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Doofer

Credit-crunch quadrocopter

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I've had a Jump Jet for a while, and they are undoubtedly the ultimate indoor flyer, providing a size and degree of control far ahead of any micro helis/planes/toys. Essentially a micro quadrocopter, it comes with a light foam superstructure that renders it inherently stable (hands off sticks = stabilises), but it's much more fun if you remove this and fly it as a still very stable, but more frisky, quadrocopter.

IR control comes as standard, and there's now a R/C module (including 72MHz option, oh colonial brethren), which vastly increases range and fun. The only problem with R/C is that it is so small it gets out of visual range very fast.

It occurred to me that FPV was the solution!

The inventor Phil had already shown you can fit a camera to it, so I followed his suggestion: remove everything you can to keep the auw at or below 65g, then add a cheapie CMOS cam/Tx combo (remove all the casing you can = 8g). I used the voltage regulator you can prise out of the bulky power plug it comes with. I should add some filtering to remove motor noise, but so far this isn't too bad.

The result isn't pretty... naturally it has a certain beauty in my eyes... Rising vertically off the ground to above house height is real joy, and although conditions have to be pretty calm, the 3D IMU does a great job of keeping it stable in flight.

Highly recommended.

(US chaps: Remember, the pound has collapsed to nearly £=$, making one of these a mere 70 dollars :( )

post-1834-1232042474_thumb.jpg

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I'll try and get some this weekend, given a lull in the weather.

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I've got one of these too :)

But I don't have the RF module, and with IR it's really too limiting so it doesn't fly much. Getting the RF module sounds a bit complicated too, if one needs to send the model for firmware upgrade shipping and all will cost more than the model itself...

post-30-1232191567_thumb.jpg

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Well, the RF module refit takes about 10 minutes, and it does work with 4-channel transmitters - not an expensive addition.

I asked Phil (the designer) about the oddness that you can't buy a Jump Jet with the software upgrade. His reply:

"Thanks for this - a fair question. Actually we have sold quite a few to US customers on the existing basis. The reason for it is as follows:

Although we were heavily involved in the designing of Jump Jet, we are not the manufacturer. Snelflight used to manufacturer model helicopters right here in the UK, but we no longer do so. We are primarily a design/development company now. We import and re-sell the Jump Jet, and we are planning to do the same with other products in the future.

We have designed and independently produced the RF module, which for the time being is only available directly from us. We do not at present have the option to import the Jump Jet with the RF module pre-fitted, and we do not have the production capacity here to unpack, modify and re-box a large volume of product ready for sale. Therefore the RF module is sold as a customer-fitted upgrade only - many other hobby items are sold in this way. Depending upon the take-up we may seek to have an RF version of Jump Jet made for us, but this will add the complication of supplying an RF handset, which will have to be developed and tested for compliance with various regulations. This will not be worthwhile unless there is a large demand, and it will add to the cost of the product. Unfortunately, what makes perfect sense to us as engineers and hobbyists does not necessarily sell well in the marketplace, where product categorizing and "price point" are crucial.

This brings me to the software update. We are offering this service as an option for customers who, having bought and fitted the RF module, find that they cannot get satisfactory performance with their transmitter. In a lot of cases the software change will not be necessary - just buy the RF module, fit it and go fly with a 4-channel radio; it works really well! In future we plan to bring in Jump Jets with a new software version pre-installed, but this needs to remain compatible with the IR handset. However it will support computer radios across multiple brands, so it should eliminate the need for our upgrade service. In the meantime we have to continue as we are, because we cannot unpack and modify a large volume of product in-house."

I asked about people updating the software themselves, but he's not keen on releasing the software (to protect against counterfeiting), and a special jig would be needed to re-program the PIC in situ.

However, he might supply PICs with updated software, for folk to solder in themselves as a replacement. Not a solution for the mass market, but perhaps something to try before sending the whole thing back.

I wonder how much interest there would be in this option? Still a little cheaper than other quadrocopters out there...

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I'd personally go for PIC swap or self-made FW upgrade, but then again I'm equipped with all that's needed...

The problem is that many "4-channel" transmitters nowadays actually transmit more (like 8), with just dummy values on the last ones (neutrals). If I understand well, these wouldn't work. I don't have one that really only sends 4 channels.

