4 replies to this topic

[Darth Legolas]

Yes, it's self explanatory. I've worked out my big technic PF project thingie, and it works great! Automated lights, driving, steering, winch, and pistons and everything!

There's only one problem. It sounds terrible. I searched and found no techniques to muffle the back motor. The front motor doesn't make a sound, so it's not big deal, but the back one drives the thing and sounds like a dying cat.

I want the engine to keep quiet, but I don't want it to overheat or blow up, for obvious reasons. So does anyone have any PF muffler techniques?

Thanks!

[Mark Bellis]

Darth Legolas, on Dec 12 2009, 04:56 PM, said:

Yes, it's self explanatory. I've worked out my big technic PF project thingie, and it works great! Automated lights, driving, steering, winch, and pistons and everything!

There's only one problem. It sounds terrible. I searched and found no techniques to muffle the back motor. The front motor doesn't make a sound, so it's not big deal, but the back one drives the thing and sounds like a dying cat.

I want the engine to keep quiet, but I don't want it to overheat or blow up, for obvious reasons. So does anyone have any PF muffler techniques?

Thanks!

The noise is due to the PWM signal causing the motor armatures to vibrate.  It is a feature of the variable speed control and should go away at full speed.

There will also be more noise the harder you drive the motor, so consider reducing the gearing if there is any spare speed capacity you don't use.

Unfortunately smoothing out the signal with a capacitor defeats the object of the PWM, which is to give the motor plenty of starting torque, which is especially important in a motor that is driving the wheels!

It would be possible to:
- Take a PF extension lead and cut it in half.
- separate the 4 wires from each other with a knife (not recommended for under-16s) to a depth of 20-30mm.
- strip the insulation from the wire ends, to a depth of 5mm.  There is a wire stripper tool to do this.  Picture (unseparated)
- twist the strands and fold them back alongside the insulation of each wire.
- attach single 12V plugs to the 4 wires, or at least to the two middle wires if you have just 2.  Put the strands on the opposite side to the screw when inserting into the recess in the metal part of the plug.
- Add a capacitor by pushing its leads into the ends of the plugs, between the 4 lobes.  This is easy with 1/0.6 bell wire but the capacitor lead might be a bit fatter.  This picture shows wires in the plug ends.

Mark

[Darth Legolas]

Mark Bellis, on Dec 12 2009, 12:52 PM, said:

The noise is due to the PWM signal causing the motor armatures to vibrate.  It is a feature of the variable speed control and should go away at full speed.

There will also be more noise the harder you drive the motor, so consider reducing the gearing if there is any spare speed capacity you don't use.

Unfortunately smoothing out the signal with a capacitor defeats the object of the PWM, which is to give the motor plenty of starting torque, which is especially important in a motor that is driving the wheels!

It would be possible to:
- Take a PF extension lead and cut it in half.
- separate the 4 wires from each other with a knife (not recommended for under-16s) to a depth of 20-30mm.
- strip the insulation from the wire ends, to a depth of 5mm.  There is a wire stripper tool to do this.  Picture (unseparated)
- twist the strands and fold them back alongside the insulation of each wire.
- attach single 12V plugs to the 4 wires, or at least to the two middle wires if you have just 2.  Put the strands on the opposite side to the screw when inserting into the recess in the metal part of the plug.
- Add a capacitor by pushing its leads into the ends of the plugs, between the 4 lobes.  This is easy with 1/0.6 bell wire but the capacitor lead might be a bit fatter.  This picture shows wires in the plug ends.

Mark

Wow that seems an awful lot! I was just hoping you could put a scarf over it to keep it quiet or something. I might try your idea, but I'm in no hurry to strip any wires.

Thanks anyways!

[Parax]

Darth Legolas, on Dec 13 2009, 08:17 PM, said:

Wow that seems an awful lot! I was just hoping you could put a scarf over it to keep it quiet or something. I might try your idea, but I'm in no hurry to strip any wires.

Thanks anyways!

Alternatively you could try putting a scarf over it......


Is there a thermal cut out in a pf motor?


I would expect reducing the load might help.. but more gears might be noiser still.. you could try two motors?

[Burf2000]

Ear defenders?