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Is this motor suitable ...
#1
I have been researching building an autopilot for my old steel sailboat for a long time, and am finally at the stage where I am gathering the bits.  I am moored at a rundown site of an old shipyard/chandlery and I went up to one of the buildings to grab a spool of network cable I had stashed up there from when I set up a wifi network for the docks, and as I'm walking through the building sitting amongst all the junk on the floor is this motor, apparently a 12V AC blower motor (pm354). 
   

   

I tried to look up the specs on stall current and draw but there did not seem to be that info on the automotive sites I found the motor listed on. Is anyone familiar with this type of motor and if it will work well. When hooked up to 12V it spins quite well in both directions.

That leads to my next question, is should I order the basic motor controller for this motor, or should I wait to pull the trigger until Sean releases the new heavier duty controller. I plan to be driving the inside helm steering wheel (hooked up to a hydraulic steering system).  I really don't want to have to tap a new pump into the old 2 line wagner system then have to figure out how to bleed it all.

   

This is all for this wonderful boat that I call home on the West Coast of Canada, named the Scallywag.

   

Thanks for any info that may help,
Seamus
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#2
If you intend to use this motor you will have to gear it down to spin the wheel. The windshield wiper motors typically use a 4:1 or 6:1 reduction to the wheel, but the wiper motor also has an internal worm gear of 30:1 or 50:1 ratio. This way it takes 4-6 seconds to rotate the wheel one full turn. It also depends on your wheel how much force it needs.

So this motor you have found, I would try to determine the rpm so you can know the reduction needed and figure out how you are going to achieve a 10-20 rpm high torque output from it. It may require 2 or 3 stages of belts, chain or gears. In the meantime you could measure the current draw without any load using an ammeter. You really needed to take this measurement spinning the wheel, but if the unloaded current is only 1 amp or less, then the regular controller can handle it if you gear it down sufficiently, but you may have slow reaction times, it's really difficult to say without knowing the rudder shape, and it will depend on conditions, most difficult is high winds. If unloaded it's less than 2 amps, it's probably ok, more than 2 amps and I would not recommend the regular controller. Again, you should ideally make the measurements while it's driving the wheel, and for this, if it's below 5 amps (at dock) it should be ok.

Otherwise, high power controller... I need to do more tests like shorting rudder feedback out and driving 30 amps for a while to see what happens... it has 4x the current ability of the regular controller and also supports 12 or 24 volts.
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#3
(2021-01-09, 03:23 AM)seandepagnier Wrote: If you intend to use this motor you will have to gear it down to spin the wheel.   The windshield wiper motors typically use a 4:1 or 6:1 reduction to the wheel, but the wiper motor also has an internal worm gear of 30:1 or 50:1 ratio.   This way it takes 4-6 seconds to rotate the wheel one full turn.   It also depends on your wheel how much force it needs.

So this motor you have found, I would try to determine the rpm so you can know the reduction needed and figure out how you are going to achieve a 10-20 rpm high torque output from it.   It may require 2 or 3 stages of belts, chain or gears.   In the meantime you could measure the current draw without any load using an ammeter.  You really needed to take this measurement spinning the wheel, but if the unloaded current is only 1 amp or less, then the regular controller can handle it if you gear it down sufficiently, but you may have slow reaction times, it's really difficult to say without knowing the rudder shape, and it will depend on conditions, most difficult is high winds.    If unloaded it's  less than 2 amps, it's probably ok, more than 2 amps and I would not recommend the regular controller.    Again, you should ideally make the measurements while it's driving the wheel, and for this, if it's below 5 amps (at dock) it should be ok.

Otherwise, high power controller...  I need to do more tests like shorting rudder feedback out and driving 30 amps for a while to see what happens...   it has 4x the current ability of the regular controller and also supports 12 or 24 volts.

After a bit of testing with my multimeter it seems to draw 1.4-1.5amps spinning with no load. Fingers adding friction brought it up to about 5 amps before my fingers couldn't stand it.  When I hold the spindle with a pair of pliers to completely stop it and briefly connect power it shows about 11amps.

Google netted me the info that they are specced to run at 4200rpm.  How much reduction would you reccomend? One idea I had was attaching a 10 tooth pulley to the motor and a 120 tooth pulley to the center cap of my wheel, with a continuous MXL belt, which I can relatively easily order from robotics stores online. Would this potentially be enough reduction?

The other idea if this motor isn't suitable is could you point me to a part number of a good windshield wiper motor thats not too hard/expensive to track down at the local to me auto shops.

As for rudder shape a picture speaks a thousand words:
   


Thanks again,
Seamus
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#4
After a bit of testing with my multimeter it seems to draw 1.4-1.5amps spinning with no load. Fingers adding friction brought it up to about 5 amps before my fingers couldn't stand it.  When I hold the spindle with a pair of pliers to completely stop it and briefly connect power it shows about 11amps.

[/quote]
It is probably ok with the standard controller for that motor then.

Quote:Google netted me the info that they are specced to run at 4200rpm.  How much reduction would you reccomend? One idea I had was attaching a 10 tooth pulley to the motor and a 120 tooth pulley to the center cap of my wheel, with a continuous MXL belt, which I can relatively easily order from robotics stores online. Would this potentially be enough reduction?
If you have two stages of that. This would give you 144:1 reduction which would be about right if it actually spins 4200 rpm at 12 volts unloaded. Is there any way you can determine the rpm?

10 tooth pulley is not very efficient. The smallest I would consider is 16 tooth, but I prefer 24.. then I 3d print larger pulleys like 180 or 240.

How many turns does the wheel rotate?
Quote:The other idea if this motor isn't suitable is could you point me to a part number of a good windshield wiper motor thats not too hard/expensive to track down at the local to me auto shops.

As for rudder shape a picture speaks a thousand words:
You can use just about any windshield wiper motor. They typically have 2 windings, one is 60rpm the other about 90. This you can reduce down to get 15-30 rpm you need to turn the wheel.

your rudder appears unbalanced.
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#5
(2021-01-09, 02:30 PM)seandepagnier Wrote: If you have two stages of that.  This would give you 144:1 reduction which would be about right if it actually spins 4200 rpm at 12 volts unloaded.   Is there any way you can determine the rpm?
Not sure how I would go about measuring it, any suggestions?

Quote:10 tooth pulley is not very efficient.   The smallest I would consider is 16 tooth, but I prefer 24..   then I 3d print larger pulleys like 180 or 240.
I wish I had access to a 3d printer to make that possible. The one business I know of locally that does 3d printing has their office completely closed to the public for Covid.

Quote:How many turns does the wheel rotate?

3 and a half turns for full rudder movement from one side to the other.

Quote:You can use just about any windshield wiper motor.   They typically have 2 windings, one is 60rpm the other about 90.  This you can reduce down to get 15-30 rpm you need to turn the wheel.
Would this be a good alternative? https://www.robotshop.com/en/12v-16rpm-h...ction.html

Quote:your rudder appears unbalanced.
What do you mean by unbalanced?     (EDIT: quick google search told me the answer)




Thanks,
Seamus
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#6
that could work to drive the wheel directly perhaps, though I think the motor is too weak.

I would look for a motor rated at 60-100 rpm and then use a belt drive for additional ratio. This is why windshield wiper works well. In many junkyards you can get these, the one here charges $6 for them.

Otherwise try to gear down your other motor, but you likely need at least 100:1 ratio maybe a bit higher.
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