Society of Robots - Robot Forum

Mechanics and Construction => Mechanics and Construction => Topic started by: johnny5 on September 24, 2011, 10:01:39 PM

Title: Help me out to build a RACE ROBOT !
Post by: johnny5 on September 24, 2011, 10:01:39 PM

Need to build a Race Robot
Vehicle(bot) speed must be : 1-1.5 metres/sec
Required Torque : I have no idea how much torque i need BUT it must easily jump through 5cm dia speed breakers(bumps) and should climb a          slope of 40degrees.
Check this out - a sample track -

(http://www.techfest.org/img/competitions/hydra1.jpg)

Robot dimensions : 25*25*25 (l*b*h)
Robot weight: 500 gms  (can be changed if necessary - depending on motors)
Drive: planning for a 4 wheel drive (all four wheels are connected to motors) and Steering front two wheels (instead of differential drive)
Note: None of the robot parts should be readymade (like gearboxes, steering connectors used in rc cars)
         Robot must be controlled wirelessly using accelerometer
So, kindly suggest me some specific motors that are good at this stuff and serve my purpose. Also provide some resources regarding the bot construction :)

Title: Re: Help me out to build a RACE ROBOT !
Post by: georgeecollins on September 25, 2011, 01:19:23 PM

Is this robot supposed to follow the track only via an accelerometer or can you use IR or Color Sensors to detect the edge of the track?   If you are only trying to follow a course like the one described with an accelerometer it seems extremely difficult, particularly with bumps.  Hopefully you are talking about some sort of line following robot, otherwise I don't really understand what you are doing. 

If you are building 500g robot for speed I would not recommend using four motors.  You don't need four motors and having four adds weight and complexity.  But for the scale and speed you are talking about I would suggest looking at the motors here:

http://www.fingertechrobotics.com/products.php?cat=8 (http://www.fingertechrobotics.com/products.php?cat=8)

Depending on your budget you can power these with a NiCd or LiIon battery via either an H-Bridge circuit or an electronic speed controller (ESC).  An ESC is better, but a little more expensive. 

You didn't mention what sort of controller you were thinking of.  Axon? Arduino?  Stamp?  PIC etc.  Really you should use whatever you are familiar with and if you aren't familiar with anything try a BASIC Stamp because it is easiest. 

Title: Re: Help me out to build a RACE ROBOT !
Post by: Soeren on September 25, 2011, 05:02:00 PM

Hi,

Quote from: georgeecollins on September 25, 2011, 01:19:23 PM

[...] either an H-Bridge circuit or an electronic speed controller (ESC).  An ESC is better, but a little more expensive. 

Unless you're talking about an ESC for a brushless motor, an unidirectional ESC or similar, an ESC is an H-bridge, so why do you think that it's better?

Title: Re: Help me out to build a RACE ROBOT !
Post by: johnny5 on September 26, 2011, 05:29:45 AM

Thank you for suggesting the motors, they are good and I think a 20:1 gear ratio suits to the bot. Now, coming to controlling the robot, we must control it by our hand gestures, so im thinking to fix accelerometer on my hand and as the hand moves up n down the bot should go front and come back and as i tilt my hand it should turn left n right. You can view the hand gestures here.

(http://www.techfest.org/img/wristandhandterm.jpeg)

 
     So, you were telling that it would be difficult to control it with an accelerometer, what would it be ?
And controller - I am comfortable with arduino, I'll go with that. Coming to batteries im thinking to go for a 11.1v, 3Ah LiPo.
I have a doubt regarding the motor speed controlling and the motor driver. If the motor has no load speed of 500rpm, can it be increased by using a motor driver, or can it be only decreased ? and how do we connect the motor driver to an arduino?
Please provide with some resources regarding this. And I can't afford for esc, im thinking to get a L298 or L293 motor driver, but I don't know how do we control it by arduino !

Title: Re: Help me out to build a RACE ROBOT !
Post by: georgeecollins on September 26, 2011, 01:17:15 PM

Quote from: Soeren on September 25, 2011, 05:02:00 PM

Hi,

Quote from: georgeecollins on September 25, 2011, 01:19:23 PM

[...] either an H-Bridge circuit or an electronic speed controller (ESC).  An ESC is better, but a little more expensive. 

Unless you're talking about an ESC for a brushless motor, an unidirectional ESC or similar, an ESC is an H-bridge, so why do you think that it's better?

You have a point in that an H-bridge is a basic circuit that is analogous in function to the circuits that are in an electronic speed controller.  You can reverse direction and control speed with an H-bridge.   An H bridge is by definition a very simple circuit: http://www.modularcircuits.com/h-bridge_secrets1.htm (http://www.modularcircuits.com/h-bridge_secrets1.htm)

Electronic speed controllers, the kind you buy for a radio control car or a combat robot, have a different circuit that in my experience is always more complicated.  In my experience these are much more efficient, allow for more precise speed control, and they are more expensive.  The practical difference for robotics is that an electronic speed controller usually only takes one input per motor and is controlled by pulse width modulation whose range encompasses forward, backward and neutral. 

I'm not an electrical engineer, or an expert, so if you can help me better understand the distinction (if any) I really appreciate it. 

Title: Re: Help me out to build a RACE ROBOT !
Post by: Fr0stAngel on September 26, 2011, 10:32:44 PM

acceleromoter hand control : one way to do it is via wii-mote. connect it to your laptop via blue-tooth, pick it up and use the accelerometer data to send control signal via laptop.
http://ezio.ovh.org/index.php?slab=g-force-analyzer-for-wiimote-&PHPSESSID=3b1ba5bafee8d9d7cfa6ae29665c20d9 (http://ezio.ovh.org/index.php?slab=g-force-analyzer-for-wiimote-&PHPSESSID=3b1ba5bafee8d9d7cfa6ae29665c20d9)
here's a nice program to visualize how  the data changes with the direction.

for the speed and torque requirements , go through the RMF tutorial on SoR, : http://www.societyofrobots.com/mechanics_dynamics.shtml (http://www.societyofrobots.com/mechanics_dynamics.shtml)

i'd say you should go for a differential drive. its easy to implement, and control.
if you have enough time, you could also add some safety features to make it semi-autonomous, like add a couple of IR sensors, so it does not collide with the walls.

Good Luck..!