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1  Topics / Robotics / Re: Why Skid turn is more popular? on: April 14, 2014, 11:03:14 pm
Hi! I just wanna know why Skid turn Car is more popular in Robotics than the one that can turn it's front wheels?(don't know what to call it).

What you have termed "skid turn" is more properly called "differential steering", though you also see the more colloquial "skid steer" used as well (typically in relation to heavy equipment - ie, "skid steer loader"):

http://en.wikipedia.org/wiki/Differential_wheeled_robot

The other method is known as "Ackermann steering geometry":

http://en.wikipedia.org/wiki/Ackermann_steering_geometry

I thought the one that can turn front wheels is cheaper, can use only one motor, no need for H-Bridge,less programming??

I wouldn't say it is cheaper or easier, just different; you still need some kind of actuator to turn the front wheels to make the robot go in the desired direction. Invariably, this actuator is some kind of electric motor (although either pneumatics or hydraulics, among other methods, can be used). If using some kind of electric motor, you still need an h-bridge (even if using an RC servo - there is an h-bridge inside it). You also need some kind of feedback mechanism to know where the wheels are pointing (built into an RC servo, but other methods will need something custom if the actuator doesn't already have such a positional feedback mechanism). This may translate into more programming as well...

All in all - Ackermann steering can be more difficult to implement, both mechanically, as well as in software - for instance, to be able to get such a platform from one point to another, you have to know when and where along the path to angle the wheels, how much, and when to angle them back to keep advancing toward the goal location (and how to adjust if bumps, friction, or other problems cause the robot to deviate from the course). That's just one example of the extra software complexity involved.

Differential steering, on the other hand, is much easier to implement, and easier to program for; movement from point to point becomes a matter of vectors, which are fairly easy to visualize and code for. Of course, it makes for a more "jerky" movement - real differential steering is done so that the speed of the wheels is varied smoothly; this is especially important with real-world tracked vehicles (such as tanks and bulldozers, for instance) - because on certain terrain attempting high-speed central pivoting can actually cause the tracks to come off the wheels ("throwing a track"), because the rear and front of the track is being dragged sideways, pulling it off the idlers and such - which is why when such a maneuver is done, it is done fairly slowly, and only in soft ground to minimize this issue.

In the case of a multi-wheeled robot using differential steering, you don't have the issue of a track being thrown, but you do have the issue of the tire contact areas being "scrubbed" - literally the tread is ground off (particularly, again, on hard surfaces like asphalt and concrete), which can lead to other issues, least of all being the need to constantly put on new tires. There is also the issue (same as on tracked vehicles) of extra wear-and-tear on the wheel bearings, axles, drive system, etc - caused by the side-loading (this can be mitigated somewhat by using proper bearings in those areas).

Lastly - those two options aren't the only means of wheeled propulsion, but they are the two most popular, mainly because they can both be implemented using mostly or wholly off-the-shelf components. Other methods which you may run into (or you might want to investigate) for wheeled vehicles:

http://en.wikipedia.org/wiki/Omnidirectional_wheel

http://en.wikipedia.org/wiki/Mecanum_wheel

See also: http://www.ehow.com/list_7374953_types-steering-systems-used-robots.html

Both of these (and a few other methods) tend to be much more complex to implement, and don't typically lend themselves to off-the-shelf parts solutions (which tend to drive up the cost, sometimes greatly). But they should be kept in mind as potential alternatives, depending on what you are trying to accomplish.
2  Using Arduino / Motors, Mechanics, and Power / Re: Toy car h-bridge for Arduino ? on: April 13, 2014, 12:03:23 pm
i found an h-bridge in its circuit is it okay to use it to my arduino ?

First off, how do you -know- this is an h-bridge IC? The markings in your image certainly don't seem to convey that impression to me.

Given that it came from a "toy RC car", and that it is a 16 pin DIP IC, and without seeing the rest of the PCB from which it was removed from - my first impression is that it is the RX2 half of the TX2/RX2 chipset (or one of the other TX/RX variants).

