Mode Zero

It seems to work, and it's installed now. I'll try to get some pics and maybe video of the Pulstar when I have some daylight to work with. Here are a couple of snaps of the works.

The little orange thing is an Orange! Spektrum compatible 4-channel parkfly receiver. The power connector is an XT30, and I made a Y-lead from XT30 connectors so the same battery can power both the ESC for the motor and the galloping ghost gubbins.

Just one of the Chinese motor / gearbox things that work off up to 12V, with some 3D printed bits to mount it and couple it to the torque rod. The electronics consist of a pro-mini Arduino mated to a L9110 dual H-bridge board, with both the H-bridges wired in parallel to share the motor current.

Arduino sketch is home brew and does rudder and elevator (mark-space and pulse rate) with a third auxiliary channel controlling the 'drive power' which is the amount of time the motor is driving in either direction versus just coasting. The auxiliary channel can also be used to stop the pulsing altogether - for example prior to launch or after landing.

I wanna build one, please send details...

Hi Martin,

it´s always a pleasure to see, what you come up with. Very interesting. I am looking forward to hear more about it.

Frank

I wrote a long detailed post this morning before I went out with links to all the parts on Ebay, and attached files for the 3D print files and Arduino Sketch. When I clicked the 'Submit' button some temporary problem with my internet connection resulted in me losing the post.

I'll rewrite it fairly soon once I've completed the mourning process for the lost post. I should have highlighted all the text and copied it before posting - I will for long involved posts in the future, if I remember.

if you are fast enough and are a little lucky....Ctrl-z might do the trick

You need:

1. A motor/gearbox.
2. An Arduino Pro Mini (I guess you could use any 328Mega Arduino, but the Pro Mini is small and cheap).
3. A programmer for the Arduino. A USBASP or Serial adapter. (A USB equipped Arduino, if you have one, can be used as either sort of programmer too, but dedicated programmers are cheap and easier to use).
4. An H-bridge board that allows the Arduino to drive the motor. I used the L9110S.
5. Some parts to mount the motor and connect it to the torque rod that drives the tail surfaces. I designed and 3D printed mine, but they're not complex so you could equally make them out of balsa and plywood.
6. A small tension spring that pulls the gearbox output back towards the centre of its swing. I robbed a joystick centring spring from an old broken transmitter. I guess you could use a rubber band instead, but a metal spring is more durable and reliable.
7. Thin gauge piano wire for the torque rod drive, the 'birdcage' links on the rudder (and elevator if required), and the small pins that secure the spring ends. The last short ones you could actually use bits of dressmaking pins, but for the torque rod and birdcage you need some longer pieces.
8. Bits of thin electrical wire to connect it all up, and some competence at soldering.
9. A capacitor (about 0.1 microfarad) to solder across the motor terminals. I'm not sure if this is necessary, but it's generally recommended for brushed motors and reduces electrical noise and motor brush wear.

Items 1 to 4 can be bought on Ebay, and each item can be had for about £2 or less.

The motor/gearbox I'm using is the 12V 600 RPM one. Search for 'N20 12V Motor Gear box' The 300 RPM one should also be okay. https://www.ebay.co.uk/itm/6-12V-300-60 ... 2390504738

Arduino Pro Mini https://www.ebay.co.uk/itm/1-2-5-10PCS- ... 2178637340 Ignore the 'nano' in that description - Arduino Nanos are a bit bigger than pro minis (!) and have a USB interface built-in.

USBASP programming tool https://www.ebay.co.uk/itm/New-USBASP-U ... 1938838504

H bridge https://www.ebay.co.uk/itm/For-Arduino- ... 1437337515

The 3D printed parts are:

A plate to mount the motor/gearbox with an attachment point for the centring spring.

You need some tiny screws (smaller than M2) to fit the threaded holes in the gearbox. One source of these (the one I used) is to buy a second motor / gearbox and rob the screws that attach the gearbox to the electric motor and cut them down to length.

A coupler that joins the gearbox output shaft to the torque wire and holds the 'crankpin' that the other end of the spring rides on.


I used a mount for the plate as one of the fuselage formers in the Pulstar. The motor / gearbox on its mount plate on my Pulstar is slid into this mount upwards through an open hatchway on the bottom of the model behind the cabin area. With hindsight, It might have been better to fit it under the wing opening as there is plenty of room there to also fit the Arduino, H-bridge, receiver and ESC for the main (propeller) power motor. - that would help move the c.g. forwards. The mount is 17.4 mm wide (11/16 inch) and this sets the internal width of the model fuselage, if you use it as a fuselage former.


