dc motor voltage

[tipipliou]

hi
when we say a : 12V dc motor,or 24 dc motor,we mean the maximum voltage,don't we?
i belive i can use a 24 V motor with a 12 v  power supply
I mean ,even if i use a 24 V power supply,i'll drive the motor with PWM  ,so by using 12V power supply voltage,i could only reach half motor capacities (velocity ,torque),but I believe it will work
am I right?? will it work?
the problem is that i can't afford a 24 V power supply
and i really want to buy this motor : http://www.robotmarketplace.com/products/ML-52-53.html
and if you can show an equivalent 12v dc motor (strong enough ,geared + encoder) ,i would be pleased
thanks
PS: sorry for english mistakes

[knossos]

I'm still new to the engineering and design aspects, so I would defer to anyone with more experience, but my two cents worth:

Motors do have a minimum operating voltage, and operating this as a 12v motor, if it works, would result in greatly reduced capability. Considering the cost of the motors ($120 ea) i would consider looking for another option, you wouldn't be getting your money's worth.  If you do want to go with those motors I'm sure you're aware that you can connect to 12v batteries in series to create a 24v power supply.  I assume your power source for your motors is unregulated, so it should be a fairly easy task.

Anyone feel free to correct me if I'm wrong here.

[tipipliou]

thanks for your answer,i think the best thing i can do is looking for a 12 v motor
thanks

[amando96]

He does have a point, you wouldn't buy a ferrari to cruise at 40kph round town would you?

I advise you to look around for portable electric drills, they have a strong ass motor, and are cheap.

used two in my AATV project, link in signature.

[tipipliou]

portable electric drills look great
can you tell me more about their control system ?
thanks :

[knossos]

This should give you some info on how to do it:

http://www.wa4dsy.net/robot/drill-motor-hack

The only difference from a geared motor I am aware of using a drill motor (besides disassembly of course) is that most drills have a torque limiter.  Other than that they are a standard planetary gear motor.  The above link talks about how to deal with the torque limiter.  I just quickly skimmed the article above, but if that doesn't give enough info, I know there are at least several others out there.

[tipipliou]

would it be easy to mount an encoder to these motors?

[Soeren]

Hi,

when we say a : 12V dc motor,or 24 dc motor,we mean the maximum voltage,don't we?
i belive i can use a 24 V motor with a 12 v  power supply
I mean ,even if i use a 24 V power supply,i'll drive the motor with PWM  ,so by using 12V power supply voltage,i could only reach half motor capacities (velocity ,torque),but I believe it will work
am I right?? will it work?

24V and 48.3 W that's 2A current draw and an equivalent resistance of 12 Ohm.
Running it at 12V would mean a max. current of 1A and hence 12W
Looking at it as a pure Ohmic load (which it isn't), when you halve the voltage, you also halve the current (depends on motor type and construction though), so the power goes down to 1/4

Try searching the surplus market and you can get a 12V geared motor much cheaper.

the problem is that i can't afford a 24 V power supply
and i really want to buy this motor : http://www.robotmarketplace.com/products/ML-52-53.html

If you cannot afford a 24V battery, then how can you afford that motor? 

and if you can show an equivalent 12v dc motor (strong enough ,geared + encoder) ,i would be pleased

Have you considered what exactly you need (RPM and torque)?

Here's a bit of this and that: http://www.surplustraders.net/a/0184.shtml

[tipipliou]

hi
 
"If you cannot afford a 24V battery, then how can you afford that motor?  "
the asnwer is :i have exactly 240 $ 
but i've already forgot these motors (very bad idea)
i'm very interested in the electric drills motors,but i'm scared that I couldn't mount an encoder on it easily(I've never done it before)
and what encoder to choose?
so if you have information about it,please help
PS: sorry for english mistakes

[knossos]

If you have up to $240 to spend, you have more options than just a drill motor.  As Soeren said:

Have you considered what exactly you need (RPM and torque)?

There are so many options available within your price range, that it would save you a lot of trouble and hassle to find out what you actually need first.  There are some excellent tutorials here on SoR that will give you an idea of how powerful your motor needs to be.  I would start by reading through the tutorials on the mechanics page, particularly this one on dynamics.

[Soeren]

Hi,

the asnwer is :i have exactly 240 $ 

Don't spend it all on motors then (save something for booze and loose women  )

i'm very interested in the electric drills motors,but i'm scared that I couldn't mount an encoder on it easily(I've never done it before)

There's a first for everything and you have this board to pull you through, so don't worry too much 
Encoder discs can be mounted in so many ways and if the motor won't cooperate, you can mount it on a cog wheel (or even use the cogs for counting).

and what encoder to choose?

Let that come second to the motor, there's a lot of possibilities (IR and hall effect springs to mind).

But what about your robot, what does it weigh, how fast does it need to go and how fast would you like it to go?