My scope has a CFZ of 88 and 23mm per turn. so I woudl absolutely need a geared system for direct drive.
I wonder if i could get some quick advice on stepper motors. I am finding it hard to source a planetary geared motor here but have found a spur geared motor with 30:1 reduction.
Hi
I see the rating of the stepper motor as
The motor offers a step angle of 1.8° for precision accuracy, with relatively low voltage and current ratings of 3.6V and 1.2A. The holding torque is 0.26N.m before gearing, while the rotor inertia is 54g.cm2. These features all combine to make an impressive little motor with high power for high torque applications – with great positional accuracy and reliable operating efficiency.
With a rating of 1.2A, then with both coils powered this is 2.4A which exceeds the rating of most stepper driver modules - net result is the possible burnout of the stepper driver module.
You need to look for a 12V geared NEMA which has a current of 700mA or less.
1.6a per coil = blown up controller - even the tmc chips do not support that much current. You need to keep in mind that the stepper motor has 2 coils, and there are times in the step sequence that both coils are ON, meaning 3.2A total. That is a lot of heat to dissipate, as well as being way above the current handling capacity of the stepper chip. And from a protection point of view, the stepper leads/cable represent an inductance, the more current one has to switch, the higher the back emf one has to think about and give extra protection in the circuit to handle that. With the heat dissipation requirements of using 3.2A even for short times, the stepper module will not last long and you may even damage the PCB (assuming you are using a PCB)
You see the rating on the tmc2209 reference
1.7A RMS | 2.5A Peak
That in itself tells me that you should not use it.
So that is not up to driving the stepper motor either, because 3.2A is way way above the max limit.
We do support the BIGTREETECH tmc2209 stepper module only.
The tmc2209 modules from other suppliers like MKS and FYSETC are NOT supported because they handle communications differently. there is no future track at present for supporting other types of TMC stepper modules from other manufacturers.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
My idea is to use an ESP32 and an 8825 driver board like below , I am good with electronics and soldering but getting PC boards made here is a real pain.
I try to avoid micro-stepping.
Each time you micro step you lose power.
By the time you get to 1/16 microstepping you have lost too much power.
It is better to use a geared motor - planetary gears increase torque so even if it is a PG5 or PG14 then you can half step it and not be concerned about lack of torque.
The only other way is using gears. This also increases torque meaning you can also go to half stepping the motor.
So if you took a 200 step motor, half stepped it = 400 steps, then used 3:1 gearing that is gone from 200 steps per rev to 1200 steps per revolution.
When the scope is pointed towards zenith, and you have a filter wheel, imaging camera around 1/2kg, that is where high torque is your friend.
I often say that the most important decision in astronomy is buying the most expensive mount you can afford.
But it applies equally to automating a focuser - the better your stepper motor, the rest becomes easy and trouble free. The very last thing you want is to be arguing with the equipment - so buy the best motor you can get that fits all the requirements, the most important of which is current.
Cheers
Robert
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Hi
My scope has a CFZ of 88 and 23mm per turn. so I woudl absolutely need a geared system for direct drive.
I wonder if i could get some quick advice on stepper motors. I am finding it hard to source a planetary geared motor here but have found a spur geared motor with 30:1 reduction.
https://www.diyelectronics.co.za/store/stepper-motors/480-nema-17-stepper-motor-with-301-gearbox.html
Do you fell this motor will work, from what I can tell the backlash is <3degrees.
Regards
Cliff
Hi
I see the rating of the stepper motor as
The motor offers a step angle of 1.8° for precision accuracy, with relatively low voltage and current ratings of 3.6V and 1.2A. The holding torque is 0.26N.m before gearing, while the rotor inertia is 54g.cm2. These features all combine to make an impressive little motor with high power for high torque applications – with great positional accuracy and reliable operating efficiency.
With a rating of 1.2A, then with both coils powered this is 2.4A which exceeds the rating of most stepper driver modules - net result is the possible burnout of the stepper driver module.
You need to look for a 12V geared NEMA which has a current of 700mA or less.
You did not say what the focal ratio is?
