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31
Misc / Re: Dramatic career change - please help
« Last post by jkerns on August 08, 2014, 06:11:51 PM »

I chose mechanical engineering as I think it gives me the best base. Unfortunately studies here look a bit different than in US for example. We do not have elective and core classes. Your only option is specialization which you can pick after 3rd year. Here is the list of the courses that my program has (it is my translation so some of the names may look a bit odd). Could you take a look at it and tell me your opinion?

Looks like a mechanical engineering curriculum  ;)

As long as you don't feel that there is too much repeat of your architecture background, and that's what you want to do, then there is no reason not to.

Is there an option for a graduate degree instead of a second bachelors degree? (You would probably have to pick up several classes to fill prerequisites - that would be the down side.)

Whatever degree you end up with, there will be a lot of "on the job" learning - my original degree was in mechanical engineering back in the day when you used punch cards and Fortran IV for programming (and mechanical engineers got a single two credit hour class in "programming"). But, by the time I left industry I was writing control system software in C.
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Mechanics and Construction / Re: Motor selection - trying to understand stall torque
« Last post by jkerns on August 08, 2014, 04:10:28 PM »
Torque for a given motor will be proportional to current which will be, in turn, proportional to the applied voltage at any given speed.

So, if your motor has a stall torque of 700 at 12 volts, at 9.6 volts it will be about 700*(9.6/12) = 560 (ignoring any losses in the drive circuits, etc. )
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Mechanics and Construction / Re: Motor selection - trying to understand stall torque
« Last post by pterrus on August 08, 2014, 03:00:16 PM »
What do you mean by drive circuit, the electronics?

Re: 420 vs 700, part of my concern is I'm not sure it's an apples to apples comparison.  The old motor data sheet has 7.2 V nominal, versus the new motor sheet which appears to be based on 12V.  Am I reading all of this right?  I'm assuming that stall torque varies appreciably with the actual voltage applied (that's true, right?)

The old motor only worked when it was significantly lighter.  By the time everything I want to add is on there, the weight will probably be double what it was.  Hence the concern that I didn't actually add enough margin.
34
Mechanics and Construction / Re: Sensor help
« Last post by Billy on August 08, 2014, 01:06:03 PM »
I need a sensor on a robotic arm that can detect humans.

Maybe use a long sharp metal pin on the arm. Then use a microphone to listen for screams of pain.
Otherwise it's hard to make sure you've hit a human, and not some other obstacle.
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Mechanics and Construction / Re: Motor selection - trying to understand stall torque
« Last post by Billy on August 08, 2014, 01:02:41 PM »
As you pointed out, the calcs show you have almost enough torque to climb a wall.
Assuming you are not climbing a wall but instead rolling over a mostly flat level surface, you have plenty.

But drop the calcs and think about it. The old motor had a stall toque of 420 and worked for a while. The new motor has 700. It should be good.

I only question how you determined the motor was the issue and not the drive circuit.
36
Mechanics and Construction / Motor selection - trying to understand stall torque
« Last post by pterrus on August 07, 2014, 11:08:28 AM »
This is kind of a follow on to this thread.

The short story is I need to replace a motor because my previous motor stalls and no longer drives my heavier robot.  I bought a new motor based on RPM alone, and now I'm concerned that I should have paid more attention to the stall torque.  I don't really care how fast the robot goes, but it needs to not stall!

I googled the previous motor, RS-360SH-2885, and it looks like it has a stall torque of 420 g*cm.

The new motor has a stall torque of 700 g*cm.  I'm using a 9.6 V battery rather that the 12V maximum rating of the motor so that makes my actual stall torque even lower, right?

Other relevant information: the robot currently weighs about 4.5 lbs (2041 g) but I plan on adding an arm and other equipment that should be around 2 pounds for a grand total of 6.5 lbs (2948 g).  The wheel radius is about 7 cm.  There is a gearbox between the motor and the drive shaft with gear ratios of 10:34, 12:36, and 14:43, for an total ratio of 0.03192.

