Rover Project

[Misterbenn]

Hey there guys, now i dont want you to think i'm just another student asking you to do his project for him, i'm starting work on a autonomous roving vehicle for my 2nd year project and would be thankfull for any input / shared experience you can give me.

so starting spec:
vehicle followes a reflective track on a smooth surface (so were talking optical sensors .... advice welcome!)
at the end of the track a reflective strip will be layed across the track at 90deg to the main guide strip. at this point the rover has to reverse around the course. (the course is an octogon shape .... so we have corners of pre-defined angle to negotiate)
both strips will be 25mm wide.
to carry a container of 600g,
to clime and desend slopes of 5%
vehicle must not exceed 160mm in width lenght or hight.
no comunication with vehicle after it has entered the course.
slidding contact between rover and strip is not allowed.
a bugget of max £25 for the entire project

the spec is fairly detailed so not all that much design involved really.
i'm thinking 3 wheeled vehicle with the two back wheels providing the drive via a DC motor, and then via a gear box.
the single front wheel to control direction with a stepper motor
we'll be using the pic16F84A or pic16F628
in order to stay on track and detect the end of course line we'll be using 2 optical sensors further apart than the track width (taking into acount the corner width of the track) thus thus when an optical sensor is triggerd by light the rover will steer in that direction in order to keep the track between the sensors if you see what i mean. when both sensors are triggerd then we kno we've reached the end of the track.
we were also thinking of slowing down at corners because we heard a major problem is the rover just shooting off the track at corners...prob due the the fact that the steering lags behind a lil. Also we want to think about steering angle and if we should turn around or just reverse at the end of the course?

saddly because of the bugget i'm getting most my components from ebay so we wont have best performance in that sence.... i think i heard some1 say in a previouse thred that floppy drives have a nice stepper motor in them ...i could prob get one of them quite cheep.

if any1 has any thoughts or suggestions or experience they wish to share please add to this thred

Thanks
Andy

 

[audioguru]

Be very different in your design: use only a single wheel. Use blasts of compressed air or CO2 for steering. Gyroscopes can be made from motors from broken CD players.

 

[Nigel Goodwin]

Hey there guys, now i dont want you to think i'm just another student asking you to do his project for him, i'm starting work on a autonomous roving vehicle for my 2nd year project and would be thankfull for any input / shared experience you can give me.

so starting spec:
vehicle followes a reflective track on a smooth surface (so were talking optical sensors .... advice welcome!)
at the end of the track a reflective strip will be layed across the track at 90deg to the main guide strip. at this point the rover has to reverse around the course. (the course is an octogon shape .... so we have corners of pre-defined angle to negotiate)
both strips will be 25mm wide.
to carry a container of 600g,
to clime and desend slopes of 5%
vehicle must not exceed 160mm in width lenght or hight.
no comunication with vehicle after it has entered the course.
slidding contact between rover and strip is not allowed.
a bugget of max £25 for the entire project

Tough budget!.

the spec is fairly detailed so not all that much design involved really.
i'm thinking 3 wheeled vehicle with the two back wheels providing the drive via a DC motor, and then via a gear box.
the single front wheel to control direction with a stepper motor

I should try checking the thousands of small robots on the internet, they almost all use two DC motors and differential steering - using car type steering is too complicated and far too limiting - check micromouse sites as well, they are generally good examples.

You might try and see if you can get some Cybot parts cheap off EBay, that should be ideal.

we'll be using the pic16F84A or pic16F628
in order to stay on track and detect the end of course line we'll be using 2 optical sensors further apart than the track width (taking into acount the corner width of the track) thus thus when an optical sensor is triggerd by light the rover will steer in that direction in order to keep the track between the sensors if you see what i mean. when both sensors are triggerd then we kno we've reached the end of the track.
we were also thinking of slowing down at corners because we heard a major problem is the rover just shooting off the track at corners...prob due the the fact that the steering lags behind a lil. Also we want to think about steering angle and if we should turn around or just reverse at the end of the course?

