Conceptual design of a mobile robotic car

Ah.and the prototype is really small.like a toy car.thank u.(i'm the questioner above)

You might try going to a RC (remote control) Hobby Shop for some ideas. They might even have components for the robotics hobbiest if it is a large shop.

Hi Julie,

Since you are a mechanical engineering student I just realized that you may not have come across stepper motors before. If that's the case my previous post will most likely be meaningless. If you don't understand how a stepper motor works or what they are pleas ask and I will post a summary of how they work and how to use them.

hi .....

I'm studying mechatronics and i think i can help u with that

what exactly your going to do with the car , what u r thinking of

tell me all about it i may help u with pic programing and send u some links

what do u want from that car to do

The car's main task will include:

1)detecting line on the floor

2)collision avoidance from the front & the back

Regarding PIC programming,that will be discussed later (which i am zero on that).But right now,my lecturer wants me to show the conceptual design of the car.I want to use all-wheel drive so sensors will be used at front & rear wheel.I'll also use servomotor (which I'm also zero on that.haha).

So,right now,I want to know if u have any idea what conceptual design I can come up with?Maybe there are some options on how we're going to choose sensors for different functions or how to locate the sensor to detect the line,etc.Or maybe there are other ways for its moving mechanism or whatever.I also found out that some researchers want to solve problem of erased/damaged line on the floor by putting a beacon on the car to back-up the sensors below the car.Is there any other way to solve that?Anything on its conceptual design.Perhaps some links can help.(hard to get the right one)

Thank u so much.

Before you finish school I pray you learn how to spell, capitalize, and punctuate your sentences. It is very difficult for an old fart like me to attempt to read your writing.

I hope you are more serious about your other subjects than you are for your concern for the English language.

Nimrod

I must admit I agree with Nimrod in that I detest, hate, deplore, am disgusted by and find this sort of pseudo English annoying, arrogant, ignorant and time wasting. It doesn't save time because it slows down the multiple readers far more than is saved by the single writer.

If you can't be bothered to type out what you are trying to say properly then don't bother in the first place.

That's my opinion, so be a good student and go and write the following

I will not use abbreviated pseudo English in CR4 posts.

100 times.

every year there are roboter compettion holding in the world. you can refer to that game and can find some useful information for your making.

At first I think you'd better use photo deoid fro your detecotor or a camera if you like to detect the line to trace

and extra UT for font and back detecting. and

If you're programming pics...I'd recommend MikroBasic for PICs. You can get it at www.mikroe.com It's a cross compiler that lets you program in basic with lots of established libraries (so you don't ever really have to fight with assembly code) and can even provide you with the evaluation boards to cut through a lot of the breadboard work and get to testing.

I minored in mechatronics (Mech'Eng major) and this was the kind of tinkering I wish I would have had more exposure to in school. Good luck!

Thanks for the reply!

So,does anyone know if I can have many options when designing the robotic car?Perhaps its sensors location?Or type or sensors to be used?

"I want to use all-wheel drive so sensors will be used at front & rear wheel.I'll also use servomotor (which I'm also zero on that.haha)."

Since you are using a microcontroller then I would suggest using stepper motors rather than servo motors. There are a several reasons for this.

• No position sensors. Stepper motors don't need any position feedback. If you have sized the motors correctly then you now how far they have moved by counting the steps they have moved through.
• No analogue circuitry. Stepper motors don't require any analogue regulation of the current to control the speed. The speed is controlled by the frequency that you switch between each step.
• Simple circuit. Each coil only requires a single transistor that drives the coil fully which means either fully on or off.
• Zero speed torque. Stepper motors will provide torque even while they are not rotating. This means that if the car is on a slope it can't move unless you either power off the stepper motors or step them so you don't need to design braking system.

Since you wish to use an all wheel drive system then it you uses four stepper motors you can steer the car by stepping one side more than the other.

You could actually get by with a couple of photo diodes that are looking for the edge of the line, four stepper motors to propel the system, a PIC microcontroller and that's all. I think you can even get a PIC demo board that already has all the circuitry for driving a stepper motor on it already.

