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Old Oct 17, 2014, 06:31 AM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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The official Lemon DSM2/DSMX Telemetry system thread

A comprehensive set of instructions are now available here.

http://www.rcgroups.com/forums/showp...02&postcount=5


DISCLAIMER

With Lemon's blessing I have called this the "official" thread so there is one place to find things, but I have no connection with Lemon.

I don't work for them, never met anybody from there and don't get paid by them. I cannot answer questions about their product plans or deal with complaints.

I'm just a modeller who came across their product in the early days of sale and really liked them. Lemon sometimes send me protypes for my opinion as they do with other modellers. But that's it.

Lemon sent me the prototype of their DSM2/DSMX telemetry system and also one of the first production samples to have a look at. This thread is an attempt to gather all the information about it in a single place for convenience. Note this new product is not a copy of anything Spektrum, but an original design that uses the Spektrum data transmission protocol. Lemon have established a reputation for excellent long range reliable DSM2 and DSMX receivers at very low cost and are starting to expand their offerings. Their 7-channel DSMX receiver integrated stabilizer has also proved very successful.

So far I have verified the following:

1) The new telemetry unit works perfectly both with my Spektrum and Lemon receivers. I assume it will also work with Orange receivers but have not yet tested that. The connection lead plugs into the Bind port just like the Spektrum TM1000 unit. It works with all Lemon receivers that have bind connection pins including the 7-channel Stabilizer. Note that if you use Aux2 out on the stabilizer bind pins, the telemetry unit will work just fine using a Y lead. Lemon have fitted the telemetry system into the same case they use for their 7-channel stabiliser and provide a Temerature/RPM probe and compact Pack Voltage and Current sensor with the unit.

See picture 1 for a comparison with the Lemon 7-channel stabiliser and 10 channel DSMX receiver and satellite.

2) It gives all the telemetry readings automatically on a telemetry transmitter that a Spektrum unit does - except the Fades and Holds numbers and the 4 receiver/satellite individual values A, B, L and R. My understanding is these are a Spektrum receiver exclusive. However Lemon have used the A reading for a "quasi" RSSI calculated from the fade rate. It works but Lemon have said they have a much better version of the software nearly ready that will be close to a true RSSI number.

See picture 2

3) The base unit is half the weight of a TM1000.

See picture 3.

It is however full range and includes internal temperature measurement, receiver voltage and altitude without any external sensors. Altitude is AGL by default (set when you power up) but can be changed to an absolute value based on standard sea level of if you want to. It uses a Bosch BMP180 integrated digital pressure and temperature sensor which assumes an absolute pressure at sea level of 1013.25hPa. So the absolute height it reports will vary depending on barometric pressure at your location at the time. For example I live near sea level and on the dayI tested it the pressure was low and the altitude reported as -215ft! The calculations are all done by an Atmel Mega 88PA microprocessor.

See picture 4

4) It comes with a compact pack current and voltage sensor with Deans connectors in the first batch. I swapped mine easily to XT60 but Lemon will be providing an XT60 option very shortly. It also comes with an external temperature sensor and RPM indicator. The pack sensor is factory calibrated but can be recalibrated if you change it. Voltage limit is up to 30V and current up to 60 Amps.

5) It works with my Spektrum STi Telemetry interface (SPMTR1000) for the iPhone/iPad.

See picture 5

6) No idea on price and availability. You need to ask Lemon about that.

UPDATE: Lemon have just listed the telemetry unit on their web page for $44.80.

I will reserve the next few posts for additional information as it becomes available.

WARNING
Just a warning to anyone who has both a Lemon and Spektrum telemetry system.

The hardware is not interchangeable.

They both use the JST-ZH 1.5mm 3 pin connectors but neither the sensors nor the cables from a Lemon telemetry or Spektrum TM1000/1100 should be interchanged.

For instance the data cables that connect the telemetry unit to the receiver bind connector have opposite supply connections.

John
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Old Oct 17, 2014, 06:32 AM
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
7,450 Posts
Testing

I tested the prototype and first production unit on the bench. I will do some flight testing at the weekend.

