SatNOGS rotator v3.1- rotary encoders?

Hello,
I want build myself my first satNOGS rotator, but I came up with a question that I can not figure out.
I am planning on using NEMA 17 stepper motors. Do I still have to use rotary encoders? Or are these optional for the stepper motor version?
Thanks in advance!

Hi crosswalkersam,
The rotary encoders are optional when using the stepper motor version.
The endstop switches do a very good job alone.
You will have lots more questions, don’t hesitate to ask.
Regards
Steve VK4SMC

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Thank you, in that case I will skip them.
I actually have another question: How do I prevent the lower mast from “slipping” through the bottom construction? As far as I understand it, the whole weight of the rotator is on the gears and 4 set screws, is that right?

Hi,
The rotator is supported by 4 set screws on the shaft collar(shaft gear), plus 4 screws in the encoder gear, which you need to include even if not using encoder.
This, with a very snug fit through the bearings, supports the rotator.
Hope that makes sense.
Steve

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I might add some threadlock to secure the shaft to the ball bearing.
Just for some extra riggidity.I have two more questions:

  1. Is the rotator suitable for a permanent installation? I am a bit concerned that some 3D printed parts might deform if it sits in the sun for too long.
  2. How many Amps should the PSU have? I have two options: 15V@4A or 12V@17A.

Sam

Hi Sam,
I’ve just remembered that on the shaft I drilled into (not through) the aluminum just enough so the setscrews had a bit of grip. I did this after a few months when I noticed it was a bit too loose.
As for
1.
I have my rotator enclosed in a aluminum box made from very thin (1mm?) sheet,
Purchased from hardware store.
This stuff is very easy to bend and cut, but robust enough to stop the elements.
It also helps stop RFI from the stepper motors interfering with the RTL-SDR or the RPi’s wifi, which are both in separate plastic enclosures.
It’s all been outside for WELL over a year with zero plastic problems.
2.
Just had a look a current draw with a reading from my solar regulator’s load (Rotator) -
0.5A when steppers moving and 0.2A when idle at 12V (I would only take this as rough guide)
My setup is 2 x 100 AH 12V SLA deep cycle Batteries in parallel.
This is charged by two 160W solar panels through a proper MPPT solar regulator.
May seem like overkill but we often get days of rain/overcast conditions in a row and since installed hasn’t needed a top up charge for over 6 months.
Both of your power supplies will be able to to handle the load of the rotator.
I would choose the one with less RFI, VHF is the worst for me.
Also if you are using the Satnogs Rotator Controller remember you will need to change a few components to cater for the lower voltages.
This is getting too long winded now, I hope it all makes sense.
Regards
Steve

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Hello Steve,

thanks for the help, I appreciate it.
I used PETG instead of ABS, but I dont think thats a problem. I just finished all the 3D printed parts.
The 2020 should arrive next weekend, and then I will build it.
I used the Arduino Uno + CNC shield option which supports 12-36V. The Arduino is powered through the USB, so higher voltages should be fine I guess.

I was planning on using it for HRPT with a 2.4GHz Grid antenna. I reckon it should be possible if I use a counterweight? But I am a bit concerned how it will behave during e.g. a storm. Do you think it will hold up?

Sam

Hi Sam,
Counterweights are a must with any antenna on this rotator.
Storms, Mine have been through several, rotator generally fine.
As for my homebrew antenna not so fine.
Can’t stop nature.
Good luck with the build.
Keep us updated.
Steve

Hi Steve,

I just completed the assembly. However, the motors do not work.
They go forward 1/4 rotation, backward 1/4 rotation and then just stop and apply holding torque.
If I use a different motor (same model, just nothing mounted to it) it works fine.
I am guessing the motors do nat have enough torque, but usually that would result in lost steps and not a backwards rotation. Or am I mistaken?
Any ideas?

Sam

EDIT: Turns out I am just very stupid. I put the End-Stop wires into the same CAT-7 Wires as the Motorwires. So as soon as the motors start, the motor-current induces a voltage into the End-Stop wires which makes the arduino think the end-stop is reached. I will add some pull-down resistors to fix this.

Hi Sam,
Glad you discovered the cause.
Never would have discovered that for a long time.
My first guess was going to be stepper motor drivers not set correctly.
You’re almost there.
Steve

Okay, its homing correctly now. But it does not have any torque, so I cant actually attach anything to it without the motors stalling.
I set the drivers to 1.7A (since I use 1.7A Motors), but I could increase it to 2A if necessary.
Any tipps on how to reduce the worm gear friction? I turned it with a drill for ca. 5 Minutes at full speed, but its still not as freely moving as I would like it to be.

Sam

EDIT: And again, I found the error myself. My A4988 do not have the standard 0.05 Ohm current resistor, but 0.1 Ohm resistors. So when I thought that I set it to 1.7A, it really was delivering 0.85A only. Now she’s rolling :). I’ll report back once it is set up on the roof.

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Hi Sam,
Great news.
Before you install on roof, I would setup with easy access for a few passes to test first.
Well done.
Steve

Jup. I have a pretty flat roof, so I can access the rotor whenever i need to.
The drivers get fairly warm (ca. 80°C), can I lower the temperture by bumping up the VMOT voltage?

Sam