Just some thoughts on how I would go about it and it may not be the way you supervisor wants but I hope it has helped.

Hi.Thanks for the reply.It does help me out a bit for now.

I'm sorry.Am I the one who's using that abbreviated pseudo English?I don't really know what that means actually.My English is not that good.And sorry again.

Regarding stepper motor,yes,I actually didn't learn about that particularly in my course (especially when I'm majoring in Industrial).But I try by surfing the net for some info.It takes time to understand.

So,I guess for now I can have some conceptual design on:

1)What type of motor I can use (stepper or servo right?)

2)The steering mechanism (all-wheel,front or rear right?)

Is there any other ideas?How about the sensors?Its location and its type to use?Can have many options on that or not?

By the way,sometimes I saw people wrote DC servomotor,and then I saw they wrote DC motor at other side and servo motor at another side (as if it's different component).What actually does that means?

Thank you so much!

"I'm sorry.Am I the one who's using that abbreviated pseudo English?I don't really know what that means actually.My English is not that good.And sorry again."

No you are not the one using the pseudo English, and you English is quiet good. Pseudo is actually a Latin word and it means similar or like so when I say pseudo English it means that it is like but not really English. What we were having a go at was the sort of thin that is in post #2 where capitalization has been omitted and abbreviations like "u r" have been used instead of "you are". This sort of abbreviation came about because of the system used to type in text messages on mobile phones and has no place where a full keyboard is available.

I must actually complement you as you English is pretty good and certainly better than many of the posts we get at CR4 so pleas don't worry.

"By the way,sometimes I saw people wrote DC servomotor,and then I saw they wrote DC motor at other side and servo motor at another side (as if it's different component).What actually does that means?"

Technically it means the same thing but when people refer to a DC servo motor they are usually referring to a DC motor that has some sort of feedback mechanism that allows you to control the movement of the motor.

Stepper motors are in really useful when you are trying to control the position of something. If you have an electronic watch that has a second hand that jumps from second to second in steps then it is using a stepper motor. In the case in a watch they usually use a 4 coil motor that steps through 6° every time you step between the coils. The way they work is that you have four coils that we will call A, B, C and D. If coil a I energized the motor will be locked in position and will not free wheel. This is the breaking that I was talking about earlier. If we now turn coil A of and energize coil B then the motor will step through 6° and then lock in position again. This goes on in 6° steps till we are at coil D. The next coil we energize then becomes coil A and the motor steps a further 6°. The advantage is that all you need to drive them is four transistors, one for each coil and by keeping track of how many steps have been applied you know exactly how fare the motor has moved. These motors come in a variety of voltages, sizes, number of coils and angle that they will step through but for your application I would recommend using 4 12V 4 coil/phase 1.5° motors. Doing it this way means you can steer it by making the motors on one side step through more steps than the other and therefore steering the system. Also if you are using a microcontroller you can figure out where you have gone by keeping count of the steps.

Have a look on the Microchip site, they have several buy off the shelf microcontroller kits and I am certain that there is one specifically for controlling stepper motors.

If you would like more info on how stepper motors work please don't hesitate to ask. I have no problems with spending as much time as it take with people like yourself that are willing to learn.

Education and employment REQUIRES research. If your professor has given you x number of hours to deliver a answer then he/ she will not be expecting a doctoral theis. If you do not yet know how to find answers for yourself then begin with google and its advanced features. Your asking others to do the basic stuff for you and missing out of the fundimental knowledge they already graps.

So what kind of questions are allowed to be asked here?I'm a Mechy student & if I have to google everything and read all the books,1 semester is not enough since I have other subjects to focus on.

Actually I'm just asking for IDEAS on conceptual design.I already have some ideas and since my knowledge in electronics are very basic,perhaps someone can give me some insights on that so that it's easier for me to carry on with my research.Besides I can get fresh ideas too.The title of my thread actually has a narrow scope rather than asking people the step to build the whole product.I already borrowed a book wrote by Kachroo and it contains from A to Z on how we can design a mobile robotic cars.So i was JUST asking for people's opinion.That's all.

