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This instructable was created to be entered in the Robot Challenge. If I win, the parts will of course, go into robots like this one. Notes on how to include some of the very components in the prize packages are given in the last step. I am 28, so of course, I'm not going for the student prizes.

I created this as a simple project for those just starting out in robotics. It is relatively inexpensive, requires minimal tools and is easy to build. Once finished you have an expandable robotic platform that fits in the palm of your hand and can be easily programmed in the Arduino environment.

Here is is driving in a triangle, without any special add ons


In the instructions I'll walk you through how to:
  1. Modify the servos for continuous rotation
  2. Fit the track hubs on to the servos
  3. Make a custom battery pack
  4. Wire it with a few connections
  5. Assemble it
  6. Program it
  7. Customize
These and other additions can be mixed to make your own custom micro robot

For the basic platform the following supplies are needed:
an Arduino nano
a small rechargeable battery
a pair of 9 g servos, modified for continuous rotation
part of a Tamiya track set
a 40 pin dip socket
a rubber eraser
some zip ties

Step 1: Construction: Modify the servos

Micro servos modified for continuous rotation are the heart of this design. They give you so much of the hardware; the motors, the gearbox, the driver and control circuitry, all in a tiny cheap package, and in this implementation they also act as the frame of the robot (seen in the next step). There are many instructables on modifying servos for continuous rotation. But here is how I did it for the micro 9g servos I am using.

Pictures:
  1. Remove the tiny screws and open the case
  2. Cut the potentiometer wires, these are where you will attach the resistors
  3. If you have surface mount resistors, place a 5k (1k to 10k should work) on the pad from each of the side pads to the middle pad, if you don't twist a pair of through hole resistors like this
  4. Break out the stop on the potentiometer with some small pliers, you need the pot for its use as a rotational bearing
  5. solder on the resistors, if you used the pair of through hole ones, I recommend bundling them in electrical tape like so. For the servo that will go on the front, cut a notch for the wire to exit through the side so it doesn't come from under the robot.
  6. (not shown) Before you close up, put a hole in the back part of the case opposite the spline to mount the idler (wheel with no teeth).
  7. Use some angle cutters or pliers to remove any mounting flanges from the cases and file or sand down the ridges they leave, these can get in the way later.

