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1
DIY AstroEQ / Re: Astoeq tracking pause every seconds.
« on: October 05, 2015, 13:42:50 »
Hello Doramason,
Change the motor is the best solution if you want keep the 1/32 microstepping. if I had to change my motors Iwill choose the: http://www.omc-stepperonline.com/nema-14-bipolar-stepper-75v-05a-23ncm326ozin-14hs170504s-p-94.html , but the inductance is very high (26mh)... I'm not electronicien, and i don't know if it is really critical. i think that limit the maximum speed. if an electronicien could confirm this...
For the potentiometer, it jump 0.38V to 2.5V on clockwise or counterclockwise? If it's on clockwise turn it's not good... if it's on counterclockwise it's just a "cleat" is brocken and it's nothing.
Change the motor is the best solution if you want keep the 1/32 microstepping. if I had to change my motors Iwill choose the: http://www.omc-stepperonline.com/nema-14-bipolar-stepper-75v-05a-23ncm326ozin-14hs170504s-p-94.html , but the inductance is very high (26mh)... I'm not electronicien, and i don't know if it is really critical. i think that limit the maximum speed. if an electronicien could confirm this...
For the potentiometer, it jump 0.38V to 2.5V on clockwise or counterclockwise? If it's on clockwise turn it's not good... if it's on counterclockwise it's just a "cleat" is brocken and it's nothing.
2
DIY AstroEQ / Re: Astoeq tracking pause every seconds.
« on: October 05, 2015, 12:11:49 »
Hello Doramason.
For your test with the nema14 4V 0.8A 5ohm, the minimum current with the drv8825 is: 1.44V/5ohm= 0.288A.
You have tested with:
- In 1/16, the second microstep is 10%, so 0.8Ax0.1=0.08A or 0.08<0.288 it's not good.
- In 1/8, the second microstep is 20%, so 0.8Ax0.2=0.16A or 0.16<0.288 it's not good.
- In 1/4, the second microstep is 38%, so 0.8x0.38=0.304A or 0.304>0.288 it' good.
Your test confirm what i saw in the datasheet.
For 9V power supply:
- The minimum voltage with drv8825: 9V*0.12=1.08V
- The minimum current with your motor (nema 14 4V 0.8A 5ohm): 1.08/5=0.216A
So for :
- In 1/32, the second microstep is 5%, so 0.8x0.05=0.04A or 0.04<0.216 it's not good.
- In 1/16, the second microstep is 10%, so 0.8Ax0.1=0.08A or 0.08<0.216 it's not good.
- In 1/8, the second microstep is 20%, so 0.8Ax0.2=0.16A or 0.16<0.216 it's not good.
- In 1/4, the second microstep is 38%, so 0.8x0.38=0.304A or 0.304>0.216 it's good.
So no change with 9V power supply.
For the potentiometer it' nothing just be careful when you set the vref...
For the hot nema17, set the vref to something smaller until the motor temperature is good.
For your test with the nema14 4V 0.8A 5ohm, the minimum current with the drv8825 is: 1.44V/5ohm= 0.288A.
You have tested with:
- In 1/16, the second microstep is 10%, so 0.8Ax0.1=0.08A or 0.08<0.288 it's not good.
- In 1/8, the second microstep is 20%, so 0.8Ax0.2=0.16A or 0.16<0.288 it's not good.
- In 1/4, the second microstep is 38%, so 0.8x0.38=0.304A or 0.304>0.288 it' good.
Your test confirm what i saw in the datasheet.
For 9V power supply:
- The minimum voltage with drv8825: 9V*0.12=1.08V
- The minimum current with your motor (nema 14 4V 0.8A 5ohm): 1.08/5=0.216A
So for :
- In 1/32, the second microstep is 5%, so 0.8x0.05=0.04A or 0.04<0.216 it's not good.
- In 1/16, the second microstep is 10%, so 0.8Ax0.1=0.08A or 0.08<0.216 it's not good.
- In 1/8, the second microstep is 20%, so 0.8Ax0.2=0.16A or 0.16<0.216 it's not good.
- In 1/4, the second microstep is 38%, so 0.8x0.38=0.304A or 0.304>0.216 it's good.
So no change with 9V power supply.
For the potentiometer it' nothing just be careful when you set the vref...
For the hot nema17, set the vref to something smaller until the motor temperature is good.
3
DIY AstroEQ / Re: Astoeq tracking pause every seconds.
« on: October 05, 2015, 11:25:55 »
To compare with the A4988, the blanking time is 1µs minimum and the dead time is 30µs so 3.33% of power supply.
4
DIY AstroEQ / Re: Astoeq tracking pause every seconds.
« on: October 05, 2015, 11:04:59 »
Hello,
The 12% is in the datasheet, but not clearly. The minimum blanking time is set at 4µs and the dead time is 33µs(30Khz). So 12% of the power supply (4µs on and 29µs off).
I have a 1/16 microsteps it's a little better. I have tried with the 9.2V power supply, it's little better.
On the web the problem is know, try a search on google with: DRV8825 low motor voltage.
But i don't departs the possibility of my DRV8825 isn't great quality... especially after the post of Doramason...
The 12% is in the datasheet, but not clearly. The minimum blanking time is set at 4µs and the dead time is 33µs(30Khz). So 12% of the power supply (4µs on and 29µs off).
I have a 1/16 microsteps it's a little better. I have tried with the 9.2V power supply, it's little better.
On the web the problem is know, try a search on google with: DRV8825 low motor voltage.
But i don't departs the possibility of my DRV8825 isn't great quality... especially after the post of Doramason...
5
DIY AstroEQ / Re: Astoeq tracking pause every seconds.
