johnpcunningham

retiredbri,

1) The large chip is a Hynix 8-bit MCU from china
2) The smaller chip is an MC3361 equivalent narrowband FM chip

The signal gets received from the 3361 and gets passed to the MCU as a series of pulses that are time divided for each servo and throttle position. If these vary due to a noise issue, it could make the servos jitter.
But from what you described, that might not be the issue. You are correct on the FET, motor gets high-side voltage and the FET switches via PWM. It is possible that the FET still works but has been damaged internally.
Might try changing it out with a International Rectifier IRLI3803 (via www.digikey.com). Which has lower Rds. Before doing that, you check out the default voltage on the gate of the FET. It could be floating electrically
and this could cause some noise. If that checks out OK, take a 3 amp diode and put it across the leads of the motor with the cathode to "+" battery side. This will greatly reduce the EMF. I believe these boards uses the internal
parasitic diode built in the FET, and it is just not enough.

Also, I have found that 7.4 volt lipos give better performance than the 8.4 NiMh and last longer. I'm wondering if your longer motor leads are causing an inductive effect that is creating noise on your board. Try out
a Lipo and see what that does.

Just some ideas to try in testing.

JC

retiredbri

Thanks for the reply.

If the pulse timing varies, wouldn't the motor speed jitter? haven't noticed any motor speed problems.

From what I remember, the jitter only started when I used Deans with longer leads to my original Rx board. I observed the jitter and went around re-soldering the servo joints as I had done before and blew the board up. I then replaced the Rx and with Deans fitted, it too had servo jitter.
Don't have a 'scope so not really viable but I have soldered a IN4004 onto the motor terminals. It didn't make any change. I think the board has a SM IN4001 rather than rely on the parasitic diode built in the FET.

Again not really an option with all my limited funds in the NiMH basket.
I thought that the lower impedance of the 16AWG wire I used, even though it is longer would not have made much difference. I'll get some heatshrink and shorten the leads on Wednesday and let you know.

I also need to see if the jitter has any real affect on the flying. All the days so far have had turbulent winds so can't tell if the rudder/elevator is causing the plane to be all over the place or the winds.

Thanks again for you ideas. I certainly can't afford to go to 2.4Ghz to get rid of the problem.
Regards, retiredbri

johnpcunningham

RF pulse timing would not effect the motor. The motor drive circuit is very crude. The difference between a few microseconds would not be detectable on the motor. There is a lot of dead space at 0% throttle
and this does not get through at low throttle. Brushed motors do not act linear; meaning a 50% duty cycle versus a 60/40% duty cycle is about impossible to detect in terms of motor speed. You could see it on
a scope but not in motor pitch.

retiredbri

Hi all

I've done everything and still have jitteres. [>:]
You will recall that the problem started when I fitted longer leads for Deans connectors. I shortened the leads and thought it was better but it wasn't consistent - different batteries were better/worse.
On a really calm Monday morning, the Cub waggled its tail all the way aroud a slow circuit and just as it landed, the elevator went full up and locked. It was only inches off the ground with no damage done. It was well past its normal travel and needed to be forced back to centre. [sm=48_48.gif]

I've given up with the stock electronics - it's cost me a fortune trying a new Rx and new motor without any improvement so am replacing the electronics with Spektrum Dx6i/Ar6200, 3 wire servos (with the future to add in ailerons) and ESC/BEC. I'll keeping the brushed motor and NiMH batteries. This will get me on the path of "proper" mode 2 Tx and to then after a good number of hours, to using ailerons and maybe flaperons.
The Cub is such a tough bird that I can fly without worry while I get the experience.
Regards
Retiredbri

richg99

Yep, that is where I went, after crashing the SC dozens of times with the original equipment, .... used while flying in a park surrounded by people and police on phones and radios.. I thought it was just fumble-fingers me, but a change in radio and systems makes her fly nearly daily. Smooth, easy and no surprise dives into the dirt. regards,Rich

cbatters

Longer leads add stray inductance that can cause induced noise on the PCB especially when the motor is run at partial throttle. Adding additional capacitors across the power leads on the receiver board can help eliminate the problem. (Problem is not unique to Supercub REC/ESC. You need to be cautious about adding addiitonal battery lead length to any ESC.)



Clint

lutz2

What is the minimum voltage needed to use the 6 channel zx10 receiver for a glider? I have a CH4 27 Mhz transmitter/receiver from an in the aerobird swift, it looks just like the one found in the Parkzone 2Spitfire MkII manual, except it has no case. I would like to greatly minimize the battery weight by using a lipo instead of the 8.4V 1000 mAH that came with the swift. I'm not sure how small I can go with this. By the way, this receiver seems to have an esc problem where the motor worked for a total of maybe 10 minutes and then never worked again. Otherwise it seems fine. Thanks

lutz2

FWIW, The 6-channel ZX10 receiver does work, without motor, with 6V from a Radio Shack 4xAAA battery holder, which is 52 grams with batteries vs. 151 grams for the 8.4V NiMH that came with the Swift. This is probably viable, since my older Great Planes Spirit RTF uses the same battery holder to power its Hobbico AM receiver. 3xAAA, 4.5V made the servos twitch but the transmitter didn't work. Maybe 5 or 5.6 is the minimum?

cbatters

Has anyone found good low cost source for HobbyZone 27MHZ receiver crystals. I use to get them from RadioShack but it appears RadioShack is no longer stocking the XMOD parts including the crystals.

12414454 CRYSTAL BAND 1 (26.540MHZ) RX $1.99
12414512 CRYSTAL BAND 1 (26.995MHZ) TX $1.99

12414520 CRYSTAL BAND 2 (26.590MHZ) RX $1.99
12414553 CRYSTAL BAND 2 (27.045MHZ) TX $1.99

12414561 CRYSTAL BAND 3 (26.640MHZ) RX $1.99
12414595 CRYSTAL BAND 3 (27.095MHZ) TX $1.99

12414603 CRYSTAL BAND 4 (26.690MHZ) RX $1.99
12414637 CRYSTAL BAND 4 (27.145MHZ) TX $1.99

12414645 CRYSTAL BAND 5 (26.740MHZ) RX $1.99
12414678 CRYSTAL BAND 5 (27.195MHZ) TX $1.99

12414686 CRYSTAL BAND 6 (26.800MHZ) RX $1.99
12414710 CRYSTAL BAND 6 (27.255MHZ) TX $1.99

lowdrag

Match up color codes to 27MHz Ch 1-6:

http://www3.towerhobbies.com/cgi-bin...Fb%3Etals+sets