Author Topic: major robot noob...help (Read 16474 times)

tjpark1111 · « **on:** December 30, 2007, 10:24:14 PM »

i read the helpful guides posted in this website (thank you!) but i'm still a bit bleak on what to do. i have to build a robot for science olympiad and it has to be able to pick up/move stuff like tennis balls and pop balloons that are inside a box. it has to have wheels so its more of a car that has arms on it. i still really don't understand how to install a servo... you attach a microcontroller to it... then how do you control it?

im guessing for the arms i need to attach some kind of cable to a servo... but overall im just really confused about what to do can anybody help? im really sorry if this is sort of a redundant post.

ed1380 · « **Reply #1 on:** December 30, 2007, 10:32:11 PM »

what size robot are we talking about?

you control teh servo through pulse width management which is programmed into the MCU

tjpark1111 · « **Reply #2 on:** December 30, 2007, 11:00:02 PM »

the robot has to fit in a 30cm cube in the beginning, so 30cm x 30cm x 30cm. it's gonna be run on a carpet, no hydraulics, pneumatics, or fluid mechanisms.
batteries can't exceed 9.6 volts. radio frequencies, if wireless, need to be in 75, 49, or 27mhz.
i have to move 4 tennis balls, a stack of 5 index cards, and 3 d-cell batteries into a goal box which is also 30x30x30. i need to pop 2 nine inch balloons which is inside the goal box, and take out 2 nine inch balloons from the goal box, then dump all of the stuff in.
this is the playing field: http://www.soinc.org/events/robotram/RRplayfield08.pdf
i really hope this isn't too hard to do...?

tjpark1111 · « **Reply #3 on:** December 30, 2007, 11:01:33 PM »

and if possible can you like sort of explain in laymans terms what all of that meant with the programming? i don't understand..

tjpark1111 · « **Reply #4 on:** December 31, 2007, 08:57:42 AM »

arms are probably much more complicated so i could have sort of a rotating mill that can pick up stuff, or a door design which is just back and forth motion, but i still really need to understand how to program a servo, or how to use it, just in general.

Admin · « **Reply #5 on:** December 31, 2007, 09:52:26 AM »

What about something like this?
http://www.societyofrobots.com/robot_asme.shtml

also useful for you:
http://www.societyofrobots.com/batteries.shtml
http://www.societyofrobots.com/actuators_servos.shtml
http://www.societyofrobots.com/remote_control_robot.shtml

tjpark1111 · « **Reply #6 on:** December 31, 2007, 11:22:00 AM »

oh jeez i never found that tutorial, that's almost exactly like what i'm doing! thanks!
so for servos, if you have a RC receiver and a transmitter, it just automatically programs the commands for you?
the tutorial says: So how do you apply this square wave to your servo? If your robot is remote controlled, your RC receiver will apply the proper square wave for you. so does this mean i just connect some wires and if i turn all of the stuff on it'll just start working and i can control it with my transmitter?
i don't have power tools or even a hacksaw (i guess i could buy one easily) readily available with me, although my school has a robotics club with a big woodshop, so maybe i could utilize that.
can i get that HDPE stuff or any reasonable building material for the robot at home depot? or is it really special so i need to order it online?

Admin · « **Reply #7 on:** December 31, 2007, 12:19:13 PM »

yes, to all of your questions.

tjpark1111 · « **Reply #8 on:** December 31, 2007, 06:02:19 PM »

ok yay!

so ive watched that video of yours of that robot with the arm like 1500 times, and i've found one problem. one of the objectives in my competition is that i need to pop 2 balloons and also take out 2 balloons from a box, and i dont think an arm like that can really reach in a box that's 30cm high...
you're allowed to move the box, flip it over, whatever, so do you think it'll be better if i have something that'll move the box itself, or do you think it'd be better to add some sort of extension to the sort of arm you had so i can reach inside the box? thanks so much!
and one more thing: i don't have any of that fancy software nor do i have a very powerful computer to run that kind of program. can i just take the good ole' pencil and paper? or is that risking accuracy?

Admin · « **Reply #9 on:** December 31, 2007, 06:07:10 PM »

well, that arm was designed to lift a lot of weight. you can instead make the arm much thinner and longer to reach in the box or something.

a good engineer develops multiple ways to solve the same problem, then picks the best. usually your first idea is a typically obvious solution, but not always the best.

