Step 16: Electronics time

With the heavy-duty construction out of the way, it's time to focus on electronics.

Since I didn't have budget for a motor controller, I decided to use relays to control the motors. Relays only allow for the motor to run at one speed, but that's the price you pay for a cheap controller circuit (no pun intended).

For the robot's brain, I used an Arduino mircocontroller, which is a cheap, open source microcontroller. Tons of documentation exists for this controller, and it is very easy to use (speaking as a mechanical engineering student who had no microcontroller experience prior to this past semester).

Since the relays being used are 12 V, they can't just be controlled with a direct output from the Arduino (which has a max voltage output of 5 V). Transistors connected to pins on the Arduino must be used to send the 12 V (which will be pulled from the lead acid batteries) to the relays.

You can download the motor control schematic below. The schematic was made using CadSoft's EAGLE layout program. It is available as freeware. The wiring for the joystick and switches/buttons is not included because it is very basic (the joystick just triggers four switches; a very simple design). There's a tutorial here if you're interested in learning how to properly wire a switch or push button into a microcontroller.

You'll notice there are resistors connected to the base of each transistor. You'll need to do some calculations to determine what value this resistor should be. This website is a good resource for determining this resistor value.

*Disclaimer* I'm no electrical engineer. I have a somewhat cursory understanding of electronics, so I'm going to have to gloss over the details in this step. I did learn a lot from my class, Making Things Interactive, as well as tutorials like this one from the Arduino Website. The motor schematic, which I drew, was actually designed by CMU Robotics Club Vice President Austin Buchan, who assisted me a great deal with all of the electrical aspects of this project.
<p>hiii.... i want to do this stuff for my engineering final year project....<br>i want to make it with low cost,,, and dont want to include any circuits at all....<br>can i use it direct with 12v battery connected to motor.... to go forward and backward direction.... <br><br>please help me......</p>
You could do that as long as you use a switch that can handle the electrical current drawn by the motors.
which type of motor can be used....<br>
<p>12V or 24V motor and gearbox from an electric wheelchair would work best.</p>
This is an absolutely exceptional project! Seriously well done on it. :) Do you know how much it cost you by the end?
<p>Thanks! Out of pocket expenses were under $200, but keep in mind I had a lot of parts donated (motors, batteries, steel tubing).</p>
Hi rpantaleo! Question: What did you end up doing with it in the end? I'm looking to exit my hexarideablepod gracefully, so I'm thinking of scrapping it for parts. Did you just end up hanging it from the ceiling or leaving it with your department or something?
I stripped the motors and batteries out and gave them back to the Robotics Club. The rest of the machine has been sitting in my garage for a couple years - I plan on turning it into a coffee table (welding the legs in place then putting a piece of plate glass on top).
thanks for the info! okay, I will probably take it apart for scrap steel and parts then.
This is AWESOME. If I can get a hold of the parts I'm totally doing this. I may want to invest in some shocks though...
How fast does it move with 24 V?
Never tried it. Probably about twice as fast?
you should put some tennis balls on tha feet so it doesn't scrape so much on tha floor. <br>
Just posted a video of a build derived from this instructable<br><br>http://www.youtube.com/watch?v=0jMmebn49EM
This is awesome! Great work!
@rpantaleo do you have dynamics calculations for finding minimum torque at the robot?
Unfortunately, I do not.
can this be made with just 2 batteries 2 motors and 2 seprate switches for the motors?
what a nice robot... i have a question about the motors. So those 2 motors are different type aren't it ? the one is for left side, and the other one for right side??<br><br>and those motors are for wheel chair motor? I'm from Indonesia , and I must think where can I find the motors.. please reply.. thank you very much
The motors are identical except for the gearbox. One has a gearbox that outputs to the left, the other to the right.<br><br>You may be able to find these motors on ebay.
Wow awesome! This wheel chair is amazing; if you would add treaded feet and shock absorbers to the chair then it will much better.<br><br>http://www.metal-supplies.com/12201/index.html
Yes, very cool project. <br><br>Rubber treaded feet with absorbers was the first thing that came to mind for me too while watching the video<br>
I think that if you put rubber pegs on the legs, you might be getting better results considering movement!
Wow awesome! This wheel chair is amazing; if you would add treaded feet and shock absorbers to the chair then it will much better.
sir please send microcontroler circuit <br>
I'm afraid the only circuit/schematic I have is the one in Step 16. Sorry.
sir i am using two 12v 4Amps batteries those are sufficient for run the motor
If you plan on riding on it, no. Otherwise, it may work with no load on the robot.
not for riding on it ,if riding on it what is the capacity of batteries means voltage and current
One or two batteries like this should be sufficient.<br> <br> <a href="http://www.amazon.com/UB12180-Sealed-Lead-Acid-Batteries/dp/B001DL7D1O">http://www.amazon.com/UB12180-Sealed-Lead-Acid-Batteries/dp/B001DL7D1O</a><br>
circuit for connecting two motors
which micro controler is used for this project and also mention the number of micro controler<br> circuit board for connections<br>
I used an older version of the&nbsp;<a href="http://arduino.cc/en/Main/ArduinoBoardUno">Arduino Uno</a>&nbsp;for this project. I used 4 digital input pins for the main control circuit.&nbsp;
how to analyse this model in ansys for static and dynamic analysis
I haven't used ANSYS much, so I'm really not sure. I used SolidWorks to make the model, and SolidWorks has a built-in analysis program, which is what I would use.
2 3&quot; 3/4-10 bolts what is this means<br>
2 bolts, 3 inches in length, 3/4 inch diameter, 10 threads per inch.
thanxs dude
This is brilliant. I wonder how much better it would be if you would add treaded feet and shock absorbers to the chair (kind of like what they use on public buses.) <br> <br>Build it bigger and with armor plating, you'd get the military's attention!!
where did you buy that mill and how much?
I believe the mill was a donation from the CMU Robotics Institute machine shop. We didn't buy it.
where did you guys buy the mill and how much?
can u upload a pdf file of microcontroler and relays because i am not good in electronics and it is confusing and i am new in robotics
I'm afraid the schematic on Step 13 is the best I'm going to be able to provide.<br> <br> In light of that, here is a forum thread on connecting relays to an Arduino: <a>http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1196698219</a><br> <br> Keep in mind that you really don't need to use a very complicated circuit to control the hexabot. I used a microcontroller and more complicated circuit because it was required for the class I was taking, but realistically all you need is a couple high-current rated switches to turn power on and off to each motor.
Great project, looks like loads of fun. <br><br>I do see some room for improvement in the legs. Why not hook up small shock dampeners in the legs, between the tubing and the feet? Something like the air shocks that hold open the rear hatches on SUVs should do the trick. I think one of those in each wheel, with of course a plastic foot on it, would even out the ride considerably, and make the whole process a bit more effective (not to mention easier on your spine!).<br><br>Even as it sits, it's an awesome project. When I get old, screw a wheelchair, I'm building one of these. XD
can we use other types of moter like 'a car starter or moter used in wiper in car'
A car starter motor would require some sort of gear reduction to reduce the speed and increase the torque. <br><br>A windshield wiper motor would work but the torque output would be too low for you to ride on it.

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