Autopilot motor current.

[pandos]

I have a wheelpilot which works ok.

I was thinking of some backup. I removed an old rotary drive from the steering system shortly after I bought the boat. This is nicely engineered but has ancient electrics and no electronics.

I can take a feed for a clutch from the brains of the wheelpilot, but I could not draw sufficient current from the wheelpilot to operate the rotary drive.

I cannot use a contactor like the windlass because that has a common negative and two positives

If it was a simple stop go, a relay could be used, but as left and right are obtained by reversing polarity of the 12v sent to the motor, how could I use the feed from the wheelpilot brains to switch a higher current.

The Pypilot store used to sell a setup that I was interested in but for now the store is closed.

 

[B27]

I would use an H bridge of MOSFETs. Either discrete parts or a motor drive IC.
You could drive the FETs from an arduino or similar, do you need 'analogue' PWM control or just Left/Off/Right?
There are lots of arduino articles about DC motor drive, just upscale the FETs to handle plenty of current.
You could even use a class D audio amp.

You may(will!) want current limiting for a stalled motor.

 

[pandos]

I would use an H bridge of MOSFETs. Either discrete parts or a motor drive IC.
You could drive the FETs from an arduino or similar, do you need 'analogue' PWM control or just Left/Off/Right?
There are lots of arduino articles about DC motor drive, just upscale the FETs to handle plenty of current.
You could even use a class D audio amp.

You may(will!) want current limiting for a stalled motor.

Thanks for that, don't really understand some of it.

From googling it seems the existing pilot will probably be using a h bridge to controll the left /off/right


Don't need anything other than left/off/right.

What I ienvisage is something with two inputs from the autopilot, two from the battery and two outlets to the motor. So that the output from the pilot is essentially the input signal that switches on and off the feed from the battery to the new motor (and reversing it as polarity of the input is changed)

Would a MOSFET bridge do this?.

I don't want to introduce Arduinos or that kind of thing. (mini computers and programmable things with tiny power supplies hate me)
..

 

[B27]

The problem is translating the output levels of whatever circuit you already have, to the levels required to drive the FETs.
There are standard ICs which do this.
You might find one already mounted onto a PCB for amateur use, this may be sold as an Arduino accessory or 'shield' , it might be a good way to go even if you don't use an Arduino to drive it.

There are a few different types on ebay, but the data is sparse.
This maybe?
BTS7960B 43A Double DC Stepper Motor Driver H-Bridge PWM Arduino Smart Car | eBay
I'd start by studying the data sheet of the driver IC.

It might be possible to just upgrade the FETs in the existing bridge?
Or use the old FETs to drive the new FETs directly. That needs care, because it's messy if you don't turn one FEt off fully before turning on the opposing one.

 

[PaulRainbow]

I have a wheelpilot which works ok.

I was thinking of some backup. I removed an old rotary drive from the steering system shortly after I bought the boat. This is nicely engineered but has ancient electrics and no electronics.

I can take a feed for a clutch from the brains of the wheelpilot, but I could not draw sufficient current from the wheelpilot to operate the rotary drive.

I cannot use a contactor like the windlass because that has a common negative and two positives

If it was a simple stop go, a relay could be used, but as left and right are obtained by reversing polarity of the 12v sent to the motor, how could I use the feed from the wheelpilot brains to switch a higher current.

The Pypilot store used to sell a setup that I was interested in but for now the store is closed.

Some windlass contactors do this. Look for a 4 pole one and check it does what you want.

 

[pandos]

Some windlass contactors do this. Look for a 4 pole one and check it does what you want.

That would be useful, I'll have a look, would they be quick enough for an autopilot in terms of switching back and forward?



Winchmax 12v Winch Solenoid for ATV, Boat Trailer and Marine use. Amazon.co.uk
Something like this?



Thanks

 

[PaulRainbow]

That would be useful, I'll have a look, would they be quick enough for an autopilot in terms of switching back and forward?

Thanks

Not 100% certain, as never tried one, but Garmin recommend using relays for certain installations.

 

[pandos]

Not 100% certain, as never tried one, but Garmin recommend using relays for certain installations.

I'll give it a try then..small money to bench test it...

Many thanks

 

[pandos]

The problem is translating the output levels of whatever circuit you already have, to the levels required to drive the FETs.
There are standard ICs which do this.
You might find one already mounted onto a PCB for amateur use, this may be sold as an Arduino accessory or 'shield' , it might be a good way to go even if you don't use an Arduino to drive it.

