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ankur1986
02-15-2008, 09:25 PM
Hi , I have 3 stepper motors which run on 12V power supply .
I have a 0-15V 2 A transformer which is connected to a 12V regulator IC 7812 .
Now my problem is that 7812 max current rating is around 1.2 or 1A and one of my motors is drawing up way too much current . arnd 1.5-1.8A.

Now coz of this the 7812 IC is getting very hot and im afraid it will blow up.

I wanted to know whether i can remove that 7812 IC and directly supply 15V to my motors ?
what will happen if i supply 15V to my 12V motors?

debu
02-16-2008, 12:07 AM
@ankur1986: Probably Nothing. But, dont take my word for it. I suggest you reffer to the datasheet for your steppers. Normally the coils in stepper motors can do 12-24V without trouble, but again, I'm generalizing, don't blame me if your stepper coil burns out.

Regards,

Debu :)

ankur1986
02-16-2008, 12:16 AM
Thnx debu for ur reply .
I am contructing a robotic arm that can pick n place objects.
i have used 3 motors : base , shoulder , gripper.
Here are my motor specs :
Base :
12V
0.4A
Torque : 5.5Kg

Shoulder :
12V
1.5A
Torque : 3.3 Kg

Gripper :
12V
0.4A
Torque : 1-2 Kg

Is it possible to figure out from this info whether the motors could run at 15V ?
Also will there be changes in the step angle and speed of rotation for the motors ? Will it affect the torque of the motors ?
Torque is very crucial for my project.

allbits
02-16-2008, 02:46 AM
Steppers are wrong choice for a robotic arm. Use Servos. Steppers cant give you enough torque, you can take it from me.


12V
0.4A
Torque : 5.5Kg

Not quite sure about this. 5.5kg @ 400mA??
The simple rule is, if you need to lift more weight, you need to give more energy. The energy is your current. I dont think you can run a load at 4-5kg @400mA, especially if it is a stepper.

Anyway, you can readily give 15V, all you have to do is switch it. But again, you can expect a lot of slips, and less efficiency, when you use steppers for arms. If possible, use servo motors.

ankur1986
02-16-2008, 08:41 AM
thnx for ur response. Well i could have gone for servo's if there was no constrain on my budget .
Also i am not exactly trying to replicate a robotic arm. What i am tying to do is build a prototype that will be able to perform yaw and pitch motion and the gripper will be used to lift object.
I assembled everything and ran the stepper which is supposedly 5Kg torque and it was able to take the load of the complete assembly .
Also precision movement is not required again as it is a prototype. Even the object that the robot will pick up will be decided by me .

Lets hope if everything works out. AS of now i am racking my brains in connecting 2 L923D's in parallel to obtain more current.

docel
02-17-2008, 12:05 AM
Whats happening???
I just can't believe this!!

400ma + stepper + 5.5kg torque ????? 8O

Man !! What do they teach you in College??

ankur1986
02-17-2008, 05:54 PM
Whats happening???
I just can't believe this!!

400ma + stepper + 5.5kg torque ????? 8O

Man !! What do they teach you in College??


Well they teach us nothing in college. I am a final year post grad student doing MSc IT so obviously electronics is not my cup of cake. Inspite of that i have taken up a robotics project and have been kicking myself for doing so [:)] ..
Now obviously the software thingy is totally done . Only prob is with the electronic part of it. Its a totally self study and self sponsored project.
So the specs for the 5Kg motor is as given by the shop keeper [:d]...
May be its less i guess 3-4 Kg and my complete assembly is arnd 2-2.5 Kg so it is able to carry the weight.
I will probably learn how to use a multimeter tomorrow and test the motor current. [:d]

allbits
02-17-2008, 09:10 PM
The torque in the spec, is normally the stall torque. And normally in Kgcm.

It simple means, You can barely lift/move an x Kg load placed @ 1cm from shaft.

If the load is at 2 cm, you need at least double of the rated torque!!
Now imagine if its at 5cm from the shaft!!

I find it very difficult to digest when people say they had very successful construction of arms with steppers (not pointing at the OP). Its fairly difficult to make a 15cm long arm with a standard servo - rating at 4-5 Kgcm, which can lift 50 grams. @3DOF. and remember - servos weight only 30-50 grams.
And now how on earth is it possible to make it with steppers??

The cheaper, and more efficient method will be to use simple DC geared motors. They have far better torque/weight ratio, and are cheap!!!
Just forget the feedback (however, steppers also have no feedback!!)