« on: October 04, 2015, 10:42:12 »
Hello Doramason, i missed your post. For the " jumps forward like a clock ticking", yes it's the same for me. Are you sure that the Ra motor work fine? Following a star without autoguidage, it's ok? If yes, I ask myself questions about my problem with DRV8825... For your problem I would advise you to change the DRV8825 by A4988. You lose the 1/32 microstepping, but it's cheaper than changing the motors...
Cordially, Cedric.
Cordially, Cedric.
6
DIY AstroEQ / Re: Astoeq tracking pause every seconds.
« on: October 03, 2015, 20:03:17 »
hello
Today i received my A4988. They work fine with my motors!!!
Cordially, Cedric.
Today i received my A4988. They work fine with my motors!!!
Cordially, Cedric.
7
DIY AstroEQ / Re: Astoeq tracking pause every seconds.
« on: October 02, 2015, 19:28:40 »
Hello
For my lost microstep. My motors are 3.6V 1.2A 3ohm.
On DRV8825 the PWM frequency (for current control) is 30Khz and the blank time is 4µs (time to the driver "measure" the current).
1 period of 30Khz is: 1/30000hz=33µs and 4µs is 12% of 33µs.
I powered my motors with 12V. 12% of 12V is 1.44V.
So with my motor the current with 1.44V and 3ohm coil resistance that is 1.44/3=0.48A.
In 1/32 microstep at the second microstep the driver limit the current at 5% of the motor current so for me 1.2A*0.05=0.06A, it's not possible for the DRV8825 with my motor.
At ninth microstep the driver limit the current at 38% of the motor current, for my motor that is 0.456A;
So i lose 9 microstep/32 microstep...
I do not know if it is fully correct, what do you think?
For my lost microstep. My motors are 3.6V 1.2A 3ohm.
On DRV8825 the PWM frequency (for current control) is 30Khz and the blank time is 4µs (time to the driver "measure" the current).
1 period of 30Khz is: 1/30000hz=33µs and 4µs is 12% of 33µs.
I powered my motors with 12V. 12% of 12V is 1.44V.
So with my motor the current with 1.44V and 3ohm coil resistance that is 1.44/3=0.48A.
In 1/32 microstep at the second microstep the driver limit the current at 5% of the motor current so for me 1.2A*0.05=0.06A, it's not possible for the DRV8825 with my motor.
At ninth microstep the driver limit the current at 38% of the motor current, for my motor that is 0.456A;
So i lose 9 microstep/32 microstep...
I do not know if it is fully correct, what do you think?
8
DIY AstroEQ / Re: Astoeq tracking pause every seconds.
« on: September 30, 2015, 19:54:23 »
Hello,
My drivers are the clones of drv8825. I don't think if the quality is at issue, because the problem explanation lies is in the drv8825 datasheet. I will anyway check the curent sens resistor value because when i set the vref at 0.6V for 1.2A the motors are a little hot.
My drivers are the clones of drv8825. I don't think if the quality is at issue, because the problem explanation lies is in the drv8825 datasheet. I will anyway check the curent sens resistor value because when i set the vref at 0.6V for 1.2A the motors are a little hot.
9
DIY AstroEQ / Re: Astoeq tracking pause every seconds.
« on: September 30, 2015, 11:04:31 »
Hello The_Geth.
With my old test motor the fast decay mode solve the problem. With my final motors (nema14 3.6V 1.2A) the fast decay mode don't solve the problem... I try with the soltion with the diodes ( in link of The_Geth post), it work fine, but the diodes are very hot... i want to try with the a4988 if the problem persists. when i receive it i post the result.
Has anyone have a config work well with the drv8825 in 1/32 microstep, can you tell what motor you use? i think the problem appears when the voltage motor is under 5V...
Cordially, Cedric.
With my old test motor the fast decay mode solve the problem. With my final motors (nema14 3.6V 1.2A) the fast decay mode don't solve the problem... I try with the soltion with the diodes ( in link of The_Geth post), it work fine, but the diodes are very hot... i want to try with the a4988 if the problem persists. when i receive it i post the result.
Has anyone have a config work well with the drv8825 in 1/32 microstep, can you tell what motor you use? i think the problem appears when the voltage motor is under 5V...
Cordially, Cedric.
10
DIY AstroEQ / Re: Astoeq tracking pause every seconds.
« on: August 29, 2015, 09:45:54 »
Hello, my problem is solved by switching the 8825 on fast decay mode. I applied the method on this site: http://reprap.harleystudio.co.za/tag/pololu-drv8825/ . Thank you for all!
11
DIY AstroEQ / Re: Astoeq tracking pause every seconds.
« on: August 22, 2015, 11:55:27 »
Hello, thank you for the rapid response. My motor is an 4.1V, 1.1A. I have set the vRef to 0.5V, the problem is the same and the motor is very hot about 5min... My drv88225 have not a vRef "via hole", I set the vRef with the center pin of the potentiometer.
12
DIY AstroEQ / Astoeq tracking pause every seconds.
« on: August 21, 2015, 23:36:41 »
Hello.
Thank you for your project! I made an Astroeq 2560 with drv8825. My setup is 1.8 stepper angle, 1:3 motor gear ration, 1:102 worm gear ratio, 32 micro step. In goto mode it work fine. But in tracking mode, the motor make a short pause every second. What can do this?
Sorry for my poor English... And thank you!
Thank you for your project! I made an Astroeq 2560 with drv8825. My setup is 1.8 stepper angle, 1:3 motor gear ration, 1:102 worm gear ratio, 32 micro step. In goto mode it work fine. But in tracking mode, the motor make a short pause every second. What can do this?
Sorry for my poor English... And thank you!
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