Quote

i don't have any of that fancy software nor do i have a very powerful computer to run that kind of program. can i just take the good ole' pencil and paper? or is that risking accuracy?

search for a free CAD program called google sketchup

tjpark1111 · « **Reply #10 on:** January 01, 2008, 09:03:47 PM »

is there any way i can look at the files you created for your ASME robot? (without paying like $500 for software?)

Admin · « **Reply #11 on:** January 01, 2008, 09:48:51 PM »

solid works has viewer programs to let you see but not modify files . . . i dont know it off hand, but if you google it you should be able to find it . . .

ed1380 · « **Reply #12 on:** January 02, 2008, 10:05:57 AM »

i believe it's called edrawing

tjpark1111 · « **Reply #13 on:** January 05, 2008, 10:20:43 AM »

thanks! the program worked!
anyway should i use continuous servos for the wheels? (making a differential).
im wondering how i should connect the servo to the wheels, how to make an axle, how to attach the wheels to the chassis.....
i noticed a 100 people have viewed this thread already it'd be great if you could help. thanks!

Admin · « **Reply #14 on:** January 05, 2008, 10:25:45 AM »

This should help you a bit:
http://www.societyofrobots.com/mechanics_chassisconstruction.shtml

SmAsH · « **Reply #15 on:** January 10, 2008, 05:00:00 PM »

yea as admin said make the arm a bit thinner but u should also make 1 or 2 more joints so it can reach in box...or just tip the box over XD...
anyway hope it helped

garriwilson · « **Reply #16 on:** January 10, 2008, 11:05:24 PM »

You do not need an axle at all. You can use velcro to attach the servos to you chassis but if you don't have any, you can go to a store like radioshack or staples that has school supplies and get double sided tape. You attach the wheels with the servo horns which come with the servo. They look like this:

http://www.futaba-rc.com/parts/futm1980.jpg

I actually made a thread for and R/C project which has a lot of useful info but it's kind of long: http://www.societyofrobots.com/robotforum/index.php?topic=2648.msg19356#msg19356

You don't really attach the wheels to the chassis, but attach the wheels to the servos and then attach the whole component (servo+wheel) to the chassis with velcro, double sided tape, or servo mounts.

You don't need an axle because the wheels are separately attached to two servos like this: http://www.societyofrobots.com/images/sbs_8.JPG

And for chassis construction this part of the $50 tutorial is really useful: http://www.societyofrobots.com/step_by_step_robot_step2.shtml

I've never made a robot arm so I'm not going to say anything in fear of misleading you. Good luck!

EDIT: Just remembered about this tutorial on how to attach wheels to servos: http://www.kronosrobotics.com/an118/GAN118.shtml

tjpark1111 · « **Reply #17 on:** January 11, 2008, 10:12:28 PM »

thank you all so much!!
i just realized that the 2 blue balloons have to be popped, and HAVE to stay in the box, even after popping, at all times. in addition, the 2 red blues need to be taken out, but they can be blown to any size, or just left deflated. i was thinking i could just move the box around as i want with suction cups(saw this in a youtube video) but since the balloons can't leave the box, i cant really use that idea anymore....
do you guys know if lasers can penetrate plexiglas? if so, how can i turn it on/off wirelessly on a robot? using a servo just to press the switch on the laser would be pretty stupid (im thinking maybe i can pop balloons inside the box using a laser, although im not sure if they're allowed, i asked).

SmAsH · « **Reply #18 on:** January 13, 2008, 04:00:30 AM »

yea but the only problem with lazers is that if theyre strong enough to pop a balloon theyre strong enough to blind someone...you might want to take that into consideration if using lazers and warn EVERYONE to to look at it. but even if they dont look down the robot could slip or a wheel come off (happened to me many times) and it could point up at someones eye.
anyway check with your teachers

Trumpkin · « **Reply #19 on:** January 13, 2008, 06:04:41 PM »

lasers that powerful can cost lots like $500 at least

tjpark1111 · « **Reply #20 on:** January 14, 2008, 08:48:00 PM »

yeah i asked the competition people if lasers are allowed and they haven't responded.
in the meantime, i have a few ideas ive taken from other contenders from pats years and i want to know which one you guys like hte most:
1) longer, thinner arm to reach in the box to take out balloons, pop balloons, and put stuff in (i was thinking this would take too long, i have 3 minutes max).
2) tip over box with a level/arm design:

http://youtube.com/watch?v=mGxK7feikcw

the only problem: is there a way i can design this so i can put the box back to its original position? the box needs to put open side up at the END of time (can do anything with box before time is called).
3) pick up mechanism

http://youtube.com/watch?v=nTcX5S3kql0&feature=related

problem: i need to unload all of that stuff into a 30cm high box... how can i do that with this mechanism? and how would i be able to pop/take out balloons if this was my only mechanism on my robot (or, is there a way to attach an arm in addition to this method? that would be killer).
and any other alternates would be MUCH MUCH MUCH appreciated.

