Converting a gas Quad to AC

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Johny
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Converting a gas Quad to AC

Post by Johny » Tue, 17 Jul 2012, 22:04

It looks to me like you have room to put the fan housing cover back on and mount a slim fan inside it - provided it misses the encoder.

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Post by peskanov » Wed, 18 Jul 2012, 14:41

Johny,
The current clamp meter is unlikely to be able to accurately read the PWM signals that are being fed to the motor phases.

When you revved up, the PWM became closer to a normal steady waveform so the meter may have seen this "more correctly".

I would not take much notice of motor current as read by a clamp meter - unless you knew it was OK with PWM.
That's certainly a posibility. However, now we also have a DC amp meter installed on the battery bus, and that one seems precise. We also detect high current in low revs (in the Quad, didn't check without load).

Our AC clamp ammeter is a very cheap one; its reading changes very slowly, so I guess it takes the average of lots of samples to calculate the amps. I know this means nothing, as the important factors are its sampling rate and its capability to adapt to different frequencies (not just 50/60)...however, my intuition says the readings shown are not misleading.
If you are worried about a fan in a dusty environment use a 6-8 inch car radiator cooling fan. While your internal cooling was an interesting idea, it means that you a blowing rubbish (even if filtered) into the inside of the motor. I'd seal it up again and cool externally as thingstodo suggested.
I am not very worried about some a bit of dust, as AC motors look really resistant to it. Recently I opened a 5 kw motor and found about 1 liter of water inside, clay and mineral formations everywhere. It was still working! Image
We will probably end using external cooling as you say, but I will try to read temperatures before disassembling the air pump. I want to know how this concept works, as I have seen something similar working on DC motors.
It looks to me like you have room to put the fan housing cover back on and mount a slim fan inside it - provided it misses the encoder
Unfortunately, there is little space there. We would be forced to rebuild the brake pedal in order to add the original fan + encoder.
We will probably try external cooling using multiple fans set on the sides of the motor. We are also pondering liquid cooling, using copper tubes.

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Post by peskanov » Wed, 18 Jul 2012, 15:28

Thingstodo,
thanks for your comments; are you the same thingstodo converting an S-10 to AC? I've been following your thread on ecomodder, I found it after seen your car on EValbum. Really great work, I am learning a lot in your thread. BTW, you are using a beast of a motor, industrial 30KW AC. It must weight a ton!Image
If you saw 30A on the clamp display for a few seconds as you were speeding up, something is not matching between the Kelly and the motor. No load, the motor should not be pulling 30A. The Kelly output voltage is too high at low speeds. This should cause rapid heating in the motor.

I have no experience with the Kelly, so I'm not much help with the specifics. On industrial controllers the current does not go above 35 - 50% as you accelerate slowly (10 - 15 seconds from 0 - 100% speed) with no load. The voltage rises pretty close to proportional for the speed.
Well, as the motor was rewound to 63V, I am not sure what the Amps rating is now (but it should be quite higher). I am still learning to calcule amps on 3 phase systems; still, 30A seems higher than 50%, no matter how I calculate the nominal amps.

I think you are right with the voltage clue. I checked the minimal voltage setting, and it was setup quite high, to 9V (as we wanted to improve acceleration time in our previous project). I will change it and try again.
Motor vibration is not normal near rated speed. Again, I'll blame the Kelly and a setting of some kind for that. When you are starting up a bit of vibration (when you are turning less than 50 rpm) is normal and is called cogging.

