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1  Using Arduino / Project Guidance / Re: feasibility question: turning dc motor to servo? on: October 13, 2012, 10:24:03 am
This Arduino robot won't leave time to do that, so will continue completing it and researching needed mechanisms, thanks.
2  Using Arduino / Project Guidance / Re: feasibility question: turning dc motor to servo? on: October 11, 2012, 04:53:54 pm
JohnHill,
Yes worm is good, and this is actually a neck, so it is necessary that it moves slowly.

GoForSmoke,
Well I'm not really sure I could use a pencil there. Also, if to use a servo to be a brake for a dc motor with the aim of making the dc motor function as a servo, then it seems to be better to forget that and use 1 servo from the beginning. I'm still looking if I can put my cnc machine to use for Arduino robot and create mechanical advantage so hopefully: use those 8$ dc motors, some cnc machined mechanics (may be a solenoid) and get a servo-mechanism for neck, which costs in whole less than a 15$ hs-422. This may be a closer formulation of my initial goal.
3  Using Arduino / Project Guidance / Re: feasibility question: turning dc motor to servo? on: October 10, 2012, 03:49:48 pm
Thanks I'd study what rotary encoders I can get, by the way the photo shows the machined parts. They are from a very cheap wood to just test, I plan to after corrections (changing encoders, etc.) machine final design out of plastic for inside, and from outside it will be covered by fiberglass.



4  Using Arduino / Project Guidance / Re: feasibility question: turning dc motor to servo? on: October 09, 2012, 03:24:35 pm
well, I used the system in this following way:

1. the left-of-neck limiting switch was triggered, so robot knows that could only turn right
2. the set-point of turning write is chosen,
3. motor is commanded to turn, and reading pot, until pot<=x (x being the set-point)

I actually tested this system and not that bad, but one thing is really awful and that is the main concept I was for: keeping the load.

If I command motor (still not by PID) to keep on a position, say, if pot<x turn right and just as pot>x turn left, the noisy movement is not only coming from the fact that I didn't use a PID, but also from the pot being a <1$, too noisy type.

I guess - and look for your kindly guides to get sure - that beside PID I must change to a pot type which is less noisy but same time not on cost of 30$ as the question was "turning dc motor to servo", to try to pay less than the servo cost.

Now if the original question is someway wrong (impossible to turn dc motor to hold the load like a servo but for less price), then well, I have nothing more to say, or ask    smiley

5  Using Arduino / General Electronics / L293B signaling problem on: October 08, 2012, 04:55:45 pm
Hi,
My L293B was functioning a year the right way. Newly, when I connected it to pwm 9pin of Arduino and digi-pins 7 and 8, it did not respond to flipping HIGH / LOW (didn't change direction). It all the time turns in one direction as if it can't see the signal is switched.

To test it, I first checked the pins: connected pin 7 to an LED, then setting HIGH/LOW, switched the LED on/off correctly. Next, I took GND and +5v of Arduino to a breadboard, then sent Enabling signal from Arduino pwm pin 9 to L293, but for commanding, plugged the Input A, B of chip directly to GND and 5v of Arduino on breadboard. Result: chip changed direction as expected!

I also measured the output of chip and I read that when I use GND and 5v of Arduino, I get +11.5 and -11.5 when flipping wires, from my 12v battery, so all ok. When I command from digi-pins 7 and 8 of Arduino, the measurement says +11.5 but never changes to -11.5!

I changed the chip with L293E: this behavior didn't repeat and the system worked ok.
So, is it enough to conclude that the Chip must be changed?
6  Using Arduino / General Electronics / Re: debounce problem on: October 06, 2012, 03:44:10 am
Quote
You have started an interesting string Ironbot.

Definitely smiley

"ironbot" got started when I bought Arduino on 2009, Arduino started all!

Many thanks to whole the community and forum with great respect!
7  Using Arduino / Project Guidance / Re: feasibility question: turning dc motor to servo? on: October 06, 2012, 03:30:44 am

I suspect you will find some useful stuff here... http://www.openservo.com/

Thank you, indeed!
8  Using Arduino / Project Guidance / Re: feasibility question: turning dc motor to servo? on: October 06, 2012, 03:09:15 am
Tylernt, Far-seeker:
My pots are ordinary under 1$, the neck and head motor both will have less than 180deg. movement.

The state of neck and head (turning left or right, up or down) will be reported by pot for the process and by limiting micro switches for end points so this should not be a problem. I first added micro switches and implemented them, then I had a problem with debouncing and turned to forum and made a post some days ago. Got great new ideas like always. Now in redesigning (will use debouncing with flip-flop chip this time, as suggested by community people).

Any comment will be greatly welcomed.
9  Using Arduino / Project Guidance / Re: feasibility question: turning dc motor to servo? on: October 06, 2012, 02:56:37 am
PeterH,
Quote
You may be surprised how easy it is once you have got your head around the basic concept.
This really helps to not to fear to give it a try yet before reading the control theory book, thanks :-)
Could you please point me to any tutorial/example project, where I can implement any simple movement (a line follower, or any other thing) isolated from my own project, toward known, target results (already achieved by the tutorial / example project) to develop some skill?

