Newbie needs help on parts.
eminem
Posts: 8
im building an electric vehicle that is supposed to travel a straight path from A to B. since distance isnt given to me, i want to be able to simply reprogram a set distance for my needs. the vehicle is traveling on a flat surface btw.
i want to know, what do i need to buy for programming and rotating wheel+stopping with a time/distance interval?
im a noob i have no clue as to the technical jargon. i have no experience with robotics/basic stamp... i did however took some vbasic a few years back. thanks for any help.
i want to know, what do i need to buy for programming and rotating wheel+stopping with a time/distance interval?
im a noob i have no clue as to the technical jargon. i have no experience with robotics/basic stamp... i did however took some vbasic a few years back. thanks for any help.
Comments
Take a look at StampWorks experiment #26 and #27. This can be found on the Parallax web site
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im starting from complete scratch so i have no clue what wheel encoders or anything else means. can you link me to all the parts i need to
1) connect to my pc to program
2) whatever device i am programming and all necesseary parts for it
by just specifying the X and Y direction.
I can machine the parts, but we will need a programmer.
Let me explain how it works.
1. The center ball acts like an old mouse pointer maintaining the center of the robot.
2. Two encoders from an old mouse keep track of X and Y axis position.
3. As the robot moves, or rotates; the Hitachi HM55B will keep the X and Y position
4. by rotating and maintaining the axis pointing at the same direction, with a stepper motor or a motor.
5. and if we get fancy display the direction and X, Y cordinate on a display.
What you guys think?
http://forums.parallax.com/showthread.php?p=641371·= $10 Stepper motor Controller
·http://forums.parallax.com/showthread.php?p=641605·= Serial to paraller expander
·http://forums.parallax.com/showthread.php?p=637017·= Robotic arm
·http://forums.parallax.com/showthread.php?p=656332·= CNC Project
·http://pinellas-sign-manufacturer.com
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Fernando Gomez
Never compare yourself with anyone else, there will always be someone bigger·or·smaller·than you.
Post Edited (willy1067) : 12/16/2008 3:43:30 AM GMT
Good robot design! However, for traveling in a straight line (with no turns expected or planned for) then four wheels with no option to steer would be best.
with my design anyone can just tell the robot where in the room to go, and it does it by itself, just add few sensor for object detection and you can have a great BOT.
What the heck, lets build it anyway.
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Fernando Gomez
Never compare yourself with anyone else, there will always be someone bigger·or·smaller·than you.
this is for the electronic vehicle for science olympiad. this is my first time doing this.
CONSTRUCTION: The vehicle should be designed to travel between 5 and 10 meters and come to a complete stop withuot straying from the track'scenter. The exact distance will not be announced until all vehicles have been impounded on the day of the competition.
Sighting devices that do nut use electricity are allowed.
Vehicle's wheel base must be 28-32 cm and vehicles track/width may not exceed 20cm.
Post Edited (eminem) : 12/16/2008 5:29:10 AM GMT
Is there a line on the ground that it can follow? If so, then you can use a steerable robot that has line following capability, and you won't have to worry about going straight, just finding a distance.
it means that i cannot use laser sensors or the like and RC is completely out of the question. this is sort of a UAV.
what i am looking for is to somehow mount 2 of these (if they function the way i think they do) on an axle and attach them to wheels so that it spins and propels the vehicle forward.
http://www.parallax.com/Store/Accessories/MotorServos/tabid/163/CategoryID/57/List/0/Level/a/ProductID/65/Default.aspx?SortField=ProductName,ProductName
but i want to know if there is something that can controll/reprogram (very simply) the amount of time that the motors spin (so that the vehicle can come to a stop) or something of the like to stop via X amount of distance. i plan on just doing multiple test runs of various distances so that i can chart out time x distance so that i can reprogram the vehicle to suit my needs when the judges announce the distances required for the vehicle to travel.
and yes, there is a line of tap on the floor, but since i cannot use any sighting devices that are electrical, sensors are out of the question.
i am very new to this so i have no idea where to get started.
