Author Topic: Motor Advice  (Read 1928 times)

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Offline dualTopic starter

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Motor Advice
« on: August 15, 2009, 09:24:11 PM »
Hi, beginner needs an advice. Right now I have two DC Motor ($10.99 each)that runs 6V at .33A and I've just ordered a SN754410 H-Bridge Driver (internal switch, $2.50).
But I also have the option to buy a Standard Futabu Servo and hack it, ($8.99 each, i believe).

Does it matter which one I pick for now? I rate myself above average with my knowledge in AVR but I've never designed anything Robotic so I can use any programming method for both options.

What are your opinions?

Thanks in advance

Offline MangoBot

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Re: Motor Advice
« Reply #1 on: August 15, 2009, 09:27:22 PM »
the servos would be easier, you would just have to modify them and plug them into the microcontroller. I would go for the servos because they would be cheaper, but are still good

Offline SmAsH

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Re: Motor Advice
« Reply #2 on: August 15, 2009, 09:37:39 PM »
it all depends on the speed and torque requirements...
sometimes motors can be more desirable for their speed and torque.
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Offline dualTopic starter

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Re: Motor Advice
« Reply #3 on: August 15, 2009, 09:56:21 PM »
Servos are definitely cheaper by atleast 6-7 bucks when I calculated them. But my design plan for the robot has one specific objective, I want to be able to easily control the speed and turning of the robot so I think that not having to worry about PWM in using a Motor is an advantage.

What are your thoughts on this? Am I correct in understanding the fact that controlling speed and turning is easier when using a Motor/HBridge design?

Offline SmAsH

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Re: Motor Advice
« Reply #4 on: August 15, 2009, 10:10:40 PM »
not really, servos require one digital pin, whereas motor controllers generally require two.
controlling and turning isn't any easier when using motor controllers or servos, its mainly all software that is different.
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Offline madchimp

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Re: Motor Advice
« Reply #5 on: August 15, 2009, 10:21:15 PM »
But my design plan for the robot has one specific objective, I want to be able to easily control the speed and turning of the robot so I think that not having to worry about PWM in using a Motor is an advantage.

Well if you want to control the speed of a motor that is usuall accomplished with PWM so either way you will be useing PWM.

Offline dualTopic starter

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Re: Motor Advice
« Reply #6 on: August 15, 2009, 11:03:58 PM »
or just use delays ^-<

Offline madchimp

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Re: Motor Advice
« Reply #7 on: August 15, 2009, 11:55:52 PM »
or just use delays ^-<
isn't that pretty much software PWM?

Offline SmAsH

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Re: Motor Advice
« Reply #8 on: August 16, 2009, 12:02:47 AM »
yup, i think :-\
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Offline Soeren

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Re: Motor Advice
« Reply #9 on: August 16, 2009, 12:16:14 PM »
Hi,

What are your opinions?
Go with the motors, that will give you way more freedom.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline blackbeard

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Re: Motor Advice
« Reply #10 on: August 16, 2009, 12:25:26 PM »
allot of people like servos and they're pretty good for most things. thing is they're generally REALLY weak and i've broken one or 2 trying to hack them. the good thing is they only need one i/o pin each. a big gear motor is cheaper then a servo of the equivalent power and can be easily controlled with an H bridge but they need 2 i/o pins each. i like to go with motors when i can but servos are easier for some people
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Offline Soeren

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Re: Motor Advice
« Reply #11 on: August 16, 2009, 12:38:45 PM »
Hi,

[...] but they need 2 i/o pins each.
That depends on the controller, motors can be controlled with a single pin as well.

Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline blackbeard

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Re: Motor Advice
« Reply #12 on: August 16, 2009, 12:41:32 PM »
Hi,

[...] but they need 2 i/o pins each.
That depends on the controller, motors can be controlled with a single pin as well.



that's true but a simple transistor Hbridge usually takes 2 pins. a motor controller is better though
"sure, you can test your combat robot on kittens... But all your going to do is make kitten juice"

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Next step: Give them vaginas

Offline SmAsH

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Re: Motor Advice
« Reply #13 on: August 16, 2009, 03:38:56 PM »
yeah, generally two, but you can get circuitry like that found in servos on its own which would only take up one pin.
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Offline dualTopic starter

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Re: Motor Advice
« Reply #14 on: August 16, 2009, 06:28:01 PM »
I've read some tutorial about a futabu servo and found that they require a PWM period of 20ms (or some other number). If the period that they require is constant, doesn't that mean that you can't control the speed of the servo? What about the direction then?

Offline madchimp

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Re: Motor Advice
« Reply #15 on: August 16, 2009, 06:59:32 PM »
yeah, generally two, but you can get circuitry like that found in servos on its own which would only take up one pin.
I know people are going to think I'm being mean but seriously Smash If all you are doing is repeating don't. Both points have been made already! If you don't have anything to ADD (as in something that makes the thread more usefull not take longer to read) to a thread DON'T add anything. I've been holding back for a long time. I would be willing to bet only 30% of what you post if that is actually adding value to the threads the rest just wastes everyone's time.

Offline Razor Concepts

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Re: Motor Advice
« Reply #16 on: August 16, 2009, 07:07:08 PM »
I've read some tutorial about a futabu servo and found that they require a PWM period of 20ms (or some other number). If the period that they require is constant, doesn't that mean that you can't control the speed of the servo? What about the direction then?


Speed and direction is controlled. The PWM period is 20ms, but the actual high pulse ranges from 1ms to 2ms. 1.5ms is center and no movement. 1ms is full speed one direction, and 2ms is full speed the other direction.

http://www.societyofrobots.com/actuators_servos.shtml

And I must kind of agree with madchimp also

Offline dualTopic starter

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Re: Motor Advice
« Reply #17 on: August 16, 2009, 09:58:45 PM »
Hang on, you said that speed is controlled? I know that you can control direction based on the duration of the pulse, like how 1.5 is straight, 1.25 is 90 and 1.75 is 180 or something along the lines.

But the tutorial i read really did not mention how to change speed. But are you implying that the closer I get to 1 ms, the faster I get? and the closer to 1.5 the slower I get?

And all that is after hacking the servo right?

Offline Razor Concepts

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Re: Motor Advice
« Reply #18 on: August 16, 2009, 10:10:46 PM »

But the tutorial i read really did not mention how to change speed. But are you implying that the closer I get to 1 ms, the faster I get? and the closer to 1.5 the slower I get?

And all that is after hacking the servo right?

Yup that is all correct! But the change in speed depending on the length of the pulse is not linear.

Offline Truckstop

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Re: Motor Advice
« Reply #19 on: August 17, 2009, 04:59:55 AM »
Check this out.

http://www.trossenrobotics.com/store/p/4267-BaneBots-Motor-Controller-45A-peak-.aspx

its the bane bots motor controller. I ordered one of these to play with for my MAX project, im using a pair pf 28 Amp motors, there very reliable and easy to use, they allow you to use any motor you want yet still have control like a servo with speed and direction with a single pin... they also have ones with a lower amp rating (18 and 9 )that are cheaper.

I was so impressed with it i ordered a second one...

Just an idea

Truckstop
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The Hyena: Nature's A$$hole
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