The Valor FX board is powered by a 7.4VDC battery, and its documentation didn’t mention what kind of tolerance it had for that, so I bought the recommended battery, plus a spare. That board will power the LEDs with 5V and the fan with the native battery voltage, and will provide a couple of always-on 5VDC outputs. One of those outputs is running to the wireless remote receiver board that activates the effects. There’s also a separate power switch for the Valor board, so by itself it’s pretty straightforward for power requirements and on/off control.

The audio amplifier I picked uses 9-24VDC, which is a good flexible range but doesn’t match the FX board. And the ultrasonic driver boards for the exhaust system run off of 5VDC, so that’s three voltages I need to handle.

The Valor board did have an extra 5V output that I could run to the remote trigger board and then to the exhaust drivers, but I didn’t want to further tax the little 7.4V battery. I figured 12V would be a good middle-ground for the amp, so I needed something that would provide both 12V and 5V. I came up with a clever solution, which didn’t completely work out.

My solution was to use a USB battery pack that offered multiple USB-C Power Delivery ports, which can (depending on the device’s negotiation) provide 5V, 9V, 12V, 15V, or 20V of DC power. I combined that with some handy and cheap PCBs that do the USB PD negotiation for you — just set some DIP switches to the voltage you want, plug it into USB-C, and it outputs the selected voltage from a terminal block.

This plan had the benefit that I could run both the 5V and the 12V devices off of the same battery pack, which would also be easily rechargeable or replaceable if needed. It did require that the battery pack be able to output two different PD voltages at the same time, but in my initial testing, it looked like it was fine with doing that as long as one of the voltages was 5VDC.

The little PD negotiation boards are great, and a convenient way of getting a standard voltage out of a battery pack or USB-C charger. So my plan involved having one USB-C cable running to the adapter set to 12V, connected to the amp, and another USB-C cable with an adapter set to 5V, running to the remote receiver board, which was then running to the ultrasonic driver boards.

I built out the different parts of this separately without issue, while I sorted out various versions of the exhaust solution. Once the design was settled, I reached the stage where I was could hook everything up together, and then I started running into problems.

The first problem was that the remote receiver board is only rated for 2A of output current, and the ultrasonic driver boards each draw about 1.5A when running. So they were fine when I was working on one at a time, but once I hooked up both, it triggered an auto-resetting fuse on the remote board. Thankfully, I had some little 5V relay breakout PCBs sitting around from a previous project. I could have used one of them in with the electronics in the central part of the jetpack, but that was getting pretty crowded, so I opted instead to put one relay on each engine, which required an additional signal running to the engines, but I still had one unused wire on the cat5 cables connecting them. Once I had those hooked up, the exhaust system was fine; the remote receiver board only had to power the two relays, which then switched the full 5V power to the driver boards.

The second problem was that apparently I’d missed something in my initial testing of the USB battery pack, and it doesn’t output two different voltages at the same time. If I just plugged in a 12V device, it would output 12V with no problems, but as soon as I connected a 5V device as well, the 12V output dropped out and came back at 5V. I tried a few different USB-C battery packs and they all had the same behavior, so it wasn’t just the cheap one I picked up for this purpose.

To solve this, I picked up a 12V->5V buck converter board, which does exactly what it’s supposed to. That way I can run a single USB-C cable to the battery pack, connected to the PD adapter board set for 12V, and use that to power the amplifier and the buck converter, which can then power the 5V devices. If I’d caught this limitation earlier, I might not have bothered using USB-C power in the first place, and just used a 12V battery pack. This would have made power control easier, because I could have a single DPDT switch controlling power to both the 7.4V and 12V batteries. I have some of those switches left over from a previous project, and I ordered a 12V lithium-ion battery so I could convert the jetpack over to that, but so far I haven’t felt the need to replace what’s currently working.

In addition to providing power to everything, the other considerations were charging and switching it on and off. Both batteries are attached via velcro strips, so worst-case they could be removed and charged separately. I put the 7.4V FX battery towards the top of one tank, so it can be reached by removing the nose cone. The USB battery pack is deeper in the central section, but I put a USB-C panel-mount extension cable from it to the top of one tank, so you can remove the nose cone and plug a charging cable in there.