Did I read that right - no motor heating when you had 30 amps going through that motor?
We did not sustain the speed of the motor in those high currents...and that test had no load. My comment about heat really meant something like "fortunately, nothing burned on 1st try".
The case looks totally enclosed, fan cooled by the ribbing on the outside. Did I miss holes in the end bells where you can see the rotor?
It is, enclosed like all classic AC motors. Original cooling was also the usual one, as you described.
I think that external cooling only would work for you. If you go with external cooling only, you can use a larger diameter fan so the noise goes down but the amount of air that it moves goes up. If you are driving at 60 kph I don't think the motor would even need a cooling fan. At 10 kph, yes I think it would. Perhaps use 2 or 3 of the 12V computer fans with plastic blades, but real bearings.
Yes, we are thinking about that and this scheme will probably be the definitive one.
Computer fans seem a bit weak for this application. The ones I have seen only have 3 or 4 watts of power...
If the motor is TEFC like I think it is, there is heat in the rotor and in the stator. If the only cooling used to be the fan on the end bell, the motor is designed to get rid of the heat through the outside surface only.
Yes it is. However, I thinked that removing the heat directly from the coils/squirrel cage would reduce the posibility of coil's copper insulation burning (it seems all AC motors die that way, when they do). Also, heat raises the electrical resistance, and I thought lowering the temperature of those core components (which bear the electrical currents) could increase slightly the efficiency of the motor. A bit optimistic though, I guess. Image
I agree that external fans get dusty and they fail. If the motor gets up to 130C you will be able to tell from the heat you feel on the inside of your legs as you ride it!
That information leaves me more relaxed about the whole temperature thing, thanks a lot!

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Post by peskanov » Wed, 18 Jul 2012, 15:50


Some new information about our conversion: weight.

Original weight (without gas in the tank) was
180 KG, 88.5 front, 91.5 rear (pounds: 397, 195 & 202)

Current weight, with nearly all EV components installed:
212 KG, 122 front, 90 rear (pounds: 467, 269 & 198)

Increase in weight is ~30 KG, not bad. But the vehicle is too heavy in the front now, and we are not very happy with that.
I think we should have used aluminum for all the new structures (battery boxes, motor base, etc...). That means learning to weld aluminum & buy/rent the equipment...but I think it's probably worth the effort.

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Post by thingstodo » Wed, 18 Jul 2012, 21:58

peskanov wrote: Thingstodo,
thanks for your comments; are you the same thingstodo converting an S-10 to AC? I've been following your thread on ecomodder, I found it after seen your car on EValbum. Really great work, I am learning a lot in your thread. BTW, you are using a beast of a motor, industrial 30KW AC. It must weight a ton!Image
Yes, thingstodo is the same guy - me - on both sites. Glad to here that you are enjoying the thread.

Yes, the 40 HP motor that I am attempting to use without a transmission is over 600 lbs. A beast by any measure.

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Post by thingstodo » Wed, 18 Jul 2012, 22:26

peskanov wrote:Well, as the motor was rewound to 63V, I am not sure what the Amps rating is now (but it should be quite higher). I am still learning to calcule amps on 3 phase systems; still, 30A seems higher than 50%, no matter how I calculate the nominal amps.


Another quote from the motor faceplate posting
but choosing the unheard-of voltage of 63V/110V
Let's try the easy way - straight proportions.
Start with 220V delta and 16.4A. 220V / 63 is pretty close to 3.5. The voltage goes down, the current goes up. So 16.4A * 3.5 gives just over 57A, lets round to 57.5A. That should be a good ballpark number but it assumes a few things about the rewind that I don't know - the gauge of the wire is the same, the number of turns on each coil is the same, the number of coils is the same, the cross-sectional area of the coils is the same ...

30A is just over 50% of 57.5A so a reading like that when starting to accelerate is possible - as Johny mentioned, the digital clampon meter could read a bit erratic.

How did your motor rewind guy come up with a drawing to rewind a motor between 1/3 and 1/4 voltage? I'd like to see a wiring diagram if you have one.

Why am I interested? The motor rewind shop I have talked to has drawings to 'split' the 'normal' (in north america it's normal) 460/230 induction motor coils. The splits that they list are 1/2 voltage, 1/3 voltage, 1/4 voltage. These drawings only work if there are the right number of coils per phase, so they can be evenly divided into 2, or 3, or 4.

Each coil in the motor is connected in series or parallel with other coils in the same phase. The sets of coils match current, and are put in series to add the voltages and get 'standard' voltages at the motor terminals. To reduce the rated voltage, sets of coils are put into parallel instead of sets in series with other sets.

