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Timing an electric motor
From an article in the E-zone. Written by Paul Michaelson
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Let's talk about timing your electric motor. Why? Well suppose you have a nice new Astro Cobalt 15 and you have been using it in an aerobatic plane. Then you decide to put it in a nice big sailplane with a gear box. Geared motors turn the opposite direction direct drive motors turn. You have to re-time the motor to allow it produce the same astounding output you got before. This is due to the fact that the motor had been timed for anti-clockwise rotation. Now when you run the motor the other direction, the timing will be way off. If you have just installed new brushes or other parts like a new armature you should re-time the motor. You can also change the timing to alter the way the motor runs. If you advance the timing the motor will put out more power at less efficiency and run hotter. Some people like to fine tune the timming to get the exact trade off of efficiency and power they want. On the other hand if you run the motor with retarded timing the motor will not produce the power it is supposed to.
For all of these reasons (and a few more) you need to know how to time your electric motor. For the remainder of this article I will use the Astro Cobalt motor as an example. But this applies to any electric motor with adjustable timing. People do modify motors that provide the user with no easy way to adjust the timing. But I feel that hacking up "can" motors is beyond the scope of this article.
The Astro Cobalt motors are very easy to time. All you have to do is loosen the two screws on the end of the motor that the shaft sticks out on. Then just rotate the magnet housing (the black part) the correct amount and re-tighten the screws. But how much is the right amount? Also which direction do you turn the magnet housing? Let me try to answer these questions.
To start out we need a current measuring device, one that is capable of measuring the high amperages that these motors draw. I am not going to describe how to connect an amp meter here so read the manual if you need to. Once you have the meter connected you can measure the amount of current that the motor is drawing and use that as an indication of timing. Timing is best set by measuring the current the motor draws when free running. By this I mean with no load on the motor. So remove props or anything else from the motor shaft.
The first thing to do is to find the "neutral" point. This is the point where the motor draws the least current. Hook up your meter and run the motor at normal operating voltage. Now rotate the magnet housing until you find the point where the motor draws the least current. I often put a small mark on the motor here. It is nice to have a mark to use as a reference. Now all you have to do is to rotate the magnet housing in the direction of motor rotation until you reach the desired current draw and timing.
Astro states that the best mix of power, brush life, and efficiency, will all be found at the same point! This is 2 to 4 amps above the free running neutral point current. Remember to set timing with the motor running free. This means without ANY prop or other load! For standard motors use 2 amps and for FAI type "winds" use 4 amps. Once you have found the timing point you desire, just tighten the case screws and you are done.
Astro motors have two sets of screw holes in the brush housing. The left hand holes are for direct drive and the right hand holes are for geared motors. Please remember to use the correct set of holes. This is important if you are going from direct drive to a geared set up.
If you are timing a motor other than an Astro, you can use the same procedure to set the timing. Just remember that the best timing point will not be the same as an Astro motor, so you will have to "find" the best timing setting. If your motor does not come with instructions for timing it, then try to find the point where you get the longest run times without sacrificing power. Remember that as timing is advanced power will also increase. BUT if you go too far the efficiency will suffer the motor will run hot and you will get short runs due to the poor efficiency. Soon you will find a point at which you get the most power and longest runs. Measure the free running current when you have found this point so you can just set it next time with an amp meter.
If you keep your motor properly timed you will always get the astounding performance and reliability that has made electric flying so much fun.
Good lift, and safe landings.....
Link to the article in the E-zone: http://www.ezonemag.com/articles/1996/time.shtml
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Even though standard Speed 400 and similar motors (almost all of the same Mabuchi 380 type) are mounted with a fixed back plate, it is possible to time them whithout any special tools. This is how you do it:
1. Mark the location of the back plate, so you know the standard position.
2. Hold the front end firmly with a poly grip (pipe grip?) or similar tool. Use some padding if you don´t want to make ugly marks on the motor casing.
3. Use a plier with bent grips (or some similar two-point tool), and stick the grips in the two holes on the back plate.
4. Note the red dot on the backplate and the nearest cooling slot on the side of the motor.
5. Turn the backplate anti clockwise until the red dot is lined up with the edge of the cooling slot. This is a 5 mm (3/16") rotation.
Now you have a timed motor for normal rotation. If you want reversed rotation, you just turn clockwise 5 mm.
Remeber: The current draw will increase and the motor life time will be reduced!
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