ELECTRONICS

Other Hardware General Electronics
1

Hello i am a fifth year mechanical engineering student so for my final year project im building a robot.i almost finished constructing the mechanical parts but i havent done any of the electrical circuit analysis since i don’t have any background in circuit analysis ,i do have a lot of questions but i hope you will reply me with the answers.

MATERIALS THAT I HAVE USED

*i have attached a screen shot of my circuit design from Proteus
*im using dc motor with 24V & 1.2 AMPS
*im using TIP 122 Darlington transistors
*im using arduino uno board, so taking this into consideration.…..

1.is my transistor choice good?
2.is my electrical circuit design in Proteus correct ? Especially the H-BRIDGE circuits?
3.how much resistance should i use to protect my arduino uno board and to run the circuit SAFE ?
4.should i use a capacitor in parallel with the motor, if yes what should be the capacitance?
5.the motors that im using can go up to approximately 1875 rpm,but i want to decrease that to 10-20 rpm so how can i achieve that?

6.what kind of diode should i use to prevent from back EMF?

THANK YOU

2

Well, no attachment to look at, but a few pointers can still be had

Instead of darlington transistors, use mosfets. They are still a transistor, but a different type.

To have speed control, use PWM to drive the mosfets.

Using PWM will give you speed control, but without any type of feedback circuit it will be difficult to know HOW fast, and trying to match speeds to a second motor will require human input on a joystick for correction inputs.

Just taking a motor and PWMing it down to 20rpm if it is not designed for it can lead to poor performance and max current issues. Using a geared motor that stays within operating limits is a good idea.

The back EMF diode just need to be within current/voltage tolerances.

Try to post a diagram (hand-drawn or other) of the entire circuit you are looking at. While there are only 2 ways to do it (right or wrong) there are countless ways to achieve either. We cannot guess what and how you have it connected up as. Include part numbers.

3

My advice to students seeking advice is to partner-up with another student... I assume there is an electrical engineering department at your school? Maybe there's a robotics club?

*i have attached a screen shot of my circuit design from Proteus

It didn't get attached.

1.is my transistor choice good?

They should be able to handle the current (if heatsinked). A MOSFET would probably run cooler, but you might still need heatsinks.

Or, you can buy pre-assembled motor driver boards. (There is a popular H-bridge driver chip, but I've never used it and I don't know it's voltage & current ratings.)

2.is my electrical circuit design in Proteus correct ? Especially the H-BRIDGE circuits?

If I could see your schematic I might notice if something's wrong, but personally I wouldn't be comfortable "approving" your design.

3.how much resistance should i use to protect my arduino uno board and to run the circuit SAFE ?

You don't put a resistor in series with the power. If you are running I/O lines to the "outside world" you can sometimes use resistors, sometimes along with diodes to protect the Arduino. But, in most designs there's no need for that... Design your circuit correctly and you won't fry your Arduino. (There is something called the [u]Ruggedunio[/u] if you want to look into what they do.)

4.should i use a capacitor in parallel with the motor, if yes what should be the capacitance?

No. If you get noise that causes the Arduino to glitch, you may need a capacitor or other filtering for the Arduino's power.

5.the motors that im using can go up to approximately 1875 rpm,but i want to decrease that to 10-20 rpm so how can i achieve that?

You'll have to do that mechanically (gears or pulleys). You can slow a motor with PWM, but without speed-measuring feedback it's impossible to get the "right" speed. Even with feedback that's very-slow, and probably impossible, especially with a load. And as you know, if you gear-down you'll get more torque.

6.what kind of diode should i use to prevent from back EMF?

The diode has to handle the same current as the motor. Give yourself some safety margin and get a diode with at least twice the motor-current rating. The voltage rating isn't critical because any diode can handle 24V or more (that's the reverse voltage rating).

4

Hi,
Welcome to the forum.

Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html

Do you want your motors to change direction?

If you are on campus, then you have the best source of advice to your queries.
Go to the Electronics Faculty and ASK, they are obliged to help as it is a scholastic project that you need to complete your course.
Ask for a referral from your Mechanical tutor/lecturer, I worry that you are in 5th year and asking here.

Tom.... :slight_smile:

5

DVDdoug:
My advice to students seeking advice is to partner-up with another student... I assume there is an electrical engineering department at your school?

Or better yet, have studied mechatronics / electro-mechanical in the first place, not that that helps now in 5th year. (That interests me: I didn't know any unis did a 5-year u/g degree, assuming OP is still u/g. But it makes sense: as time goes by, the body of knowledge just gets so big, and a new grad may be expected to know so much more than decades ago that just to cover the entry level material could take 5 years I suppose.)

6

as time goes by, the body of knowledge just gets so big, and a new grad may be expected to know so much more than decades ago that just to cover the entry level material could take 5 years I suppose.)

Exactly the opposite.
In all Universities the syllabus has been cut back and cut back because students are arriving knowing less and less and you have to spend longer getting them to a level they were 20 to 30 years ago. This is especially true of Maths which you need for Science and engineering.

7

Grumpy_Mike:
Exactly the opposite.

That's scary. So first year uni is (say) like final year of high school (at least as far as maths and physics), and then you still need the 4 years I had?

8

Or the three years I had in the late 60’s

But then only 5% of the population did a degree, it is up to 45% now and you can’t do that without making things easier.

9

Grumpy_Mike:
Exactly the opposite.
In all Universities the syllabus has been cut back and cut back because students are arriving knowing less and less and you have to spend longer getting them to a level they were 20 to 30 years ago. This is especially true of Maths which you need for Science and engineering.

I agree.
[soapbox]
Late 1970s University, engineering Diploma 3 years, Degree 4 years.(Electrical, Electronic)
Full on course, finals 2nd year was 13 exams in 2 weeks (10days), to use the Electrical Lab and Electronic Lab you were time tabled due to heavy usage.
Final year project was 1/2 of the scholastic year.

Early 2000, Diploma now called Associate Diploma, taught at a trades school, 2 years.(Electrical, Electronic)
Early 2000, Degree at Uni 3 years, Ohms Law was not taught until second year, first year was spent making sure all students were on the same page, maths/science wise.
To use the Electrical Lab and Electronic Lab you were time tabled due to availability of staff member.
[\soapbox]
Tom... :slight_smile:

10

TomGeorge:
Ohms Law was not taught until second year

Ok well that's scary: I'm pretty sure I knew Ohm's Law at primary school, although that might just have been family influence, too long ago to remember. But in any case it was covered very early in high school, I'm 100% certain.