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Post by thingstodo » Wed, 18 Jul 2012, 22:28

peskanov wrote:
I agree that external fans get dusty and they fail. If the motor gets up to 130C you will be able to tell from the heat you feel on the inside of your legs as you ride it!
That information leaves me more relaxed about the whole temperature thing, thanks a lot!
Your welcome!

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Post by peskanov » Sun, 22 Jul 2012, 12:40

Ok, I take back what I said about our cooling experiment. Airflow is enough, it works.

We tested the Quad on a very hot day, about 40o C (we rarely see higher temperatures here, hottest I remember was 45).
We have a thermistor set near the coils, and out of the air flow path.

We ran the Quad on a small circuit, with battery bus amps going up to 60. Lots of acceleration over slopes, regen, etc...

Internal motor temperature stabilized around 60o C, and never rose over that. External motor was lower, maybe 50o C.

Still, the 12V pump we are using is too noisy, so we are going to look for some alternative.
We will also add 2 external fan on the sides of the motor.


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Post by peskanov » Sun, 22 Jul 2012, 14:05

thingstodo,
Yes, the 40 HP motor that I am attempting to use without a transmission is over 600 lbs. A beast by any measure.
Maybe you will find this interesting. Wayland (from "white zombie" dragster fame) had a motor lightened machining new motor end plates (using aluminum).
http://photos.plasmaboyracing.com/purpl ... minum_Work
How did your motor rewind guy come up with a drawing to rewind a motor between 1/3 and 1/4 voltage? I'd like to see a wiring diagram if you have one.
I am not really sure about the way he chose that voltage. He said that the main dificulty was inserting the wires into the slots, and he had to choose a new wire configuration easy to fit in.
He kept the same general winding scheme, this one:
Image
I think he even used the same wire, but instead of using the original 3 parallel wires, he used 10. Unfortunately I am not sure about all this.
BTW, I made a comment previously about the new wiring having 6 wires, and the old one 2. That was wrong, the new coils has definitely 10 parallel wires.

Hope it helps!

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Post by thingstodo » Sun, 22 Jul 2012, 16:49

peskanov wrote: thingstodo,
Yes, the 40 HP motor that I am attempting to use without a transmission is over 600 lbs. A beast by any measure.
Maybe you will find this interesting. Wayland (from "white zombie" dragster fame) had a motor lightened machining new motor end plates (using aluminum).
http://photos.plasmaboyracing.com/purpl ... minum_Work
That is some pretty impressive work!

I will do some (if perhaps not all) of my testing with the big beast as-is. For me, being mechanically challenged, the task of connecting the motor directly to the transfer case is an issue. If I end up keeping a gearbox of some sort, many of the advantages of a big, heavy industrial electric motor go away.

I'm cheap, so I won't put any work into the motor until I am sure that I will be using it for more than testing.
peskanov wrote:
How did your motor rewind guy come up with a drawing to rewind a motor between 1/3 and 1/4 voltage? I'd like to see a wiring diagram if you have one.
I am not really sure about the way he chose that voltage. He said that the main dificulty was inserting the wires into the slots, and he had to choose a new wire configuration easy to fit in.
He kept the same general winding scheme, this one:
Image
I think he even used the same wire, but instead of using the original 3 parallel wires, he used 10. Unfortunately I am not sure about all this.
BTW, I made a comment previously about the new wiring having 6 wires, and the old one 2. That was wrong, the new coils has definitely 10 parallel wires.

Hope it helps!


The diagram helps a lot, thank you.

Perhaps the reason that the voltage changed to a number different from 1/3 or 1/4 is that he used smaller wires but more of them? The inductance of the motor changes with several parameters, including number of turns and cross-sectional area (gauge of the wire).

Thanks for satisfying my curiosity.

