The really short answer is that you can stop by my Tindie store and grab one of my new no-sew Velcro strap doodads. I am not the first to have this idea. I am absolutely positive that you can buy something similar from Amazon. I have seen them before, but no matter what I put into the search box today, I just can’t find them!
This idea has been in the back of my mind for years, but I had no reason to execute on it. That is until I bought a small shoulder bag to fit my new 14” laptop. I take this bag on rides to the park, and I thought it would be handy if I could use one of my drone battery straps to secure a bottle of water to my bag, and I’ve been cutting carbon fiber and iterating ever since.
Why are these carbon fiber strap plates so small?
The first set that I cut wasn’t small. It was a 30 mm square with a pair of slots to slide the Velcro strap through. This is probably the more aesthetically pleasing design.
One of the things I sell on @tindie leaves behind these long 15 to 20 mm strips of carbon fiber remnants that I just don't want to throw away. I keep thinking I'll find a use for them. Maybe I can adjust my bookbag Velcro strap mount thing to fit in this space? pic.twitter.com/LNp6YiggXA— Pat Regan (@patsheadcom) May 31, 2022
Attaching things to my bookbag is only one of my problems. The other is that I generate quite a lot of waste carbon fiber, but it is almost entirely lengths of narrow 300 mm and 400 mm strips. I’ve always thought it would be nice to find something useful to put in this space.
It is nice that I can cut useful items out of the remnants of carbon fiber that would eventually wind up in the trash. I can also add a whole mess of these pieces to the end of my regularly scheduled cooling duct job.
Using the wasted carbon fiber plate still isn’t free
In my mind, I’ve been thinking of these Velcro strap holder parts as being completely free. There is some cost involved in turning trash into treasure!
It takes an extra 30 minutes to cut these strap holder pieces out of the edges of the 400mm x 300mm plate. That’s nearly as long as it takes to cut 15 ducts out of the rest of the sheet.
I tend to think that there’s no cost in running the Shapeoko. It isn’t like I stand there and stare at the machine for the entire hour, but I do have to keep an eye on things. I am also wearing out endmills a lot faster—carbon fiber is MEAN to endmills!
Why do these things even work?!
What if you poked a hole in the canvas-like material of your backpack, pushed an M3 screw through the hole, and tightened a string to that bolt? You wouldn’t be able to hang much weight on that string before it would tear its way through the fabric.
We are poking two holes, and we are sandwiching the fabric between two ridiculously sturdy pieces of carbon fiber plate. We are spreading the weight out across a much larger area, and I am assuming that the pressure from the plates being squeezed together is preventing the fabric from fraying.
When I saw the words "demolition drones," I immediately thought of this crash of mine. In the goggles, it felt like I was playing KerPlunk. pic.twitter.com/3j4tktqKpc— Pat Regan (@patsheadcom) June 1, 2020
The carbon fiber really is ridiculously strong. This is exactly how we strap 220-gram LiPo batteries to our 750-gram FPV drones. We can smash into a tree at 100 mph, and the carbon fiber and Velcro strap won’t break. The weakest link here is going to be the material of your bag.
Even if you can sew, this seems like a tricky problem!
I have bags with integrated straps. When they are sewn directly to the bag, the stitching covers a lot of surface area! Usually at least three inches or more across the top and bottom of the length of the strap, then there’s some pattern across the strap near the edges. The straps are thick, and so is the bag. This requires a lot more force than sewing a button on a shirt!
I have other bags with a loop of fabric to thread your beefy strap through. Those loops of fabric are always three or more inches long, and the sewing looks just as difficult as sewing the strap directly to the bag.
I can’t sew, but I can cut two tiny holes.
How much weight can this safely hold?!
I don’t know, but I am excited to find out!
I have been bouncing around riding my electric unicycle with my small AmazonBasics DSLR backpack. I sometimes have my 700-gram FPV freestyle drone strapped on, other times I have a 16.9-oz bottle of water or my smaller 280-gram drone.
