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Old Feb 07, 2013, 07:22 AM
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FlyBoy20's Avatar
United Kingdom, Wales, Swansea
Joined Aug 2012
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Question
High/Low Kv and ESC timing...?

I've noticed with some motors that they don't all 'kick in' at the same point with stick movement. Sometimes they won't get going, initially, at all unless the stick is moved well up the range. I suspect I'm not getting the most out of my motors. I've made a point of registering the max. travel with all my ESCs, but some motors still seem reluctant to start spinning. I'm thinking it's maybe a timing issue, so my question is what timing setting is appropriate for a given Kv? Or is it more a question of how many poles a motor has?

I'd like to optimize my motor/ESC set ups, so some guidance on this would be really helpful...

I don't have a programming card yet, so it's gotta be a stick-waggling job, and because I have different makes of ESC, each one presents a different challenge. Anyway, I've ordered a card for the Turnigy Plush ESCs because I have a couple of them already, and in future I'm gonna stick with them - just for simplicity's sake!
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Old Feb 07, 2013, 08:14 AM
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flypaper 2's Avatar
Kingston, Canada
Joined Jun 2004
12,753 Posts
If the motor starts right up when you hit the throttle, use the low throttle endpoint programmed in the trans. I have mine start up about 17% off the bottom throttle stop, but that's your choice where to start it.

Gord.
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Old Feb 07, 2013, 08:55 AM
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Lnagel's Avatar
Moab, Utah, USA
Joined Apr 2003
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The start up issue you are having is one of the disadvantages of using sensorless motors. Unfortunately, there's not much you can do, if anything, to change it. It is an initial synchronization problem between the ESC and the motor that has nothing to do with timing.

A sensorless ESC relies upon a feedback signal from the motor to determine when to switch comutation phases. That feedback signal from the motor is generated by the motor's magnets passing the motor's windings. When initially starting a motor there is no feedback signal available because there is no relative motion between the motor's magnets and its winding. At startup the ESC has no idea what position the motor is in so it initially just energizes two of the motor's coils. Depending upon the relative position between the motor's magnets and its windings, those energized coils will cause the motor to turn either clockwise or counterclockwise. The ESC will then switch to the next of its three phases and that again may turn the motor in the correct direction or the incorrect direction. The initial startup phase and the rate at which it changes is determined by the ESC's programing.

Consequently upon startup the motor will most likely do a little dance one way and then the other until it is spinning fast enough in the correct direction to generate a feedback signal strong enough for the ESC to synchronize on. Once the ESC locks onto the motor's feedback signal then the motor will spin in the correct direction and change speed smoothly until the motor stops.

Some ESCs are simply better at locking on to a motor's initial feedback signals than others. It's primarily how the ESC's program handles the startup procedure and how sensitive the ESC's feedback detector is.

As far as what timing to use, that is not determined by Kv. Timing is a dynamic thing and is more dependent upon the number of poles combined with the motor's highest RPM. For the best motor efficiency you want to use the lowest timing setting that allows the motor to run smoothly when quickly throttled up from a low RPM to max RPM. Using a higher timing setting will increase the motor's maximum power slightly, but at the expense of increased current flow and heat.

Larry
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Old Feb 07, 2013, 09:36 AM
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FlyBoy20's Avatar
United Kingdom, Wales, Swansea
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Quote:
Originally Posted by Lnagel View Post
..Once the ESC locks onto the motor's feedback signal then the motor will spin in the correct direction and change speed smoothly until the motor stops.
So, does it have to do do this every time you start the motor, because it doesn't 'memorize' at all?

Quote:
Originally Posted by Lnagel View Post
Timing is a dynamic thing and is more dependent upon the number of poles combined with the motor's highest RPM.
So can we formulate a general rule for low-Kv/high-Kv and the number of poles to avoid excess heat?
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Old Feb 07, 2013, 10:09 AM
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Willmar, Minnesota, United States
Joined Sep 2004
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Quote:
Originally Posted by FlyBoy20 View Post
So, does it have to do do this every time you start the motor, because it doesn't 'memorize' at all?



So can we formulate a general rule for low-Kv/high-Kv and the number of poles to avoid excess heat?
it has to do this synchronization EVERY time, because the motor does not stop in the same place (and stay there) every time ... on startup, the ESC has no idea what the relative position is between the coils and the magnets.

as a rule of thumb as Larry pointed out: start with the lowest timing, if the motor runs smoothly when quickly throttled up from a low RPM to max RPM, then leave the timing there. only use the higher / faster timing settings if the motor does not accelerate and run smoothly.

again, that's a rule of thumb, it's not set in stone.
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Old Feb 07, 2013, 10:34 AM
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United Kingdom, Wales, Swansea
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Quote:
Originally Posted by Jim Buzzeo View Post
..as a rule of thumb as Larry pointed out: start with the lowest timing...
So, as Del Shannon would say, it's 'Hats off to Larry', then (and you Jim too)!

Cheers..
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Old Feb 07, 2013, 05:23 PM
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United States, AZ, Mesa
Joined Jul 2007
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I've only ever had to adjust timing once, and that was with a very unusual motor, and only on the advice of a Castle engineer.
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Old Feb 08, 2013, 03:30 PM
Registered User
United States, CA, Sebastopol
Joined Aug 2011
15 Posts
Quote:
Originally Posted by FlyBoy20 View Post
I've noticed with some motors that they don't all 'kick in' at the same point with stick movement. Sometimes they won't get going, initially, at all unless the stick is moved well up the range. I suspect I'm not getting the most out of my motors. I've made a point of registering the max. travel with all my ESCs, but some motors still seem reluctant to start spinning. I'm thinking it's maybe a timing issue, so my question is what timing setting is appropriate for a given Kv? Or is it more a question of how many poles a motor has?

I'd like to optimize my motor/ESC set ups, so some guidance on this would be really helpful...

I don't have a programming card yet, so it's gotta be a stick-waggling job, and because I have different makes of ESC, each one presents a different challenge. Anyway, I've ordered a card for the Turnigy Plush ESCs because I have a couple of them already, and in future I'm gonna stick with them - just for simplicity's sake!
I've made the same observations about throttle stick position vs motor speed, but only during initial motor/esc setup.

I don't know if my solution is optimal, but it seems to work.

I use the channel 3 (throttle/esc) endpoints and channel 3 subtrim on my transmitter to achieve the combination of 0 speed at throttle stick minimum (the motor starts tuning as soon as I advance the throttle a “tiny bit”) and maximum speed at full throttle. It takes a fair amount of fiddling to achieve that condition but once you do, it should be stable until you change either motor or esc.

I have found that channel 3 endpoins of +- 120% and subtrim of + 40 or 50 often works but I'm sure it depends on the specific setup.

Hope this helps.

Bill.
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