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Old Jan 03, 2012, 05:27 PM
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Originally Posted by Mukenukem View Post
Andy told me that, too. I wrote in the service form that they should also calibrate the battery voltage when sending it in for the complete package (gimbals, DSM-2 update). They didn't. Voltage is still off by 0.3V.

I do not need wrong values displayed. I want the real thing. Period. It is really annoying. Also SOME of the telemetry modules are .2-.3V off on the flight battery (compared some TM1100 and TM1000, same battery with no load, same RX, different values). Not all, so it seems that the resistors in the voltage divider on the input are not precise enough (or the values are not calibrated). Either is annoying. I want exact values, not "something around".....

"Safety margins" should not be hidden behind wrong values. Just make the alarm voltages fool-proof. Either it's poor design or a bad marketing decision (we know how good marketing guys are in making weong decisions).
As an Electronics Tech/Electrician I agree 1000%!

VP

PS: As an RC Enthusiast I agree 500%
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Old Jan 03, 2012, 05:30 PM
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Originally Posted by beltec View Post
Hi I've just purchased a new AR6110e receiver but find it won't bind to my DX8 (2.04). However it will bind to the club's DX6i.

The DX8 has been back to HH for the RF deck upgrade.

Should the AR6110e and DX8 be compatible or I am missing something?
Try keeping the Tx at least 6 feet away from the rx during a bind.
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Old Jan 04, 2012, 07:36 AM
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Taking normal working voltage as 4.8v and a 0.3v variance this gives a readout error of around 6.5%


LizardMan - Try the same test at 1/8c or 250ma as this is probably a more realistic average current draw. I've conducted many controlled battery experiments before and it's often possible with quality cells to exceed the quoted ma rating by 10-15% when discharging at low currents such as 100ma.
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Old Jan 04, 2012, 07:43 AM
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Originally Posted by badger-b View Post
Try keeping the Tx at least 6 feet away from the rx during a bind.

Thanks badger-b. Tried it at various distances but the RX still won't bind with the DX8. I'll find another club member with a DX8 to determine whether it is the RX or the DX8 that has to go back to HH.
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Old Jan 04, 2012, 09:15 AM
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Originally Posted by Mukenukem View Post
Andy told me that, too. I wrote in the service form that they should also calibrate the battery voltage when sending it in for the complete package (gimbals, DSM-2 update). They didn't. Voltage is still off by 0.3V.
I think this voltage difference is software/firmware driven, as everybody's TX seems to be 0.2/0.3v out. And when the DX8 1st came out and had V1 firmware my voltage was correct then from the very 1st update that's when the voltage difference occurred, well it did on mine anyway!
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Old Jan 04, 2012, 09:31 AM
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They probably want to keep displaying the correct voltage exclusive for dx10 only. You know, they pay more, so should have advantages.
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Old Jan 04, 2012, 11:34 AM
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Originally Posted by struggleforlife View Post
they probably want to keep displaying the correct voltage exclusive for dx10 only. You know, they pay more, so should have advantages.


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Old Jan 04, 2012, 01:41 PM
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Originally Posted by struggleforlife View Post
They probably want to keep displaying the correct voltage exclusive for dx10 only. You know, they pay more, so should have advantages.
Ha Ha ! Funny!

VP
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Old Jan 04, 2012, 03:38 PM
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I had the same. When I got my first, fresh off the boat DX8 when it appeared, the voltage was correct. After some firmware updates, the voltage was wrong. Either the firmware-update messed with the calibration data, or the false reading was introduced by the firmware.
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Old Jan 04, 2012, 05:55 PM
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I apologize in advance if this has been discussed before, but my search turned up nothing useful.