Switching the whole thing on and off isn’t as convenient as I’d like. The FX board has a power switch, but it’s mounted to the fan motor in the central section, and the radiator has to be removed to access it. I suppose it would be easier to unplug its battery instead. The USB battery pack wasn’t perfect either — it has a button that will wake it up, and it will also wake up if a device is plugged into it. But it will go to sleep after 30 seconds if no device draws more than minimal power. The audio amp draws enough power to keep it on, thankfully. I went through some less-convenient arrangements before I got the buck converter, but now I just have the single 12V USB-PD adapter connected via a long cable running to the USB-C extension connector under the nose cone. So I can just unplug that cable to turn off the 12V and 5V devices, and plug it back in to power them back on.

But probably the next time I have a reason to disassemble the jetpack, I’ll replace the battery pack with the dumb 12V battery and a single power switch.

I feel the need to include some photos with this, so here’s a shot of the hardware on top of each engine:

Top to bottom, you can see the relay breakout PCB, then the RJ45 breakout board, then the 6-disc ultrasonic driver board, all mounted on the back of the 4″ speaker.

And here’s a view of the central section from above, when the radiator is removed:

This is without the engines installed, or else you’d see the tops of them in the tanks. In the central section, you can see the audio amp with the RJ45 breakouts on top of it, then the fan motor with power switch, and then the FX board. There’s also a good view of the threaded rod that secures the radiator and holds the top of the tanks in position.

Once I saw the animated lights from the Valor FX LED rings, I really wanted to see them lighting up some kind of exhaust. You can buy small battery-operated fog machines for this purpose, but I didn’t want to have to worry about potential sensitivities people might have to the special liquid used in those. I was particularly intrigued by the existence of cheap, readily-available coin-sized piezoelectric discs that used ultrasonic vibration to turn water into vapor. These get built into little humidifiers a lot, and you can get one with a driver board that runs off of 5VDC for a few bucks. I picked one up and tested it out, and it looked great. The only problems were a) it wasn’t nearly enough vapor, and b) it was designed to emit it upwards. Also I’d have to fit whatever I wanted into the space inside the LED rings, without blocking too much of the hollow channel in the middle of the engine where the sound comes out, and make it feasible to refill the water reservoir and replace the piezo discs (which are reportedly a consumable item).

As a first pass, I picked up some small watertight storage bottles that would (barely) fit in the required area, and designed & printed an enclosure to hold three of the discs in the lid. This way, the bottle could be unscrewed for filling or emptying. It would still emit the vapor upwards, but I figured I’d stick a small fan up at the top of the engine, blowing that downwards.

The fan options did not work. I started out with quiet little fans that could fit entirely underneath the speakers, and they didn’t move nearly enough air. I tried replacing them with larger fans that would require making a mounting bracket for the speaker, and just never got a decent result.

So, new plan: how effectively could I just mount the emitters upside down? They came with little silicone grommets, but their included plastic enclosures were definitely not designed for any non-upright arrangement. I tried designing a new enclosure for them that used some nitrile o-rings, and it seemed promising. Also the 3 emitters didn’t seem quite sufficient, so I came up with this:

This assembly held five emitters, with a tube that would lead up and out of the top of the engine, all the way to the top of the tank so it could be refilled via the nose cone openings. Some aspects of it looked good, but it just wasn’t the right answer. So I took a step back and questioned some initial assumptions.

The answer I settled on was to replace the LED rings with smaller versions of the same thing, then I could fit the exhaust emitters around the LEDs rather than in the middle of them. I found a compatible LED ring with the same number of LEDs, that was a drop-in replacement, and about as small as it could be and still fit those components. (I eventually realized I could have tried flex-cable mounted LEDs and wrapped them around the inside circumference of the engine nozzle, but this worked well.)

With the smaller LED rings, I could fit six emitters, which seemed like a good number — one of the available kits included a cheap 5VDC driver board that handled six discs at once, and I figured I could mount one of those on each engine. I still wanted them to be serviceable and easily fillable though, and designing a donut-shaped exhaust assembly seemed like it was asking for trouble.

