PMB-NZ

Mostly electronics design, build and repair. Electronics for the RC hobby. Based in Upper Hutt, Wellington, New Zealand. Been a member of WMAC since about 2010 or 2011. Flying RC for a few years before joining. rcbeacon.com and pmb.co.nz

Motor Size and Power

 misc  Comments Off on Motor Size and Power
Jan 032016
 

I have just been looking at some 1804 motors; just an example.  The theory applies to larger motors as well, probably more so as there is more variety.  Thought I’d make a few notes.  Please comment if you see any major errors.

Hobbyking 1804 motor1804 refers to the size; 18mm diameter and 4mm long, usually of the stator or internal windings, but can occasionally refer to the overall motor size.  This tells us the size of the motor and provides only a rough idea of what it is capable of.  The KV and power rating consisting of Volts, Amps and Watts is probably more important.

Hobbyking list two 1804 motors, the “DYS 1804-23 2000KV BX” and the “DYS 1804-2300KV BX“.

  • RPM/V: 2000kv or 2300kv
  • Dimensions: 23 × 13mm
  • Shaft: 2mm main shaft and 5mm prop shaft
  • Voltage: 2S~3S (7.4v to 11.1v)
  • Weight: 16g
  • Watts: 55.5W (2000kv) and 89W (2300kv)
  • Max Current: 7A (2000kv) and 8A (2300kv)
  • ESC: 7amp to 12amp
  • Suggested Prop: 5×3~6×2 and 5×3 (3S 11.1v) ~ 6×2 (2S 7.4v)
  • Motor Mount Holes: M2 x 12mm

Performance Figures for the 2000kv motor:

  • 7.4V with 5×3 prop: 14,600rpm/2.9amps/21.5watts
  • 7.4V with 6×2 prop: 14,600rpm/2.8amps/20.7watts
  • 11.1V with 5×3 prop: 19,450rpm/5amps/55.5watts
  • 11.1V with 6×2 prop: 19,450rpm/5amps/55.5watts

Notice that the 2300 is rated 1A more than the 2000, but 44 watts more. That’s a lot more power. I suspect there may be a typo in there somewhere 🙂

Notice also in the performance figures, that on 2-cell they only show 21 watts from a motor that is supposed to deliver 55 watts. A larger diameter and/or larger pitch prop would increase the load and power delivered. This would have to be tested as there may be greater efficiency losses.

Ratings

The KV rating refers to RPM per volt applied with no load. So 2000KV on a 11V supply will theoretically want to spin at 22000 RPM. The speed controller etc. will affect this.

The power rating should be considered  a maximum with good ventilation. all that power is going to heat the motor and needs to be removed by air-flow or the motor will overheat and fail; probably burning out the windings.

The maximum current rating tells you how much current the motor windings should be able to handle.

These all come together: Volts * Amps = Watts. But not always without a catch.

So a 7A maximum current and 55 watt rating means you should not load the motor to the full 7A on 3-cell because it would draw 77 watts.  On a 3-cell it should be limited to about 5 Amps. On a 2-cell supply you can run to the full 7A and the motor will draw about 50 watts.

The motor will try to deliver as much power as it can based on the load applied. The propeller is the load on the motor.  A larger prop (either in diameter or pitch) will apply more load to the motor and draw more current and therefore more power (watts).

Propeller

Propeller size and power is also complex. A higher KV motor will spin the prop faster. More pitch and/or more diameter means more load for a given RPM. There are on-line calculators that help with prop selection and suggest maximum possible speed etc.  Generally, a larger diameter and more pitch spinning at a lower speed is more efficient, providing longer flight times.

Power in watts relates to “get up and go”, but prop diameter, pitch and speed determine how the “get up and go” works. Whether it’s a glider that flies out of your hand and goes vertical, or a fast sport model that you have to catapult into the air.

FPV and Other Stuff – parts

 Uncategorized  Comments Off on FPV and Other Stuff – parts
Aug 272015
 

show and tellNotes from Gordon

Here are a few links to some of the items I bought along for Show and Tell this evening.

Mobius Camera

Mobius Camera (latest and widest angle version – note mine has the C lens. Now replaced by C2 lens).

Note – to change the options available in the camera and to update its firmware you use a little program called mSetup. These cameras are a little picky about which micro SD cards work. One I tried would not work last evening – as shown by mSetup not finding the camera when plugged into my pc via the usual mini USB cord. Worked just fine with another class 10 card and updated the firmware easily.

Mobius Instructions etc.

Banggood have them too.  Note there are 3 versions available from A to C with increasing wide angle lenses.

RCGroups Mobius owners support thread – over a 1000 pages to read!

Note – the Mobius is known to have a slight lag of 0.1sec. This is only likely to be a problem if you are Quad Racing between trees etc. Quad racers use a dedicated camera plus a Mobius to make video for later bragging etc.!