Sorry and thank you for all the helpful response.

So what kind of questions are allowed to be asked here?

Anything you find you are having trouble with, you will find that if you are genuinely stuck and are willing to learn then most here at CR4 will help you out. If you are too embarrassed to ask a question publicly you can send anybody you think may be able to help a direct question by clicking on their name and following the sent email to link.

I have helped several people this way and if you would like I can help you the same way.

By the way I am a control systems engineer by trade that ended up in the large computer system game.

Julie --- please do not pay much attention to the GUEST who seems to want to hit you and others with petty issues. Maybe he's the "FORUM COP". This guy probably has no idea what kind of information you need or is not willing to share it. I've assumed you already Googled and didn't get enough info. or possibly didn't understand what you found.

I didn't view your question as a plea for someone to do your homework, just as a request for some ideas in areas which you are not familiar. Keep studying and learn much. Your questions as a student are welcome by me; as I don't know it all yet, so when you question I also learn.

I am sorry that I do not have the answer to your question. I am just irritated by this guy who has time to criticize but no time to help. It seems that most of the other posters here are very interested in your endeavor.

you can use linear resistanace with link with fix multiturn potentiometer just like bridge for measuring hight of your each tyre from ground of measure with load balance concept

arun

I will throw in my 2 cents worth... although I don't claim to be an expert in the field.

First of all, use two drive motors probably DC variable speed, one on each front wheel. You can then steer the car by varying the speed of each motor relative to the other. If you stop the right motor and power the left, you will make a sharp right turn (for example). Of course for following a straight line, you would not use such radical correction.

To follow the line, If I can assume this is in a lit room, use two photodetectors on the front of the car. If the car is started "on the line", any change in output on one or the other photodetectors would indicate deviation over the line, and would then the car would have to correct using the motor speed control.

Photodetectors feed the computer, possibly using a/d converter, computer controls motors through two D/A converters and drive circuitry.

Anyhow this is just a collection of ideas. Have fun on the project.

Bill

Thank u so much for the responses and support.I already google a lot & borrow books and now studying it.I'll not regret for choosing a project which is not within my expertise but I really want to learn because it seems fun to do this project.By the way,thank you and if anyone got any new ideas,I'll be so glad to hear from you guys and thank you so much.This is fun indeed.Thank you!

Hi Julie,

There is just one thing that I would ask in return and that is when you finish you project could you post a photograph or something on this thread of what you ended up doing. After all we are all learning and it would be nice now and then to see the results of our input. Anybody that has subscribed to the thread will automatically get an email whenever there in a new post regardless of how long ago the thread was started so all you need to do is add a post to this thread with your final results.

Regards MASU

Hi Bill,

I am curious as to why you would prefer to use two variable speed DC motors rather than stepper motors?

Two four phase stepper motors require a total of eight transistors connected to eight output lines on the microcontroller. If you know the characteristics of the motor and the diameter of the wheel you know how far the wheel will turn with each step. By counting the steps you know how far that motor has moved in total and by adjusting the dime delay between each step you can adjust the speed. There is no feedback necessary as you can calculate everything you need by tracking the steps.

Compare this to a couple of DC motors with a H drive and feedback. Firstly you need a digital to analogue converter to take the signal and turn it into a useable signal for the motor then 4 transistors in a push pull format to drive and break the motor. On top of this you need some sort of sensor to monitor the speed of the motor and an analogue to digital converter to convert this signal into a useable format for the microcontroller. Alternatively you could use a photodiode, LED and optical encoding disk for speed and position feedback.

Personally I have found that in most situations that involve digital control stepper motors driven by transistors in a saturated mode is a much simpler method than a DC servo motor with transistors operating as current amplifiers in an unsaturated forward bias mode.