I have already tried "Arduino PID" on google and there lots of examples, but getting direction from you is the point.
10  Using Arduino / Project Guidance / Re: feasibility question: turning dc motor to servo? on: October 05, 2012, 03:51:52 pm
Thank you all! I Attach my design and you could see pots beside the neck and on top of head motor. I'm thinking may be good idea to double pot per motor, then feed each pair to a filter and get rid of error, then try a PID (don't have skills for).
.....................................................................
Zoomkat,
I'd study the search, sure I must know in detail the internals of servo and hope it ends to learn to hold the load with dc motor.

PeterH,
Quote
There's nothing stopping you from putting a feedback loop on your motor control
Well, unfortunately what is stopping me is lack of skills in control theory: I've not done the homework, not finished a single control theory book (but have chosen what to read, it has matlab simulations to pass to hopefully couple theoretical understanding with some intuition). I'd give a try to the PID lib you kindly suggested but hardly imagine that in this concept any good result comes without sound theoretical background and gained intuition in putting them to work.

DVDdoug,
I want to create a friction device but have nothing to start from other than my own idea. I learned that better to find examples of others, before realizing own idea, so not to reinvent the wheel. I don't know any similar project or what to google for. If you got something, please kindly leave me some links.

Dhenry,
I have a small experience in feedback: I used an IR-range finder sensor and programmed it so that:
1. servo on which the sensor is installed, turns right all the time until detecting an object
2. when detected, servo turns to left edge of object until losing it, back to 1.
The result was not bad: robot could follow the object by edge.
I think with pots on the neck I'd have the same story: motor turns toward set point and sure won't stay on it but pass it over, then returns. The error of pot will make problems I think.
==================================
Design:






11  Using Arduino / General Electronics / Re: help: Killer Flying Robot HEAD :-( on: October 05, 2012, 01:57:59 pm
Thanks, thanks and again thanks!
12  Using Arduino / Project Guidance / Re: feasibility question: turning dc motor to servo? on: October 04, 2012, 11:48:32 am
First I correct a mistake I may had in some place above:

It is an ordinary dc motor, not a servo type, so no torque report available :-(

Next, well yes, I had experience with Kalman filter and I can put there IMU (cheapest to implement for me) etc. and keep the motor in pos, but...

I was trying to find 1 mechanism to use both for arms and head, in arms it is ok to have the motor slightly move left / right to keep with pos, but for head, no.

So as I understand, I must go to feedback and correct motor position if arm, and for the head I must use a mechanical solution like:
1. move motor to the desired position and stop it
2. apply a mechanism that mechanically prevent it moving
3. to move it again, first release that

Also I don't want to go to servos for cost: the head will be from fiberglass material and not really at the weight that my hobby servos could handle and don't like to take model airplane servos each by 30$ (need 2 motors for head).

It will be very helpful if you could please suggest a cheap idea to implement in a small robot neck for this (up-down movement on 1 motor is enough).

Thanks again.

Edit:
The bot has a router with 400Mhz Broadcom processor running on and in case of using a filter for noise or heavy PID algorithms there is no load to Arduino processing power from it.  
13  Using Arduino / General Electronics / Re: help: Killer Flying Robot HEAD :-( on: October 04, 2012, 11:38:51 am
Hi,
Thank you, I will try the relay and have no question about that implementation, but the second response opens me new questions:

I wrote about relay because my motor is 12v and around 2A because I don't know what transistor to use to implement the switch and the best schema for it so not to get it hot, etc. in terms of a safe design, could you please suggest?

And yes: this is a question of safety, 2 motors will turn the head up and down, left and right (installed vertically to each other) and I am trying to approach full guarantee that no movement will happen out of expectation, specially 'when something goes wrong' based on "if something can go wrong, will go wrong", but again, we have another from Murphy: "if all seems working correct, something is wrong!" :-(

May only Arduino help to be sure that motors never go out of control :-)
14  Using Arduino / Project Guidance / Re: feasibility question: turning dc motor to servo? on: October 04, 2012, 11:19:48 am
Thank you,

I think that I did not explain my problem clear enough. I already have the shaft position as I embedded a pot with gears in, so when motor turns, my pot value changes accordingly.

What I exactly meant is that, when I stop a servo motor in a pos, if it is keeping a load on it, say it is an arm and servo lifted something, it keeps the position. I try to move my servo by hand but it resists. Same time, when I break my dc motor in a position (reading the pot as feed back), I can turn it still by hand (it won't resist, as if its power is disconnected) and also if any load on it, will fall down!

I think it could be done only mechanically, that is something keeps the motor from turning in any position while fixed, and just before moving it is being released.

What I would like to know:
1. some google key word to search for the right mechanism,
2. if there is any hardware (electronics) / software solution to this and if os, keywords to google

Please give ideas smiley
15  Using Arduino / General Electronics / help: Killer Flying Robot HEAD :-( on: October 04, 2012, 08:20:44 am
Hi,
What is the solution, so that my dc motors receive power "if and only if" the sketch is running? Well for starting, I can use a relay, but what about this unhappy use case that follows?

1. relay is off
2. arduino goes on
3. sketch starts (variables initialized)
4. relay goes on
5. motors start running, constrained to sketch variables (say, L298 by Arduino PWM passing 3v)
6. Arduino restarts (say, accidentally, and same time L298 being no more constrained by MCU, passes full 12v and my robot head starts to fly, instead of turn! :-) )

Perhaps the question is: what to do so that L298 is off, if Sketch is not running? (pass power to it by Arduino sketch? or better solution please?)
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