Trim motor playing up

[rhtrudder]

Having intermittent problem with my up trim , down works always but up stops now and then, don’t think it’s in the switch, pulled apart and looks ok, can sometimes get it to work if I touch the down trim , not sure how to the thing is wired, looked up a  wiring diagram and looks like it earths out back at the switch but I can’t figure out how it reverses the polarity , would there be another relay or controller to do that, there is a birds nest of wiring behind the panel so not easy to trace 

[RFguy]

Mostly, for simple series motors,  the reverse is handled by a cross wiring arrangement on the back of a DPDT centre off toggle switch
+ and - go to the switch, and two wires go to the motor.

 

Some motors have three wires, which becomes 1 common and direction selection. There might be a common ground (return) , and two positives (one for each direction) . Or the positive might be common, and have two switched returns.

if it doesnt always work, check that there is sufficient voltage at the motor (pair of crocodile clips etc and a multimeter) , watch the voltage when it stalls or doesnt move. 

THE OTHER thing is, all motors will have (or should have)   microswitch limit switches- you might have a dicky switch / actuator causing the system to think it is end of travel when it is not.

Failing all that, do a no load test on the motor- IE without the crank connected and see if it behaves. 
-glen

[rhtrudder]

Trouble is the thing only stops working in the air, would be better if it didn’t work at all, it has 5 wires, I think 3 are for the indicator 

[RFguy]

Flaps are under a fair load when airborne. I can tell that because in my Archer, the flap lever "Johnson bar" is quite heavy compared to stationary on ground. 

For me, this suggests a LOAD issue- IE the flap motor is under load.

I'd start by checking on the ground, over full range, visual inspect every mechanical linkage and joint , arm, crank - for "good mechanical behaviour' over full range of travel.

IE everything that should be square is square, flap tracks run easily etc.  You might disconnect from the motor and push/pull wind yourself to see if there are any hard spots over the travel. 
If you can measure the motor current in flight. see what it does.

I think its either 1) mechanical issue (leading to a motor load issue)  2) motor fault / wiring fault. 

 

Edited May 18, 2023 by RFguy

[rhtrudder]

Sorry should have said it’s on the elevator, I’ve got manual flaps

[RFguy]

OK, well same instruction applies I think. mechanical inspection etc etc etc

[facthunter]

Trouble with electric actuation you have NO feel of anything getting stuck or stiff in operation Nev

[rhtrudder]

10 hours ago, RFguy said:

Mostly, for simple series motors,  the reverse is handled by a cross wiring arrangement on the back of a DPDT centre off toggle switch
+ and - go to the switch, and two wires go to the motor.

 

Some motors have three wires, which becomes 1 common and direction selection. There might be a common ground (return) , and two positives (one for each direction) . Or the positive might be common, and have two switched returns.

if it doesnt always work, check that there is sufficient voltage at the motor (pair of crocodile clips etc and a multimeter) , watch the voltage when it stalls or doesnt move. 

THE OTHER thing is, all motors will have (or should have)   microswitch limit switches- you might have a dicky switch / actuator causing the system to think it is end of travel when it is not.

Failing all that, do a no load test on the motor- IE without the crank connected and see if it behaves. 
-glen

If there is a DPDT switch could that be the problem, not easy to get to the trim motor 

[RFguy]

I'd be looking at mechanical issues first, since that might uncover something wrong that is hazardous. runaway/stuck trim is nasty. Anyway, see how you go with the switch.

[IBob]

RHTRudder the basic arrangement in microlights is usually a Double Pole Double Throw (DPDT) switch with 6 terminals.
This is the trim switch on the panel.
Internally it is two separate switches, mechanically linked (DP). The switches have a central neutral position and, up and down active positions (DT) with spring return to the neutral position.

They are wired so that when the switch is up, the two wires going to the trim motor one polarity (eg 12V/0V) and when down that polarity switches (0v/12V). This drives the trim motor in one direction or the other.
Here is how they are wired:

[facthunter]

You must have limit switches also and still have control of the system.  Nev

[IBob]

Yes. If he's using the ubiquitous Ray Allen trim servo, the limit switches are built in.

What aircraft is this, RHTRudder?