Here's what I found out about the various readings.

Altitude

One of the fun things with telemetry for ordinary planes is knowing how high it is. It is not much use if that figure is hopelessly inaccurate however. It isn’t all that easy to test an altimeter. Carrying a bunch of electronic gear with stray wires and blinking LEDs to the top of the nearest tall building of known height in the city gets you unwanted attention from the security guys these days.

I settled for fitting the unit to an exactly measured 5m pole and comparing readings at ground level.

My DX8 display showed exactly 5m a lot of the time but it fluctuated about +0.7m and -0.8m over a 5-minute period. It was a windy day and I made no attempt to shield the unit.
I then left it on the bench after zeroing it with a thick towel over the whole thing to avoid any effect of drafts. Over a 5 minute period the reading varied from +0.1m to -1.1m but it did so in a fairly predictable smooth pattern and at the end was almost exactly 0.0m again. My interpretation is that this was normal barometric pressure variation. Without doing complicated higher altitude testing with helium balloons and a measured fishing line, my conclusion is:

The Lemon altimeter unit is very accurate and any errors are likely to be due to wind pressure and normal barometric pressure variation.

See picture 1 for a typical screen at the 5m altitude.

Current and Capacity

I measured the current into 3 different loads using my 40,000 count UNI-T 10Amp DVM and my EmeterII. The readings from the Lemon telemetry system were within the resolution of the Spektrum display, which reads only in full Amps.

Actual current
Displayed current

4.58 Amps
4/5 Amps flickering
6.6 Amps
7 Amps
17.8 Amps
18 Amps
I then checked the capacity measurement displayed on the “Powerbox” screen on the DX8 by discharging a 4S LiFe pack at 1 Amp using my Hyperion charger.

Actual capacity discharged
Displayed capacity

710 mAh
727 mAh
This is an error of less than 2.5%. On another test I did, but charging a pack, I got agreement within 1%. Lemon advises that the worst case is 5%. Most of the time it should be better.

Conclusion:
The current sensor is quite accurate by hobby standards.

Receiver and Pack voltage

I checked these against my UNI-T meter (which agrees to within 0.01V with 3 other DVMs).

Actual voltage
Displayed voltage

Receiver = 5.10 V
4.9 V
Pack (LiFe 4S) = 13.15 V
12.9 V
This is again accurate within the resolution limitations of the Spektrum display (0.1V). A receiver voltage of 5.01V could legitimately display as 4.9, 5.0 or 5.1V. I would have hoped for better. The receiver should ideally read 5.0 V and the flight pack 13.0V. I queried Lemon and they advised that my prototype unit was known to read low and that it was definitely a worst-case scenario for the production one. Take away message is that it is probably just fine for tracking voltage during a flight but the actual numbers are not DVM standard.
.
Temperature

I fitted the external temperature sensor together with a thermometer inside a closed tube to eliminate any draft effects and let them stabilize for 10 minutes. The thermometer is a Kodak Color Thermometer - a 10 inch glass Fahrenheit scale thermometer, with an accuracy +/- 1/2°F at between 68°F and 75°F. It was a gold standard for room temperature accuracy in its day and has the advantage of no electronic components or calibration issues.

Actual temperature
Displayed temperature

66.5°F
66°F

Conclusion:
The external temperature probe is very accurate at room temperature. Given that it is a 10kNTC thermistor, it is reasonable to conclude it is accurate at all temperatures. The internal temperature reported by the unit when no external temperature sensor is plugged in may be a little higher due to heat dissipation on the board.

RPM

The rpm reading does not appear to be as good as I hoped. It is measuring pulses from one of the motor wires and calculating the rpm from the frequency. In bench systems, accurate pulse counting is normally regarded as an easy task. In airborne telemetry systems it is apparently not as easy as it sounds!

My EmeterII has both optical tacho and a pulse reading RPM function. They agree within 20 rpm at 10,000 rpm – so it can be done.