Why not have his RF module strip the extra channels off the stream, and only pass the 4 first ones to the JJ's main board? That would solve the problem and avoid the firmware change on the JJ.

Edited by Kilrah

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I see the Jump Jet website includes a list of 4 channel transmitters that ARE 4 channel: GWS GWT4A II, Hitec Focus 4, Laser 4, Century Lightning 4.

Interesting idea about the RF module. In theory that could cover other aspects of the software upgrade too (throttle curves etc.).

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Another solution is to put a 35/72MHz RF front end on the stock Jump Jet remote - just filter out the 38kHz carrier from the signal to the IR LEDs and "Bob's your Uncle".

I'm fiddling with this idea using the RF board from an old Micron transmitter kit, although I'm not sure about the whole gameboy aesthetic - it needs stick extensions!

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Another solution is to put a 35/72MHz RF front end on the stock Jump Jet remote - just filter out the 38kHz carrier from the signal to the IR LEDs and "Bob's your Uncle".

Oho! I hadn't looked at the signal and didn't think it would actually be PPM... In that case it's easy. Take either a small RX from the market or even Snelflight's one, grab PPM, put a PIC inbetween with a quick program that strips channels above number 4, and there you are.

I figured there would be some different "proprietary" format like on the Silverlit X-Twins and that a transcoding would be needed, which led me to think Snelflight's receiver would have a microcontroller to do that job, but apparently that was too far fetched... That's why I wondered why they wouldn't just ignore other channels themselves.

I actually have a Graupner XP4 tiny RX somewhere around, I'll maybe have a poke at it today if I can find a crystal for it.

Edited by Kilrah

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It flies :)

I poked a bit around on the JJ board, found the signal going out of the IR receiver to be a low amplitude negative PPM. I followed the trace and found it was then conditioned into a nice ~4V positive PPM further down the line.

I did the same on my Graupner RX, and it actually uses a PIC as a servo decoder, so has the same kind of conditioning to give a nice clean 5V PPM on the PIC's input.

So I tapped into that PPM on the RX, disconnected the JJ's conditioning transistor's output, put a wire instead and found some 5V. Result is 3 wires (+5V, GND, 0-4V 4-channel positive PPM in) on the JJ, and same 3 wires (+5V, GND, 0-5V 8-channel positive PPM out) from the RX. Just perfect as that means I don't have to do any conditioning myself.

PICT4459_s.jpg

Disconnected transistor and PPM in wire

PICT4454_s.jpg

Power supply

Only missing is something to strip the last 4 channels of the RX's output before feeding it to the JJ. Let's get out a breadboard, a PIC, reuse some lines of code from another project, and here we go :)

PICT4447_s.jpg

Only step left, integration:

PICT4469_s.jpg

Finished :)

And it's amazing, it's a LOT more precise and easier to fly that way... Definitely a cool little rainy sunday hack ;)

Now one could think of lots of neat features to add in the PIC, like failsafe... it seems the JJ doesn't like it much when there are little R/C drops. But it already was the case with IR...

JJRF.zip

Edited by Kilrah

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Nice hack!

I got mine flying with a 35MHz Rx after reading on RC Groups about the good news that the JJ uses 4 channel standard PPM, but couldn't get it under about 5g; at this weight it only just lifted off.

The RF module from Snelflight -AT-2g or so leaves one with more headroom, but I've been assuming that the reason mine can lift off with an extra 8g of cam/Tx on it is to do with the altered/boosted throttle curves in the software update. What can yours lift?

(Come to think of it, you probably have access to one of your RC-tech 2.5g cam/Tx combos - should lift that okay!)

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Hmm when I did tests (with the stock remote) some time ago, I noticed I could lift about max 10gr.

After the mod today I noticed I had to use the radio's ATV to set the throws as high as possible or the throttle would not reach the maximum. The stock remote probably has sligthly different timings. But at 150% it was apparently fine.

Yep the camera will end on it again soon - that's what was on the photo I posted earlier. However I don't have it at hand now as it was used for a demo Friday and is at the workshop.

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Well, 10g is a 2g RF module and an 8g cam/Tx (e.g. cannibalised surveillance camera) - good news.

