Today's Tool Tuesday is a particular favourite set of tools as they often are my first port of call when beginning to design or build a rocket! I often need accurate measurements of internal tube diameters and the Telescopic Bore Gauges are an excellent approach.
Each gauge covers a range of internal diameters and features 2 sprung probe sections that can be pushed back into the centre body of the gauge somewhat. In the handle mechanism there is a spring pushed bar which when you tighten a knurled nut at the back of the handle will lock the 2 probes in their current position. To get an accurate result you push the probes into the desired internal bore and hold the gauge at a slight angle and lock the probes to finger tight. You then pull the probes so that they span flat across the bore to bring it to it's final measured size. You then remove the bore gauge and use an accurate device to measure across the jaws of the probes, a well calibrated micrometer is best but often a vernier caliper across the probes is sufficiently accurate for most needs.
I'd never built an "odd rock"! Odd rocks are a category of rocketry reserved for those who create rockets from odd materials or make odd objects fly. I've seen loads of examples from flying cars to an office fan but it's never been an area I've delved into. At the milder end of odd rocks there has been a long history of people making rockets using confectionery packaging and in particular Pringles tubes. Pringles tubes are a very worthy rocket building material but they have been done a lot and I wanted to do something different. The Dorito's STAX tubes are a pleasing rounded triangular shape and I thought it might be a worthy candidate for a build.
This build was very quick and dirty and everything was done in between work and other commitments and definitely took a back seat priority wise to other rocket projects. I started by drawing around the tube to get a rough sketch of the tube profile and took a picture of it on my phone. I dragged the image into inkscape and then hand traced to get a vector of the tube shape. The tubes aren't quite an equilateral triangle which adds a bit of faff! I laser cut some plywood centring rings into which I cut a hole to receive the motor mount tube. This was finished off with a PETG 3d printed motor retainer.
The fins are 3mm balsa laser cut to a shape that kind of looked a bit dorito-esque! I originally planned to put the fins through the wall but ended up just gluing them on. I reinforced the oversize fins with a layer of tissue paper and glue. Due to the shape of the tube this rocket is impossible to simulate using a package such as openrocket. As such I decided to go very large with the fins to try and definitely pull the centre of pressure rearward in the airframe. The nosecone offered some challenges and I didn't really have time to create an accurate fitting cone. As a first attempt I decided to model a shoulder-less nosecone which would overlap the top of the tube somewhat rather than trying to accurately model to the tube. Having my rough nosecone model in FreeCAD to 3d print I then created a stack of lasercut plywood triangles to create a shoulder piece that could be sanded to a decent fit inside the tube. The recovery bridle was some thin kevlar and I flew this using a proven hexagonal annular parachute I'd made some time ago. Finished with a bit of satin black spraypaint and a quick vinyl cut graphic, DSTAX was finished!
Photo credit Peter Barrett
Due to this not being sim'able, once together I decided to add around 18 grams of nose weight (some small flat lead panels epoxied into the nosecone bulkhead) and this seemed to make the airframe stable when performing the classis "swing test". The swing test is where you attach a string at the centre of gravity (with the airframe loaded with a motor etc) and then swing it in a circle, it should correct itself slightly into the wind and then remain stable, an old school approach that works well to give you some indication of the stability. The other consideration was the maximum lift off weight limit of the target motor, an estes D12-5, which is 283 grams. All up weight of the rocket came in under the maximum at 224g.
As you can see in the video the first light was successful albeit with a slightly late deploy of the recovery system. I think it's a little over stable by the way it turned into the breeze but it's certainly within acceptable limits. If I built another I would consider reducing the ridiculously large fin area somewhat!
I've written about stud clamps before, both here and in Hackspace magazine, but, due to their usefullness, they need a Tool Tuesday post of there own.
The stud clamp allows you to work on bolts or threaded items whilst holding them securely without damaging the thread. Or they can be used to aid removal of threaded studs from assemblies. Essentially they are a piece of material with holes drilled and tapped to receive bolts or threaded bar of the corresponding thread type. They are then carefully cut, either by hacksaw or a slitting saw in a mill and this creates the clamp. Thread your target material in and pinch the clamp shut in a vice or using some other type of clamp, mole grips or a G clamp for example, and your work is held super securely for you to work on.
