What happens when motor is re timed? - RC Groups
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Jun 19, 2003, 03:15 PM
Registered User

What happens when motor is re timed?


I just retimed my motor and flew my Zero thanks to a pictorial on the subject in e zone.

I could not beleive the increase in performance! What happens (technically) when the motor is retimed?

Thanks for the info.

Jim
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Jun 19, 2003, 03:31 PM
Registered User
Assuming that this is a brushed motor I will do my best to explain timing to you. If you are familiar with timing in a combustion engine it is somewhat similiar. You are twisting the commutator in a specific direction to adjust when the windings are energized (by contact from the brushes to the commutator) in relation to the stationary magnets.

So when in the old timing say the winding was energized at 5 degrees before it was in the center of the magnetic field now you "advance" the timing and energize the winding at 10 degrees before center of the magnetic field. If you twist the other direction you "retard" the timing and it will have adverse effects.

Now, (disclaimer) I am not an expert on this subject and I probably have the terminology wrong. That is the basic principle however. I am not sure how adjusting affects RPM or Torque. maybe someone else can chime in and fill in the gaps that I have left.
Jun 19, 2003, 03:48 PM
Fixed Wing Fanatic
Jim Walker's Avatar
I think Huff has the basics correct. As you advance the timing by moving the magnets farther away from the middle of the magnetic field of the energized coil you cause them to accelerate more to catch up. Thus you get more rpms for a given voltage. You don't get something for nothing though, you give up torque to get the rpms. So conversely as you retard the timing back to neutral you get more torque. This is all based of course on you changing the timing from the optimal setting for a certain direction of rotation.

This brings us to why your motor performs so much better. The gearing on GWS gearboxes actually makes the 6V S300's run in reverse to get the prop to spin in the correct direction. This makes the motor's timing seriously retarded as the S300's timing is advanced for the other direction of rotation from the factory.
Jun 19, 2003, 03:50 PM
Registered User
WJ Birmingham's Avatar
You stated it pretty well...

As a further explanation, I'll add this comparison...

Timing a internal combustion motor changes where the spark plug fires in relation to where the piston is in the bore. Most motors require a total of 38 degrees of advanced timing.

This means, that 38 degrees of rotation before the crankshaft reaches top dead center, the spark plug fires. In that 38 degrees, compression is built during the time the flame burns, thus causing a more volatile expansion of the gases.

Now, conversely... in electric motors...

Just as Huff said, it's almost an apples to apples comparison. The magnets in the "can" attract or repel the armature windings, depending on the polarity of the windings. When you change the timing of the motor, you're changing the point at which the magnetic pulse is applied.

This makes it more, or less efficient, depending on what you do.

WJ
Jun 19, 2003, 04:08 PM
Registered User
The armature of an electric motor is made up of many windings of wire which have the property called inductance which impedes the flow of a CHANGING current.

As the armature turns and the commutator switches windings, the current through the winding does not immediately flow, but rises relatively slowly because it is impeded by the inductance.

By adjusting the switching point so that it comes sooner, the current will have risen to a maximum by the time the winding is fully within the magnetic field of the magnet associated with that pole of the motor and more torque and higher efficiencies will be produced.

This is only an approximation, however, because the timing is also a function of the speed of the motor.

There are some mathematical techniques for determining an approximate optimum point for timing a motor, but one that is relatively simple to do is to run the motor under load and adjust the timing until arcing is at a minimum.
Last edited by Martyn McKinney; Jun 19, 2003 at 04:21 PM.
Jun 19, 2003, 05:46 PM
Registered User
Therefore does the number of amps you draw also increase ? I would assume so. FYI, I connected a multimeter to my GWS300C gear with a 10x8 prop (stock GWS Mustang kit). According to the GWS web page it should draw about 8A, but on my (cheap) multimeter, It only recorded 5.5. Would the website refer to retimed motor (wouldn't think so). If I remtimed the motor, would I get about 8A then ?
Jun 19, 2003, 06:06 PM
Registered User
What voltage were you using compared to the GWS data and what was the resistance of your ammeter ? Both of these can have significant effects on motor current.

Under no load conditions the minimum current point is close to neutral (zero degree) timing.

Retarding the timing will cause a significant increase in current.

For a particular RPM and load, advancing the timing so that the current is minimum is the optimum point for best efficiency, but may not meet your performance requirements.

Advancing the timing under no load will increase the current.
Last edited by Martyn McKinney; Jun 19, 2003 at 06:16 PM.
Jun 19, 2003, 06:59 PM
Registered User

Hey hey! I was right!!


~I was right!~

Way to go Huff!!