Stepper motors would make good engines to propel the robot, since you can tell them how much to turn. If you use them, then you don't need any encoders. All you have to do is to figure out how much distance is traveled each step of the motor, and you can simply use that to estimate the distance. With steppers, you have complete control over their motion. I'm slapping myself on the forehead right now for not thinking of stepper motors...
Anyway, the hardest part will probably be hooking up the wheels to the shaft, and possibly making sure that you don't draw too much current with the motors. I tried the hardware setup that parallax provided with sample code (using the L293D driver chip), but found that it was drawing too much current for the driver, and overheating. I'm guessing that a darlington array would work to fix this, but I'm mostly coder, and only part hardwarist. Some day.
When starting a project, I like to take a piece of colored, unlined paper and draw out / diagram exactly what I want the project to do, and how it should be built to accomplish my goals. I never look at the paper again, it's simply there as a feedback device.
On a lighter note, since electronic sighting devices are not allowed, have you thought about using some other type of sighting device? I'm thinking that you could use a lens of some kind, and a candle, to project a dot for the trajectory of the robot when you position it [noparse]:)[/noparse] Also, a definition of sighting might be in order. You could use a compass to help you go in a straight line, but it would depend on the rules.
im sorry for being a complete illiterate but what is a stepper motor/darlington array, etc? and how do i get it to stop spinning/brake? how would i get the entire vehicle to start?
excuse my very primitive and barebone(more of inexistence as to say) idea but what i was gettin at was simply this so far.
ASSUMING, based on my primitive knowledge (im only a junior in HS), connect the batteries to the motors and the circuit is complete and it will spin? connected to two motors to get it spinning/propulsion, but how to brake the vehicle, i have no idea. the only thing im worried about as of now is getting it to go forward/stopping. straying slightly from the straight path, i can deal with that later. my primary focus right now is somehow to get it started/stopping.
Post Edited (eminem) : 12/16/2008 7:05:41 AM GMT
The stepper motors will need quite a bit of circuitry to power them. You can't just hook them up to a battery source and have them turn. You'll need a microcontroller (like the BS2 available from parallax) and a special chip that allows you to drive the stepper motor (L293D if I remember right). The tradeoff for this circuitry is high accuracy. Unlike the regular DC motors that you're thinking (apply voltage and it turns...) stepper motors need a specific sequence of power on the wires to make it turn correctly. Take a look at the datasheet on the product page for more information. It's your primary source. As for braking, a stepper motor will 'automatically' brake when you stop giving it the sequence. So, no worry's there (although, you may want to slow down first before you stop so that you don't skid). For another resource, take a look at the Nuts and Volts article titled Stepping Out with Spin. It's not for the BS2, but it does give you a good idea of what does what. It's available from the main parallax website.
Also, google is your friend. Very few people know everything about electronics, so search for the term. If you get a wikipedia article about the term, so much the better.
You can make the project as complicated as you want. Simple would be a DC motor with a microcontroller: the microcontroller turns the motor on for a time, and it coasts to the destination after that. Okay, but not too accurate. You could use continuous rotation servos, but those would probably veer from the straight line over long distances. You could use a DC motor with encoders, and that would give you fairly accurate distances at the expense of more complicated coding. Finally, stepper motors would allow you to assume the position of the wheel (with using encoders) and get very accurate distances. Those are the main choices that I can think of, although I'm sure that there are more hanging around out there...
Finally, take a look at the Basic Stamp from Parallax, and their Stamps in Class series book. There're available for free download from parallax, and give good overviews of the subject of microcontroller programming.
Post Edited (SRLM) : 12/16/2008 4:39:01 PM GMT
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How do you like my name change?
aka G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan
A tread and motor set that can only move forward or backward (not turn):
http://www.robotmarketplace.com/products/AB-70108.html
($14)
You said the exact distance is not provided, so you will need some way to control the vehicle... So you need a microcontroller.