I tested the Lemon RPM reading against a digital optical tach, which is known to be accurate. For example, it reads exactly 3000rpm when pointed at a 240V 50Hz incandescent source. I tested at various speeds using a motor known to have 6 poles (magnet pairs).

Optical tacho
Lemon displayed rpm

960 rpm stable
930 rpm stable
1160 rpm stable
1065-1117 rpm fluctuating
1392 rpm stable
1222-1275 rpm fluctuating
I do not have an RPM sensor for my TM1000 so cannot comment on whether this is similar to the Spektrum accuracy. Any body who has one - please comment.

My conclusion:
The RPM reading is fine for everyday use but don’t expect the kind of precision you get from an optical tacho or a proper bench quality Wattmeter like the EmeterII.

I understand from Lemon this is unlikely to change for the following reason. The RPM reading can only be an approximation as the data fed to the telemetry display is not a simple count of pulses. Thus the approximation is not due to a hardware issue. Lemon are limited by the Spektrum protocol and admit the RPM value submitted for transmission is a troublesome item. Their reverse engineering process came up with a complex equation to fit the data. Lemon suspect that Spektrum can't send the exact RPM value to the transmitter either (suggested because it can display more than 65535 RPM count while only 16 bits are used).

Frame Losses, Holds and RSSI.

The Lemon system does not report Frame Losses (F) and Holds (H) since this is data generated only by Spektrum receivers. Nor does it report individual packet losses on the 4 receivers/satellites A, B, L and R that Spektrum shows.

However Lemon DO use the A display for an RSSI value. The current version is a fairly crude scale of 0-100% based on the number of packets received about every half second and is not terribly useful in my opinion. However Lemon advise the next revision of telemetry will show an accurate RSSI value and they already have a bench prototype.

See Picture 2 for the current display.

Range

I will do some range testing when I get a chance to go flying with the system. Lemon claim it is in the same class as with the TM1000 system. The Lemon telemetry has slightly higher RF transmission power (Spektrum peak at 17dB. Lemon telemetry system peak at 22dB). However the telemetry system will disable transmission (like the Spektrum design) if it does not receive anything from the Spektrum transmitter so higher RF transmission power is just to guaranteed higher reliability in the return path for RF transmission.

From reports on a number of threads, the Spektrum TM1000 telemetry system does not have a great reputation for reliability at long range.

Be interesting to see how the Lemon one works out in practice.
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Old Oct 17, 2014, 06:32 AM
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
7,450 Posts
What's in it?

The telemetry unit fits in the existing lemon 7-channel stabiliser case (clever move to save production costs).

There is one pot on the PC board which is hidden under the label (which easily peels back to access it).

For most users this can be ignored. The stabiliser is factory calibrated and ships with Altitude as AGL by default. The altimeter rests to zero when you power up the unit.

The only time you need to access the pot is:

1) If you change the current sensor. You then have to power the unit and turn the pot fully clockwise. This calibrates the current sensor offset and is indicated by a solid green LED.
2) To change from AGL to ASL altitude. If the pot is in the centre, the altimeter automatically zeros at power up and shows altitude above the start point. A double blinking green LED confirms this. If it is fully anticlockwise it registers absolute altitude. The green LED is off.

See picture 1

The telemetry unit itself is pretty simple. Picture 2 shows the top view. There is a spare set of solder pads for a second Bosch BMP180 sensor below the xtal and microprocessor which Lemon may to use for air speed indication and a spare JST connector which may be used for an external gas engine RPM sensor or aGPS sensor in the future. None of this is confirmed however.

The bottom view shows the very neat double layer construction with a separate RF daughter board and the micro aerial connector. The telemetry unit uses Lemon's new long thin aerial with micro connector.
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Old Oct 17, 2014, 06:33 AM
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
7,450 Posts
Hints and Tips

Sensor compatibility with Spektrum
Fmak (Mr Lemon) just added this on the lemon receiver thread.

"The sensors will not be compatible with Spektrum sensor. That's why we have included all sensors. We don't want the flyer spending too much time on thinking what to buy and then how to make the connections to here and there to make it works. "


From Post #272
Just a warning to anyone who has both a Lemon and Spektrum telemetry system.