Julie,

I found this kit from Silicon Laboratories that has everything you will need for your project on a single board as well as a stepper motor and all the software for US$119. You may need two of these since you are going to need at least 2 motors but if your lecturer will let you use something like this it is going to save you an enormous amount of time, effort and frustration.

Regards MASU

Dear Masu

As I said, this is not my speciality. Yes... stepper motors would work just as well if not better. I don't know the details of using either of them.

I also wanted to add to something you mentioned earlier... the fact that some of these people cannot use "the Queen's English" or at least bloody American English on this sight. Now I realize that English is not the native language of many of our contributers, and while not perfect, they are giving it their best shot. I can live with that. BUT these people who use pseudo-English here, I skip over their entries. I don't know about you, but I don't have the time to try and decode that crap.

Oh! what I was thinking about with variable speed motors, was that I believe they can run backwards... basically giving a zero turning radius... but there I would power all 4 wheels. Can you back step a stepper?? I have no idea.

Bill

Hi Bill, you asked;

"Can you back step a stepper?? I have no idea."

Yes you sure can. Basically what you have is a series of windings, usually 4, that you energies one at a time in sequence. As you step from one coil to the next the motor will jump through a pre determined angle. In an electronic watch this angle is 6°. You can reverse the direction by reversing the sequential order that you energize the coils in. You vary the speed by varying the speed that you step from one coil to the next. The great thing about stepper motors is that they can only be at defined positions, for example with a wrist watch the second hand can only be at the second marks and not between. This means that by keeping track of the steps you know where the motor is without the use of any feedback mechanism.

Modern brushless DC motors are actually a form of stepper motor and require a package of electronics to turn the DC power into sequenced pulses that drive the multiple coils within the motor.

I think the big problem with stepper motors is that the majority of people don't understand yow they work so they don't use them and stick with what they know.

Just for a mental exercise, I did some calculations. With a 6 degree stepper, and with direct drive to 2 inch wheels, each step would result in linear motion of .052 inches. Interesting! If I had the time, I would love to duplicate this project just for the fun of it, but I don't.

On the subject of position sensors, I would place two of them, one on each front corner of the car, and given that they provide a binary output, they can go directly to the micro-controller (possibly with some signal conditioning to get proper voltage levels). So we can forget A/D converter in my original ideas. With the sensors at the corners of the car, it would probably follow an s curve, back and forth as it follows the line, but this could be reduced by moving the sensors towards the center, but still beyond the width of the line itself. One could use a single sensor in the center of the the car (front) which could tell you whether you were on the line or not, but it is not enough information to tell you which direction to correct.

THIS IS FUN!!

Bill

That's pretty much what I had in the back of my mind. By the way most of the upper end PIC microcontrollers have analogue to digital converters built in and I think some even have digital to analogue as well.

I purchased a PICkit 2 a few months back to play with but havn't got round to really seeing what it is capable of yet. Considering how complex a microcontroller is they are incredible value. Back when I started my training as an engineer something like the PICkit 2 would be a multi board device that would set you back thousands of dollars.

It helps me a lot reading replies from you guys.I want to ask but I think I should study what you guys talk about first and then if I face some difficulties to comprehend it,I'll ask for your opinions.I think electronic is harder than mechanical.

You have exactly the right attitude and there should be more people out there like you giving it a go. If you do get stuck please don't hesitate to ask. I will not have access to a broadband link from next week for several weeks so I will be cutting back on my posts. If you do get stuck and think I can help send me an email directly using the CR4 mail system. You can use this link MASU or alternatively click on my name in any post and follow the send masu and email link.

"I think electronic is harder than mechanical."

Electrical engineering is by far the most mathematical of all the engineering disciplines and most people believe it the be the hardest. I think the hard bit is that for the best part you can't touch or see what is going on, it's all just conceptual. People have become complacent and take modern electronics for granted. They forget that something like the Pentium processor chip probably consumed more labor in its design that the construction of some of the biggest bridges.

Hi masu! I send you a message. Please check your mailbox. I'm hoping for a positive feedback from you as soon as possible. Thanks!