There are a few different types on ebay, but the data is sparse.
This maybe?
BTS7960B 43A Double DC Stepper Motor Driver H-Bridge PWM Arduino Smart Car | eBay
I'd start by studying the data sheet of the driver IC.

It might be possible to just upgrade the FETs in the existing bridge?
Or use the old FETs to drive the new FETs directly. That needs care, because it's messy if you don't turn one FEt off fully before turning on the opposing one.

Don't think I will go at the existing innards. Paul's suggestion for a solenoid is probably what I need and I suspect that is the word I should probably be concentrating on.

Many thanks.

 

[rogerthebodger]

I have used 2 change over relays to reverse the direction of permanent magnet wiper motors

One relay for one direction and the other for the reverse direction

The common connection of each relay goes to the poles of the motor and the N/O goes to +12 Vdc and the N/c goes to
the negative )0) volts connection

Enginsing one relay power the motor in one direction

Enginsing the other relay powers the motor in the opposite direction

If both relays get enginsied the motor will receive no y power as + 12 vdc goes to both sides of the motor and the motor will not run.

https://content.instructables.com/F...it=bounds&md=3485d368b3fc1b58255f65fd92576def

https://content.instructables.com/FWL/B1NN/JRGOMX8C/FWLB1NNJRGOMX8C.png?
auto=webp&frame=1&fit=bounds&md=2d79b923f616cae05a8637871f10b416

DC Motor Controller With Two Relay

 

[pandos]

I have used 2 change over relays to reverse the direction of permanent magnet wiper motors

One relay for one direction and the other for the reverse direction

The common connection of each relay goes to the poles of the motor and the N/O goes to +12 Vdc and the N/c goes to
the negative )0) volts connection

Enginsing one relay power the motor in one direction

Enginsing the other relay powers the motor in the opposite direction

If both relays get enginsied the motor will receive no y power as + 12 vdc goes to both sides of the motor and the motor will not run.

https://content.instructables.com/F...it=bounds&md=3485d368b3fc1b58255f65fd92576def

https://content.instructables.com/FWL/B1NN/JRGOMX8C/FWLB1NNJRGOMX8C.png?
auto=webp&frame=1&fit=bounds&md=2d79b923f616cae05a8637871f10b416

DC Motor Controller With Two Relay

I thought that would not work for me as I have only two wires out of the pilot and these are +/- depending on the way the pilot wants the motor to turn.

But perhaps I can take a negative from the battery as a common , and connect the two wires from the pilot to separate relays such that it is only when the respective wire is positive that the relay operates. (As per your last onstructible...)

At any stage where movement is required, one relay would have a positive and a negative and the other would have two negatives. When the polarity in the feed reversed the relays would reverse. ?

 

[rogerthebodger]

With a motor with just 2 wires + and - the circuit I use id exactly the one you need.

The 2 wires from the motor go to the motor connections as shown

The power from the battery would go to what is shown as Vmotor.

The control from the pilot would be connected to the control input of the relays.

The output of the pilot control my need some diodes to convert the + and - pilot output to drive the relays

to direct the line that is + in one direction and the + when the pilot is in the other direction. to in1 and in2 from the diodes

The relays signat negatives would go to Gnd and a battery + to the red liput

This may also help

DC Motor Reversing Circuit | Timer or Remote Control | Quasar Electronics Limited

As aid the relay coil would be driven gtom yr 2 output wires from the plot with a diode to only send the + to the 2 relay coils and the negative would go to the battery -

 

[pandos]

With a motor with just 2 wires + and - the circuit I use id exactly the one you need.

The 2 wires from the motor go to the motor connections as shown

The power from the battery would go to what is shown as Vmotor.

The control from the pilot would be connected to the control input of the relays.

The output of the pilot control my need some diodes to convert the + and - pilot output to drive the relays

to direct the line that is + in one direction and the + when the pilot is in the other direction. to in1 and in2 from the diodes

The relays signat negatives would go to Gnd and a battery + to the red liput

This may also help

DC Motor Reversing Circuit | Timer or Remote Control | Quasar Electronics Limited

As aid the relay coil would be driven gtom yr 2 output wires from the plot with a diode to only send the + to the 2 relay coils and the negative would go to the battery -

That seems to make sense.
thanks..