Also note there are probably fakes out there too.

Mobius Docking Station with 32 channel 200mW 5.8Ghz transmitter.

Note – if you already have a video transmitter you can just buy the video out leads (or choose a Mobius option with them).

OTG Cable – plug your Mobius into your phone or tablet. I have not tried that yet, but it should be useful for viewing video off your Mobius.

Other Parts

Open Pilot CC3D Flight controller.

Quanum FPV Goggle Version 2, DIY Goggle with 5 inch LCD Monitor. Do not bother with earlier and cheaper version also available as a set etc. – much lower quality screen etc.

Receiver – FR632 dual aerial diversity is used by some of the Quad race guys. Needs 2 aerials so more expensive.

These blue ones fit (blue ones are SMA – Red ones are RP-SMA, both are Right Polarized) the FR632 or the RC58-32 channel Receivers. Both these receivers have channel display led and channel search)

More links:

Hobby King : The New FR632 Diversity 5.8GHz 32Ch Auto Scan LCD A/V Receiver.

Banggood : FPV-RC58 32CH 5.8GHz Wireless A/V Receiver Auto Signal Search.

Antenna: Hobby King : CP 4-leaf Antenna – SMA-RHCP

Note – I do not know if this is the best option available but is somewhere to start. They are pretty robust etc. though the thicker wire is probably a compromise in terms of performance.

There are others available including an expensive new one from Hobby King – Tx aerial.

Other Transmitters from Hobby King – 200mW RP-SMA.

6 channel Micro receiver for DSM2/DSMX and CPPM output to plug into a Flight Controller.

Hobby King Servo tester – this is a must have! http://hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=14774

Painless360 Youtube Videos – heaps of instructional videos on setting up your Taranis, Naze32, CC3D what have you. This one is about great FPV on a budget.

In the description below he lists the items used.

Note – the Camera and Tx combo – most likely works better than random parts put together.

Published on May 29, 2015

Thanks to Banggood.com for sending me the camera, transmitter and receiver for me to try.

If you would like to see more about the products mentioned on this video you can by visiting –

  • RC58-32CH Receiver – Here.
  • FPV Camera and Tx – Here.
  • Circ. Pol. Antennas – Here.
  • RP-SMA Adapter – Here.

NZ Multi Rotor Shop – (not the only one!) – Here.

Additional

Here is one I missed, the  Mini Talon FPV plane.

Note – there is a bigger version as well. I have not flown it as yet but there is video of one flying. Will be quite fast I think. Video Link. Actually looking at that video it slows down nicely.

And the one Mark had on display : Phantom 1550mm.

I am pretty sure both are available from other stores too. (look them up – you may get a better price).

eg. Mini Talon from Banggood. US$79.99 shipped (Hobby King are $81.89 plus shipping).

Hobby King have others too …

Hobby King Mini SkyHunter FPV Platform PNF. This looks good.

Hobby King Durafly SkyMule Twin FPV Sports Model EPO 1500mm PNF. I have seen this one fly\, went well and looks pretty!

It is also available in kit form from Hobby King: Here.

Note – the Durafly planes are usually well engineered and finished.

Hobby King page for more FPV planes.

Note – read reviews. Some of them are heavy or will only fly fast etc. The Bixler is the original and might be the best for you!

.

 Posted by at 12:55 am

FPV Video Transmitter Reliability

 equipment  Comments Off on FPV Video Transmitter Reliability
Aug 252015
 

fpv video transmittersIt sounds like an overheat failure

This picture shows the miniature 32 channel transmitters as supplied (before overheating) and a New Zealand coin to indicate size.

I have used, seen and repaired some video transmitters with very poor thermal design. Overheat failures are quite common. Many underestimate the need for cooling. The VTX produces heat even when the model is not moving; unlike the ESC.

It is probably a reverse polarity protection diode that has failed; if it is a series. If the board has not been badly burnt, it may be repairable.

Measuring the current draw before extended use is a good idea as it gives an indication that all is well. An antenna fault or connection problem can greatly increase VTX current draw and heating.

Video transmitters are very inefficient; transmitted power is a fraction of the power in. Therefore a lot of heat is dissipated in the transmitter. Voltage regulators on transmitters are almost all switching types now, to reduce the heating problems; but it’s only a partial solution.

I sometimes include a switch to turn the VTX off while the model is on the bench or waiting for GPS lock etc. It reduces internal heating when there is no flight induced air-flow; and it saves the battery. Also handy if you want to swap or adjust the VTX antenna without powering down the model.

I recently bought two 200mW and two 600mW miniature video transmitters from China (just arrived – pictured above) for my mini-fpv-wing project. VTX power supply and cooling are major design considerations. It will have RTL, but it’s always a good idea to include a reliable video transmitter.

