Introduction: Flapping Dragonfly BEAM Robot From a Broken RC Toy

About: Hi, Im Jack Spiggle. I enjoy all aspects of DIY and my interests include robotics, origami, woodworking, leatherwork, electronics, blacksmithing, animation, small engines, vintage machinery, stop motion, anim…

Long ago I had a model RC dragonfly. It never worked very well and I broke it shortly after however it was always one of my biggest fascinations. Over the years I have scavenged most of the parts off the dragonfly in order to make other BEAM projects and such however I always left the gearbox intact for the day I decided to make something like this.

Later I hope to make more freeform beam circuits so this model was mostly an experiment for me to practice soldering brass rod.



Small stump

Brass rod and tube (I used a variety as explained in step 1)

Broken RC dragonfly toy


A BC557 and a BC547 transistor

2.2k resistor

2 red FLEDs

6v solar panel (As we are using two FLED's as for our threshold voltage, full explanation in step 10, our solar panel must provide >4V. For two panels the same size, one 6v and one 12v, in the same light the 6v will provide twice the current as the 12v panel. Hence I opted for a 6v panel so that the circuit works in slightly low lighting yet still provides enough current for our dragonfly to flap regularly)

Enamel copper wire

An assortment of capacitors from 220-47uF

One 4700uF capacitor

Step 1: The Base for the Sculpture

Starting the sculpture with the base I found a suitable section of a branch and cut it down to size. I drilled a 1.5mm hole in the wood to insert a 1/16 (~1.6mm) brass rod with a very tight fit. It has to be tight as this brass rod will eventually support the entire dragonfly sculpture.

In order to make things easier for myself I used a variety of soft and half hard brass rod (all from K&S metals) For structural components like this support or mostly straight components like brass sections in the wings I used half hard brass however for sections with lots of bends like the body or face I opted for soft brass.

Step 2: Constructing the Wings

The wings were constructed from 0.8mm brass rod (and a small section of 2mm brass tube on each wing tip).

The pictures explain my process much better than I could in words but the basic method was to print the plans at a 1:1 scale. Then I would lay brass rod on top of the plans and bend each section until it matched the drawing. I then soldered each section in place, often while the brass still lay on the drawing. The brass does wick up more heat than a thin component leg but other than that it is just like soldering a circuit together.

This project was mostly just practice for more complicated and more aesthetic free-form circuits than I have been making so these wings were a great way for me to practice designing and free-forming a purely aesthetic "circuit" in brass.

When brass is heated to soldering temperature it develops an almost pink oxidation. I removed this with some brasso and/or a toothbrush and hot water. The brasso works a lot better but is hard to get into some areas.

Step 3: Constructing the Head (1/2)

The head design I did not include in the plans as I just roughly sketched it in and designed it as I went. (It later turned out to be my least favourite part of the dragonfly, I wonder what that says about good planning.)

The head was constructed from a mix of 1/16, soft brass and 0.8mm brass rod.

The head was pieced together in a similar manner to the wings. One tip I realised when making these parts is that it is hard to hold the parts in place and make nice solder joints so what I would do is not worry so much about the cleanliness of my solder joints until I had secured the part in at least another location. Once I had these rough, normally cold solder joints holding a part in place I could then go back to the other attachment points for that piece and clean up my joints a little better. Almost like tack welding.

I left a long tail coming off the head that would be used to attach the head to the body as well as acting as the belly of the dragonfly.

Step 4: Constructing the Body (1/2)

The body was made from 3/32 soft brass and the back was made from 1/16 half hard brass rod that slides into a 3/32 tube in the back. I did it like this as I has to remove and resolder the back a few times while building to test wing mechanisms and such and this way I would only have to resolder one joint instead of two

Step 5: Constructing the Body (2/2)

The wing's stub things were constructed from brass tubing (2mm in this case which was a little large for the 0.8mm wings but I just crimped them a little) with small sections of 3/32 brass tube to slide of the back of the body. This all could have been done in either imperial or metric I just happen to have these sizes of brass anyway.

Four single connections were made and two double connections with an extra pivot hole which would facilitate the actual flapping of the wings. I ended up doing some testing with the original, plastic wing connectors and realised they work too well for me to bother messing around with replacing everything with brass. I often tend to overcomplicating mechanisms like this and introduce way too much friction for anything to work especially with the small amount of power delivered by the solar panel.