This is the Board of Education. It comes with everything you need to run a Basic Stamp 2 microcontroller.
http://www.parallax.com/Store/Microcontrollers/BASICStampProgrammingKits/tabid/136/CategoryID/11/List/0/SortField/0/Level/a/ProductID/294/Default.aspx
($99)
Finally you need an H-bridge... a way to control the motor of the tread kit.
http://www.sparkfun.com/commerce/product_info.php?products_id=315
($2.35)
If absolute exact distance is required, then you'll need an encoder to read the holes in the treads.
The most common encoder is an Infrared transmitter/receiver pair.
You can use either a digital one or the RCTIME command for the BS2 to read the encoded signals.
Here's one that may work (Although I don't own it)
http://www.sparkfun.com/commerce/product_info.php?products_id=246
($1.13)
That'll give you a total of $116.48 for a robot that is pretty exact at judging distance, and can move only forward
or backward.
Or you could get a BOE-bot... one of the more famous robots available for hobby and education use.
http://www.parallax.com/Store/Robots/RollingRobots/tabid/128/CategoryID/3/List/0/SortField/0/Level/a/ProductID/302/Default.aspx
($159.99)
If you don't need the robot to be exact, or to decide when its supposed to stop and start, the tread kit at the start might be
all you need. Just build it, turn it on and it'll go until the batteries die.
There are so many options that its really impossible for us to suggest what to get until you give us more info.
We need to know:
Is the distance going to be absolutely fixed? Or will it change?
Is it marked by anything to make it stop? (A wall, a bit of tape, ect)
Will the vehicle need to be upgradable to do other things in the future? (turn, avoid objects, ect)
What do you have now that can be used (A microcontroller? Motors? Old RC car lying around? Materials for a frame like wood?)
Most importantly... whats your budget for this project?
The distance will change (i think there are three different test runs, each with an absolute distance yet to be announced)
there is a line of tap on the floor, but electrical sensors such as lasers cannot be used.
the vehicle will not be needed to upgrade for anyhting else in the future. this is a one time project. i just want to build something simple so that i wont disappoint my teacher with no vehicle at all.
as of now, i have nothing (not even any knowledge with robotics/servos/microcontrollers etc.) the only thing i do have some experience in is vBASIC programming from freshman year.
my budget is preferably less that 100$. i emphasize the word less.
also, would that boe bot run on a single 4.5v battery or 4 x 1.5v batteries?
what are the barebone minimum needed/
Post Edited (eminem) : 12/16/2008 10:01:30 PM GMT
I have an idea that may or may not work... if it does, it may allow you to manage this for under $50
If a simple, non-microcontroller based project is permitted... then we can do a bit of ancient egypt inspired mechanical engineering.
Using a kit like the $14 tread platform I mentioned above, you can attach a string to the shaft coming out of the gearbox, or perhaps to the
gears somehow. Not sure how you'd attach it, you'd have to work that out.
On the other end of the string you'd put a simple way to unplug the batteries from the motor... a clip or something that can be easily pulled
off yet sturdy enough that it won't come off during use.
For each length of "distance" you'd measure out different strings.
The shaft rotating would wrap up the string until it reaches the desired length then pull the clip lose, cutting the power and killing the motor.
If the clip is large enough, it could tangle in the shaft/gear system and cause the vehicle to stop.
This is a very low tech concept... if it doesn't meet your requirements or desires, then we can come up with something else.
The problem is, there are cheaper microcontrollers than a BS2/BOE setup... but they all require an initial investment that's quite high.
To answer your question, the BOE would need the 4x 1.5v batteries.
It can also run off 5 rechargable 1.2v batteries but you'd need the BOE-boost add-on.
Edit: hmm. Two completely independent string theories [noparse]:)[/noparse]
with this
powered by 4xAA batteries and connected to two stepper motors be able to do the job of simply starting + stopping?
would that be all i need to connect the Basic Stamp 2 to my pc and program it, or do i need something else to do that?
also, whats the difference between that board and
also, here is a video of what the competition is like.
1. an external regulator. Although the BS2 has an onboard regulator, it can't really power too many external components with it. Regulators are a couple of dollars at radio shack.