FPV Monitor Problem

 equipment, fpv  Comments Off on FPV Monitor Problem
Aug 172015
 

fpv monitor testingThe Problem

This monitor-receiver combination looses the image to a snowy screen regularly, even when the 200mW video transmitter is within 10 meters.

The way it would suddenly come and go, it looked like a connection problem or bad joint on the video lead between receiver and monitor.

We were expecting a more consistent better image with occasional noise and some interference. For FPV, a noisy image is better than no image.

To eliminate the connections a direct soldered lead replaced the two leads and RCA connectors. But the problem continued.

fpv monitor testingTesting the Receiver and Monitor

I resurrected an old 10mW 5.8GHz transmitter with clover-leaf antenna and mini camera to provide a relatively weak signal that could be easily blocked to simulate a longer range. Also a second receiver and monitor to sit nearby just to keep an eye on the transmitter and as a comparison.

The RC-832 receiver seems to be fine. The receiver was compared against an older RC-305 and there was no noticeable difference in sensitivity or image quality.

The other receiver-monitor would indicate interference and noise but would not loose the image completely.

As a second comparison I connected two monitors to the RC-832 receiver; it has two AV outputs. The suspect monitor and another monitor that looks identical but is just from a different seller. The suspect monitor was cutting out while the other was displaying a noisy image. To be sure it wasn’t the AV output, the monitors were swapped over; the problem remained. So it is definitely a problem with the suspect monitor.

 

fpv monitor testingThe suspect monitor passed the bump/vibration testing,confirming it’s not a vibration or movement induced problem.It doesn’t take much interference to completely loose the image, which takes a second or two to return. Not much use for FPV.

Using a clover-leaf antenna on the transmitter and linear antenna on the receiver is not ideal and the problem is quite bad, even over just a few meters. Using a circular polarised antenna n the receiver (clover-leaf or skew-planar) noticeably improves it; fewer drop-outs. Which makes sense, but does not really solve the problem.

fpv monitor testingTest Conclusion

Image loss does coincide with signal level fluctuations and interference. It even completely looses image when simply moving about near the receiver.
It seems that this is just how this monitor responds to a noisy signal or interference. It is not very good at detecting the video sync of a noisy signal. Or it’s a left over of a blue-screen function.

Of 3 monitors that look identical, only one has had this problem. It is sold on various sites as a cheap 7″ LCD monitor for FPV. The problem now knowing how to avoid the dud.

Other Notes:

  1. I sat the test transmitter rig in our microwave oven to reduce the signal. It didn’t work. Those little holes in the screen behind the window are apparently not small enough to block 5.8GHz. Either that, or there is another leak somewhere. I haven’t seen anything glowing in the dark yet.
  2. Two apparently identical monitors behave quite differently. One has no blue-screen but cuts out with interference. The other does blue-screen but displays very noisy images and only blue-screens when the image is unusable. One displays much brighter and more colour when both at the same settings.

Multirotor racing adjacent channel Interference

 multirotor  Comments Off on Multirotor racing adjacent channel Interference
Jun 112015
 

The Problem

When multiple quads are racing around a course with pilots at the start-finish line, FPV video channels interfere with each other. Pilots loose their video as another quad races past.

Possible Improvements

There are 8 channels within the allowed 5.8GHz frequency band. The transmitters are not of the highest quality and adjacent channels interfere, especially when an adjacent transmitter is much closer to your receiver.
High power transmitters will just make the problem worse. Lower power transmitters, channel allocation, antenna selection and course layout etc. should help.

Pilot position:

If the pilot position is set back from the course, you will benefit from the relatively short range of adjacent channels.

The problem will be worse when the model passes close by a pilot on an adjacent channel. If all models are always some distance from the pilots, the relative signal levels received will be more consistent over a smaller range. Receivers will be more selective and not swamped by powerful nearby signals.

Antennas:

The 5.8GHz band is quite wide and typically antennas are not at their best over such a wide bandwidth.

I think that due to the short wavelength at 5.8GHz, antenna dimensions and construction are quite critical when looking for best performance. Mass produced off-the-shelf antennas may be centred on the band but possibly not that good.

Although making these antennas is a PITA, if made for the lowest channel, may be less responsive to the higher channels etc.

The original antennas I made were dimensioned for the channel I was using at the time; the lowest frequency. These are the RH antennas I tested mated with the LH Hobbyking low-cost types, and found that mixing LH and RH didn’t work. Something that can be used to an advantage.

 Posted by at 11:58 pm

The new web site is up at last

 misc  Comments Off on The new web site is up at last
Apr 092014
 

This site is as of 5th August 2015 live.

We invite content and comment from anyone; well almost anyone, no dodgy adverts :).

Special note to WMAC members or anyone local who may be interested, we can put up any build threads, reviews or interesting stories. Please let us know if you are interested. There is a contact form Here..