Motors start up at too high a R.P.M.

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nicholasjacobs1958
Posts: 10
Joined: Fri Sep 20, 2013 12:57 am

Motors start up at too high a R.P.M.

Post by nicholasjacobs1958 »

MW 2.2.

I'm using some 22 sized motors on a bicopter. After calibration of everything, including direct rx to ESC I found the the minimum speed (start up) of the motors is too high - in fact the copter jumps up uncontrollably.

My Futaba tx is set to +- 125% (no trim) on the throttle. I'm using plush 18A controllers (but that makes no difference, because I swapped them out for Afro's with Simon K s/w and get the same result).

When direclty connected to the the rx, the esc fires up very slowly (both Plush and Afro), as I advance the stick just past resting spot. The tx shows -114%.

I plugged the gui in and see the tx values at rest is 993, and the motor starts up 1100 in the gui - much faster than they did when connected directly to the rx.

What I think should happen is that at 995 - 1000 the motors should spin up slowly, but instead they don't start up until 1100, and are in second/third gear already at startup!

I've played with MINCOMMAND, MINTHROTTLE and MAXTHROTTLE to no avail.

I searched the code for 1100 and found MINCHECK set to this value. It appears to constrain the minimum value for throttle sent to be 1100, not 995 - 1000 as is needed for the minimum value to the ESC to spin up the motor slowly.

I think the code below should be modified to use MINTHROTTLE instead of MINCHECK and MAXTHROTTLE instead of 2000 and that should resolve my issue.

tmp = constrain(rcData[THROTTLE],MINCHECK,2000);
tmp = (uint32_t)(tmp-MINCHECK)*1000/(2000-MINCHECK); // [MINCHECK;2000] -> [0;1000

There is also a MAXCHECK set to 1900. This is not, but probably should be linked to MAXTHROTTLE.

Am I on the right track or did I miss something or do something out of order.

I also tried the MW calibration (cannot fly) but it didn't make any difference.

Thanks In advance
Nicholas

tovrin
Posts: 705
Joined: Tue Sep 20, 2011 4:08 pm

Re: Motors start up at too high a R.P.M.

Post by tovrin »

First, please make sure you have properly calibrated your ESCs so they all match, huge issues if you skip this step

//#define ESC_CALIB_CANNOT_FLY // uncomment to activate
uncomment this after removing your props, load the sketch reboot your FC using LI-Po
comment above and reload sketch, reboot FC and you are properly calibrated.


secondly the one you need to play with is this;

#define MINTHROTTLE 1064

keep turning this down until your motors do NOT turn on when armed, then turn it slightly back up, BUT IT WILL ONLY WORK RIGHT IF YOUR ESCS ARE CALIBRATED PROPERLY. see First.

I hope this helps, it sounds like a common problem.

nicholasjacobs1958
Posts: 10
Joined: Fri Sep 20, 2013 12:57 am

Re: Motors start up at too high a R.P.M.

Post by nicholasjacobs1958 »

Tovrin

I have already calibrated (run through ESC_CAILB_CANNOT_FLY as I indicated) and yes, did restart using the LiPo (and disconnected the usb after sketch load )

I also #define MOTOR_STOP which prevents the motors from spinning up when armed (this forces MINCOMMAND instead of MINTHROTTLE on arming)

The problem is not that the motors do not arm, they do. The problem is that they do not start spinning until the throttle gets to 1/4 full, (and GUI shows a value of 1100 ) and then they are spinning at 1/4 speed already.

I want the motors to start spinning slooooowly as soon as I raise the throttle from rest position, this would be when the GUI shows a value > 995.

Thanks for your help
Regards
Nicholas

tovrin
Posts: 705
Joined: Tue Sep 20, 2011 4:08 pm

Re: Motors start up at too high a R.P.M.

Post by tovrin »

ok, lets start by disabling motor_stop this confuses things, turn it back on later when you have the other issue worked out, if you desire, i never use this function, my props spin at slow speed when armed at min throttle, i like it.

once motor_stop is disabled, use the above method tuning minthrottle until you get it where you want it. and go from there.

drongo
Posts: 1
Joined: Tue Dec 03, 2013 4:21 am

Re: Motors start up at too high a R.P.M.

Post by drongo »

Hi did you fix this problem? I have the same problem .In multiwiiconf as i increase throttle from 980 to 1099 motors all stay on 1000 and don't spin. As soon as throttle goes over 1100
motors all jump up to 1300-1350 and spin quite quick. I tried flying it but as throttle gets to just under quarter motors start up and it climbs very quick and if i back off just a little they stop dead and the quad drops out of the sky. I have tried adjusting #define MINTHROTTLE, #define MINCOMMAND and calibrated esc a dozen times with //#define ESC_CALIB_CANNOT_FLY // uncomment to activate. If you found the answer please share.

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Hamburger
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Joined: Tue Mar 01, 2011 2:14 pm
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Re: Motors start up at too high a R.P.M.

Post by Hamburger »

When you change minthrottle in config.h you must reset via gui or previously erase eeprom to see the new value active because minthrottle is stored in eeprom.

isladelobos
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Joined: Sat Feb 06, 2016 4:43 am
Location: Spain

Re: Motors start up at too high a R.P.M.

Post by isladelobos »

This thread was userfull.

i have maked a table with the velocity in (rpm) with and without calibration.
with a digital tachometer.

Image

Now the min velocity is ok.

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