The hardware is not interchangeable.

They both use the JST-ZH 1.5mm 3 pin connectors but neither the sensors nor the cables from a Lemon telemetry or Spektrum TM1000/1100 should be interchanged.

Here is the Lemon and the Spektrum data cables that connect the telemetry unit to the receiver bind connector. Note that they have opposite supply connections.

GPS plans
"We should have GPS module very shortly. The GPS module will be likely to be very small and fit inside the satellite casing. We don't want the plane carries too much weight except battery."

Pinouts
From Post #273.

I had a poke around the telemetry unit with a multimeter and as far as I can tell this is what the various pins do.

Red, Orange and Black coloured pins are all connected together as far as I can tell. The Green pins are the data pins that accept incoming sensor signals.

Disclaimer: I have no knowledge of the exact circuit of the unit and some of this is just guesswork.
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Old Oct 17, 2014, 06:34 AM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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Reserved 2

For future info. To be added
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Old Oct 17, 2014, 06:34 AM
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
7,450 Posts
Reserved 3

For future info. To be added.
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Old Oct 17, 2014, 08:34 AM
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Joined Aug 2012
350 Posts
Hello John,

Thanks!

We will have the very first batch ready on Monday. The quantity is very limited until OCT 24 2014.

Best Regards,

Lemon Rx Officer

Quote:
Originally Posted by jj604 View Post
DISCLAIMER

With Lemon's blessing I have called this the "official" thread so there is one place to find things, but I have no connection with Lemon.

I don't work for them, never met anybody from there and don't get paid by them. I cannot answer questions about their product plans or deal with complaints.

I'm just a modeller who came across their product in the early days of sale and really liked them. Lemon sometimes send me protypes for my opinion as they do with other modellers. But that's it.

Lemon sent me the prototype of their DSM2/DSMX telemetry system and also one of the first production samples to have a look at. This thread is an attempt to gather all the information about it in a single place for convenience. Note this new product is not a copy of anything Spektrum, but an original design that uses the Spektrum data transmission protocol. Lemon have established a reputation for excellent long range reliable DSM2 and DSMX receivers at very low cost and are starting to expand their offerings. Their 7-channel DSMX receiver integrated stabilizer has also proved very successful.

So far I have verified the following:

1) The new telemetry unit works perfectly both with my Spektrum and Lemon receivers. I assume it will also work with Orange receivers but have not yet tested that. The connection lead plugs into the Bind port just like the Spektrum TM1000 unit. It works with all Lemon receivers that have bind connection pins including the 7-channel Stabilizer. Note that if you use Aux2 out on the stabilizer bind pins, the telemetry unit will work just fine using a Y lead. Lemon have fitted the telemetry system into the same case they use for their 7-channel stabiliser and provide a Temerature/RPM probe and compact Pack Voltage and Current sensor with the unit.

See picture 1 for a comparison with the Lemon 7-channel stabiliser and 10 channel DSMX receiver and satellite.

2) It gives all the telemetry readings automatically on a telemetry transmitter that a Spektrum unit does - except the Fades and Holds numbers and the 4 receiver/satellite individual values A, B, L and R. My understanding is these are a Spektrum receiver exclusive. However Lemon have used the A reading for a "quasi" RSSI calculated from the fade rate. It works but Lemon have said they have a much better version of the software nearly ready that will be close to a true RSSI number.

See picture 2

3) The base unit is half the weight of a TM1000.

See picture 3.

It is however full range and includes internal temperature measurement, receiver voltage and altitude without any external sensors. Altitude is AGL by default (set when you power up) but can be changed to an absolute value based on standard sea level of if you want to. It uses a Bosch BMP180 integrated digital pressure and temperature sensor which assumes an absolute pressure at sea level of 1013.25hPa. So the absolute height it reports will vary depending on barometric pressure at your location at the time. For example I live near sea level and on the dayI tested it the pressure was low and the altitude reported as -215ft! The calculations are all done by an Atmel Mega 88PA microprocessor.