SmAsH · « **Reply #21 on:** January 14, 2008, 08:57:33 PM »

yea trumpkin you can make your own lasers powerful enough to pop balloons...take a look on youtube ive made a few before but they all got confiscated at school

tjpark1111 · « **Reply #22 on:** January 14, 2008, 09:06:23 PM »

and also, i really wanna make this clear, im still a little confused.
say i have 2 continuous servos for 2 wheels on my robot attached to one RC receiver.
let's say i have a 6 channel transmitter like this: http://www.robotmarketplace.com/products/0-GWS-GWT6A.html
to make the car go forward (both servos turning), do i press forward on two of the joysticks? how can i make it so that i have those 2 servos controlled specifically by 2 adjacent joysticks (and not like two random toggles on the transmitter). is there a way to organize which toggle controls which servo on a basic transmitter like this?
also, is it true that lasers can't pop balloons when there's lights on or if the balloon isn't a dark color?

SmAsH · « **Reply #23 on:** January 14, 2008, 11:35:45 PM »

hmm....yes u would have to press both joysticks forward if you have two that will go forward....its a lot easier if you have on joystick controlling one servo...im not sure about the balloon thing tho...

~smash

tjpark1111 · « **Reply #24 on:** January 15, 2008, 03:42:16 PM »

i looked at the trasmitters more closely, and it looks like they only have 2 joysticks and the rest of the buttons are all just trim controls (can anyone explain what these are?). am i missing a few buttons on the top/side of the transmitter or something, or are there erally only 2 joysticks even on a 6 channel transmitter? also, since i have an arm and possibly other functions on my robot, do i need to change channels to move the arm, use the joystick, then switch channels again to control the servos on the wheels? i would have to have some pretty swift hands....

paulstreats · « **Reply #25 on:** January 15, 2008, 06:22:19 PM »

maybe the joysticks go up/down/left/right individually. This would account for 4 channels...

The trim controls are so you can set the joysticks to center. Sometimes if youre trying to drive straight with a car with the turning joystick centered, it will still veer off slightly so you use the trimmer to adjust the output signal of the central position.
It can also be used to set helicopters etc... to hover rather than cut off at center position.

Theres could be an extra pot that can be used to remotely turn lights on etc... this would take up a channel too.

Also with the which controls do i press to make the servo's move - then it depends on how you program it...

tjpark1111 · « **Reply #26 on:** January 15, 2008, 07:24:21 PM »

that's the thing - i heard there IS no programming when you use RC. do you think maybe i should plug in servos one by one into the receiver, turn transmitter on, etc. to make it programmed into 1,2,3, accordingly?
also, do i need to get the same brand, transmitter, receiver, and servos for this whole thing to work?
anyway, thanks for the other tips from everyone else!

paulstreats · « **Reply #27 on:** January 15, 2008, 07:37:14 PM »

no, you dont need the same brand.

The only thing that needs to be the same is that the transmitter and receiver are both set to work with the same amount of channels and at the same frequencies.

If youre not using a microcontroller, then you will have to have 1 servo on each channel, You will have to check with the documentation for the receiver since its likely only set up for certain ports to use servos on

tjpark1111 · « **Reply #28 on:** January 15, 2008, 10:32:49 PM »

how come this receiver says "futaba only" if brand doesn't matter?
http://www.robotmarketplace.com/products/0-GWR4PII75HF.html
do the transmitter and the receiver have to have the same CHANNEL (as labeled on the crystal?) how can i buy transmitters/receiver that have same channel? buy a package?
where can i buy pre-modded continuous rotation servos?
i need help calculating the torque needed for the robot arm. it's confusing because even if i use minimal values i get like 34 POUNDS PER INCH which you can't get with like ANY servo, that's friggin 544 oz/in!! it's a little complicated because im not exactly lifting the object, im pushing a box up from the box's bottom so the box can tip over back to its original orientation. so i'm not really lifting the box off the ground or anything. what am i doing wrong?

SmAsH · « **Reply #29 on:** January 16, 2008, 01:39:27 AM »

hmm...yeah that is tricky..sorry cant help you...

~smash

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Author Topic: major robot noob...help (Read 16474 times)

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