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Post by peskanov » Mon, 23 Jul 2012, 13:25

Maybe you will find this shaft connection interesting. I found it recently, it's pretty simple and it even implements a cheap encoder.

http://www.evalbum.com/1687

About the coils; I am pretty sure the technician was determined to use the same wire size, in order to fit the new coils in the same space of the older ones.
When we talked, he was very reluctant about using thicker wires. In his opinion, problem number one in a work like this is slot aperture and size. He also commented on ABB motors; he said ABB were the best motors for rewinding operations.

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Post by weber » Mon, 23 Jul 2012, 15:01

peskanov wrote: Maybe you will find this shaft connection interesting. I found it recently, it's pretty simple and it even implements a cheap encoder.

Image

I note that this kind of coupling is only possible when there is a sliding joint in the propshaft. And I note that this DIY encoder proved to be too coarse to allow the VFD to work properly and a regular encoder was fitted elsewhere.
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Post by peskanov » Wed, 25 Jul 2012, 14:42

weber,
that's good to know, because we were interested in that kind of encoder in the past.
We even have a 36 teeth cog for it. I thought 36 pulses would be enough for the controller, now I know better. Thanks.

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Post by peskanov » Wed, 25 Jul 2012, 15:11

We have been toying with the Quad several times now, and I am already finding limits I cannot surpass changing the settings of the Kelly KIM.
Of course, my understanding of the settings is limited and Kelly's documentation is minimal.
My biggest problems right now:
- Locked rotor torque, and pull-up torque (at very low RPM) seems poor. The Quad will not even start moving on some slopes.
- Maximum amps & power we have seen on the DC bus is 90A. I don't expect to get 200A, as I understand these are motor amps, but 90A seems too low.
I think that could be related to motor voltage. 63VAC * sqrt(2) is 89VDC. Our pack usually shows ~80V, but voltage sagging will reduce that number...
- There is a problem with the max. acceleration slip setting...if I push it over 7Hz, the motor starts with severe cogging and I am not able to supress that.

Here there is a capture of the settings. The KIM is quite simple, there is only about 40 settings (not all of the shown here).
Image
Image
I still have to understand what "proportional coefficient" and "integral coefficient" are. Kelly's explanations are extremely vague.

Any suggestions? Low RPMs torque is our main interest.

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Post by woody » Wed, 25 Jul 2012, 15:16

peskanov wrote: I still have to understand what "proportional coefficient" and "integral coefficient" are. Kelly's explanations are extremely vague.

Any suggestions? Low RPMs torque is our main interest.
Proportional / Integral / Derivative Controller is very common way to adjust inputs to achieve a stable targeted output without taking too long and without overshoot / hysteresis. I'm not sure how Kelly is using it in their controller.
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Post by Johny » Wed, 25 Jul 2012, 16:03

I think woody is right - "proportional coefficient" and "integral coefficient" have to do with how they control the motor loop with regard to speed feedback from the encoder.

The Kelly appears to be a speed controller that uses acceleration ramps to control the rate of increase of frequency. A controller that used torque control wouldn't have these issues.
I would suggest dropping the minimum voltage and frequency to try to help with low speed starts. Also dial back the acceleration so that the motor better follows it's ability to accelerate the vehicle mass without slipping so far that it cogs??(term here).

I have seen earlier on this thread that it's a 4kW motor rewound to 63 volts. Is this star or delta voltage and how have you got the motor wired?
How many cells are in the pack. I count 32 but I might be wrong.
If you give me your final figures - tyre diameter, pack voltage, controller output max. current, motor voltage - I can use woody't SS to estimate your max climb gradient. That won't help with starting or stall torque though - see following.

Note that a speed only V/F controller (which I think the Kelly is) will not give max. torque at stall. A vector controller will provide full torque at stall.
See graph for V/F controller.

Image

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Post by peskanov » Thu, 26 Jul 2012, 14:04

woody,
thanks, there is a lot to learn about this PID system! Fortunately the KIM only uses 2 parameters of 3, proportional & integral. So less fooling around trying to adjust it...

