Basys �

[ricardo_lara_gomez]

I need a program to count the turns of a motor, could tell me I need?????????

[hamster]

Although this isn't using a Digilent FPGA board, here is how to drive a low-cost stepper motor and to count the steps taken. It is using a 5V stepper motor, but if you have 12V motor & driver board it may also work for you.

 

http://hamsterworks.co.nz/mediawiki/index.php/Stepper

[JColvin]

Hi ricardo_lara_gomez,

 

Counting the number of complete turns a motor takes will depend on what you have available to you and your application, so I'll need to know a few more things before I can effectively help you.

 

What kind of motor are you using? A DC motor, servo motor, or a stepper motor?

Are you using the motor to go both forwards and backwards? Are you wanting the motor to just go at full speed or a variable speeds?

 

Thanks,

JColvin

[ricardo_lara_gomez]

I have a dc motor. I want to count the turns forward and backward with a pwm vary its speed.

 

thanks for your help jcolvin

[JColvin]

Hi ricardo_lara_gomez,

 

The truthful answer is that there is no "easy" way to count the number of turns accurately on a DC motor because they are not designed to be able to purposefully rotate a specific amount.

 

That being said, what I would consider the easiest would be to determine the approximate maximum rotation speed at its rated voltage from the motors datasheet. After we know that value, we can then calculate the mid-range speeds from pwm pulses of that same rated voltage.

 

For example, if a motor had a rated rotation speed of 125 rpm at 5V, then we could say that if we supplied a 5V pwm signal at a 50% duty cycle (on for half of the time and off for half of the time), this would effectively give us 50% of the rotation speed (62.5 rpm). 

 

We could then use a timer of some sort to measure how long we sent the pwm signal to the DC motor. So, if we took our same 5V motor and gave it a 50% duty cycle pwm signal for 24 seconds, we can calculate how many rotations our might have taken. What we would need to do is take the full 125 rpm times the 50% duty cycle times the amount of time we spent driving the signal.
125 rpm * 50% duty cycle * 40% minutes = 25 rotations

 

As nice as this looks though, this equation is not guaranteed to be accurate. If we have any sort of load on the motor (like having the motor act as a shaft to move a robot) or from the fact that not all motors are exactly the same or from the fact that the motor will not instantly stop spinning the moment the pwm signal is stopped, the amount of full turns our motor actually took may be different than what we calculated. However, the equation we made will give you a good estimate of the total number of turns.

 

Let me know if you have any more questions.

 

Thanks,

JColvin

[ricardo_lara_gomez]

ooo all sounds great, but I have a motor of 12v  as would be the calculation for that engine?

[ricardo_lara_gomez]

but i dont know the specifications of the motor

[JColvin]

Hi ricardo_lara_gomez,

 

The calculation style would essentially stay the same. The key here is knowing what your motors reported speed is at 12V, which you would be able to find in the datasheet for your motor. Once you find that and apply your 12V PWM signal you can use the same equation to figure out the number of turns that your motor took.

 

(full speed rpm at 12V) * (pwm duty cycle %) * (% of minutes that you are applying a pwm signal) = number of full rotations.

 

Again, as not every motor is perfectly accurate and do not stop and start instantly, this equation will not get you the exact number of rotations, but it will pretty close for most purposes.

 

As for the specifications of the motor, I recommend "googling" the number/letter combination that should likely see on the side of your motor in order to find the datasheet for the motor.

 

Let me know if you have any more questions.

 

Thanks,

JColvin

[ricardo_lara_gomez]

I understand, but as would make the code in vhdl?

[ricardo_lara_gomez]

I have another question could see the speed in displays

[hamster]

I hope everybody here realises that the staff at Digilent can only really be expected to offer help on how to use thier products, not actually do any design work for you.

I doubt you would walk into a computer shop and ask them to do programming assignments - likewise I think you are being unreasonable to expect them to answer you request as it is presented.

Perhaps if you request was "I want to drive a standard 540 size hobby motor, rated at 8V 4A, can you recommend which PMOD I should use?" It would be reasonable to expect an answer.

Likewise if it was "I want to use an optical sensor to measure motor sapped at up to 12,000 rpm, will sense on X actually work for me?" You would get an answer.

Both questions show that you know your problem, you have given it a at least a little thought, and you are asking Digilent about their products.

So what was you question again?

[ricardo_lara_gomez]

then could help me, telling me that I can buy to build my project?

[ricardo_lara_gomez]

what kind of xilinx sensor I need, or what kind of pmod need