So here’s my solution: I designed separate interchangeable exhaust modules, each of which contains 2 emitters and its own little reservoir. (And a printed TPU plug you can pop out to refill or empty them.) They attach magnetically, and even have little magnetic pogo-pin connections for the electrical hookups. You can see the modules up top, and the rounded mounting points at the bottom. Here’s what it looks like with them in place on an unpainted test engine:

There is just barely enough room in the middle for the smaller LED ring. The idea is that this way, I can reach up into the engine and just pull the modules out in order to refill or service them. And installing them consists of reaching up into the engine and clicking them into place.

The driver boards are hot-glued onto the back of the speakers at the top of the engines, and the wires from the module mounting points run up through the center channel of the engine:

You can see the RJ45 (ethernet) breakout board next to the driver board, for easy connection/disconnection between the engine and the central electronics. There are 8 conductors in that cable, and initially I was only using 7 of them: 3 for the LED rings, 2 for the speaker’s connection to the amp, and 2 for 5VDC power to the driver board.

Here’s what the inside of the engine looks like without the modules in place:

This plan has worked pretty well, and had a couple of complications that slowed things down. First, I kept getting leaks no matter how I managed mounting the discs and their o-rings, until I found that the water was leaking through the 3D-printed surfaces themselves. Solid-looking PETG prints were apparently more porous than I realized. So I followed the Bambu Lab wiki instructions for making things watertight, and that problem went away.

The other problem was power, which I’ll explain in a separate post.

Once it became clear that the jetpack might be comparable in appearance to the production hero props, I was motivated to put in a lot of extra effort. Among other things, I decided that adding electronics effects was something I wanted to do now, as opposed to maybe something at some point in the future. As mentioned, the Veepy jetpack design included mounting options for engine speakers (both 3 and 4″ speakers, seriously that design is so good), LED rings in the lower engines, and a central fan motor and PCBs for electronics.

A lot of the motivation for the project is learning new skills (and collecting their associated tools), which I always love. With my previous microcontroller work on vintage keyboard conversions, I could certainly have come up with an effects solution from scratch. But my time does have value, and I’m happy to spend money on solutions that are probably better than whatever I’d have come up with.

So, I ordered the Valor Jetpack FX Kit, and I’m certainly pleased with it. It’s a single PCB (with a daughterboard handling audio) that fits on the Veepy mounting bracket, it comes with RGB LED rings that mount onto the Veepy LED ring mounting points, It comes with a single cheap 3″ speaker, and connections to a fan motor. It’s powered off of cheap, readily available lithium-ion batteries marketed for heated gloves, and it has external connections for the activation trigger, an on/off switch, and a couple of always-on 5VDC outputs.

The Valor FX board includes additional instructions/diagrams for some upgrades: powering and hooking up a wireless remote trigger, and hooking up an external audio amplifier, since the built-in amp is pretty weak. I went with both of those options.

(This isn’t the final version of the central electronics, but it’s close. The Valor FX board is on the left, the fan motor is in the middle, and the audio amp is on the right. The amp has a couple of RJ45 (ethernet) breakout boards on it for the connections to the engines.)

For the audio amplifier, I picked up a cheap little class-D amplifier with flexible power requirements (9-24v) and bass/treble adjustments. It has bluetooth support which I didn’t want or need, but it looks like all the options in this category include that now. I planned to power the amp off of 12VDC. To go with the amp, I picked up a pair of Pioneer 4″ speakers and mounted one on each engine.

I bought the RF remote trigger boards that were recommended in the Valor instructions. They consist of a small PCB with four wires sticking out — input (VCC/ground, the VCC will take a good range of voltages) and output (not a relay like I expected, but the same VCC/ground as the input. Surprisingly the output VCC line is connected all of the time, and it switches the ground connection to open or not. Odd. The output current is limited to 2A or so, and they mean it — this became important later when I was making the exhaust system. The included RF remotes have 2 buttons, but I was only planning on using one. The remote receiver boards had two nice features that were very convenient for me: first, they had no problem pairing the same remote to two separate boards, which means I could use separate receiver boards to trigger the exhaust and FX board, but triggered from a single remote. Secondly, they were configurable for different behaviors, so I could set it up as a momentary button instead of an on/off toggle. This was critical if I was using two of the receivers with one remote, because I wouldn’t want the receivers to get out of sync with their power states.