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Post by peskanov » Thu, 26 Jul 2012, 14:33


Johny,
the settings I posted work ok, no cogging. I get this cogging or jerkiness problem only when pushing "max acceleration slip" over 7 Hz, and only on start. I guess this slip frequency is too high when the motor is only working at 5 hz or less; I feel the motor is trying to reverse the spin fordward-backward continuosly.

About minimum voltage and frequency, we rose them trying to get better starting torque. We started with voltage 2V, and gradually rose it to the maximum, 10V. Each time, start torque improved.
I will try to reduce minimum frequency, as I am not sure rising it helps with the start.

Current data for our Quad:

- Motor 4 KW, frame 112. Most motors of this size/power have a nominal torque of 26-34 Nm. Not sure about ours.
- Delta/Star 63V/110V. Connected in Delta, 63V.
- Pack: 24 cells of 60AH, lifepo. We usually see 76V-81V unloaded.
- Tyre diameter: 47 cm.
- Transmission 11:45 (so 4.1 torque factor)
- Weight: 220 KG + passenger, about 300 KG in out trials.
- Max. current: Kelly say 200A, but not sure if they are talking AC or DC.
- Motor wiring: you can see the scheme posted in this thread a bit earlier, I posted a picture of it. I hope that's what you are looking for.

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Post by Johny » Thu, 26 Jul 2012, 16:05

Sounds good - you are clearly on top of it.
I'm pretty sure that the controller is 200 Amps motor current.
Given the data you just supplied:
Image
Yellow is km/h.

I have assume Tn of 27NM (typical for 4kW, 4 pole ACIM) and Tmax/Tn of 3.3. If I increase TMax everything improves dramatically so the controller isn't current limiting you.
Since any motor's Tmax appears to be somewhat dependent on the controller and/or V/Hz these figures probably aren't that meaningful but I thought I'd post them anyway.

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Post by thingstodo » Thu, 26 Jul 2012, 18:00

peskanov wrote: woody,
thanks, there is a lot to learn about this PID system! Fortunately the KIM only uses 2 parameters of 3, proportional & integral. So less fooling around trying to adjust it...


Here is a decent description - perhaps not technical enough - for PID control using cruise control as an example

http://auto.howstuffworks.com/cruise-control3.htm

On my test 5 HP motor, 4 pole 220VAC, a starting frequency of 0.9 Hz seems to give me the best starting torque. I have not gotten SalvageS10 rolling yet so I can't comment on the max acceleration.

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Post by thingstodo » Thu, 26 Jul 2012, 18:30

peskanov wrote:
Johny,
the settings I posted work ok, no cogging. I get this cogging or jerkiness problem only when pushing "max acceleration slip" over 7 Hz, and only on start. I guess this slip frequency is too high when the motor is only working at 5 hz or less; I feel the motor is trying to reverse the spin fordward-backward continuosly.

About minimum voltage and frequency, we rose them trying to get better starting torque. We started with voltage 2V, and gradually rose it to the maximum, 10V. Each time, start torque improved.
I will try to reduce minimum frequency, as I am not sure rising it helps with the start.

I have measured the most torque out of my test motor at 0.9 Hz (from 0 speed) and at the maximum boost - listed as 36% but measured at around 23 VAC. I think this is what your setting for minimum voltage would match. The motor heats up. Testing has been for 10 - 15 seconds at a time and I am trying to figure out max torque.

My motor is rated at 1745 rpm, so the slip for rated torque should be 1800 - 1745 = 55 rpm. 55 rpm / 1800 rpm * 60 hz should be 1.8333 Hz, but 0.9 Hz works better - I'm not sure why. And for higher starting torque I should have to use a larger slip, like 2, 3, or maybe 5 Hz like you have used.

When I try 1.8 Hz, I observe what I think you are describing as 'cogging'. Large torque, then no torque, then large torque again. I think that the slip is too high. The motor slips too far and produces no torque at all for a short time.


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Post by woody » Fri, 27 Jul 2012, 04:00

thingstodo wrote:
My motor is rated at 1745 rpm, so the slip for rated torque should be 1800 - 1745 = 55 rpm. 55 rpm / 1800 rpm * 60 hz should be 1.8333 Hz, but 0.9 Hz works better - I'm not sure why. And for higher starting torque I should have to use a larger slip, like 2, 3, or maybe 5 Hz like you have used.