That's one reason NOT to use car steering.

saddly because of the bugget i'm getting most my components from ebay so we wont have best performance in that sence.... i think i heard some1 say in a previouse thred that floppy drives have a nice stepper motor in them ...i could prob get one of them quite cheep.

Not 3.5" floppies, they are rubbish ones, you want old 5.25" ones, they have really nice stepper motors. But in any case, you don't need steppers, you just need two geared DC motors.

 

[Misterbenn]

Be very different in your design: use only a single wheel. Use blasts of compressed air or CO2 for steering. Gyroscopes can be made from motors from broken CD players.

hum ... interesting idea, it would make use of moderately complex control theory like the upsidedown pundulum experiments. however i imagin such a design would break the hight restriction and also i would like it to work!

 

[JimB]

A well described problem, with some thought given to possible solutions.

Dont spoil it by writing any1, the word is anyone.
You may also want to consider your punctuation and spelling. Dont spoil a good project with a poor write-up.

The technical bits.

Consider using two stepper motors, one to drive each rear wheel and use feedback to ensure they are running at the same speed where required. Then you could do away with the need for a steering motor and just have a castor for the front wheel.

The return journey. If the robot is to turn around, consider how you are going to ensure that you have found the "track line" and not the "stop line".
If you decide to run in reverse, I think that you will need line sensors at the rear of the robot as well as at the front. If you are reversing using the sensors at the front (now the rear), the front will follow the line OK, but the driving wheels could (certainly will on corners) drift off to the side and the sensors will not detect until it is too late.

JimB

 

[srimannarayanakarthik]

its better to use DC motor than stepper motor for motion as u need more power to travel inclinations. connect it to the mosfet and conect the gate sources of mosfet to the IC.this can help you to limit the voltage to be use or the power of the motor because of iC input voltage limit. voltage level convetrors are also eliminated

 

[Misterbenn]

Dont spoil it by writing any1, the word is anyone.
You may also want to consider your punctuation and spelling. Dont spoil a good project with a poor write-up.

sorry about that i was in a rush, also i'm slightly dislexic .... although that didn't stop in getting into the top university for ElectroMechanical engineering in the UK, also in the top ten for the world. Though you can prove anything with stats can't you. (University of Southampton by the way)

I hear what you all saying, i'll have to look up on diferential drive systems. JimB i also had the idear of using two wheel drive, however.....

This project is inherently a time invarient system, that is to work out its state at any moment in time you need to know the initial conditions as well as all the consiquental states previous to the moment your trying to calculate.
So i'm thinking .... if i use a stepper motor then i can control the turning far more acuratly than simply turning on a DC motor for a set time, or having one motor go faster. This means in theory each state can be calculated much easier, making it a more pradictable solution. (this is all more than likely BS)

my second reason.... In order to make this project travel the course as fast as posible i want to reduce the side to side wobble (track wobble) it will have (the two sensors will help with this, by decreasing the amount off-track travel before detection) but i also want my rover to when it senses its back on track to steer straight ahead, reducing the track wobble. or as i afectionatly call it now Twobble.

also Jim, i was giving thought to the problem of turning around, as i see it there are two solutions (i cant afford more sensors i dont think....we'll see)
one put the sensors in the middle of the rover so it can use the same programing and give the same performance both forward and in reverce.. but will require more development time and trial and error.
or work out a routine to put in the programing that will turn it around nicely, use tryal and error untill its perfect and hope it finds the line ok on the evaluation day!


....or mayb try and find some cheep optical sensors.... yes mayb that.

thanks guys

 

[Misterbenn]

Just looked up differential steering and realised that nigel and jim are on about the same kind of steering. also realised my points i made before against the differential method are on the whole invalid, i could indeed determin the angle of turn, however the turning angle would be bigger. i haven had a look at the track yet to see if that would be a problem. also i would then have a whole DC motor control issue, tho thats not two bigger deal.

thanks!

 

[philba]

I agree with the differential steering comments above.

you should go dumpster diving to reduce your costs. dead printers are a gold mine of parts. dead laser jets are particularly good. Look for motors and sensors. lots of little mechanical parts as well as electronic components. scanners are good too.