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81
Mechanics and Construction / Re: Servo or geared motor with encoder?
« Last post by Joseph Thurlow on August 14, 2015, 02:05:42 AM »
If possible I could use a GPS module to work with the distance sensors. Would this work?

I've decided to use differential steering for my robot.
 
Thanks for the reply :)
82
Mechanics and Construction / Re: Need Help to make a low cost bot
« Last post by sdlsahan on August 13, 2015, 10:43:49 PM »
Thank you very much for your reply.

https://www.google.lk/search?q=kilobot&es_sm=93&source=lnms&tbm=isch&sa=X&ved=0CAgQ_AUoAmoVChMI5vCa-96nxwIVBhqOCh1KNA6l&biw=1366&bih=667#imgrc=TcyCHN4MlbWFaM%3A

The size of the robot should be a little more than this. Robotics is not the area of my expertise :) Is there some place where I could but these small ones?

Since the size needs to be small, I was thinking of maybe using a PIC microcontroller.

Thanks again :)
83
Mechanics and Construction / Re: Need Help to make a low cost bot
« Last post by cyberjeff on August 13, 2015, 07:05:51 PM »
There's a ton of them around.

Here's a cheapy from our friends at Servo City:

https://www.servocity.com/html/peewee_runt_rovertm__637158_.html#.Vc07zflViko

Arduino's and their clones are cheap, so are IR sensors. Easy to hook up, the IR code is simple.

Buy local at Microcenter ($6 for a UNO R3, last I looked) or buy online For what you are doing a UNO is easy and sufficient.

If you buy on Ebay or some place like Banggood, and I do, be aware of where it is being shipped from. China can take a while.
84
Electronics / Re: What Wheel Encoders To Buy
« Last post by ProgressiveAutomations on August 13, 2015, 12:40:00 PM »
A wheel encoder is a disk with slots cut in it.  Some more advanced ones have differently cut slots to have more precise control. Here are some levels of complexity: http://www.avrfreaks.net/sites/default/files/SevenWheelsXparent.gif

But they all work on the same principle.  You have layers of slots on the disk, and for each layer you need a light/sensor pair.  In the image above, the first two pictures are 1 layer, the next 2 are 2 layer, and the absolute position ones are 8 layer.

You connect the light to always be on, and connect the sensor to an interrupt pin.  As the wheel spins, the disk spins, and as the slots spin past the light, it causes flashes of light to be detected by the sensor.  By counting these flashes, you can know how far the wheel has moved, to determine position.

By counting the flashes over a certain time interval, you can determine speed.

If you already have an encoder disk, then the only sensors you need are small LEDs, and a small photoresistor.  Put the LED on one side of the disk, and the photoresistor on the other to count the pulses.
85
Mechanics and Construction / Need Help to make a low cost bot
« Last post by sdlsahan on August 13, 2015, 11:41:18 AM »
Hello there,

I'm an Engineering undergraduate doing Electrical & Electronic. I'm doing a project related to the 'kilobot' project. I need to create a small robot ( I guess it's called a 'bot') at very low cost. It just needs to have a method for locomotion & a IR module to communicate with each other. Further, it needs to have a microcontroller.

Can I buy it from somewhere like 'ebay'? I need to have atleast 10 of these.

Any help is appreciated. Thanks :)

86
Software / Rotation angle of Servo???
« Last post by ecaits on August 13, 2015, 03:30:13 AM »
I am using Vigor VS 2 servo. As per data sheet, its output angle is >=170 degree and pulse traveling 800 to 2200 μsec.

When I give command of 90 degree to rotate, it rotate slightly more than 90 degree but when I give command of 85 degree then it is looking like exact 90 degree.

I have written simple program as written below.

Servo myservo;
int pos = 0;
void setup()
{
myservo.attach(9);
}
void loop()
{
myservo.write(85);
}

What I require to modify to get the exact angle as per program code.

Thank You,

Regards,
Nirav
 
87
Software / EM parking sensor
« Last post by treywatson on August 13, 2015, 12:59:01 AM »
I have been trying to figure out the algorithm/c code for an EM parking sensor:-

http://www.amazon.com/HAMSWAN-Electromagnetic-Parking-Sensors-Assistance/dp/B00M1LIK76

I also have a sample with me which i opened and found out Atmel at89c2051 with a lm393 comparator on it. How to interface the comparator with the microcontroller? Or Is there a way to extract the code from the IC?

Pins used are:-
20-vcc,
10-gnd,
9-P3.5-T1,
8-p3.4-T0,
6-p3.2-INT0,
5-xtal1,
4-xtal2,
1-vpp

the comparator appears to be connected to T1. INT0 and T0 are shorted.I badly need any help possible.  :'(

Any sort of assistance is appreciated.  :)

88
Steering via the front wheels like a regular car (which is what I think you mean by differential drive) is a complex mechanical task.  The electronics of it is easy, it's just a servo that turns back and forth, but the mechanics needed to actually turn the wheels the way you want them is hard.

If you're talking about differential drive, like spinning the right wheel forwards and the left wheel backwards to turn left, that is really easy to program and make.  With 4 wheels its a bit more difficult, and you won't get as smooth control as you would with 2 wheels and a castor wheel.

Using a castor wheel with 4 wheels doesn't make sense to me... What did you have in mind for the wheel base?
89
Electronics / Re: HELP: DC MOTOR & DRIVER
« Last post by ProgressiveAutomations on August 12, 2015, 06:46:00 PM »
Connecting a pot to a motor will vary the speed, but you're burning up lots of energy in the potentiometer.  If you get to a sizable motor (even a 1 amp draw is getting sizeable) you'll be looking at tons of energy waste.

The best way to control the speed of a motor is with an H bridge and a PWM signal.  The H bridge acts as a switch that can turn power to the motor on and off, as well as reverse direction.  The PWM signal commands the speed that the switches turn on and off, determining the speed.  PWM runs at thousands of cycles per second, so the motor runs smoothly.  For example, if you turn the switches on for 25% of the time, off for 75%, the motor will run at 25% speed.

H bridges and motor controllers can be found at many electronics stores, including ours.
90
Electronics / Re: What Wheel Encoders To Buy
« Last post by cyberjeff on August 12, 2015, 05:44:03 AM »
I don't have any direct experience  with this.

If the encoders have slots, you need a different kind of sensor  then if it is a wheel with light dark/dark segments it is unknown to me which you have.

Take a look at this:

http://ardadv.blogspot.com/2012/03/using-sen0038-wheel-encoders-arduino.html

and then look at this:

https://www.sparkfun.com/products/12617

Either way, you will have to set up an interupt on your MCU as it will otherwise stay in the loop and not know or miss that there was a count change. None of this is trivial.

I'd like to say this about why I reply to questions like this. I am by no means an expert, but I have been around long enough to know when a question is likely to lack getting any replies. So, I'll give something to go on, which I feel is better than nothing.

I'm actively researching robotics at the moment, so I have resources fairly fresh in my mind. I'll be around here for a bit longer, and then I'll be gone as suddenly as I arrived.
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