# Need to choose motor

Hello,

Wondering if I can find some small and fast programmable stepper or something else

so desired size diameter 25 maximum 30mm on width 20mm maximum 30mm, which can provide a sharp turn and speed, make turn to 900° in one direction and then go back to opposite direction to 900° and do all for 1 second or better even faster, so in other words total for both directions 1800° for 1 second there and back

I think it must be bipolar stepper because I need step point on every 180° but not sure about other

Stepper motors are not fast, and rapid steps require high voltages.

Now I found

BDR-33-23 DC Brush Motor

but not sure is that exactly what I want or I’m on the wrong way, maybe you could suggest some models or examples meet my requirements, because I still have not tried any of them in practice, except servo, so first need a proper choice

Can you post a detailed drawing of the actual robot or mechanism? The total weight and all the dimensions, including wheel sizes, are very important.

For the basics on robot design, which include motor torque calculations, see these tutorials societyofrobots.com/robot_tutorial.shtml

of course thank you again

so specific tool for my soft testing, the entire mechanism is composed only of three parts capsule, motor and plastic disc, I added the image below

``````disk: ⌀ 44 mm
width 5 mm
``````

dimension of motor is important because I must put it in capsule with limited dimensions, so size of motor must be:

``````Diameter:  25 or at least ⌀30 mm maximum
Width better 20 mm or at least 40 mm maximum
``````

but but main thing, motor must give me exactly this possibilities, so here is sequence, but first, description what is what, to be clear:

[ul]A. Step … < step point of sequence
B. = +180° < addition of distance from step to step in other words turn on 180°
C. (get this step…) < movement to get actual point from zero and back to zero, except 0° which returns to itself.
D. On first and last steps is shown the same maximal diapason from actual point to most distant point and back to itself - 900° + 900° in total 1800°[/ul]

here is exactly what I want from motor in terms of time/speed and control possibilities:

[ul]
Step -1 = -180° (get this point from 0° -180° and back +180°) from step-1 to step4 + 900° and back - 900°total distance 1800°
Step 0 = 0° (from 0° to 0° in minus -180° and +180°, in plus + 720 and -720°)
Step 1 = +180° (get this step from 0° + 180° and back - 180°)
Step 2 = +180° ( get this step from 0° + 360° and back - 360°)
Step 3 = +180° ( get this step from 0° + 540° and back - 540°)
Step 4 = +180° ( get this step from 0° + 720° and back - 720°) from step4 to step-1 - 900° and back + 900°total distance 1800°[/ul]

so I need possibility of movement from 0 for example to the most distant (point4) what is (+ 720°- 720°) in this case time of this action as any other depends on time of action of this: if I go from last step in this sequence (step4) through the whole steps diapason this way: 4, 3, 2, 1, 0, -1, and back 0, 1, 2, 3, 4. whole this movement (- 900° and back + 900°total distance 1800°) must be equal 1 second or at least 1.5 sec

I’m not sure which motor can give me this speed when it makes movement in opposite direction and control possibilities of course, meets all of these requirements including size, so here I need your help please

I don’t understand the drawing and it still isn’t clear what you want to do.

It is not possible to specify the motor torque until you supply the masses of all the moving components and the exact time required to make a particular motion.

How will this thing be powered and controlled? With a D.C. motor, a shaft encoder is required to specify angular position. I doubt it is possible to buy components which will fit into the limited space.

You must do some reading on force and torque. Please start here: pololu.com/blog/10/force-and-torque

[quote=“Jim Remington”]
I don’t understand the drawing and it still isn’t clear what you want to do.

It is not possible to specify the motor torque until you supply the masses of all the moving components and the exact time required to make a particular motion. [/quote]

Drawing is location of motor with approximate dimensions (because that is actually what is the subject of my question) and disk, which is only one moving component, shown from front or backside same diameter 44 mm and from side 5 mm. mass 53.75 grams

Exact time required to make a particular motion is 1 second as I described it above, ok same again: if I go from last step (step4) through the whole diapason of my steps like this: 4, 3, 2, 1, 0, -1, and back 0, 1, 2, 3, 4. whole this movement (total distance 1800° with direction change point on 900°) must be equal 1 second or at least 1.5 sec

I can contorl it just with arduino and what about how powered is, well depends on what device you advise me, I dont need limited space, need just two things the power on point of change direction and possibility of steps on 180° in both direction, so if motor can do this things, I guess I can limit, bipolar stepper can do all these things, except speed

I need this tool for testing my visual analyze program. disk is not in contact with ether mechanism after motor. On the front side I have characters and symbols on the flat and the curved surface of disk, another one disk must be located on the back side on distance 60mm that’s why size of motor is important. two disks have own sequences of rotation, and both have one axis of rotation, but its not important, because just rotates platform on which they are fixed… the camera is looking at them from different distances and gives me the analysis

Only thing I want from this tool is a rotation possibility as I described it in previous post

OK, that disk is rather light and small, so it won’t require much torque to rotate.

The basic movement is 900 degrees (2.5 revolutions) in 0.5 seconds, if I understand you correctly. That corresponds to 300 rpm. In turn that would be 1000 steps/second, which is possible with small stepper motors at 200 steps/revolution – if you use proper software that accelerates the step rate from 0 to maximum at the beginning, and decelerates back to zero at the end.

The torque required to accelerate a disk of mass 53 gm and the given dimensions, from 0 to 300 rpm in, for example 0.1 seconds, is as follows:

moment of inertia I = (1/2)MR^2 = 13 x 10^-6 kg m^2
torque = I*alpha = 0.004 Nm = 0.6 oz-in

This motor, with 2.5 oz-in of torque, should be sufficient: pololu.com/product/1204

You will need a bipolar stepper driver and probably, a compatible high voltage motor power supply (e.g. 24-36 volts) to get the desired step rate. Disregard the voltage rating of the motor, as it is not important in this case, but make sure to set the current limit properly.

This is not a trivial project no matter how you approach it.

EDIT: corrected calculation of I and torque (use disk radius instead of diameter)

My huge thanks for your help and knowledge sharing Jim!

it’s all I need and more than enough!

Very Happy

[quote=“Jim Remington”]

EDIT: corrected calculation of I and torque (use disk radius instead of diameter)[/quote]

ok got it thanks