Motor Recommendations

Hi all, Thanks to anyone who replied to my previous post, with your help I have managed to determine the values that my motor will work at. I am looking for a dc motor that:
.runs at a maximum of 400rpm
.has a maximum torque of 0.3Nm
.has a power requirement of approx 13 watts

I am not looking for anything fancy, my price range is between £5-£15 per motor. Also, do you recommend buying from Alibaba?

That will be a gearmotor, about 10:1 or 8:1 reduction, in practice. Finding proper specs for a motor
is often an issue with chinese suppliers, esp on eBay "high torque" is meaningless... Go for one
rated 400 or 500rpm and 20W to 25W might be about right - gears are a source of inefficiency, you
may lose 30% or so. Rate the motor generously and it will last longer and run cooler too.

All of the repetitive code like:

    analogWrite(9,100);    // set the motor_1 speed to 100 ;
    digitalWrite(4, HIGH);   
    digitalWrite(5, LOW);  // Set the rotation of motor_1

would be much simpler and less error-prone if put in a function (and then you wouldn't need the comment):

void set_motor_1 (int speed, bool direction)
  analogWrite (9, speed) ;
  digitalWrite (4, direction) ;
  digitalWrite (5, ! direction) ;

or something like that.

Also all of your if-statements in a row might overlap - surely you should be
using if, else if, else if, ... since there should be one action for each circumstance.

With independent if statements several of them might be firing up without you
realizing, which often confuses.

Thanks for the reply, I have looked around many websites and can only find motors with the specs that I need going for between £60-£100. Maybe I am just looking in the wrong places but if I cannot get each motor for any cheaper than £25 then I may have to buy from overseas. Do you know any good European/American suppliers?

Voltage? 5, 12, 24, 3810? :slight_smile:

Voltage? 5, 12, 24, 3810? :slight_smile:
Pololu - 20.4:1 Metal Gearmotor 25Dx50L mm HP 6V

12 is preferable but 24 would be fine

Scroll down the page, they have 12V versions, unfortunately, looks like they are on backorder >:(

Thanks outsider! These motors are perfect in terms of performance and price :slight_smile:

Voltage? 5, 12, 24, 3810? :slight_smile:
Pololu - 20.4:1 Metal Gearmotor 25Dx50L mm HP 6V

Not powerful enough by a huge margin, its a 3W motor. Perhaps you thought the stall
torque was the rated torque?

Some of Pololu's larger motors don't even have a continuous rating - seem to only be "free-run"
and "stall". And they don't give power ratings, and they give torque in quaint old imperial,
altogether rather shocking considering their nice range of motor drivers and controllers!

The spec's you need to see are motor constant, continuous current, rpm, winding voltage, and its good
to have no-load rpm, stall current / torque. A good datasheet for a motor gives graphs
of torque and speed v. loading and safe continous operating regions.

Motor constant can be derived from no-load rpm and winding voltage, or from stall current and torque,
since its V/(rad/s) or equivalently Nm/A

Thanks for the reply, Could you perhaps recommend any motors that fit your description? I've been looking for days and cannot find anything that suits my needs. Those motors that outsider recommended looked perfect for me, which shows how little I know about selecting the correct motor. Do you think that getting the right motor is feasible at my price range?