Can DC Motors have the same circuit as AC Motors?

Thread Starter

sidcircuit

Joined Apr 26, 2016
6
Hello,
I have a raspberry Pi and as a school project I am building a robot with it. So far everything has gone well but now I've realized that my DC motors are not strong enough. I have one motor on each side and for steering I had planed just to accelerate one side. But since my DC motors are not strong enough I thought I could just buy AC motors and just replace them. Well I thought that since they both have two pins and work about the same way I can just replace them and even keep the programs as I have them now. Is that doable? I've followed this tutorial by building the circuit: http://computers.tutsplus.com/tutorials/controlling-dc-motors-using-python-with-a-raspberry-pi--cms-20051

Thank you for your acknowledgements.

Friendly regards
Sidney
 

Marley

Joined Apr 4, 2016
311
Having a brief look at your link, only DC motors will work here.
This is because the direction of the motors is controlled by reversing the voltage.

Not quite sure what you mean by AC motor. Can you post some details?
 

Thread Starter

sidcircuit

Joined Apr 26, 2016
6
Having a brief look at your link, only DC motors will work here.
This is because the direction of the motors is controlled by reversing the voltage.

Not quite sure what you mean by AC motor. Can you post some details?
I have installed everything already with the DC motors and they work fine but they are not enough for the robot I want to build. With AC Motors I mean alternative current motors, the way I see it they work the same way as DC motors, just that I can adjust the voltage that goes through it and by that make it stronger. And for reverse Voltage don't you think that it would also work for alternative current motors?
Thanks for the reply
Sidcircuit
 

Thread Starter

sidcircuit

Joined Apr 26, 2016
6
I am getting the strong impression you know very little about how each type of motor and electrical current works.:(
No I know how they work and they seem quite similar to me so I'm asking if I can just exchange them. Since they both work the same way I don't think there should be any problems.

Thanks for the reply
Sidcircuit
 

GopherT

Joined Nov 23, 2012
8,012
It is not a question of your motors being "string" enough, it is a question of gearing in most cases. Robots generally don't have enough room for much user-designed gears or pulleys to convert a high-speed/low torque motor to decrease speed and increase torque. Check your motor specs, it you are trying to connect the motor directly to the axle of the wheel, you need some type of gearbox to get the torque you need.

If the wheels spin very fast when held in the air but stop as soon as you set it on the ground, the bot needs more torque (from a gearbox, not from an AC motor). Here are some examples.

http://www.robotshop.com/en/gear-motors.html
 

Alec_t

Joined Sep 17, 2013
10,592
AC motors are totally unsuitable. You need more powerful DC motors, or else use the present motors with more reduction gearing to give higher torque (albeit lower speed).
 

Thread Starter

sidcircuit

Joined Apr 26, 2016
6
post specs/part numbers on the motor you have?
Just get a more powerful DC motor..
Thank you but I think I'ce firured a way out how to do it more powerful. I will just use bigger tooth-wheels.
Thank you anyway for your help. I realize now that an AC motor is about 250 bucks and usually quite big so I would've never bought one anyway.
Sidcircuit
 

tcmtech

Joined Nov 4, 2013
2,868
No I know how they work and they seem quite similar to me so I'm asking if I can just exchange them. Since they both work the same way I don't think there should be any problems.

Thanks for the reply
Sidcircuit
That statement right there pretty much shows you have no real understandings of how either works with its related power source. :oops:

Ter are three main types of electric motors.

DC motors.

Universal motors.

AC motors.

The universal ones are the only ones that can run on both types of electrical current.
 

Papabravo

Joined Feb 24, 2006
12,693
To add some final points about DC motors:
  1. Torque is proportional to current and inversely proportional to speed.
  2. The rise time of the current in the motor coils is proportional to the applied voltage and inversely proportional to the L/R time constant.
 

cuyler1

Joined May 27, 2015
15
Maybe the young person is speaking of ac motors as brushless rc aircraft are basic requirements today. I grew up from nitro powered rc planes to the advent of dc motors. now brushless ac motors which require an ESC to convert dc to ac for operation.
 

GopherT

Joined Nov 23, 2012
8,012
Maybe the young person is speaking of ac motors as brushless rc aircraft are basic requirements today. I grew up from nitro powered rc planes to the advent of dc motors. now brushless ac motors which require an ESC to convert dc to ac for operation.
Perhaps but new entrants to the robotics world want to put two 8000 rpm motors on a 1kg box of parts and put a wheel on the motor shafts and expect the "robot" to zoom all over the place. Instead, it sits there like a 1kg box of parts with two motors on it. Those motors just cannot supply enough torque to directly turn a 2" diameter wheel with out any reduction gearing. Lets hope the OP comes back with a story describing his success.
 

cuyler1

Joined May 27, 2015
15
i forgot to mention my fathers quote from 1965 "you can gear a washing machine motor to pull a freight train" and i was just thinking small.check out internationals hybrid truck models down to honda hybrids all powered by a
 

chanelok

Joined Apr 2, 2016
1
Hey Guys, I read the replies and they seem a bit abrupt. No one really seemed to want to help with understanding the difference between the AC and DC motors. To his credit, tcmtech did mention that there are three general types. I have not looked at the circuit tutorial being used by sidcircuit, nor do I really have a feel for the physical size of his project. I suspect that the DC motors he is using are PM. If they were wound rotor, the field strength could be varied to change torque. Also, as was posted, DC motors are very easily reversed. With the advent of IGBT controllers, the same is true for AC motors but I have no clue as to the budget for this project. The variable frequency controllers have an abundance of programming capabilities about which some of you may be interested in learning. I use them extensively in my home machine shop.
 
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