1. ## elliptical path...help!

i want my bot to follow an elliptical path....
without any sensors....
i.e there'll be no any white/black paths on the floor..
somebody suggested to keep one wheel smaller than the other...
i'm a newbie....and know lil bit of mc programming....
is it possible..
help...
ellipse has a major axis - y - 5m
minor - x - 3.5m
initial position of bot will be at 3.5m away from centre..
i.e in x axis...
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2. bro though i was poor at geometry i still know that a bot will transverse a circular path if one of the tyres is smaller...
ever heard of a thing called stepper motors??
use em.

3. hUH??!
Thats tough kinetics indeed !
Different size wheels will take the bot in a circular path. The same can be done with a differential drive with same wheel dia., with different speeds for the outer(fast) and inner(slow). But an ellipse?
This needs some real programming with a micro and steppers. The speeds of the 2 motors have to be varied in a 'pendulum oscillation' manner to describe an ellipse, in a sine wave function.

There may be some electro-mechanical means of doing it without a processor. You can ramp the motor currents using PWM.

....and where do you live??

initially i thought about the steppers for my drive wheels....so that somehow i can program it to follow the ellipse.....but my bot should carry atleast two 250 gm basketballs plus the weight itself of the bot ....hhmm ...can the steppers manage that weight.....plus finding similar stepper motors is really difficult over here......i cant buy it though......i'm not so extravagant to spend my money on a printer to get a stepper from it.....

Well...i'm in kathmandu.

5. alternatively.. use a cam arrangement..

but the position and shape of the cam, you have to design... you wont get an ellipse if you place it where i have drawn it....

yes, it requires some mechanical work and some thinking..(for the dimensions)

6. kATMANDU eH??....Lovely place, the best i've been to and liked yet

Well, you need a hefty stepper motor for this job and some programming, although i would suggest plain DC motors. It is quite simple to make a shaft encoder to measure and control the speed. It is just that people run off a little more work and use steppers(ugh!)

A positive part of a sinewave input to the DC motor speed controller drive will give you an ellipse.
If you plan to use DC motors and need help for the variable speed controller or the encoder bit, just let me know.

But first : decide DC or stepper :!:

:arrow: OK -allbits was posting while I was typing...

Now , a mechanical cam is a cumbersome job. While it has some excellent advantages, it is fairly expensive. Also the lead time is anybody's guess!
Unfortunately it cannot correct for skid, ground slip etc. Driving a vehicle with fixed wheels opposed with 'turn' wheelswill result in erratic behaviour, unless the speed too is varied wrt turns.

What i'm suggesting (above) is an Electronic Cam applied to a differential drive.

7. how bout using an optical mouse...

8. Originally Posted by lhx
how bout using an optical mouse...
:?: :?:

9. An optical mouse can be hacked to obtain x and y displacement there are many tutorials for this on the web.
....even a normal mouse would do in this case.

Once the robot gets to know its position it can decide its next move according to the shape of the path to be traversed

10. Hi LHX!
That is a good suggestion for a Sensor. But the question is a Bot to follow an elliptical path....without sensors.
Najirs has posted 2 problems. The op mouse will fit in to his query, maybe at http://roboticsindia.com/modules.php...t=1993&p=10026

...but still, a good suggestion!

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