Can any one give an idea to make my robot turn exactly 90 degrees ???
I am using Tamiya Dual Gearbox & My robot is a tracked Robot
Any clue ???
You probably have to use
You probably have to use some form of encoding on the tracks or a digital compass?
I have a similar setup. If
I have a similar setup. If you want very accurate 90 degree turns, then Geir is correct.
You can test different time delays to hold the motors in a spin and experiment for what gets you closest to 90 degrees. However, as battery voltage drops, this will make the motors go a bit slower, so it is not reliable.
I’m planning for encoders for GRAB-E, but I haven’t gotten there yet. If you are unfamiliar with how these work, just try searching this site and you will find some examples.
encoders as others have said
encoders as others have said are an option. You could look at electronic compass modules. Of course, if you replaced your motors with steppers this would be quite easy.
use pwm and try adding
use pwm and try adding delay
motor 1 foward
motor 2 backward
pwm motor 1 255
pwm motor 2 255
delay(x)
motor 1 stop
motor 2 stop
Good point. If you can get
Good point. If you can get some good steppers, you can control exactly how much each wheel turns quite precisely. You will need multiple i/o pins or external electronics to drive each stepper. Check Jones on Stepping for some great info on stepper motors.
I vote encoders
I have needed/wanted to do this on almost all of my robots and I have always used encoder(s). Really, you will only need one encoder on one wheel --this is assuming that your motors are pretty close to the same speed in fwd or rev (or you have made them so by PWM). The “one wheel” encoder has only one real flaw (except for syncing the motors) as it will only calculate spins and not “slides” or one wheel running and the other off. For most situations, allowing only “center spins” will actually be much easier and much less code involved.
I would not suggest you use the delay method (as suggested by djhesit8) as your motors will never run at the same speed each time. It does not matter if PWM is used or if they are just on or off. Basically, as your batteries get drained your motors slow down and thus the robot will turn less within a given amount of time.
I like the idea of stepper motors as well, but I am short the 2 cents as I have never used them.
Have anyone tried to use an
Have anyone tried to use an optical encoder on the tracks and not on the wheels. Somehow I think that would give a more accurate reading as the number of track ‘blades’ probably are higher than the number of lines one can put on the small wheels.
Probably much easier to build than a wheel based encoder.
And if the driving wheels are regular rubber wheels relying on friction the track encoder would eliminate that as well.
Thankx all
But You see in my project I am trying to replace the Digital Compass, Since My robot is a kind of path finder when I Give the coordinates for it to travel it will do it on a virtual Cartesian plane ( imaginary), So in order to make it go straight always I am trying to turn it by 90 degrees always & By doing that I am ensuring that it would always go in a straight line, ( after meeting an obstacle it would turn 90 degrees to a suitable obstacle free side & then carry on to meet the coordinates I have given)
So I need a suggestion with out a digital compass & In my project I can use a Gyroscope ( Yaw Axis) & I am not much aware of Encoders as I haven’t used them before, Any good tutorials on those ???
What about using Servos ( hacked) to drive the Tank instead of stepper motors , are they powerful & fast enough to drive my robot
I read that Jones Article Sir
I read that Jones Article Sir, But still its confusing , So can you explain a bit on this using stepper motors to make robot turnn 90 degrees ???
Can I use them with Picaxe 28X1 chip , Because I am not sure what is the stepper motor i need & how many Lines it would require to run
Well you didn’t say
Well you didn’t say anything about having a digital compass in your original post so we are trying to help you based on the little information you gave us.
With this added information I can’t see any way past having either some sort of encoder or using stepper motors. The gyro won’t help you much sins you have to know how long you have traveled each way to get back on track.
One fun way of doing this would be to have some sort of arraignment underneath the robot that would lift it up, turn it 90 deg and then set it down again.
For optical encoders, just Google a bit. Like http://abrobotics.tripod.com/Ebot/using_encoder.htm
Sorry for lack of information
Sorry for the lack of information on my first post Sir, It was my very first post here So pardon me for that & yes I have been thinking of that fun way of doing the turn too ( I have seen it on some toys ), & it is on my option list but i consider that as my last resort. So this is what I am planning to Do right now
1. Use a wheel encoder to calculate the distance traveled
2. Use a Single axis gyro to sense the rotation of the Robot platform & turn it using PWM untill I get a 90 Degrees Turn
As I mentioned before My project is based on replacing the Tasks of Digital Compass When traveling to a Given Destination & I read & googled about the use of stepper motors & Thankx for enlightening me on that aspect
So what are your Ideas about using the Gyro on this matter
A gyro seems like a complex
A gyro seems like a complex way to go, though I cannot claim to have any experience on thi.
Take a read through this wikipedia entry:
http://en.wikipedia.org/wiki/Inertial_navigation_system
There may be some hobbist systems available. Some quick googlings showed me this:
http://members.toast.net/joerger/gyro.html
Good luck.
why do you want to replace
why do you want to replace the compass? what is wrong with it?
well
Well there is nothing wrong with a digital compass My friend , I am just trying to find an alternative way to replicate the tasks of the Digital Compass using a combination of programming & other Hardware Inputs
So if any of you have any experience using gyro’s with picaxe just let me know ok
Thank you My Friend
Thank you indeed, I will be reading those things & Update the status here as a help to others who may follow these things, Any way keep helping me on this matter when a problem is raised ok
Compass and sensors in general
One of the robotics books I have read mentioned something about the use of multiple sensors so that if one failed the robot would not be without that sense. In your case would it not then be useful to keep the compass and add wheel encoders and/or steppers? This way if you know your heading from the compass and you tell the motors to spin the robot 90 degrees you can check the compass and then decide if you have in fact turned 90 degrees.
Well My friend
In My project I am trying to replace the tasks done by a Digital Compass By using other means like a Gyro + Some Coding & All , & Yes I support the idea of multi sensors & I am using that in my project Thankx for the response My Friend