<br> Really, really neat!<br> It's hard to make a narrow robot when you're using continuous rotation servos because of the gearbox height, but you've overcome this with the tracks and the asymmetric mounting method.<br> Just to clarify, you've drilled a hole for the idler pinion in the servo bottom cover in line with the spindle?&nbsp; Must have been pretty tight in there - the boards in those 9g servos don't leave a lot of room.
To mount the idler I did it just as you said, its screwed into a hole drilled on the back cover opposite the spindle. I had to be sure not to put the screw in too deep so it wouldn't hit the board, but in the ones I was using the board was slanted so it wasn't too near the back wall at that point. I've noticed with these cheap ones it isn't always the same slant, but on the ones where they installed it so that the near side is on the end I want to mount the wheel to I just tilt it the other way before I put it back in when I do the modification.
<p>Hi, great project. This may sound silly, but could you scale up this. So have the nano controlling a bigger motor? Sorry I am new to all of this kind of stuff. Thanks!</p>
<p>Gater clips??</p><p>Shouldnt this have been at the front of the project for tools and parts needed. </p>
<p>I don't think gator clips are required for any of these steps, also, I didn't make a tool list. This only requires basic electronics tools like wire cutters, pliers, a soldering iron, and a small screwdriver.</p>
<p>My servos are already continuous. So i skip this step right?</p>
<p>Right.</p>
Would a 500mah battery work?
That capacity will be enough, but many small LiPo batteries are 3.7V, and some arduino boards are 5V. If you have one that runs on 3.3 then a 3.7V cell should be fine. If it has a 5V regulator it might not power on.
It's a great robot I commented on it over 3 years ago and have been waiting to finally make it I just don't know which batteries to use
It's a great robot I commented on it over 3 years ago and have been waiting to finally make it I just don't know which batteries to use
What types of batteries can I use and what must they have?
<p>what will happen if I use more than 10k resistor? Will the servo work?</p>
It will work with a wide range of values, it's just working as a voltage divider to give the servo control IC a reference voltage that is right in the middle. In this case since the positive voltage is 5V and the other end is ground (0V) and the two resistors are equal, you get 2.5V.<br><br>The servo usually works by comparing the potentiometer voltage to the target voltage and setting the speed proportional to the difference, so that the further it is from the target position the faster it will move, and it will stop when it gets there. By setting the feedback voltage fixed in the middle of the range it moves at a speed which is proportional to the target voltage minus the middle voltage, so that it stops when it gets a neutral signal and runs faster in one direction or the other depending on the command.<br><br>But more to your question, any values that match eachother will work so long as they aren't so low that they effectively short out the controller (if you used say 7 ohms the power would all go through your resistors and the system would shut down) or so high that the reference voltage is undetectable. So anything from 2k to 1M should work, maybe even outside that range.
<p>what will happen if I use more than 10k resistor? Will the servo work?</p>
<p>what will happen if I use more than 10k resistor? Will the servo work?</p>
<p>Beautiful robot (y)</p>
Thanks!
<p>great</p>
<p>how do you wire the battery to the circuit?</p>
<p>It's just wired to Vin and Gnd on the nano, which are split to go to the power wires on the servos. But if I were to do it now I'd probably use a simple lithium polymer charge circuit that provides a charge regulator, and a little Lithium polymer cell.</p><p>For example this charger on ebay</p><p><a href="http://www.ebay.com/itm/5V-Mini-USB-1A-Lithium-Battery-Charging-Lipo-Charger-Module-for-Arduino-A866-MA-/131304520047?hash=item1e925bf96f:g:G5UAAMXQlgtSy7s0">http://www.ebay.com/itm/5V-Mini-USB-1A-Lithium-Bat...</a></p><p>and maybe a cell like this</p><p><a href="http://www.ebay.com/itm/3-7v-1000-mah-Polymer-Li-ion-Lithium-cells-for-GPS-ipod-MP3-MP4-Tablet-PC-102445-/171905017739?hash=item280656678b:g:EHYAAOSw1h5XQQVL">http://www.ebay.com/itm/3-7v-1000-mah-Polymer-Li-i...</a></p><p>Then you would just connect the battery lines from batt+ and batt- on the board to your battery. And the in+ and in- to Gnd and Vin on your arduino. Since you don't want to feed power from the arduino when plugged in straight into the battery I might suggest putting a diode on the connection between the battery and the arduino so that power can only flow from the battery to the board and not vice-versa. I'm actually not sure if this is strictly necesary as this board may be set up so the battery inputs on the board can be used as outputs when it is not powered. I'll try it and get back to you on that.</p>
<p>what is the hypothesis of this robot</p>
<p>I don't understand the question. I suppose if the robot is viewed as an experiment the hypothesis is &quot;I bet I could use these micro servos to make a very simple little tank&quot; and the conclusion was that I could.</p>
<p>can we use gear box instead of servos</p>
<p>I don't see why not. But you would need a motor driver, such as the L293 to run the motors. The advantage of the micro servos is that you get your driver, speed controller and gearbox all together for about $2 each.</p>
<p>I don't see why not. But you would need a motor driver, such as the L293 to run the motors. The advantage of the micro servos is that you get your driver, speed controller and gearbox all together for about $2 each.</p>