In discussion with Phil about these issues, he commented that most R/C sets give 1.5+/-0.4ms, whereas the stock controller gives 1.5+/-0.5ms... although my measurements in the past on various sets aren't so clear on this 'lack of throw' issue...

He also warned me that whatever throws/throttle I might get out of it, if the auw exceeds the recommended 65g I may start burning out motors: the software sets the 'max user throttle' as 50% of the total throttle available for maintaining stability.

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In discussion with Phil about these issues, he commented that most R/C sets give 1.5+/-0.4ms, whereas the stock controller gives 1.5+/-0.5ms... although my measurements in the past on various sets aren't so clear on this 'lack of throw' issue...

Personally all the sets I remember measuring were giving out 1.5 +/- 0.5ms, or at least 0.45...

He also warned me that whatever throws/throttle I might get out of it, if the auw exceeds the recommended 65g I may start burning out motors

I'm at 58.3gr with RF module.

the software sets the 'max user throttle' as 50% of the total throttle available for maintaining stability.

Something tells me I'd appreciate a hack on that one and let me limit that myself to try some stuff out ;)

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Further update from Phil:

1) Although some "4-channel" radios transmit extra dummy channels (Futaba Skysport 4 for instance), there are quite a few that don't. The next release of JJ later this year will be able to tolerate extra channels, and will also switch automatically to different channel sequences (e.g. JR). This will allow computer radios to be used, effectively eliminating the various compatibility issues. Our software update does the same thing.

2) The RF module cannot strip off the extra channels because it is just a receiver - it contains no digital processing at all. A simple PIC circuit could be interposed between the RF module and JJ to remove the extra channels. I've also attached a little analogue circuit to do this - it works by gating out pulses that occur more than 7ms into each cluster. This is exactly what JJ needs - the number of actual channels isn't the issue, it's the length of each cluster that is restricted.

3) Adding an FM transmitter section to the stock JJ controller is another approach - we actually have a working prototype FM version of the handset which may get made in future. In the meantime, the easiest way to go about it is to filter out the 38KHz carrier and feed the PPM signal into the buddy box input of an FM set. The signal can be extracted from the JJ handset by opening it up. However this is not necessary - the JJ IR receiver can be used to de-modulate the IR signal, or alternatively the attached circuit will do it, and has the advantage that it will work on whatever voltage the radio uses - this is often available via the buddy socket. The JJ does not mind which way up the PPM signal is.

4) The standard PPM channel throw used to be +/- 0.5ms. But over the last few years manufacturers have been reducing it, typically to around +/- 0.4ms, frustrating a lot of people. Futaba have gone a stage further, going to roughly +/- 0.35ms. The reason may be in order to fit in an extra channel, but we don't know because the manufacturers have never alluded to the change - they just did it and let everyone figure it out for themselves.

The JJ controller uses +/- 0.5ms to maximise the resolution available with a 38KHz carrier.

5) If anyone is interested in purchasing a PIC for their JJ pre-programmed with the updated code, please email support-AT-snelflight.co.uk. We will supply one for a flat price of £10 including VAT and worldwide shipping.

JJ_PPM_Excess_Channel_Stripper.pdf

JJ_IR_PPM_Receiver___Demodulator.pdf

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In case anyone cares, I have a similar PIC that I used in my DX6 conversion (www.rc-cam.com/forum/index.php?showtopic=1239) that limits the PPM channel count to 6 channels. I could recompile it for 4 channels which should solve the reported problem. For sure, it would be a much simpler to build than the analog version shown in the prior link. This hack would only need a PIC12F683 and .1uF cap. :)

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Has anyone used one of these as the brain for a larger quad?

Maybe convert the motor signals with a pic to drive some brushless controllers, you could up the frame rate at the same time for some controllers to 200Hz or more.

Terry

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Has anyone used one of these as the brain for a larger quad?

Maybe convert the motor signals with a pic to drive some brushless controllers, you could up the frame rate at the same time for some controllers to 200Hz or more.

Terry

What he said! ;)

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I have just got off the phone to the designer and he said he is intending to produce a controller for bigger quads but the project is not a priority, lets hope he has plenty of spare time to put into it. :)

Terry

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Is it really necessary to have one more controller for bigger quads when there are already at least 4 of them on the market? :unsure:

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The price of this one should be competitive particularly for those of us in the UK.

Terry

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