Timing Electric Motors

Published: Monday, 30 March 2009 17:16 | Print | Email
(Klaus Weiss - Heathcote Soaring League)

Geared motors run in the opposite direction to direct drive motors, so it you have a direct drive motor, and you want to bolt on a gearbox, then it will have to be re-timed, in order to produce the optimum performance. Direct drive motors turn anti-clockwise, and have been timed during the manufacturing process, so they will be quite a way out, if you just tried to fly a model with them. Likewise if you ever need to install new brushes or armature, then it is a good idea to re-adjust the timing. Note, that some 'can' motors may not have adjustable timing, so check them out first.

Timing dictates the way a motor will run. If it is advanced, then the motor will put out a bit more power, but will suffer in other areas, such as running a lot hotter. If the timing is retarded, then the motor will produce less power, which is unacceptable in most cases.

Astro Gobalt motors have two screws on the output shaft end of the motor, and it is a simple matter to just loosen them and rotate the magnet housing (which is black in colour) in order to adjust the timing. They need to be retightened when the optimum setting has been found. (You all knew that, but better to mention it, just in case). There are some iterns which are required, in order to perform the task, so it is quite possible that you may have to ask around the club members, if there is a difficulty.

You need access to an amp meter capable of reading high amperages, in order to read the amount of current the motor is drawing. It is best to test this current with NO attachments, such as props ets, on the motor. Loosen the screws and rotate the magnet housing until you find the point where the least current is being drawn (neutral point). lt may be an advantage to mark this spot on the motor. Next, rotate the magnet housing until you get the desired current draw, which is around 2 amps - 4 amps above the neutral point. This timing should give you the best wear on brushes, power and efficiency mix. Astro recommend 2 amps above neutral for 'standard' motors, and 4 amps for the FAI type motors. If you are setting up a direct drive Astro motor with a gearbox, then be aware that the left hand holes are for direct drive, and the right are for geared motor timing.

If you are timing other brand motors, then it is up to you to find the best timing setting. It may take a little longer, but run the motor and find where you get the longest run time, without sacrificing power. If the timing is advance too tar, then you will get hot motor runs and short duration times. When you have found the best point, mark the motor, so that it can be set next time by the use of an amp meter.
...............Good Luck.

How Does A Glow Plug Work?

Published: Monday, 30 March 2009 17:05 | Print | Email

(Contributed by Dave Pound)

glowPlug

Contrary to what many have previously been led to believe the following is an explanation of how a glow plug functions in a motor.
The plug is initially heated by applying a voltage (typically 1.5 volts) to it. This is to cause it to glow so as to ignite the fuel at compression and start the internal combustion cycle.
Once the cycle has started the power source can be disconnected as with the heat generated at combustion the catalytic reaction generated between the methanol and platinum in the plugs coil becomes sufficient to keep the process going.
The catalytic reaction is a reaction whereby platinum will glow in the presence of methyl alcohol vapour. This will happen without any external power source being applied!


How do you select the correct plug for your application and why?

To do this you need to understand a little more of the theory behind the process. In glow fuel the catalytic reaction is generated between the methanol and platinum only. Castor oil, synthetic oil, nitro methane etc do not generate a catalytic reaction with the platinum.
Next you need to understand that a certain surface area of platinum is required to generate a sufficient catalytic reaction to keep the internal combustion process going.
Also it is necessary to allow extra surface area for the reaction to be great enough when it diminishes with the available methanol dropping as in the case at motor idle.
Simply put, cold plugs are manufactured using a thicker wire to give greater surface area to facilitate a greater glow and thus the required catalytic reaction where less methanol is present in the fuel mixture.
So! More nitro means less methanol which in turn means a greater surface area of platinum will be required to generate the required catalytic reaction.
Correspondingly a lesser oil content can mean more available methanol and lesser surface area of platinum would be required to generate a sufficient catalytic reaction.
Suddenly it all makes sense! To work out which temperature plug to use you need to know how much methanol is in your fuel not how much nitro or oil. As a rough rule of thumb:
80% methanol or above use a hot plug .
70% ~ 75% use a medium plug .
60% ~ 75% use a cold plug.
65% or less use a very cold plug.


Idle Bars and Other Stuff

Again contrary to what many believe the idle bar on a glow plug is not necessarily what its name would suggest. It is in fact to stop any fuel not vapourised from dousing the platinum coil of the glow plug by dispersing it away from the coil.

Why are plated coils not at good as platinum alloy coils?

Plated coils suffer from very quick degeneration as the plating breaks down under operating conditions. As bits of plating come off the coil the plug is effectively becoming a hotter and hotter unit until in a comparatively short time it is no longer able to perform its function.
Conversely a platinum alloy coil will still degenerate but as it is platinum alloy throughout, the surface remains as platinum alloy and the plug continues giving much the same characteristics for quite a very long time

Why do glow plugs fail?

Published: Thursday, 19 March 2009 20:08 | Print | Email

The "ignition system" in our engines is in the main. the glow plug. The other vital ingredient - compression - actually determines the ignition timing. so it can't be totally ignored. But usually its the plug that gives us the problems.

Why DO glow plugs fail? There are four likely probabilities, five if you count old age.

Yes, old age! The plugs operate by using a catalytic (chemical) reaction with the alcohol in our fuel to maintain their heat, as the plug gets "old", it gets more and more covered up with combustion by products (carbon. etc.) which hinders the whole process.