The circular plate shown at the top of that image is just a 'skirt' or 'raft' that helps the print stick to the print bed when printing (it prints upside-down compared to how it's shown there, but the image shows it the right way up for the Pulstar as you want the torque wire output up near the top of the model). You can cut away the circular part after printing.

The 3D print files in STL and OpenSCAD format are attached.

You power your receiver via the motor ESC in the usual way, and connect the main power battery negative (which is also the receiver negative via the ESC) to the Arduino GND. If you're only using a 2-cell main power battery, then you can power the Arduino by connecting the main battery positive to 'raw' or 'V-in' (NOT VCC or you will destroy the board). If you need a 3-cell main power battery then the fully charged voltage is on the limit of what an Arduino can accept on it's V-In or 'raw' terminal. You may get away with it, but it would be safer to run the Arduino by connecting the receiver positive, powered by the motor ESC at 5V, to the Arduino's VCC pin.

You then only need three wires connecting the three receiver outputs to 3 pins on the Arduino - the Arduino and receiver will already be sharing the same GND via their power supplies. 'Rudder' on pin D7, elevator on pin D6, and 'auxiliary' on pin D5.

The auxiliary channel controls the fraction of time that the pulsing motor is powered. It's best to work it (using a modern transmitter) with a two-position switch. You can set one switch position to give -100% output which stops the motor altogether - useful before launch or after landing - and the other switch position only needs be set to about -75% so that the motor is only powered about 20% of the time - this still gives plenty of drive power while minimizing the drain on the battery (about 200 mA - one fifth of an amp).

Rudder and elevator end points and elevator sub trim can be adjusted to give the desired amount of throw and speed. My Arduino sketch puts the on-board LED on when pulsing right and off otherwise. You can use this indicator to get an idea of the pulse rate and set the aux channel before you even connect the motor. When the sketch starts but it's not receiving any pulses from the receiver, the motor is disabled and the LED flashes in groups of three.

I connected the two channels of the H bridge board in parallel to drive the motor. Not really necessary as one channel can handle the motor current, but there are two channels so why not use both. Connect the battery power positive to VCC on the H bridge board (NOT to VCC on the Arduino as already described above). Connect battery power negative to GND. Connect Arduino D2 to IA1 and IA2, Arduino D3 to IB1 and IB2. Connect one terminal of the pulser motor to OA1 and OA2 and the other terminal to OB1 and OB2. As mentioned above it's recommended to solder a 0.1 uF capacitor directly across the motor terminals.

I removed the 'terminal block' from the H bridge board to save size and weight but beware that the pins are a very tight fit through the PCB holes and even with careful de-soldering I ended up pulling the tracks off the PCB If I ever make another one I shall cut / grind away the connector block rather than try to unsolder it.

Arduino sketch is attached.

Thank you Martin, parts are ordered.
Frank

Thanks Martin, another project added to the list

Actually, I have accumulated the bits to make a GG actuator ala Twitcher's efforts, so apart from the 3D printed bits, I have everything 'in stock' or its already en-route from the Orient. I even have bench space of sorts (specifically at the moment, that's the space between removalist boxes in my study ), and rain is forecast for later in the week. I have a plan..............

I'm making a few more of these and I've made a small change to the Arduino sketch to also support a different type of H-bridge that uses positive going signals for 'on' rather than the negative going ones that the L9110 uses. I've updated the sketch (pulser.zip) attached to the post above. If you compile the new version unaltered then it works exactly the same as before but if you comment out the line:

#define L9110

by adding // like this:

// #define L9110

then it supports the new type of H-bridge I'm using.

The one I'm using now has the MX1508 chip which is supposed to be a dual L298, It's a bit smaller than the L9110 and comes without any connector blocks or header pins - which is an advantage as you'd normally have to remove those to save size and weight - and removing them is tricky. It's also a little cheaper.

https://www.ebay.co.uk/itm/MX1508-1-5A- ... 2557205988

Wiring is almost the same as the L9110 board. To use both channels in parallel (not necessary, but I do it anyway) you connect IN1 to IN3, IN2 to IN4, and join the MOTOR-A and MOTOR-B connections so that the two left hand side contacts are connected to one motor terminal and the two right hand side contacts to the other.

I'm also planning to make a small change to the 3D printed plate mount to add a small retaining pin so that the plate can't slide out of the mount. I noticed this happening on my Pulstar and glued a bit of balsa into the model as a retainer... this works fine, but a removable pin will be neater.

Hi Martin

Excellent project as usual from you.
You deserved to win that model with your Pulstar, it flew really nice with the GG system you designed.
Well done
I might have a go at one and build something for it when I get chance.

Ron.