I've been flying RC planes about a year amd recently upgraded from the DX6i to the DX8. The DX8 has two built in Mixes: Ailerons > Rudder and Elevator > Flaps. The first one make sense, but I can't think of a use for the second one. Could someone clue me in as to why one would ever need a Elevator > Flaps mix? I'm primarily into airplanes, so maybe its just something I haven't run into yet.
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Old Jan 04, 2012, 06:39 PM
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When an aeroplane lowers flaps the pitch trim can change quite dramatically. If this wasn't compensated for the aircraft's flightpath would suffer in the period before the pilot puts in a corrective input and then trims for the new attitude. This mix gives the modeller an opportunity to automatically compensate for this pitch trim change. This corrective elevator input is also common in full size fly by wire aeroplanes. As an aside, you may also consider changing the flap servo speed for a more scale flap function.
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Old Jan 04, 2012, 08:30 PM
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Originally Posted by Lilienthal View Post
The DX8 has two built in Mixes: Ailerons > Rudder and Elevator > Flaps. The first one make sense, but I can't think of a use for the second one. Could someone clue me in as to why one would ever need a Elevator > Flaps mix? I'm primarily into airplanes, so maybe its just something I haven't run into yet.
Elevator>Flaps is "snap flaps", used for high bank tight turns, like pylon racing turns. Take it easy on that one, it creates very high stress on the wings - high G loading.


Quote:
Originally Posted by 744drv View Post
When an aeroplane lowers flaps the pitch trim can change quite dramatically. If this wasn't compensated for the aircraft's flightpath would suffer in the period before the pilot puts in a corrective input and then trims for the new attitude. This mix gives the modeller an opportunity to automatically compensate for this pitch trim change. This corrective elevator input is also common in full size fly by wire aeroplanes. As an aside, you may also consider changing the flap servo speed for a more scale flap function.
That compensation would be Flap>Elevator. It's available in the flap menu.
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Old Jan 04, 2012, 09:04 PM
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Quote:
Originally Posted by 744drv View Post
When an aeroplane lowers flaps the pitch trim can change quite dramatically. If this wasn't compensated for the aircraft's flightpath would suffer in the period before the pilot puts in a corrective input and then trims for the new attitude. This mix gives the modeller an opportunity to automatically compensate for this pitch trim change. This corrective elevator input is also common in full size fly by wire aeroplanes. As an aside, you may also consider changing the flap servo speed for a more scale flap function.
Excellent explanation!

Harry
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Old Jan 04, 2012, 09:11 PM
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Thanks LizardMan. That's what I wanted to know. Makes sense now that I think about it. It sounds like "elevator on steroids".

Still not sure how this merits a "built-in" mix. Sounds like it is pretty specialized compared to the other built-in mix. In any case, I'd be happy to get rid of both of these in favor of more custom mixes.

744drv, you are talking about a Flaps > Elevator mix, but my question is about the reverse - a Elevator > Flaps mix.
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Old Jan 04, 2012, 09:24 PM
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Originally Posted by 3d Marky View Post
LizardMan - Try the same test at 1/8c or 250ma as this is probably a more realistic average current draw. I've conducted many controlled battery experiments before and it's often possible with quality cells to exceed the quoted ma rating by 10-15% when discharging at low currents such as 100ma.
10 to 15% wouldn't account for discharging over 1150 mAh after the low voltage alarm triggered. The pack's capacity is only 2000 mAh.

The discharge test aborted after 11 hours due to elapsed time, not reaching the voltage limit. During the test voltage dropped only 0.25V. It hadn't discharged to 4.6V yet, it started at 4.88V. The test termination voltage limit was set to 4.0V. The DX8 was set to the default 4.3V, which is really ~4.6V.

I'd be surprised if the DX8 draws much more than 125 mA, until the LCD back light and/or vibration are active. Those features likely consume an additional 125+ mA each. With the LCD back light and vibration motor running load is likely 500 mA, or higher.

It seems the DX8 can use less than half of its NiMH pack capacity. Not because of basic TX functionality, it's the LCD back light and vibration features that strain the NiMH battery. Other Spektrum radios lack both of these power hungry features.

It looks like the 0.3V "error" is there for a reason. Discharging to 4.3V (actual pack voltage) without the LCD back light and/or vibration active could brown-out/reboot the DX8 when they became active. That's a serious problem that must be avoided.

As others have suggested, the NiMH pack may be an after-thought to reduce costs. This would explain the decades old NiMH charging circuit design, the need for the voltage display "error", and why it seems to have appeared after a firmware update. Remember the early problem with the vibration alert? The "error" might be part of the "fix" for that problem.

Is the voltage display "error" present using a LiPo pack? It shouldn't be required under LiPo power.

I'll run a discharge test with a higher load next time the DX8 requires charging.
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