Making a Nerf Scope

For the last few years I have been working with my nephew on concepts like drawing things you want to build, making schematics, and keeping a lab notebook. We started when he was six, so at almost 8 he is comfortable with the processes. Still I was pretty blown away bow how comfortable he had become with the design process. He showed up for the visit with a bunch of designs. After a Nerf battle, we ended up designing and printing up a scope for his Nerf rifle.

Main thing that blew me away is that he drove the design process, iterating through a bunch of pretty different scope designs on paper before talking to me about what he wanted to build. Then when we were talking, we were able to refer to his drawings, even to the point where he merged two previous ideas coming up with a new one. It was actually really similar to how I normally work with professional designers. It was very cool.


Something I really liked about projects printing up my nephews designs is that he gets to work though failures, and learn about the power of iteration and value of measuring twice. In this case we designed the scope, but since we were not designing it to fit against a model of the gun – we were not checking clearances. So our first version looked good – but didn’t fit on the support rail.


My nephew got to figure out what was wrong with the design, then how to fix it. After that we revised the design and printed out a new scope, which you can see being tested here. Again, I was impressed that he was not paralyzed by disappointment, we just set to figuring out how to fix things.


Here’s an action shot of the scope.


All in all I plan on doing a lot more projects like this. Pretty much the only problems were the boring parts for my nephew. Watching the printer was cool, but after a while that changed into “hurry up and print”. Also my doing the CAD modeling while he watched was hard. I explained stuff and asked him questions so he was engaged while I implemented what he told me to – but it still taxed the attention span of a 7-8 year old. Still, over all we both had a lot of fun and learned a lot. I highly recommend projects like this if you have a printer and a little person.

A $6 Nerf Grappling hook

Started printing this version, which prints both the hook and the dart body. Problem with that is the printed dart body does not work with the compressed air spring driven Nerf guns or the electric Nerf guns dart accelerators. It was kind of a disappointment for my nephew.

My nephew and I did find this version of the grapping hook. It required cutting up a Nerf dart, but it worked amazingly well. It was also fast to print.


We bought a Nerf Jolt to use to launch the darts. Amazon has them for $6, and it works perfectly with the grappling hook dart. They also sell them in groups of 4, which would let parents and adults watching kids to stash them around the house. You know, in case you wanted to retaliate to any surprise Nerf attacks.

After we made the grappling hook, we designed and printed up a modification to the Nerf scope we designed so it clipped onto the Jolt. My nephew did the design and used calipers to take the needed measurements, and I did some translation into Solidworks for him.


With printers, VR, and AR all taking off someone seriously needs to make a decent CAD package targeted at kids. My nephew is a pretty impressive kid, but I was still surprised by how he walked through designing his scope. This was actually the second scope we built, so I’ll talk about his designing in another post, but I was impressed. He iterated a bunch of really specific designs on paper before telling me exactly what he wanted his scope to look like. He even tried out different lollipop and crosshair designs.

For “rope” we used a 15 foot section of dentil floss. Use the un-waxed type if you have a choice, it helps keep it from knotting. I added a front cross bar and spars to hold the “rope” on the grappling hook. Firing the dart would cause the “rope” to unspool as the dart flew, and winding up the rope kept it from getting tangled when not in use. Still, using the spars also meant that the kid firing the grappling hook had to re-wind after every shot. So I think I should have not added anything to my nephews design. It did provided an opportunity teach him what feature creep on a spec was, and that it is not your friend.


All in all we spent a good hour playing with the grappling hook, launching it at different things and trying to reel them in. The calipers we used to take measurement were also a bit of a hit in their own right. In retrospect though I would wait until the child in question was 9-10. The CAD modeling takes a good while even if you are keeping things simple and attention spans can begin to get exceeded.

A Non-Newtonian fluids and shear thickening science project

Non-Newtonian is both insanely cool, and something a young mad scientist in training can directly experience and play with. Cornstarch mixed with water is a shear thickening Non-Newtonian fluid.

Shear thickening is basically what it sounds like; the fluid thickens when shear forces are applied. The fluid thickens when you apply forces into the fluid. The most spectacular example of this effect is people running across tubs filled full of the stuff. Run fast enough and the fluid supports them, but stop or run slow enough and they start to sink into the fluid. Another cool example of shear thickening is to fill the cone of a speaker pointed up with the fluid. Then playing sound causes the fluid to do all sorts of weird things.

Even though larger volumes of the fluid lend themselves to spectacular demonstrations, you can do some really cool science experiments with less than a cup of corn-starch. My nephew was visiting on short notice and we were able to put this experiment together only on what I had in the house for cooking.

We mixed up a mixture of cornstarch to water at 35:65 by weight. That’s actually a bit soupy a mix, but it made it easier to work with for a longer time with my nephew. Next we covered a small speaker with plastic wrap. My nephew was able to use used a cotton swab to stir the cornstarch slurry in the beaker, then spoon it out onto the speakers surface.


Once the cornstarch was on the speaker we used a function generator to sweep different frequencies and waveform shapes. While driving at fixed frequencies let us feel differences in the fluid at different frequencies, and let us do better science, it wasn’t as interesting as just driving random sound. My nephew still thought it was cool – but I think I am going to do another run of this with him using a larger speaker and sound.


When we were driving the speaker we could turn the function generator off and on having the material in the speaker switch from acting like a fluid, to acting like a solid – which was cool for an 8 year old. What also worked was showing him how driving at different volumes and frequencies changed the viscosity.


Its hard to see in the picture, but with the shear-thickening my nephew was able to drag and lift the liquid around like it had a very high viscosity right up until it started acting like a solid and breaking. At which point it would fall back into the pool acting alike a liquid. Hard to describe, but a cool illustration of both viscosity and Non-Newtonian shear thickening.

All in all I highly recommend this for anyone wanting to show kids that science is cool. If you don’t have any of the electronics, you can mix up a small quantity of cornstarch and water in the palm of a kids hand. Then when you tap it, it turns solid for a moment. Not as cool as using the speaker, but fast and can show kids something cool in a few minutes.

Round Two on Printed Lego Walkers

The first LEGO walker was really cool, however it was more a single printed toy of the same size and scale of a LEGO mini-fig and not a LEGO toy in its own right. Looking around thingiverse a bit more my nephew and I found this walker design, which snapped together as a series of four custom LEGO pieces.


It is hard to make out details because I printed it in black ABS, but this walker really came out pretty sweet. I think I will modify this design before my nephew visits next, making the legs more easily detachable – but still – it was still really cool to be able to sit down with my nephew, pick out one toy to make from hundreds of possible options, and then just print it. I mean this is what the world is like when he is 8, he is growing up with that kind of magic being the reality of his world. How cool is that.

(3D printer + awesome nephew) = Toys!

So I have be playing with 3D printers for the better part of a decade – and I cant believe I never though of this! Most of what I do is making parts for prototypes – I haven’t been making toys.

My nephew is in town and I wanted to show him what you could do with a 3D printer. He’s 8 – and awesome – so we made some accessories for a Nerf gun under his direction. Once we were done with that though, we found this guys design for a mini-fig walker. (Design here


The designer painted his, which looks better, but I don’t really want to give kids painted parts to play with. They tend to end up in their mouths. Turns out there are a bunch of interesting designs for mini-figs out there.

At this point I pretty much need to design and make my nephew some new toys, but until I have time to sit down and design something for him myself, these designs look neat.

Lego Walker
MiniFig Mech
MiniFig Mech 2.0