So if I take 2948g * 7cm I get 20638.8 g*cm.  Factoring in the mechanical advantage of my gearbox, I'm down to 903.7, which is well above the stall torque.  But that's not quite right because I'm not exactly lifting the whole robot right?

Basically, should I be worried here?  I want to make sure I have margin before I go pressing a gear onto this motor shaft.  Any insight would be appreciated.
37
Mechanics and Construction / Re: Sensor help
« Last post by bdeuell on August 07, 2014, 08:25:37 AM »
you could turn any metal component into a capacitive sensor that would detect skin contact
torque sensors or current sensors would allow you to limit the force the robot applies and stop if it exceeds a certain value
38
Mechanics and Construction / Sensor help
« Last post by mymoon on August 07, 2014, 07:14:34 AM »
Hi,

I need a sensor on a robotic arm that can detect humans, so that i can stop the arm when it hits a human. Any ideas that i can use? thanks in advance. ;)
39
Misc / Re: Dramatic career change - please help
« Last post by aLo on August 07, 2014, 03:40:15 AM »
Hi there. I changed my faculty after 2 years of managment studies for robotics (where i come from it is called sth like automatic and robotics but it doesn't matter). I think your choice is concentrated too much around mechanical engineering as someone above already said. I will copypaste some of my subjects here (warning! their names can be strange since i have to use translator for them)
electrical engineering and electronics
logic and computing
power electronics
object-oriented programming
signal theory
Drives and controls fluid
Electric drives of machines and robots

I think you may suffer from lack of more electronic-oriented subjects since you are architect but i'm a beginner also so i may be wrong.

Sorry for my terrible English
40
Misc / Re: Dramatic career change - please help
« Last post by brad87 on August 07, 2014, 01:39:33 AM »
jkerns - thank you very much for your reply.

I wish to have another degree also for myself and to have a proof of my competences in case of future employment prospects. That is something that no one can argue with.

I chose mechanical engineering as I think it gives me the best base. Unfortunately studies here look a bit different than in US for example. We do not have elective and core classes. Your only option is specialization which you can pick after 3rd year. Here is the list of the courses that my program has (it is my translation so some of the names may look a bit odd). Could you take a look at it and tell me your opinion?

SEM 1

- Algebra with geometry
- Analysis I
- Engineering Physics
- Engineering Graphics
- IT
- Materials I
- Mechanics I

SEM 2

- Analysis II
- Electrotechnics
- IT II
- Mechanics II
- Thermodynamics I
- Strength of construction I
- CAD I

SEM 3

- Electronics
- Mechanics of fluids I
- Basics of Automation and Control I
- Basics of machine construction I
- Thermodynamics II
- Vibrations
- Computational methods
- Manufacturing techniques I
- Strength of construction II
- CAD II

SEM 4

- Economics
- Basics of machine construction II
- IT III
- Mechanics of fluids II
- Finite element method
- Basics of Automation and Control II
- Manufacturing techniques II
- Strength of construction III
- CAD III
- CAD/CAM/CAE I

SEM 5

- Environmental protection
- Basics of machine construction III
- Theory of thermal machines
- Heat transfer
- Reliability and safety
- Basics of machine construction IV
- Basics of machine construction V
- Technology
- Strength of thin walled machine construction
- Control in techniques
- Energy technologies

SEM 6

- Energy sources and processing
- Energy management
- Physics
- Biomechanics
- Basics of machine construction VI
- Aerodynamics
- Sensors
- Marketing

SPECIALIZATION (OPTIONAL)

1. Robotics

- Basics of robotics
- Theory of signals and systems
- Microprocessors
- Robotic propulsion

2. Aeronautics (which seems to be also interesting)

- Flight mechanics
- Avionics
- Aircraft design
- Aircraft propulsion
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