Such an IC is -not- an h-bridge. Typically in toy RC cars, the common TX2/RX2 chipset is used for control; the TX2 (in the transmitter) outputs a specific pulse train, which is then picked up via a receiver in the car that is connected to an input pin on the RX2 chip (which is a 16 pin DIP IC, just like in your picture); this signal is then decoded to turn on/off certain pins on the chip. Those pins are then in turn connected to various control functions of the RC car. The actual h-bridges on such a car are usually built from discrete mosfet or bipolar transistor drive circuitry (I have also seen hybrid relay h-bridges as well, but those are unusual).

Without being able to see the actual PCB of the vehicle, there isn't any way to accurately tell you what that chip you have actually is or what it does (or may do). Regardless, until/unless you can find a datasheet for it, all we can do here is simply guess at its operation. It's difficult to tell from your picture, but is there a sticker or label on that chip (ie, what reads "27 MHz") that can be peeled off? If so, do that then clean up the chip (of label goo), and post a new picture (with better lighting) so we can read what the IC really is. Again, I suspect it isn't anything like an h-bridge.

Further reading on these cheap RC cars and the TX2/RX2 chipset can be found via this thread - I suggest that you familiarize yourself with it:

http://forum.arduino.cc/index.php/topic,86883.0.html
3  Topics / Robotics / Re: uArmⅠ:An open source robot arm on: April 12, 2014, 06:20:11 pm
I worked for 1 1/2 days trying to learn AutoCad.  What a pain it is to do anything simple.  It can build a battleship, but trying to do something simple can take forever.

AutoCAD is anything but simple.

Only spending 1.5 days trying to learn something then thinking it is too difficult, though, indicates to me that you didn't give it a fair shot.

This is a piece of software that people spend years learning, and likely even after that find new methods and techniques using it on a regular basis.

I'm not a CAD expert; in fact, I've barely even touched CAD software (a bit of FreeCAD and some other packages here and there). I am not naive or arrogant enough, though, to think that I would be able to learn any CAD package in less than two days.
4  Using Arduino / General Electronics / Re: Questions on General Use of Transistors on: April 07, 2014, 10:19:26 pm
How do I know what kind of transistor works in a certain situation?

Another part needed: A bit of math. Here are a couple of links to get you started (note, this is for bipolar transistors - mosfets are a whole 'nother game):

http://www.technologystudent.com/elec1/tranfrm1.htm

http://www.physics.unlv.edu/~bill/PHYS483/transbas.pdf

By no means is the above a complete set of equations, etc needed, but it is enough to get started with. When you move into larger power transistors (TO-220 and TO-3 case devices), you'll also need to get into power dissipation equations (and how to properly size a heat sink for proper current handling). The equations aren't very hard, but they do require a bit of thought and understanding about how things work and how the devices are constructed (to understand certain terms).
5  Using Arduino / Motors, Mechanics, and Power / Re: Selfmade contact switch on: April 06, 2014, 10:14:20 pm
Does the switch have to be inside the "hot" part? Could you instead extend a lever or plunger outside of the hot area to the actual switch - allowing you to use commonly available parts?

Think about it: Should the switch fail, and you have to replace it - you'll need to make another one...versus simply ordering an existing part.
6  Topics / Robotics / Re: Robotic Arm - Are there any how-to's out there? on: April 06, 2014, 01:47:01 pm
Here is one pretty good "how to" on robot arms; however, it is in Spanish - but google translate does a fairly good job with it:

https://sites.google.com/site/proyectosroboticos/

As far as design of a robot arm is concerned, there is actually a ton of literature out there, mostly in dead-tree format - on industrial robotics design and control. A search on Amazon should turn up some titles. The uArm's design was based on an ARB palletizing robot - so it should be fairly easy to duplicate. I too am disappointed in what is quickly seeming to be turning into yet another KS scam. Fortunately, both I and another member of these forums were sent the laser cutter files for the arm - so the data isn't lost. I haven't released them yet, and I won't until I know for certain that the whole KS thing was a wash/scam. I guess I'm still holding out hope. That, and I said I wouldn't to the guy who sent them to me - but if it is a scam, all bets are off.