Step 6: Constructing the Head (2/2)

I then sandwiched two red flashing LEDs (or FLEDs) in the head and connected them in series. I then took two lengths of enamel copper wire and connected them to the remaining legs of the FLEDs.

(In this photo you can also see remnants of me trying different ways to get the wings to flap)

Step 7: Modifying the Dragonfly Toy Mechanism

In order to get the toys mechanism to fit in our model a bit of tweaking was necessary. The main goals of these modifications were to remove all unnecessary structural components and to swing the gears and motor up so that they take up less space (as previously the gears and motor went backwards in relation to the wings and left a lot of unused space as you can see in the second photo).

I started by cutting off the legs. I then removed the pin holding the two wing stub things to their support and then cut off the support entirely along with all the other supports bar the ones holding the motor and gears in place as well as a small section I will use to secure the mechanism onto the body of the dragonfly.

Step 8: Attaching the Dragonfly Toy Mechanism to Our BEAM Robot

I bent the remaining section coming off the dragonfly's head into a position wide enough to house the motor and gears. I then took the support brass rod, that we bent in step 1, out of the base and soldered it alongside the belly. In the photos you can see this support coming out the front of the belly

I also removed the back, threaded all the wing connector nubby things onto the back and resoldered the back.

Finally I used heatshrink tubing to hold the little bit of support we left on the gear mechanism to the belly

Step 9: Constructing the Tail

The tail was made from two long sections of soft brass to which I soldered an array of capacitors in parallel. These capacitors added to ~2200uF which was enough however I did add another 4700uF as I explain in step 13.

Step 10: The Classic, FLED Based Solar Engine Circuit

There are many tutorials on how to freeform a FLED based solar engine circuit but I will share my favourite way.

If you are unfamiliar with what a solar engine does I would recommend reading this

Our solar engine it simply stores energy from a solar panel in capacitors until the voltage across the capacitors reaches a certain threshold at which point it dumps all the energy into a motor or coil or whatever you want to power. This is useful as it means our dragonfly will flap even in when there is not enough light to run the motor directly.

Our threshold voltage is set by 2 flashing LEDs which for me gave a trigger voltage of ~3.8V and I used a 2.2k resistor as is generally recommended for a standard motor load. If you have a solar panel that only outputs 4V in full sunlight, for most of the day your circuit will not reach the voltage necessary to fire and hence you may want to use other arrangements to get to a more suitable threshold voltage. A single red FLED should create a threshold voltage of ~2.4V and a green ~2.8V. Adding signal diodes in series you can up these threshold voltages by 0.7V per diode. I just like using 2 FLEDs as they can be used as eyes which subtly flash when charging.

I used a BC547 and BC557 transistor which both have CBE configurations for the legs if you are using other types of transistors like 2n222s for example they might have an EBC configuration and you will have to build the circuit another way (or the same way but with the transistors back to back instead of front to front)

In the first and second photo you can see the only connections we need to make between the two transistors as per the circuit on the solarbotics page. The rest of the photos then show how I make these connections. It is helpful to use blu tack here to hold the small components together while soldering.

I will not be showing exactly how to freeform the circuit as I implore you to understand the circuit and how to connect it together rather than simply copying my exact connections. This is how I started building circuits like this and it is very easy to make a mistake and almost impossible to troubleshoot if you don't understand why you are connecting components where which is very disheartening. A little extra research will hopefully save you a lot of heartache.

Step 11: Putting It All Together (1/2)

I then placed my solar engine at the base of the tail, soldered it in place and cut everything to length.

I then twisted the motor wires and FLED wires and cut them to length too before soldering them to the solar engine as shown.

Step 12: Putting It All Together (2/2)

Two more lengths of enamel copper wire were soldered to the solar panel, twisted and cut to length. The panel was attached to the stump with double sided foam tape and the wire was twisted up the support for for the dragonfly and soldered to the tail/solar engine.

Step 13: Adding a Secret Capacitor (shhhh, Don't Tell Anyone)

The model worked well as it was however in low light, the burst from the ~2200uF capacitors was only enough to move the wings a very small amount as by the time the motor had overcome the inertia of the wings its power supply had run out. Hence by adding another 4700uF the wings are able to make almost a whole flap every cycle of the solar engine.

As I wished to keep the model looking as it did I decided to hide the capacitor by drilling a hole into the base under the solar panel.

Step 14: Final Thoughts

The wings flapping cause a substantial amount of wobble and due to me rasping the bottom of the stump, the base is slightly convex. This all makes the model wobble quite a bit so I will need to find some rubber feet at some point.

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