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Pi and motor controller in same box?
#1
Hi,

I recently aquired an old Autohelm 2000, with the intention of converting it to Pypilot.
However, as can be seen in this picture, it would be optimal if the old controller box could house both the Pi itself with IMU, display, (re-used) buttons and so on, AND the motor controller. 
Is this possible, or bound to fail?

I am thinking that perhaps the motor controller needs a significant separation from the IMU due to potential magnetic interference, and that is why they are typically kept in two separate boxes...

Please let me know your thoughts,

Otto
  Reply
#2
Hey Otto,

I did not get your picture, but I did the exercise myself with a raymarine st2000. I put the IMU on one end and the motor controller on the other end and have not experieced any interference so far. After all, these vendor's do the same thing themselves, don't they.

I documented my conversion in this thread. It's a lot of work to make it fit in!

Cheers,
  Reply
#3
(09-23-2019, 09:04 AM)ironman Wrote: Hey Otto,

I did not get your picture, but I did the exercise myself with a raymarine st2000. I put the IMU on one end and the motor controller on the other end and have not experieced any interference so far. After all, these vendor's do the same thing themselves, don't they.

I documented my conversion in this thread. It's a lot of work to make it fit in!

Cheers,

Hi,

Picture here: http://guldburken.gote.org/maxi999/Autohelm_2000.png
And I've seen your conversion, pretty impressive but you have a lot more separation to work with I think.
But I agree the manufacturers do this themselves, and in my case the compass+the motor controller is indeed inside that box. But this old Autohelm 2000 system is all analogue, so perhaps that makes some kind of difference.
  Reply
#4
(09-23-2019, 09:45 AM)ottow Wrote:
(09-23-2019, 09:04 AM)ironman Wrote: Hey Otto,

I did not get your picture, but I did the exercise myself with a raymarine st2000. I put the IMU on one end and the motor controller on the other end and have not experieced any interference so far. After all, these vendor's do the same thing themselves, don't they.

I documented my conversion in this thread. It's a lot of work to make it fit in!

Cheers,

Hi,

Picture here: http://guldburken.gote.org/maxi999/Autohelm_2000.png
And I've seen your conversion, pretty impressive but you have a lot more separation to work with I think.
But I agree the manufacturers do this themselves, and in my case the compass+the motor controller is indeed inside that box. But this old Autohelm 2000 system is all analogue, so perhaps that makes some kind of difference.

Oh sorry I thought autohelm 2000 was similar to the raymarine 2000, please disregard. Within the distance of that size box I would be concerned about magnetic interference myself.

I think the whole idea of a separate motor controller and compass unit is that the motor controller can be put as close to the motor, to reduce radio interference (AIS/Radio), and the IMU to be put away far from magnetic disturbance. The motor signal is PWM, which is bad with radio; better keep those leads as short as possible.
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#5
From what I have found, there is no proble to uselong power wires from the controller to the motor even though they carry pwm. Let's hear about any interference, but I don't think it's normally an issue.

It is important to keep the compass away from current carrying wires, steel and other ferrous metals, compasses or other magnets, and especially the motor itself since it has magnets and is usually made of steel.
  Reply
#6
(09-24-2019, 09:41 PM)seandepagnier Wrote: From what I have found, there is no proble to uselong power wires from the controller to the motor even though they carry pwm.  Let's hear about any interference, but I don't think it's normally an issue.

It is important to keep the compass away from current carrying wires, steel and other ferrous metals, compasses or other magnets, and especially the motor itself since it has magnets and is usually made of steel.

Sean, the best separation I can get if I put everything into the same box is around 16cm, see pictures here:
http://guldburken.gote.org/maxi999/pypilot/

I really want to try it, and am going to order the hardware from you shortly to start building it unless you think this is a extremely bad idea and that that I should go for 2 separate boxes.
From looking at the pictures on the Wiki it seems to me both the Tinypilot and the motor controller are small and modular enough in design that I should be able to keep the ESC and the IMU at least 16cm away from each other. I essentially plan to keep the IMU in the upper left corner in the picture, and the ESC in the lower right. That should keep the power cables as short as possible, and the drivers as far away as possible from the IMU.
This evidently is enough in the old Autohelm 2000 design, so I hope it will be enough for Pypilot?
I will keep the power supply outside the box though, and just have a 5v outlet in the cockpit dedicated to Pypilot. The power supply can sit behind the outlet panel where where I have lots of space.
  Reply
#7
If the motor is drawing 1 amps, then 2-3 centimeters is sufficient. If you have more current the distance needs to be more. 16cm should be plenty.


Its really easy to test by running "signalk_scope_wx" and plotting the "imu.compass" data. Then just move the motor manually and see if the compass changes, and move the controller closer until you see this effect. Then you will know what distance is needed. You need to do this not on a boat that is turning at anchor...

Even if the controller is too close and does affect the compass.. the autopilot will still work, but less optimal.


Sean
  Reply
#8
Thanks!

In my case, the motor/ram will be at least a meter away so I can't see how that will cause any issues.
What worries me is the motor controller, which I want to put in the same box as the pypilot itself.
If I do this, I can upgrade the old Autohelm 2000 to 2019 standards, which would be pretty much optimal for me.
See pictures in link above.
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