You might also look into how the old Armdroid and Microbot TeachMover robot trainer arms were constructed as well; there is actually a ton of info on the Armdroid out there, possibly enough to recreate it...

Finally - at
7  Using Arduino / General Electronics / Re: Take pictures with DRAM!!! on: April 05, 2014, 10:53:01 pm
I was just reading through and saving the translated version of the article, when I noticed that at the bottom, the author referenced Ciarcia's article...
8  Using Arduino / General Electronics / Re: How Do I Solder DC Motors With Flimsy Copper Pieces To Wires? on: April 05, 2014, 10:06:10 am
They are not flimsy copper, they are phosphor bronze, a tough alloy used for hard wearing
electrical parts and springs - here the spring that presses the graphite brushes against
the commutator.

As a kid, I took apart a number of these cheap toy 3-6 volt motors to know that there aren't any "graphite brushes" contacting the commutator; I don't know what the material is (could still be phosphor bronze), but inside the motor, it's basically just a simple strip of metal that contacts the copper commutator, nothing more than that.

You don't start to see graphite or carbon brushes on small motors until you start to spend more than 99 cents per each...
9  Using Arduino / General Electronics / Re: Take pictures with DRAM!!! on: April 05, 2014, 10:01:28 am
Who'd even think of trying that

Steve Ciarcia back in the early 1980s showed how to do this in his "Circuit Cellar" articles in Byte Magazine.

Martin Bradley Weinstein showed a similar (maybe same?) system dubbed "Ramera" in his book "Android Design", also published in the early 1980s.

The concept/idea might even be older than both of those pioneers.

It's an interesting way to make a camera, but unfortunately to re-create such a system today you have to basically destroy vintage DRAM; well, not really destroy it per-se, as that would render it unusable - but you are decreasing it's collector value - metal capped ceramic ICs from the era tend to have a pretty good collector value, depending on the part.

DRAM was plentiful enough that it probably isn't going to fetch a fair amount, but why bother to do this kind of thing (beyond the hack value - which was already proven in the 1980s - and useful back then) for a low-res camera when there are tons of better, more modern options out there?

I guess I just cringe at this sort of thing, because that kind of stuff isn't being made any longer, and our old vintage machines are slowly failing and needing parts...
10  Using Arduino / Project Guidance / Re: Robotic arm from scratch on: April 05, 2014, 09:53:55 am
good call on the counterweight/ spring, I didn't think about that, and I will definitely try that out, as for the variable speed algorithm, my "version" of that is to come depending on the reading from the joysticks that I'll have controlling the arm

Another thing to do is to keep as many of the servos/motors as possible close to the base of the arm; doing so means that "lower" servos/motors have less mass to move, meaning more mass which can be lifted (and started/stopped moving).

There's a kickstarter arm (also here on the forums) called the "uFactory uArm"; it's designed as a "pallet moving" type of arm (based on an ABB industrial arm design) - you might look into that to get some ideas on how you can keep the servos close to the base (unfortunately, it is unknown as to the status of the whole kickstarter thing on that arm - no one has heard from the guys behind it in a while now since the KS ended).

Other arms to look at are ones from the 1980s which used stepper motors to actuate the joints - a couple of good ones are the Microbot TeachMover, and the Armdroid; both had their motors on the "base" of the arm (really, the shoulder portion) - the former used mainly timing belts to transfer power from the motors to the joints, while the latter used cords. Plenty of information about both arms are available on the internet, enough to get ideas from.
11  Community / Bar Sport / Re: Are microcontrollers considered to be kiddies toys in real world? on: March 30, 2014, 02:49:44 pm
Perhaps what he actually means is not "Microcontrollers are kiddie toys" which would basically be the same as saying
"I forgot how to electricity....", we can give him the benefit of the doubt and assume he meant "Microcontroller development boards like the arduino are kiddie toys, and nobody should put an entire arduino to control a toaster.", which would make much more sense.