2. A serial connection on your computer (or a USB to serial device from Parallax)
3. Soldering to make it all happen
The board of education ( the second one you posted) is much easier to hook up and get going quickly. And don't forget: if you're going to use stepper motors (with either board), you need a driver chip (as listed in the documentation on the product page). If you have an old printer or flatbed scanner and are willing to tear it apart, there are several stepper motors inside and some nice belts and pulleys, that you can use in order to just have a single motor with a drive to an axle.
If so it could be a possible option.
Also I simply would not recommend stepper motors. Too much trouble and too complex for a first project.
also, i was planning to simply program the board to cut power from the motors after a given time interval to cause it to stop the vehicle's motors. would that be possible?
also, would it be possible to put the BOE on this
http://www.robotmarketplace.com/products/0-TAMX7112.html
to controll when the motor starts+stop?
furthermore, if i were to buy the BOE Bot kit, would it be able to run the bare minimum to get the job done on 4 x 1.5v or a single 4.8v battery?
http://www.parallax.com/Store/Microcontrollers/BASICStampModules/tabid/134/ProductID/302/List/1/Default.aspx?SortField=ProductName,ProductName
here is the exact requirements for the project.
Post Edited (eminem) : 12/17/2008 4:40:59 AM GMT
The L293D chip for the stepper motor can be found here. I personally like the stepper motor idea because it is more precise and you don't need encoders, but it's your decision.
little problems. So yes, 4 AAs will be fine.
You can't use any microcontroller to just cut the power without any additional circuitry because a motor draws much more current than
they are designed for. That's why you need the driver chip that SRLM or I recommended.
The upside is the H-bridge driver chips usually can do dynamic breaking. This is a process that (usually) causes the vehicle to stop dead
at a desired location.
You still have to figure out where your supposed to stop. While timing it sounds good, its rarely a good idea.
Tires skid, surfaces (like carpet and such) vary in density and motors turn at different rates depending on how charged the batteries are.
So timing it is going to be nearly impossible without using a completely fresh set of batteries every time and simply depending on luck.
Setting up an IR encoder on that kit should be fairly easy.
Put an IR pair (receiver and transmitter) between the front tires, pointing inside one of the tires.
Inside the tire put a small piece reflective substance like a sliver of mirror or a small fold of aluminum foil.
Every time the tire goes a full revolution the IR will bounce off the reflective substance and give you a clear reading of distance (excluding
skid, which isn't as huge of a factor as motor speed).
This is a quick-and-dirty encoder, but it should work fine. Parallax sells encoder pairs, Sparkfun.com sells some good ones too.
Mouser (the site SRLM linked to) sells just about everything under the sun.
If you wish to use timing, then the BOE with a BS2 and an H-bridge can absolutely do it down to the millisecond.
One way I might do distance is calculate stepper turns, and use a push button to input the distance (as it looks variable) into the robot before the start. You could track this in a variable, use it in in the subroutine of the motors. I.E., 1 push = 1 meter, 2 pushes = 2 meters... so on and so forth. Plus, using a stepper with distance counting, you will again nix the issue of fading battery power.
As for straight line, it seems if you build your frame square, the idea of 4 fixed position wheels is the best bet for such a short distance. Based on the the contest videos, it seems these are all done on smooth tile or gym floors. So the drift would be absolutely minimal at that distance provided the frame was square.
Using solid axle design would also enable you to use a single motor for control, depending on mounting, could be belt or gear driven.
Seems like a really fun project... any updates?
I would stay with the steppers if cost and complexity are a problem.If You look into steppers and the way their driven You'll see what We mean.
I see that site driven devices are a no no in Your project.I just wanted to point out the fact that the " PING " is as blind as a Bat.In fact this is how the "PING" works.It doesn't see anything. It send out a short 40kHz pulse and then _listens_ for the echo return from something in front of it or in its range.It is an excellent rang detector,But it has its limitations.
Just some more Ideas
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Post Edited ($WMc%) : 12/27/2008 5:21:19 PM GMT