A couple of pounds surely isn’t a problem. I’ve been a little more concerned about the extra force that will be applied when I ride off a curb or bounce around through a lumpy field. I haven’t seen any damage to the fabric so far. I will be keeping an eye on things, and I sure hope you will as well!
I thought about applying a bit of E6000 glue between the plates. I’ve used it on fabric before with decent results. I want to be able to test new parts, and glue would make it difficult to swap things out!
Why are main plates asymmetrical?
I am attempting to put less pressure on the Velcro strap. My first test mount was a pair of identical square pieces. I didn’t have any spacers. Once I bolted it in place, the Velcro strap was effectively locked in place.
The carbon fiber spacers that I include in the kit should alleviate most of that pressure. However, I do have one plate bolted through the padded section of my laptop bag. Once you cinch the plates together, the padding pushes up against the outside plate with quite a lot of force.
Having the connecting bar run across the edge will allow you to have those bars on opposite edges. I hope this helps alleviate that pressure in these sorts of circumstances!
How do you install the plates?
I am pretty certain this needs to be a video. It is hard to film inside a bookbag, so you will probably see me on video installing a strap on an old T-shirt in the near future.
The idea is that you poke two holes in your fabric. I have been using the reamer tool on the back of my Swiss Army knife for this.
I start by poking the first hole, then assembling the sandwich of plates and spacers using the M3 screw. I don’t tighten the first side down all the way. I want to be able to swivel it around to make sure I can install the plates as straight as possible.
Once I have the plate rotated where it needs to be, I stick the reamer tool right through the second hole in the carbon fiber. I usually can’t poke a big enough hole with the carbon in the way, but this gets me the start of a hole in precisely the correct position. I can move the carbon out of the way, then expand the hole to the correct size.
I do my best to keep the hole in the fabric as small as possible. The less damage you do to the bag, the better it will hold up in the long run. That said, I have accidentally punched some holes much bigger than I wanted. It hasn’t caused a problem so far, but we’ll see how that goes in the future!
Do these have to be carbon fiber?
Definitely not. My test parts were 3D-printed in PLA+, and they would have done the job for me just fine. I’d be a little concerned that the PLA would get soft on the passenger seat of my car if I left it out in the Texas sun in July, but I would also be concerned for the safety of my laptop in that kind of heat.
I picked up a spool of black ABS filament to use for the plastic parts. I have had a 3D-printed ABS part on my dashboard for almost three years. It isn’t as red as it used to be, but it hasn’t deformed in any way. I figure ABS will be a reasonable plastic to use for any plastic accessories.
I need to clean up the OpenSCAD code a bit before I upload the files to printables.com. I accidentally goobered up some of the parameters. They are cutting at the size I want, but if you try to adjust it, things get wonky!
None of us are planning on crashing our bookbags the same way I crash FPV drones. I bet most of us just want to strap a small tripod or drone to our backpack. A few pieces of PLA will be able to handle that!
I have a plastic accessory!
I didn’t add it to the Tindie listing yet, but I have added a 3D-printed arch on my Pi-KVM case. The arch piece is bolted to one of the carbon fiber backing plates, and it lets me loop in a carabiner so I can hook it to another bag.
I am not sure that I needed a loop like this on my Pi-KVM kit. Sure, I can quickly strap it to my small laptop bag now, but will I ever really need to? Wouldn’t I just throw my laptop in my big laptop bag and stuff the Pi-KVM kit inside with it? There’s plenty of room!
Probably more plastic accessories. The carbon fiber is awesome because it is ridiculously strong and so easy to machine, but it limits me to flat parts. I could make use of the third dimension, but I would need to buy much thicker carbon plates, and the extra work would absolutely obliterate my endmills.
I am planning on printing a TPU cover that can be used on the inside of the bag. My small laptop bag has two M3 lock nuts pointed right at the side of my laptop. I’d much rather my laptop get jostled into a rubbery print than two steel nuts!
What do you think?!
Is this a good idea? Why can’t I figure out what someone would search for if they wanted this sort of product? What other 3D-printed accessories do I need to work on?
Let me know in the comments, or stop by the Butter, What?! Discord server to chat with me about it!