Ok...OP stated that his friend "...insists that you must afterwards build the circuit in real components without microcontrollers..."?

If his friend thinks "microcontroller" means "development board" - again, how has he gotten this far as a supposed degreed "electrical engineer"?

I can understand a lay-person or some other individual not educated about the difference between a microcontroller IC and a development (prototyping) board it is a part of; for such individuals, it is the same thing.

For anyone with a title of "electrical engineer", though - it should be understood there is a difference...

Unless of course this is yet another one of those cases where to such a person, a PLC (likely using ladder logic!) is some kind of mysterious "black box" and the understanding of the components inside and their function is rudimentary at best. It's akin to a programmer who is educated in C++ but has no clue about how a CPU actually functions at the register/machine-code level (and there are a ton of them out there), while making statements indicating such ignorance.

In other words, it's the bane of being "specialized" in an educational and career-oriented fashion. This isn't a bad thing, normally - as long as one has enough intelligence not to postulate on that which they do not understand (but then...humans).
12  Community / Bar Sport / Re: Are microcontrollers considered to be kiddies toys in real world? on: March 27, 2014, 07:53:25 pm
My friend (electrical engineer) is saying MCU's are kiddies toys and are not legit.

Your friend is either lying about his "degree", or if it is real, it should be revoked from him (and he should be fired from his current employer and never be hired in that capacity again).

I mean seriously - this would be akin to someone claiming to be a plumber (or worse, being employed as a plumber), yet not know how to sweat (solder) a hose bib onto a pipe.

It's complete ignorance and disrespect to the profession - and should not be allowed!
13  Topics / Robotics / Re: uArmⅠ:An open source robot arm on: March 25, 2014, 11:16:06 pm
A quick Google search that a "Palletizing Robot" has been around for some time. The below ebay offering is interesting.

Well - uArm/uFactory never said their design was "new"; they said they based it off an existing full-sized robot arm.

However, with that posting of the ebay arm, and the video - now you have me wondering which is what?

Did someone copy uArm (easy enough to do, I would imagine)? Did uArm's plans get "stolen" or somehow lended out (I know I didn't post them anywhere, and I trust that Jimbo didn't, either)? Or did uArm get the plans from somewhere else, pass them off (or a refactored version) of them as their own (as first mover?) then create the kickstarter? Hopefully that's not the case...

Then again, that video dates long before uArm first posted. No clue on when the ebay arm was first offered...

I have yet to hear anything from uArm in a long while...

14  Topics / Robotics / Re: uArmⅠ:An open source robot arm on: March 25, 2014, 11:07:39 pm
Did you, cr0sh, ever do anything with your drawings?  

No - unfortunately I haven't.

While I have access to a laser cutter (via my local TechShop) - and I believe I have the proper acrylic for the parts, I was still looking to source the rest of the components (bearings, screws, etc). I was also somewhat hampered by some surgery I had earlier this year (thus, paying that ridiculous expense off first). Then, on Feb 6th, I was laid off my job.

I only recently got new employment (started yesterday) - but those expenses are still there, plus the expenses incurred during my "vacation" (read: repaying my savings). So for now, the uArm appears to be on hold for me for the time being...
15  Topics / Robotics / Re: uArmⅠ:An open source robot arm on: March 24, 2014, 10:07:37 pm
The arm itself appears to be a Chinese design, so not sure where the plans would be found.

They sent the plans (well, DWG file for a laser cutter) to me and Jimbo; I don't know what else Jimbo received, but I also got a part list and assembly diagrams.

So - if this thing goes south on everybody, know that the plans do exist - I'm not releasing them, though, so don't bother to ask me - not yet, anyhow.

I wasn't able to participate in the KS campaign (I wanted to, but then I lost my job - thankfully I started new employment today); let's give them time and see what happens - I'll try to email the contact I have and see what if any response I get.

I'll update this thread depending on what I hear...
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