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Brian, did you short all motor phases? I would have thought it would make more of an impact. How big was this drill anyways? :005:
I will do a few experiments myself. |
Which motor were you using and what rpm was the drill Serum? Like I said, I had the drill geared up through the tranny and it just slowed down, but didn't stop the drill. I first started by hooking the drill directly to the motor shaft and found it fairly easy to stop just by holding the motor bare-handed. Maybe my motor was not up to par??
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I meant whether or not you can only get roughly half (half wave rectifiy), or full bridge rectification? As it would be a sine wave generated, correct? |
Yup, made a Y adaptor out of 12GA wire and used some extra connectors and connected all three phases together. Shorting just two of them resulted in a "detented" feel to the resistance.
The drill was nothing special; just a 3/8" drill. I think it was a 3/4hp rating. |
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I believe it would be full-wave rectification. Each phase would need two diodes for this, which the FETs supply depending on how they are turned on. The result would be a signal that would look like the lower center part of the picture below (borrowed from ntd-ed.org): http://www.ndt-ed.org/EducationResou...WavesTABLE.gif |
Yeah, exactly. Does it have enough diodes though for this?
I just tried out motor shorting with drill, i used a 3/8 drill on 7XL, all I did was popped some 5.5mm female plugs on motor plugs and held them together. I spun the drill up and then pushed them together, good spark, but rpm's dropped by about 40%, which is alot considering. It was hard to hold onto as well. The motor was slowly getting warm, I did it for about 10 seconds. The connectors were getting very warm, almost hot, probably because from the resistance from them touching only very little. Also, when I stopped the drill, it stopped almost immediately, normally is spins down a while... From what I observed, it was far more than enough to flip a MT over, and easily stop it. |
Yeah, the motor i deanodized was a 7XL as well.
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Hmmm, even geared up through the tranny, I didn't get that much resistance. My drill also stopped pretty quickly when I removed the power, but there is a lot less inertia in a drill than there is in a 10lb truck moving at 30mph. Maybe it has something to do with the fact I used a 10XL, and you guys used a 7XL.
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I find that strange because you would think a 10XL would have more resistance.
How exactly did you de-anodize it without getting it into the motor windings? Would i be able to do it with my 540C 7XL? |
If I read his post correctly, he was using a scotchbrite pad to hold the motor and the abrasion wore away the anodixing off...
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I can explain to R&D engineer how it works and why, here we have other problems...
Post the Q and I will answer! But it is very difficult to explain how it works if there such big gaps in theory... Bring, I am sorry but while your experiment is great, but the way how you explain what happen is really bad! Do not treat it simple and do not make as complex as it looks.. |
Less resistance zero;
the lower the KV, the less resistance it has, and the less energy it produces when turning. The higher the KV, the less resistance it has, and the more energy it produces when it's turning. I did sealed the motor with tape, both the front and the rear. (so the bearings etc. where well protected) |
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I will be back later, need to go. |
Well, I don't want to seem superstitious or anything... but I think, I THINK there is a new thing out on the street, it's called inductance? :005:
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Yes, i agree |
then what makes the different KV? it's not efficiency. internal resistance varies with different KV's and since some producers of motors give the KV value with the motor as a generator, i don't think your theory is right?
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Sorry Artur; i meant internal resistance; not mechanical resistance..
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If you have motor 10 meters of copper wire goes through the magnetic flux but in one configuration you have single wire and in another double, the amount of power would be the same. One will have higher voltage another higher current... Kv is complex number based on Magnet strength, gap, core properties, windings and much more, there are complicated programs dealing with how to calculate or estimate its value and most of them still black magic, in reality it is much easier to measure... Now, definitely need to run :) On braking part, there plenty BL motor control algorithms published on line, fined them check them. There is no other magic then shorting phases to stop the vehicle. And none of real R&D engineers will publish here unless he want to loose his job :) |
Yeah, but i was talking about braking; this whole topic is about braking; so when i said that the motor of a lower kv produces less energy when turning; i meant that with the motor as a generator, and the energy it produces when the motor is turning, due to the inertia of the vehicle/moving mass. I guess i told it with too few words..
A lot of misunderstandings are going around here... |
higher numbers of turns, higher inductance, along with the core which it's wound on, and some other factors which may be out of control as far as manufacturer techniques that will probably effect efficiency as well as Kv.
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Would it be safe to use motor braking on a MM with 12 NiMh cells in a Jammin buggy with a fegiao 8xl and 14/46 gearing?
Thanks. |
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I agree with you Brian, that is the most it can do when shorted.
I think a better experiment would be to bring up to speed the wheels of a MT, and have motor connected with no ESC (motor is on motor mount). And then short them out and see how fast it slows it down. Keep in mind, it doesn't take much resistance further up in the drive train to slow things down wind (wheels). The drill experiment shows lots of resistance, but that is a drill, and a drill only puts out more torque the slower it spins.... so it doesn't show us how fast it would slow it down. I'm thinking a flywheel experiment? Artur, is there a diagram that you have, or COULD make that would show us exactly what is going on during braking in the FET; AND/OR when the voltage is high enough to charge batts? |
Just a thought, another way to brake an R/C car is to use alum. disc with neo magnet (disc type) and have a servo driven actuator to bring it into very close proximity to the disc. This creates tons of shaft resistance, and would not stress motor or anything. BUT, would not be super responsive as the servo would have to move it in and out. But would always work.
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Sounds like it would take about as much time as a normal disc brake setup since you are basically doing the same thing.
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actually probably longer, because it has to get aways away from it in order to stop resistance. (does anyone know of a magnetic transistor? :005: )
BTW, this setup cannot be explained by regular Faraday laws of induction. There have been many 'over-unity' claims by such setups. |
Saw this posted in the tekin forum:
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I guess that confirms regen on braking. |
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