I've become a big fan of cheap EMT shear type scissors. They are widely available and there are super affordable versions if you steer away from the more "tacticool" versions. As a pair of beater scissors they are great and will cut a wide variety of materials. I often use them to trim the edges of cured fibreglass layups etc and they really are tough. Just make sure you don't take them from a first aid kit you may rely on!
I know, I squandered that career in modelling I was destined for... I like playing with different materials on the vinyl cutter and I've used HTV or Heat Transfer Vinyl a little bit, but usually limited to flat smooth fabric items. At home I've used the domestic iron to apply designs to bags and tee shirts and at the Ffiws makerspace where I work sometimes we have a larger flat plate heat press. However I wanted to experiment with HTV on more awkward surfaces, i.e this baseball cap. I'd seen crafters in the US using smaller irons specifically designed for HTV but I couldn't find them in the UK or running at 240V rather than 110V. However, another area that uses these irons are aero modellers building lightweight planes which have a heat shrunk covering applied to wings made from balsa ribs and spars. I ordered one to have a play with for less than £20.
There are commercial hat presses for sale or heat presses with replaceable elements in different shapes for different objects and these obviously apply heat and pressure uniformly and make HTV hats trivial to create. However for small batches the iron works well. After cutting the HTV on the vinyl cutter and weeding (removing the parts of the vinyl that aren't part of the design) I stuck the HTV and the heatproof backing onto the cap in the correct position. Note that if you want to have a go at this you want to find a 5 panel baseball cap rather than a 6 panel baseball cap as a 6 panel has a seam vertically down the front of the cap. The curvature of the hat makes it almost impossible to stick the HTV backing down too, more because of the thickness of the backing rather than the stickiness. You also want to curve the HTV/Backing to conform to the hat rather than making the hat panel flat as that would then crinkle when the hat returns to it's normal state. I used extra kapton tape (heat resistant tape) to hold the HTV panel in place, but neither the tape or the backing adheres that well, it's only when you tack the first part of the design with the iron you can feel assured it won't move.
My original plan was to stuff the hat with an old towel to try and keep the hat firmly in shape, however I realised that it was easier to cover one hand with 3 layers of the towel and push into the back of the design with one hand and then hit it with the mini iron using the other hand. I set the iron to roughly 160C and applied the iron to each section of the design for around 15 seconds. I made a slight error on the first attempt as I hadn't noticed a bit of kapton was stuck under and lifting an edge of the design, so I opted to cut the black HTV ring around the yellow design and add that as a second layer to cover the slight error! One thing I noticed is that due to the curvature of the cap the HTV backing kind of self releases when the HTV is stuck which is very useful and means you automatically peal the backing whilst it's still hot. I'm pretty pleased with the results and the iron is great and will be useful for this as well as other model making activities.
It's pretty fair to say I love all types of pliers as tools. I have a few sets of more expensive pliers but the majority of my collection are pretty cheap and cheerful. One type that I use a lot are flat nose pliers, a sort of thin nosed pliers where the jaws bend away from the grip. The RS Pro flat nose pliers are a reasonable set of smaller ones for not too much money. They are small enough to often be used as a slightly more forceful set of tweezers and I often use them to place small nuts and fasteners where my fingers are too big to fit. I I had one small gripe it's that they aren't particularly precise in closing and the jaws don't align perfectly as you would find in higher quality tools. However they are great for many tasks and are perfect for one of my favourite little hacks, if you place a rubber band around the handles you can use them as a small low pressure clamp holder that's capable of holding the work slightly off the bench. Super handy for soldering, clamping small glued items or I've even used this to create temporary test stands for tiny motors.
I LOVE it so much when people make use of something I've shared or written about and I feel really pleased that Calderdale college elected to build their PiWars entry robot based on the opensource MTV Robot platform that I designed and wrote about in Hackspace magazine back in issue 37. The MTV robot is built around a really cheap tracked chassis that can be bought online and a stack of 3D printed parts you can add yourself.
For those of you who don't know PiWars is a brilliant robotics competition that anyone can enter and your robot has to compete in numerous different fun challenges. It's a really lovely community and even if you don't enter it's a fun group to watch to get interesting ideas for robotic projects!
The Calderdale college team made numerous changes and add ons to the MTV platform and the team came 5th overall in a beginners class of 15 entries and they even came first in one event "up the garden path" which was a challenge where you had to control the robot with voice commands. Superb stuff! Read more about the excellent Calderdale team/experience on this great blogpost and grab the free PDF of Hackspace magazine 37 to get the links and info for the MTV design files.
