Arduino autopilot and stepper motor

simonfraser

simonfraser

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i have hydraulic wheel steering, very light to steer.

thinking of setting up a stepper motor and Arduino to control it.
be easier and less bits if i can leave the stepper motor mechanically connected to the wheel 24/7:
A Pololu A4988 stepper motor driver has an Enable pin which can be used to depower the motor under Arduino control


can i still hand steer the boat with such a stepper motor physically connected but not electrically powered ?
 
The motor will probably need a certain amount of gearing to produce enough torque for the wheel.
This will multiply up the torque needed to turn the unpowered motor.
Unless you use a very big motor with no or minimal gearing, I reckon you will need a clutch of some sort.
Or, you drive the hydraulics directly in parallel with the wheel.
 
simonfraser said:
hm, yeh thought as much, any suggestions as the where to look for that ?
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You presumably want an electromagnetic one. If you can't just buy it as an off-the-shelf part (eBay is good for this sort of thing from small engineering suppliers) then I know they are available for switching on and off engine-driven bilge/deckwash pumps, and I believe are also used for car air-conditioning pumps.

simonfraser said:
connecting to the hydraulic side is going to be tricky due to access issues.
Click to expand...

That's surprising - I'd have thought one of the benefits of hydraulics would be that you can connect into the system at any point with appropriate fittings and valves (you need to ensure that your hydraulic pump doesn't just spin the wheel instead of turning the rudder :) ). There's really no access anywhere in the system?

Pete
 
'That's surprising - I'd have thought one of the benefits of hydraulics would be that you can connect into the system at any point with appropriate fittings and valves (you need to ensure that your hydraulic pump doesn't just spin the wheel instead of turning the rudder. There's really no access anywhere in the system?'

its an odd setup, wheel cable to the back, then hydraulic bits at the rear of the engine connected to the steering ram.
you'd need to a small strong 5 yr old to get in there :)
 
Stepper motors aren't terribly efficient. Especially when they're not turning. And your autopilot software is doing its best not to run the motor.
Also, be a bit careful turning an un-powered stepper motor as they make very efficient dynamos! (or is that alternators - can't remember) . I can power up the control board on my 3d printer just by spinning a motor.
 
It would not be hard to use a servo or another stepper to drive the clutch.
I would not want an electric clutch drawing power when the pilot is not turning the wheel.

But then I enjoy steering my boats, and mostly use the wheelpilot as a wheel lock.
 
simonfraser said:
its an odd setup, wheel cable to the back, then hydraulic bits at the rear of the engine connected to the steering ram.
Click to expand...

Ah - now I'm on a desktop browser I can see your avatar :). I was envisaging a yacht hydraulic system, whereas I guess yours is more of a push-pull Morse cable with hydraulic assist at the business end.

Is there something you can turn on the back of the wheel unit inside the console, or do you literally need to turn the wheel itself from the front? In the latter case perhaps your connection can be purely mechanical without needing a clutch as such?

Pete
 
lw395 said:
I would not want an electric clutch drawing power when the pilot is not turning the wheel.
Click to expand...

It's the norm on every Raymarine (and probably other brands too) below-decks pilot. I don't think they draw very much current, certainly the wires are a lot smaller than the motor ones.

Anyway, the OP has a motorboat so has power to spare when underway :)

Pete
 
prv said:
It's the norm on every Raymarine (and probably other brands too) below-decks pilot. I don't think they draw very much current, certainly the wires are a lot smaller than the motor ones.

Anyway, the OP has a motorboat so has power to spare when underway :)

Pete
Click to expand...

I think you're right. Having taken an Autohelm Linear Drive apart recently I'd say the clutch probably draws a tiny amount of current. Coil on the clutch is tiny wiring.

The OP might be better off with a motor and a variable resistor as a feedback unit (as Raymarine etc. do) rather than a stepper motor.
 
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