When I try 1.8 Hz, I observe what I think you are describing as 'cogging'. Large torque, then no torque, then large torque again. I think that the slip is too high. The motor slips too far and produces no torque at all for a short time.

I don't think slip is proportional to rpm. From the point of view of the rotor, the slip is constant, so a nominal slip of 55rpm would be 0.833Hz. I would expect more torque at 1.8Hz (about double) if you had 2 times the nominal current available.

Hope this theory helps in practice!
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Post by thingstodo » Sat, 28 Jul 2012, 12:39

woody wrote:
thingstodo wrote:
My motor is rated at 1745 rpm, so the slip for rated torque should be 1800 - 1745 = 55 rpm. 55 rpm / 1800 rpm * 60 hz should be 1.8333 Hz, but 0.9 Hz works better - I'm not sure why. And for higher starting torque I should have to use a larger slip, like 2, 3, or maybe 5 Hz like you have used.

When I try 1.8 Hz, I observe what I think you are describing as 'cogging'. Large torque, then no torque, then large torque again. I think that the slip is too high. The motor slips too far and produces no torque at all for a short time.

I don't think slip is proportional to rpm. From the point of view of the rotor, the slip is constant, so a nominal slip of 55rpm would be 0.833Hz. I would expect more torque at 1.8Hz (about double) if you had 2 times the nominal current available.

Hope this theory helps in practice!

If I'm not calculating the slip right - where did I go wrong?

1800 rpm is synchronous speed for a 4 pole motor (2 pole motor would be 3600 rpm). 1800 - 1745 rated speed = 55 rpm of slip.

1800 rpm synchronous speed / 60 hz = 30 rpm per hz
So 55 rpm / 30 rpm per Hz = 1.833 hz of slip ... how did you get 0.833 Hz .. which matches my measurements much better, by the way?

I think you are correct about the slip not being proportional to rpm - a specific slip should give you a specific torque output. The only torque that I have from the nameplate is full load torque - well, it's calculated at 15 foot-lbs torque, 1745 rpm, and that gives you 5 HP at the output shaft.

I was testing the 5 HP 460V star-connected motor (rated about 7.5A full load) at 23V measured AC output, 0.9 Hz frequency setpoint on the VFD, over 30 amps of current to the motor (problems measuring that low a frequency with my equipment, so I'm not confident of the voltage and current).

I am pretty sure that I got at least 2X full load current (about 15 amps) since I measured 180% full load torque.

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Post by peskanov » Mon, 30 Jul 2012, 04:10

Johny,
we don't have the tachometer installed (yet). That should help getting real torque numbers. However, we can measure the slopes we are climbing.
Looking at your table, steepest grade seems to be 1 in 2.6.
If I am not wrong, that is 21 degrees. That sounds right, we tried to climb a 36 degrees slope and it was impossible without high inertia.

A question about torque: which factors limit AC motors torque? Shaft mechanical strength is obviously one factor, but I don't think we are near that limit. Heat is another one, but we are still far from it, seeing 70 degrees maximum.
So, what could be limiting the torque? The controller, or magnetic saturation, or...? Any idea?



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Post by peskanov » Mon, 30 Jul 2012, 04:22

thingstodo,
we tried to reduce minimal frequency, and it seems to help a bit with low rpm torque. Unfortunately, the KIM shown a bizarre behaviour, unseen before.
When decelerating to a stop, the KIM refused to really stop the work! You could read 10A or 20A still going to the controller, the Quad being totally stopped. The only way to kill the current was shutting off the controller; brake switch or releasing the throttle was ineffective.

That happened only climbing slopes, I think it worked ok stopping on a flat.

So we had to raise the minimal frequency again, up to 2.5hz. That was the minimal value we set in order to avoid the "false stop" problem.

BTW, I would love to have my own dynamometer. You are a lucky guy Image

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