<p>What is the total cost of this project, I dont have any of the pieces that I need.</p>
<p>Thanks a ton, this Instructable gave me a great idea for our Cub Scout group.</p><p>I just posted my Instructable &quot;Arduino Robot for Under $5&quot; based what I learned here.</p>
<p>Awesome job! here is another type of microbot, do check it out: http://www.instructables.com/id/Arduino-Nano-Segway/</p>
<p>how did you attach two wheels to one servo in step:2</p>
<p>Nice cool lil robot... im gonna build one.. need to order the wheels </p>
This is awesome mini tank. What I would do when making this is add a claw and a lazer
it's awesome. but can I use a keyboard to provide the input to this minute Robo?
<p>I'm thinking of things I could add on to this. So I'd like some feedback from anyone interested. What kind of wireless would you most like to see? WiFi, Bluetooth, simple radio such as a OOK transmitter?</p><p>Any other uodates? Maybe a different miniature electro-mechanical part like a claw/grabber.</p><p>Also, changes to make it more usable. Let me know, no matter how simple or complex.</p><p>Thanks</p>
<p>thank you is very good too</p>
<p>I'm looking at some potential li-ion batteries and was wondering what you would recommend? I found a 250mAh 3.7V battery on eBay, do you think that would cause any issues with a 5V arduino nano?</p>
<p>I considered this too. I've found that in my case at least the Nano will not turn on at 3.7V. However, the chip onboard is an ATmega328, rated for 1.8 to 5.5V. The reason it won't run at 3.7V is the 5V regulator on the board. Bypass that and it will run down to 1.8V, though depending on your servos you will need more than that, 3.7V seems to be enough for the 9g servos I've been using.</p>
How much does this cost in total
<p>If you get cheapo parts on ebay*. about $30</p><p> *I haven't used these particular parts, they may be crappy</p><p>$5.50 for the micro servos [<a href="http://www.ebay.com/itm/2x-SG90-Micro-9g-Servo-For-RC-Helicopter-Hitec-JR-Futaba-Align-Trex-US-Sel-/191402239783?pt=Radio_Control_Parts_Accessories&hash=item2c90766727" rel="nofollow">for example</a> ]</p><p>$5 for the nano [<a href="http://www.ebay.com/itm/Arduino-compatible-Nano-V3-0-ATmega328-Mini-USB-Microcontroller-Board-Cable-HIYP-/221608533427?pt=LH_DefaultDomain_0&hash=item3398e5ddb3" rel="nofollow">ebay</a>]</p><p>$10 for the tracks [<a href="http://www.ebay.com/itm/NEW-Tamiya-Track-Wheel-Set-70100-NIB-/390914477064?pt=Educational_Toys_US&hash=item5b04518c08" rel="nofollow">ebay</a>] though I would reccomend making your own, since you don't need the whole kit, and I just had the small wheels left over. For example you could use plastic bottle caps and silicon bracelets.</p><p>I salvaged the battery, but if you can't find an old cell phone battery something like this would do: $2 [<a rel="nofollow">USB li-po charger</a>] $6 [<a rel="nofollow">tiny single cell li-po battery</a>] convieniently, this is already the right voltage to run the arduino nano. One could easily add jumpers to make it charge while hooked up to program.</p>
<p>Hey, I've been meaning to purchase some threads for my RC projects and on your link for the tracks[ebay] they cost 7.59+12.75 shipping when on ebay app or pc, but i check your link when on mobile it's 7.59+2 dollar shipping? I'm confused. Did you buy them with shipping for 10 dollar? are they based near you,thus shipping was lower?</p>
<p>Hi, this is great project. I'm little confused about communication between the Arduino Nano and the Andorid app.</p>
<p>I have followed the instructions on how to make the servo have continuous rotation, but as it doesn't have the potentiometer connected, the servo doesn't realize that he finished turning and it never stops. Please, someone help.</p>
<p>That is what is supposed to happen. The servo is supposed to turn continuously (around and around without a limit) rather than just moving to a position. To allow this, rather than the signal giving you a particular position, it will give you a particular speed.</p><p>So to stop, you must send the signal for zero, which is usually a 1.5 ms pulse, on a normal servo this would be the middle position. Likewise 2 ms is full forward speed for as long as the signal is applied, where on a normal servo it is full forward position for as long as the signal is applied. Likewise 1 ms will run full reverse, while on a normal signal it would hold in the full reverse position.</p><p>note: some servos vary in exactly where their forward, 0 and reverse limits are. IE they may stop at 1.3 or 1.7 ms pulse.</p>
Thanks, I discovered the numbers for my servo. <br>Full forward:180<br>Full backward:0<br>Stop:85<br>For a strange reason, the stop is not in the middle.
<p>Hello! I saw it and I wanted to help. I believe it is a problem caused from the potentiometer inside of the micro servo. But, when you &quot;hack&quot; the servo for full rotation, potentiometer will not matter and it should work just fine. For hacking the video, you can find bunch of videos online.</p>
<p>Can you do it with the raspberry pi?</p>
It could certainly handle the calculations, being way more powerful by orders of magnitude than a nano. It might be a bit big.
<p>Do you think you can try to do it?</p>
<p>I might, but I don't actually have a pi to work with. I mostly use microcontrollers on my own boards rather than dev boards. I do have a few, some arduinos, a cypress pioneer kit, some beagle bones, but no pi.</p>
Ok.

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Bio: I am a robotic engineer, and I like to make things and teach others.
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