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Author Topic: hi... i got a question  (Read 6074 times)

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Offline annoyin_kidTopic starter

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hi... i got a question
« on: January 23, 2007, 11:03:13 AM »
hi there im new to these forums and i wanted to know some more about a robot that was on this site. the servos on stampy the sumo robot are they modded so they are one of those 360 degree turn servos? and wouldn't a motor on its own also be able to do the same job as the servo or was the servos used because they can turn foreward and backward without the h-bridge?

Offline Admin

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Re: hi... i got a question
« Reply #1 on: January 23, 2007, 02:09:25 PM »
Quote
the servos on stampy the sumo robot are they modded so they are one of those 360 degree turn servos?
yeap, they are modded for continuous rotation

Quote
wouldn't a motor on its own also be able to do the same job as the servo or was the servos used because they can turn foreward and backward without the h-bridge
motors will work too, and could probably go faster. however my limitation on speed was determined by how fast the scanner could get a reliable lock on a target, and servos made that easier to do.

but i also had two other limitations:
- i wanted to build the robot with as little effort as possible, and servos are reliable prepackaged solutions. i own wired up motor drivers, too, but i didnt want to bother figuring out PID control or using encoders. as a result, that robot took me only 25 hours to make . . . ~10 hours of it correcting dumb mistakes . . . ;D

- i already owned the high speed servos, giving me a strong preference over buying something else

Offline annoyin_kidTopic starter

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Re: hi... i got a question
« Reply #2 on: January 23, 2007, 02:48:14 PM »
how much torque are those servos and what kind are they? what kind of rpm are you getting from the servos and what kind of motors would you use if you did and what are its specs?

i live down in new zealand and the parts avaliable here are quite limited so i gotta look around for ages to find a shop that sells the stuff i am after and the more specs i get about the stuff i need the easier it is to find something close to it.

also what do you mean by 'PID control' and 'encoders'? im new to electronics and i only learnt basic electronics last year at school and i only know how to use picaxe microcontrollers.

ps. nice job you did with this website and thanks for making it, it really is useful for beginers like me ;D ;D ;D

Offline Steve Joblin

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Re: hi... i got a question
« Reply #3 on: January 23, 2007, 03:13:59 PM »
Servos (modified so that they rotate continuously) have been used in small amature robotics for several reasons:

1.  they are relatively inexpensive
2.  they are easy to mount
3.  their internal gears create good torque and a reasonable speed
4.  they require no additional components (like H-Bridges)
5.  they don't require "constant" care... by this I mean that a servo only needs to be sent a comand every 20ms, so if you are using a single threaded micro processor, you can send a command, then go and do something else (like check a sensor) before you need to send a command again


Offline annoyin_kidTopic starter

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Re: hi... i got a question
« Reply #4 on: January 23, 2007, 03:23:29 PM »
ohhhhhhhhhh!!! thanks steve

Offline Admin

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Re: hi... i got a question
« Reply #5 on: January 23, 2007, 03:30:33 PM »
all the parts are listed at the bottom of this page:
http://www.societyofrobots.com/robot_sumo.shtml

the servos are HS-225MG Servos ($28 each)

Specs of all Hitec servos can be found here:
http://www.hitecrcd.com/homepage/product_fs.htm
(just look for the servo you want, and specs will be listed)

You probably would want to get the Hitec HS-311 servo, as its much cheaper and much easier to get. I guess NZ is an odd place to buy parts . . . finding parts is often a pain even in the US, I think . . .  :-\

If I was to use a motor, off the top of my head Id probably get one with no more than 300 rpm, and torque of maybe 24 oz-in. Id probably not use an encoder but instead use a tweaked fuzzy logic control system.

PID control, mathematical method for controlling robot motion:
http://www.societyofrobots.com/programming_PID.shtml

Encoders, used for measuring wheel rotation:
http://www.societyofrobots.com/sensors_encoder.shtml

ok I think I got all your questions answered . . .

Offline annoyin_kidTopic starter

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Re: hi... i got a question
« Reply #6 on: January 23, 2007, 03:50:17 PM »
ah i see thanks :D :D i can get a servo similar to the hs-225mg in nz for around NZ$30 (US$ 15-20) but i dont think it will be as small!!
do you know how to use picaxe and know the picaxe programming language? i just wanted to know so that i know if i can ask you specific questions about code, programming, etc
« Last Edit: January 23, 2007, 03:55:53 PM by annoyin_kid »

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Re: hi... i got a question
« Reply #7 on: January 23, 2007, 04:57:28 PM »
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do you know how to use picaxe and know the picaxe programming language?
nope, never used it

im positive that if you post a question on it, someone should be able to help . . .
remember, if you have questions, feel free to post the code that isnt working  :P

Offline Steve Joblin

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Re: hi... i got a question
« Reply #8 on: January 23, 2007, 06:55:13 PM »
Annoyin Kid:  seems like you are just getting into this great hobby... I might make suggestion that you consider buying a Parallax BoeBot as way to get into Robotics... Surprisingly, there are many folks from NZ that are very active on the Parallax forums and Parallax has very good tech support through their Austrailian and NZ Distributors...

AUSTRALIA

RTN
35 Woolart St.  Strathmore, Victoria  AU  3041
Phone: int + 613 9338 3306 
Fax: int + 613 9338 4596
Web: http://www.nollet.com.au
Email: [email protected]

NEW ZEALAND

E-Source Ltd.
Auckland
Phone: Intl: +64211929950 
Fax: Intl +64 9 521 3832
Web: http://www.esource.co.nz/
Email: [email protected]

It is funny that you mentioned PICAXE... I just ordered a few of the 08M chips!  It seems like a great product and I am surprised that they have not gathered more strength and popularity here in the States... It is very very very similar to PBASIC (which is the language used to program Parallax Basic Stamps).

Offline annoyin_kidTopic starter

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Re: hi... i got a question
« Reply #9 on: January 23, 2007, 11:27:35 PM »
yea picaxe is pretty good aye steve. picaxe has its own forum aswell - http://www.rev-ed.co.uk/picaxe/forum where there are lots of people to help out aswell.

Offline gamefreak

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Re: hi... i got a question
« Reply #10 on: February 02, 2007, 06:19:10 AM »
lol, I have a BOE-bot. It was my first bot.

but right now its not working because i took it apart in hopes of making me a new robot out of its board and servos.
All hail Rodney, the holy 555 timer
And Steve said: "Let there be lead!"

 


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