Author Topic: Motors and servos! Adv. and Drawbacks!  (Read 2600 times)

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Offline blackheartTopic starter

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Motors and servos! Adv. and Drawbacks!
« on: February 07, 2009, 04:02:31 PM »
Hey. I heard servos are best for robots. But I would like to use motors(brushless...yeah baby) on my robot, not because I am cheap, but because  I want it to be an off-road capable robot and I would like it to be fast. Also, I hate the part where I have to modify the servos. I did open up a gearbox from an rc car and all the gears fell and I f***ed it all up. So what else do I need if I choose to go with motors? Special code, or separate boards?

If there is too much work to be done with a motor(like way too much...), I would invest in a fast servo...but please, please tell me there are already modified servos for sale that can rotate continuously.


Thank You!
I'm out of ideas!

Offline Razor Concepts

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #1 on: February 07, 2009, 04:17:12 PM »
If you want your robot to be fast, servos are out of the question.

Brushed motors will be fairly easy to use, but brushless motors will require a brushless ESC (designed for RC cars and trucks)

Offline frodo

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #2 on: February 07, 2009, 04:20:28 PM »
i thought that all motors were the same, so what is a "brushless motor"/?
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Offline blackheartTopic starter

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #3 on: February 07, 2009, 04:42:16 PM »
A brushless motor has a different way of functioning, reducing friction, therefore reducing heat, therefore increasing lifetime. SO what do I need to do to use a brushed motor. Same as the servo? Or do I need anything else? What do you mean by easy?
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Offline Razor Concepts

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #4 on: February 07, 2009, 04:57:16 PM »
Easy as in you just need one chip to drive the motor. You connect the motor wires to the chip, and you connect two pins from the chip into your microcontroller - and that's it! But for brushless, you'll have to go out and buy a brushless ESC (gets expensive).

Offline Webbot

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #5 on: February 07, 2009, 04:59:23 PM »
Small brushed motors are easy but a bit more complex than servos. A brushed DC motor will need a motor controller to run it. But dont panic - you can either build your own motor controller (see http://www.societyofrobots.com/member_tutorials/node/159) or you can buy one already made.
But before you can find out what's suitable you will need to find the maximum current that your motors require. This is typically the 'stall current'. If you have an amp meter then connect it series with your motor to the battery. The current you see is the minimum required (as the wheels are just rotating in the air). Now grab a hold of the wheel and stop it from turning. You will see the current go up. This is the 'stall current'. Having got that then look for motor controllers that can supply that amount of current.

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Offline blackheartTopic starter

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #6 on: February 08, 2009, 05:08:24 AM »
Nothing simpler?

WHere can I find the chips for the motor? Like the motor shield for arduino, but for roboduino???
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Offline airman00

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #7 on: February 08, 2009, 10:18:28 AM »
Motor shield of Arduino is compatible with Roboduino , just change the male headers of the shield to female headers and thats it.
Check out the Roboduino, Arduino-compatible board!


Link: http://curiousinventor.com/kits/roboduino

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Offline blackheartTopic starter

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #8 on: February 08, 2009, 01:03:07 PM »
I am confused with all male and female adapters. How do I plug in a photoresistor on the roboduino? Roboduino's got male headers only. And the photoresistors are also male...
I'm out of ideas!

Offline frodo

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #9 on: February 08, 2009, 01:18:40 PM »
could be problamatic :( try male2male connector if they exist
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Offline Razor Concepts

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #10 on: February 08, 2009, 02:31:20 PM »
Solder a female connector to the photoresistor. Also technically photoresistors have a lead, not male.

Offline Tomas

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #11 on: February 09, 2009, 12:13:35 PM »
you should consider using RC parts for your robot. RC engine, RC motor controller, RC servo and so on. I actually bought a hobby grade RC car and I got all the stuff working within hours (that was with the axon, I guess its equally easy on the roboduino).

Offline blackheartTopic starter

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #12 on: February 09, 2009, 03:10:03 PM »
That is exactly what I had in mind. I like the programming of the robot a lot more. BUt it's no fun if I get a built robot and just program it. Neither it is if I have to do the board. With a special uC, and an rc car, this is just great. Although, I want this to be very fast, so I am not gonna be using the car chassis or the motors. I am using 2 airplane motors for which I will need some gears, and the chassis from an oldr small rc car which I cut down to be small.
I'm out of ideas!

Offline Admin

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #13 on: February 09, 2009, 09:30:21 PM »
Quote
But I would like to use motors(brushless...yeah baby) on my robot, not because I am cheap, but because  I want it to be an off-road capable robot and I would like it to be fast.
Actually, brushless motors will cost about 20x more than a servo (factoring in motor driver). Even more if you want feedback control . . .

Servocity.com sells modified servos (you forgot to search :P)

Offline Razor Concepts

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #14 on: February 09, 2009, 09:36:48 PM »
20x?? $200? I think not  ;)

www.hobbycity.com
Micro servos for $3.60, standard sized servos for $5, high torque metal geared servos for $9
Brushless motors, 26mm diameter (for 1/10 rc trucks) are just $30, ESCs with reverse are $40

That site is basically a RC warehouse site in China, they receive all of the factory overstocks and sell it to you for cheap. The servos are an especially good deal.

Offline blackheartTopic starter

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #15 on: February 10, 2009, 05:13:42 AM »
The brushless idea got shut down by a member of this forum. They are too expensive for now. I now they sell modified servos, but I wanted motors. I am confused now. I wanted it to be fast.


I don't kow. I will see!
I'm out of ideas!

Offline Admin

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #16 on: February 10, 2009, 11:56:05 PM »
Define 'fast' ;D

There is also the option of brushed motors, too.

You can also make your robot twice as fast (in theory) by doubling the wheel diameter. Just an option . . .

Offline blackheartTopic starter

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #17 on: February 11, 2009, 03:49:21 AM »
Definition of fast in my point of view: Something that is gonna be able to go as fast as a walmart $30 rc car. The servos are very slow. Just in case you are gonna ask me to define slow, here is what I mean by slow.


I already have many brushed motors from an airplane, but the motor driver is expensive. The servos are cheap..The hitec ones. I don't know. I am confused.
I'm out of ideas!

Offline Admin

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Re: Motors and servos! Adv. and Drawbacks!
« Reply #18 on: February 11, 2009, 04:03:43 AM »
By define, I mean objectively. An actual number, say 10 miles per hour. Fast for a snail is slow for a fox.

The motor alone doesn't define speed. Put a 2 foot diameter wheel on a high-speed servo, and it can go pretty darn fast.

I recommend using this so you can calculate and not just guess :P
http://www.societyofrobots.com/RMF_calculator.shtml

 


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