See picture 4

4) It comes with a compact pack current and voltage sensor with Deans connectors in the first batch. I swapped mine easily to XT60 but Lemon will be providing an XT60 option very shortly. It also comes with an external temperature sensor and RPM indicator. The pack sensor is factory calibrated but can be recalibrated if you change it. Voltage limit is up to 30V and current up to 60 Amps.

5) It works with my Spektrum STi Telemetry interface (SPMTR1000) for the iPhone/iPad.

See picture 5

6) No idea on price and availability. You need to ask Lemon about that.

UPDATE: Lemon have just listed the telemetry unit on their web page for $44.80.

I will reserve the next few posts for additional information as it becomes available.

John
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Old Oct 17, 2014, 09:33 AM
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United States, MO, Fenton
Joined Jan 2012
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A quick question about the amp sensor. The description mentions it can monitor mah consumed. How would that display? I don't see any field on the tx that would allow it.
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Old Oct 17, 2014, 10:20 AM
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Joined Jan 2009
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Dang... Great stuff, jj! Just Subscribe me to any threads you start!

With the internal altimeter and a DX8, is there any way to do a tonal vario on the system? That would be sweet!

-= Dave
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Old Oct 17, 2014, 10:36 AM
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United States, MO, Fenton
Joined Jan 2012
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It would be nice if the altimeter would function like the vario! Didn't think of that. I have had a lot of fun this summer with the new vario from Spek.
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Old Oct 17, 2014, 11:38 AM
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Dear Fetonflyers,

It's under "PowerBox". After making "PowerBox" available, go inside and make sure "Display" option is changed from "Inh" to "Act".

mAh display is the standard feature in Spektrum telemetry capable transmitter.

Thanks!

Best Regards,

Lemon Rx Officer

Quote:
Originally Posted by Fentonflyers View Post
A quick question about the amp sensor. The description mentions it can monitor mah consumed. How would that display? I don't see any field on the tx that would allow it.
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Old Oct 17, 2014, 11:44 AM
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Joined Jan 2012
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Quote:
Originally Posted by fmak2 View Post
Dear Fetonflyers,

It's under "PowerBox". After making "PowerBox" available, go inside and make sure "Display" option is changed from "Inh" to "Act".

mAh display is the standard feature in Spektrum telemetry capable transmitter.

Thanks!

Best Regards,

Lemon Rx Officer
Oh that is a bummer. My new DX6 doesn't have "power box" as an option in the menu. Maybe the DX9 does? I sold mine so I am not sure...

I really want to be able to monitor mah consumed. On 3d planes it can very dramatically depending on the type of flying your are doing.
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Old Oct 17, 2014, 12:05 PM
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Hello Zenmaniac,

We can put this in the wish list on the 2nd release along with RSSI!

Best Regards,

Lemon Rx Officer

Quote:
Originally Posted by Zenmaniac View Post
Dang... Great stuff, jj! Just Subscribe me to any threads you start!

With the internal altimeter and a DX8, is there any way to do a tonal vario on the system? That would be sweet!

-= Dave
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Old Oct 17, 2014, 12:08 PM
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Dear Fentoflyers,

I am just showing a DX18 here in the photo but that's exactly the same for DX9. I use DX9 myself. Perhaps it's time to get a better transmitter!

Thanks!

Best Regards,

Lemon Rx Officer
Quote:
Originally Posted by Fentonflyers View Post
Oh that is a bummer. My new DX6 doesn't have "power box" as an option in the menu. Maybe the DX9 does? I sold mine so I am not sure...

I really want to be able to monitor mah consumed. On 3d planes it can very dramatically depending on the type of flying your are doing.
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Old Oct 17, 2014, 12:10 PM
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Sorry I was attaching a wrong image.

Best Regards,

Lemon Rx Officer

Quote:
Originally Posted by Fentonflyers View Post
Oh that is a bummer. My new DX6 doesn't have "power box" as an option in the menu. Maybe the DX9 does? I sold mine so I am not sure...

I really want to be able to monitor mah consumed. On 3d planes it can very dramatically depending on the type of flying your are doing.
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