This
https://www.diyelectronics.co.za/store/stepper-motors/479-nema-17-42byghw208.html
is rated at 12V and 0.4A
If you used gears, like a 3:1 gearing this really ups the torque. Even 4:1
If using belt and gears then you can mount this under the focuser which helps with balancing the scope.
If you have a 3d printer you can even print the gears
https://sourceforge.net/projects/arduinoascomfocuserpro2diy/files/3D%20Printed%20Parts/Gears/NEMA/
Last edit: brownrb 2021-05-05
Hi Robert
Thank yo so much for the response and th e time tool up alternatives !!!!
I have three F ratios, over two scopes one with a flattener so my f rations are 7.5
5.9 6.3, see pic for full calculations.
I woudl really like to go direct drive if possible.
What are your thoughts of running the geared motor at 5v, I see the rating is 3ohm's which woudl mean 1.6a per coil. Do you think it woudl work coupled to this driver. https://www.diyelectronics.co.za/store/drivers/2790-tmc2209-v10-stepper-driver-ultraquiet-sensorless-feedback.html
Regards
Cliff
Last edit: Clifford de Wit 2021-05-05
1.6a per coil = blown up controller - even the tmc chips do not support that much current. You need to keep in mind that the stepper motor has 2 coils, and there are times in the step sequence that both coils are ON, meaning 3.2A total. That is a lot of heat to dissipate, as well as being way above the current handling capacity of the stepper chip. And from a protection point of view, the stepper leads/cable represent an inductance, the more current one has to switch, the higher the back emf one has to think about and give extra protection in the circuit to handle that. With the heat dissipation requirements of using 3.2A even for short times, the stepper module will not last long and you may even damage the PCB (assuming you are using a PCB)
You see the rating on the tmc2209 reference
1.7A RMS | 2.5A Peak
That in itself tells me that you should not use it.
So that is not up to driving the stepper motor either, because 3.2A is way way above the max limit.
https://www.omc-stepperonline.com/digital-stepper-driver-10-42a-20-50vdc-for-nema-17-23-24-stepper-motor-dm542t.html?search=stepper%20driver
will drive that motor.
We do support the BIGTREETECH tmc2209 stepper module only.
The tmc2209 modules from other suppliers like MKS and FYSETC are NOT supported because they handle communications differently. there is no future track at present for supporting other types of TMC stepper modules from other manufacturers.
Thanks great point fully understand.
My idea is to use an ESP32 and an 8825 driver board like below , I am good with electronics and soldering but getting PC boards made here is a real pain.
https://www.diyelectronics.co.za/store/stepper-motor-drivers/518-drv8825-stepper-motor-driver-module.html
It is really strange that there are so many of the low resistance steppers available but very few drivers support them, it is odd.
Ok last question do you think it is viable then to use the motor you found in a direct drive configuration using micro stepping .
https://www.diyelectronics.co.za/store/stepper-motors/479-nema-17-42byghw208.html
From the No's I woudl need to go to 1/16 microostep to get 3200 steps per revlution, see table attached.
And again thanks for all the advice !!!!
Cliff
I try to avoid micro-stepping.
Each time you micro step you lose power.
By the time you get to 1/16 microstepping you have lost too much power.
It is better to use a geared motor - planetary gears increase torque so even if it is a PG5 or PG14 then you can half step it and not be concerned about lack of torque.
The only other way is using gears. This also increases torque meaning you can also go to half stepping the motor.
So if you took a 200 step motor, half stepped it = 400 steps, then used 3:1 gearing that is gone from 200 steps per rev to 1200 steps per revolution.
When the scope is pointed towards zenith, and you have a filter wheel, imaging camera around 1/2kg, that is where high torque is your friend.
I often say that the most important decision in astronomy is buying the most expensive mount you can afford.
But it applies equally to automating a focuser - the better your stepper motor, the rest becomes easy and trouble free. The very last thing you want is to be arguing with the equipment - so buy the best motor you can get that fits all the requirements, the most important of which is current.
Cheers
Robert
Great thanks again, appreciate your insight. Will let you know how things turn out.