The LED rings consisted of 24 WS2812B units on ring-shaped PCBs, individually addressable. The rings were each connected to the FX board with 3 wires, and it made some nice red/orange/yellow animations to simulate the light from the engines. I felt like the light would look a lot better if it were illuminating some kind of fog or mist, which turned out to significantly expand the scope of the project.

The Valor FX board is also designed to drive a fan motor, and seems to use the full battery voltage (~7.4VDC) for this. The Veepy jetpack instructions called for a specific size of motor (both for mounting holes and for the fan shaft), but the only readily-available motor I found that was an exact match was designed to run at 200RPM, accomplished by having an integrated gear box. This worked, but ran a bit slower than ideal, and I didn’t like the plastic gearbox sound that it made. So I kept my eyes out for an alternative, and eventually I settled for a motor that didn’t match either size requirement. It was too small for the mounting points on the jetpack’s mounting bracket, but I designed and printed a mounting adapter. It also had a smaller shaft, so I printed something for that as well. That fan was great, and it was fast. It didn’t have the gearbox sound, but it did sound like a fan moving a lot of air. I ordered a cheap PWM motor speed controller board and wired that up, and it was perfect for letting me dial in the speed I wanted.

To start off, here’s what we’re talking about. You’ll want sound enabled for it.

This second attempt at a replica jetpack was also 3D printed (on a Bambu Lab P1S) using PETG filament, sanded and painted to achieve a metallic-looking finish. The 3D model was the “Veepy Jetpack” design, which is sadly no longer available. I am stunned at how well-designed this model is, not just in terms of being screen-accurate, but also how well things are engineered to support successful printing and assembly. There are even aspects that facilitate maintenance of it, something that I tried to continue in other areas of the build. The model was also designed to accommodate effects hardware, in order to provide lights and sound and a moving fan.

The Veepy design also incorporates off-the-shelf hardware components when possible, for things like the flap actuator parts, the braided hoses and copper pipes on the engines, the fan, and hundreds of tiny rivets. Having the rivets be a separate component not only made them look more realistic, but it made the sanding process easier without having to work around hundreds of little bumps.

To make maintenance easier, the nose cone sections are held in place with magnets, and can be carefully pried off. That gives access to the inside of the tanks (if your hands are small enough). The engines rest in a bracket inside the tanks, and are secured with a single screw each to keep them from popping out of place. Removing that screw makes it possible to remove the entire engine, at which point the tank is empty. The tanks are attached to the central section at the bottom by some 1/4″ screws, and at the top there’s a long threaded rod running from one tank to the other, through the radiator section. Those parts are designed so that once the nose cones are removed, you can unscrew the nut from one end of the threaded rod, slide it over to the other tank, and pull out the radiator. At that point you have access to the central section from the top, which is useful since that’s designed to contain the effects electronics.

I took things a step further and worked to keep the tanks separable from the central section if necessary. The little rivets are all super-glued into place, but the ones that would connect the central piece to the tanks are only glued to the central section. That made the tanks separable, but it would leave a small gap visible between the tanks and central section when things flexed at all. To counter that, I removed a handful of strategically-located rivets and replaced them with threaded fake rivets that can be secured from both sides. These are normally called Chicago Rivets, and I found some that worked for it, but installing and removing them was really fiddly. So instead I took some long-ish M3 stainless steel screws, filed the heads down until they looked like the rest of the rivets, and secured them with wingnuts on the back side. Now the tanks are securely attached to the central section, but I can undo that part and remove them if needed.

I think the only other tweak I made to the Veepy design was to replace a couple of threaded wood inserts with head-set inserts, because I was afraid the wood inserts would end up breaking the 3D printed plastic. Regardless, the Veepy design was incredibly impressive, and it inspired me to put in the extra effort necessary for other aspects of the project.

It’s worth noting how much detail the Veepy model puts into parts that generally won’t be seen: Here are the engines, which are mostly covered up when installed in the tanks:

The braided steel hoses are real, along with the brass compression rings on them, and the copper pipes. I didn’t have a proper tool for bending the copper pipes, so I used a dremel tool to cut a bunch of slots partway through the pipe in the areas when it needed to bend, which made it possible to bend it without just folding the hold thing flat.