Fitbit Backpack in Elasto Plastic

This was originally posted in the elasto contest thread, but now that I've actually gotten the prototypes I'm posting it here for any advice/thoughts others may have about this project.

I recently got a Fitbit Flex activity tracker, but I wasn't fond of wearing the bracelet that it came with, and decided I'd rather attach it to my watchband. I developed this "Fitbit Backpack" for that purpose. This is my first ever 3D printed object, and I'm pretty happy with how it turned out, though the prototype has revealed some problems with the design and also apparently with my modeling ability (using SketchUp)

Here's the backpack next to the fitbit module. As you can see on the left side there was some sort of problem with the model, and it wasn't printed solid.:

And here's the underside of the backpack, with the fitbit inside. As you can see in the above pic, I made the ring openings too big, so those will get reduced by about half:

And here's the backpack attached to the watchband:

The design works pretty well, though it does add some bulk to the fitbit. I might try reducing the thickness of the walls a bit, as I was a little over the spec'd minimum. The rings at the end, however, are too thin - they break. The elasto material does bend, but it can also develop cracks if it is bent at an angle especially when it is thin. The fitbit fits well inside, though I made the opening a bit too small - need to expand that so I can get it in and out a little easier. There's also some extra room at the top of the unit, so I can probably trim that material a bit and save myself 20 cents.

One other problem I had is that the ring one end does not seem to have been attached well. I think this is the result of creating the rings as seperate models, and then just latching them on to the body of the backpack. I don't know how best to correct this and make the whole thing "one piece" instead of three pieces connected together. Any advice on this?

Looks great! I think it came out looking better to me than what I initially envisioned from your Sketchup renderings. Shapeways will definitely need to offer a dyeing service for this material when they get around allowing products to be made with it. That beige is plain butt ugly! HAHAHA! :laughing:

Keep in mind that watch bands are standardized, so perhaps, in addition to this design you could offer an entire band as an option. You could offer the buckle part in one of Shapeways' other materials if you couldn't come up with a way of doing it completely in Elasto Plastic.

Thanks!

Yes, I've thought of doing a full strap instead of the backpack idea, but I wanted to try the material out first with something small and inexpensive. The idea for the backpack is that it could be used with several watches (I have three that I wear, depending on my mood) and that would work with leather, rubber, or fabric straps. And at just around $5 to produce, I think it could be appealing to people who use a fitbit but don't like wearing a separate bracelet.

After seeing the material, I think a pure elasto watch strap could work, though I have questions about its durability. The material seems prone to "crumbling" after being bent multiple times, and a watch strap has to take a lot of abuse. Also, a full strap would be expensive - my guess is about $30. I'll prototype one up though and test the idea - if it works and isn't more than $30 it might be a product that people would buy (though that wouldn't leave me much room for profit margin).

I haven't given up on the backpack idea - I like the fact that it's only $5, and I think I can make it work. But I did cook up a prototype for the full strap. Right now production cost is around $15 for this one side, and probably about the same for the other side as well. For $30-$35 it's not unreasonably priced if it actually works, though again the color of the material isn't exactly great and would need to be dyed, and I'm worried about the die wearing off while on the wrist.

Aw ha! I didn't think about wear! That's a good point! I am now worrying about that too for some Elasto Plastic designs I have in mind. I wonder how much penetration can be had with dyeing processes. Could it be done deep enough to outlast the life of a typical product such as yours where it could potentially receive daily abrasion for up to a few years?

Perhaps Shapeways can approach the manufacture about compounding an array of colors. That way wear wouldn't be an issue.

Nice work.

My thoughts...

1. With the watch strap you will have to be very careful positioning the 'backpack' otherwise it might sit awkwardly on the side of your wrist and compromise the smooth fit of the band;

2. The loops for the original design could be angled down and shorter. If they are printed more in the orientation that they will finally take up there will be less stress at all times and therefore they should last longer;

3. Likewise if where the loops attach to the main body you can use fillets and radius the joins you will reduce the stress in the join;

4. You could reduce the volume of your print (and thus the price) by putting more holes in the 'backpack'. These don't have to be round, they could be slots or a decorative motif. Now that you have an idea of the material's properties you can reduce the structure to its functional minimum.

Good luck!