Of the other four, LEAN RUNS is probably the most prevalent - not so much that the engine was running lean as it was HOT. Too much heat, and the element fries and shatters, or even melts.

TOO MUCH BATTERY power is another failure mode - very related to the above paragraph. Your battery should heat the plug to a nice bright orange or red orange colour: if the plug glows white hot it just isn't going to last. It's bad enough that we subject a tiny little element glowing hot to the pressures of combustion. But if we add more VIBRATION to the situation. we get trouble. Unbalanced props, loose engine mounts. etc. may all add up to plug failure, especially in combination with too much heat.

Another plug failure mode is from FOULING. The element is very small, and located down in a well. It doesn't take much trash flying around in your combustion chamber to foul (and ruin) the plug! Aside from the obvious dirt coming through the intake or with the fuel. the fouling can come from metallic sources, usually a result of bearings coming unglued, or from excess carbon deposits in the engine. If the combustion chamber is full of caked-on carbon. pieces of that can, and do, come adrift and end up fouling the plug!

A quality plug run in a sport engine should last for dozens of flights. If they don't, its probably not the fault of the plugs - its time to look elsewhere for the source of the REAL problem!

Glow Plug Selection

Published: Monday, 30 March 2009 16:53 | Print | Email
By Brian Gardiner, and Central Coast Model Aero Club Inc.

How Does A Glow Plug Work?

Contrary to what many have previously been lead to believe the following is an explanation of how a glow plug functions in a motor. The plug is initially heated by applying a voltage (typically 1.5 volts) to it. This is to cause it to glow so as to ignite the fuel at compression and start the internal combustion cycle. Once the cycle has started, the power source can be disconnected, as with the heat generated at combustion the CATALYTIC Reaction generated between the methanol and platinum in the plug coils becomes sufficient to keep the process going.

The catalytic reaction is a reaction whereby platinum will glow in the presence of methyl alcohol vapour. This will happen without any external power source being applied.

How do you select the correct PLUG for your application, and why.

To do this you need to understand a little more of the theory behind the process. In glow fuel the catalytic reaction is generated between the methanol and platinum only. Castor oil, synthetic oil, nitro methane etc do not generate a catalytic reaction with the platinum.

Next you need to understand that a certain surface area of platinum is required to generate a sufficient catalytic reaction to keep the internal combustion process going. Also it is necessary to allow extra surface area for the reaction to be great enough when it diminishes with the available methanol dropping as in the case at motor idle. Simply put, cold plugs are manufactured using a thicker wire to give greater surface area to facilitate a greater and thus the required catalytic reaction where less methanol is present in the fuel mixture.

So! More nitro means less methanol which in turn means a greater surface area to platinum will be required to generate a sufficient catalytic reaction.

Suddenly it all makes sense! To work out which temperature plug to use, you need to know how much methanol is in your fuel, not how much nitro or oil. As a rough rule of thumb, 80% methanol or above, use a hot plug. 70%-75% use a medium plug. 60%-75% use a cold plug. 65% or less use a very cold plug.

Idle Bars and Other Stuff

Again, contrary to what many believe, the idle bar on a glow plug is not necessarily what its name would suggest. It is in tact to stop any fuel not vapourised from dousing the platinum coil of the glow plug by dispersing it away from the coil. Why are plated coils not as good as platinum alloy coils? Plated coils suffer from very quick degeneration as the plating breaks down under operating conditions. As bits of plating come off, the plug is effectively becoming a hotter and hotter unit until in a comparatively short time it is no longer able to perform its function.

Conversely, a platinum alloy coil will still degenerate, but as it is platinum alloy throughout, the surface remains as platinum alloy and the plug continues
giving much the same characteristics for quite a long time.

Plated coils are very poor value when compared to platinum alloy coiled glow plugs.

Glow Plug Care

Published: Thursday, 19 March 2009 20:06 | Print | Email

GENERAL SYMPTOMS WHEN PLUG IS...

TOO COLD

1-Engine pops weakly each time it is cranked, but will not start. Also weak batteries.

2-Engine will not lean out into a smooth peaked run, but always sounds rich. Exhaust sound is extremely ragged.

3-Engine may quit running when the battery is removed, even though it may peak okay with the battery connected.

4-ln flight the engine will become progressively richer until it bogs down completely. This is due to the additional cooling in flight of an already borderline combination.

5-A mild situation will show up with the engine slowing down slightly when the battery is removed. This should serve as a warning that the plug has deteriorated and is due for replacement.

TOO HOT

1-Engine backfires when cranked and kicks back against rotation resulting in bruised fingers. Often results in reverse running. Also caused by using 2 Volts on some plugs.

2-Engine cannot be richened smoothly to break out of peaked sound. Generally occurs with highly nitrated fuel in lo-compression engines.

3-If you backed the needle valve up under (2), in flight it would go rich suddenly. Look for dirt in the fuel line, but remember this trick.

4-The engine will be more likely to overheat and sag. Always launch on the rich side of peak. Sag is characterized by a thin smooth exhaust sound. It simply sounds pooped, and it is!

5-If the engine exhaust sound has a sharp cracking note super-imposed over the steady tone, the fuel is pre-igniting, or detonating. This condition causes lost power, increases the wear on the engine,
and can lead into the overheat circle that can destroy your engine.

Note: The TOO HOT conditions can all lead to the destruction of your pet engine and they can do it in one flight! So, be particularly on the lookout for them. The TOO COLD won't generally hurt anything more than your pride.

  1. I've lost an engine