Following on from my previous post regarding the 9 V Nerf Stryfe upgrade, It occurs to me that there will be plenty of people out there who want to go to higher voltages (only reason I haven’t is lack of high voltage batteries). One thing that you’ll need to do in order to make the most of higher voltage upgrades is remove or short-circuit the “fuse” located between the negative battery connection and the motors. This is located on a little circuit board towards the rear of the gun, as shown here.
I haven’t found a good datasheet for the component, but it seems to be a Polymeric Positive Temperature Coefficient device ( http://en.wikipedia.org/wiki/Resettable_fuse ), which basically acts like a re-settable fuse. It’s to designed to protect the gun from being operated at high voltage, since this can cause motor burn out or excessive motor vibrations.
Obviously those are bad things, but as long as we don’t go TOO nuts with the voltage upgrades, it will only reduce the Stryfe’s working life, not kill it instantly.
The easiest way to overcome this, is to short-circuit the PPTC. you can just solder a piece of wire to connect the two legs of the device, twist the legs together, etc, etc. plenty of ways to dodgy that up.
Now me, I’m a big fan of reversible upgrades, where it’s easy enough to do so, so I decided to install a jumper, so that I can short this fuse from the outside.
I have a heap of male header pins (above) that I bought cheap on eBay. They come in long strips, so you can snap off as many as you need. One issue that I have with these, is that if you heat them too much while soldering, the plastic starts to melt, and the pins can slide out of position. I’ll show you how I get around this soon, but you start by pulling the pins out of the plastic row (see top of picture above).
You’ll notice that I also stripped off more of the wire than I need for soldering. You’ll see why below.
Above is the jumper that I used (it just happens to match the colour of the Nerf body). I think I got this out of an old printer, DVD recorder, or some other piece of old technology that I stripped for parts when I threw it out.
As you can see above, I wrapped the excess wire tightly around the pin, with the sheathed section of the wire starting right at the end of the pin. Next, clamp the pins in some crocodile clip style “helping hands”.
By doing this you can hold your soldering iron in one hand and your solder in the other, without having to worry about the plastic header strip melting while you solder, nor the wire wandering when you’re soldering. This lets you get a good clean solder at the very end of the pin, which is important, since we’re going to poke this through some small holes in the Nerf case, and I don’t have any excess length to play with (not if I want the jumper to have enough pin to hold onto, that is).
I then used a 1mm drill bit, and drilled two holes about 2.5mm apart (to help mark these out, scratch a straight line along the case of the gun (to act as the centreline of the pins), then use two pins that are still connected to the header strip to scratch two parallel lines, perpendicular to the centreline. Just drill at the intersection points of these lines, to make sure you’re drilling at correct spacing.
As you can see above, I then poked the header pins through, and mounted the spacer strip back on them. Above shows the strip only pushed onto the top of the pins, I pushed it all the way down, getting as much useable pin length as possible, then glued the strip (and pins) in place with superglue (see pictures below for final position).
I then trimmed the wires to the correct length, stripped the ends (fairly generously), and wrapped the stripped end around the legs of the PPTC. I used an alligator clip to help hold some stray wire strands in place, and to act as a heat sink (probably not necessary here, but a good technique to use for any semiconductor, etc, where you are worried about damaging the component with the heat of soldering).
To give you an idea of the speed increases achievable through voltage upgrades, I downloaded a frequency analyzer app on my phone, and used it to measure the primary frequency of the motors while running. This is a great way of checking relative increases in operating speed of rotating equipment.
6 V = normal voltage (~228 Hz)
9 V = 25% increase in speed (284 Hz)
12 V = 54% increase in speed (350 Hz)
16 V = 86% increase in speed (425 Hz)
This upgrade allows me to use 12+ V power supply for the nerf when I want to, by simply bypassing the PPTC. Admittedly, it would be simpler to just remove the PPTC from the circuit, or bridge it out inside the gun, but… Meh.