheel Rascal). These things weigh a lot, around 30-40 pounds for the motors and gearboxes, more with wheels; if you can get the motor controller with the motors, and it is in good shape, then get it.

On Craigslist, you are likely to only be able to find the complete chair; generally, the way it goes is that people get a chair thru Medicare, then pass away, and their family has to donate it or sell it - sometimes you can find them cheap, sometimes not, but generally they are waaay cheaper used than if you bought "retail" from a medical supply store (without Medicare). You can also find complete chairs on Ebay, too. I have also seen complete chairs at Goodwill (rare, though).

As noted, if you can get the motor controller (and it is in working shape), you want to get it. Otherwise, you are going to have to shop around for a suitably sized controller for your motors (after figuring out what the motor specs are - which may involve some phone calls, either to the manufacturer of the motor/transaxle, chair, or a repair shop who may know). Controllers are not cheap - but if you have to buy one, look into controllers for "battle robotics" platforms. There are also custom chair controllers out there designed for the mobility chair "modding" community (yes, such a group of people exist).

Finally - an option to consider (dubious, though, I'll admit) is to get the gearboxes, wheels (or at least the hubs), and motors from a dual-gearboxed 12 volt PowerWheels ride-on toy. Sometimes you can find these cheap on Craigslist, Goodwill, yard sales - sometimes people are looking just to throw them away. If you can rebuild the drive system for your custom use, they'll easily haul 200 lbs (though the motors are noisy like you wouldn't believe - unlike powerchair motors, which are designed for smooth and quiet operation).

4679  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: IR-LED as heat source on: October 15, 2010, 09:38:46 pm
You could probably get more heat out of a cheapo resistor...
4680  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Arduino Oscilloscope ? on: February 07, 2010, 03:49:28 pm
What I would like to do (if I had the time and didn't have my UGV project) would be to use the Arduino (or something similar) to act as a "go between" with my G1 (Android) phone - where the Arduino processes the signals, then outputs via USB to the phone - either over the audio connection (via a VCO done in software/hardware on the Arduino end), or USB (trickier, since you would have to make a custom "Arduino"-based interface with a chipset for USB mastering, since Android phones are slave USB devices as well). The phone would serve as a GUI and display of the waveforms.

Right now, on the Android Marketplace, there is an absolutely wide open arena in the "electronics applications" market - there are maybe 5 or 6 apps worth anything there; one is an oscilloscope that uses the microphone input (so AC audio-frequency signals only; no way to use it for DC signals like square-wave digital signals); it also is lacking in many useful features according to reviews (and you have to pay for it to find this out, $1.99 or something). There are also tons of other possible applications in the electronics arena that would be perfect for Android-based phones like the G1.

I know that with such an interface, based on an Arduino (or similar platform - the 644 like used in the Fuzebox, would make another great interface), and connected to an Android phone; you wouldn't get the fastest scope on the planet (you would be lucky to get 40 kHz), but you could make something useful and quick to use for the occasional bench or field probing.
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