Let's Make Robots!

How to make a clip for any cell phone LiPo, and how to vacuum mould

This is a small walkthrough with some tips on how to vacuum mould, in this example, a holder to a LiPo from a cell phone

Update; Version with motors here: http://letsmakerobots.com/node/23312

I would like to play around with old cell phone LiPo's. I figured it was a nice way to get some tiny batteries, including charger.

However, I needed a clip to easily insert the batteries into what ever I mas making. Since I have played around with vacuum moulding, I figured it was a nice opportunity to make a small walkthrough.

What I really wanted to achieve was what you see on the first picture below.

What you see on that picture is a flat, black end of a LiPo, with 2 metal clips touching the poles.

This picture was taken in daylight (the rest is not, sorry they are so dark), and it was from a demonstration that made some nice pictures, and went very well..  apart from the fact that I wanted to be able to solder to the metal, and the metal I used on the picture above proved to be the kind that will not stick to solder. So check that first :)


OK, on with a second version:

I took a switch apart, and found some nice thin metal that absolutely loved the solder, and I soldered wires to it.

Then I took some (black) tape, and tapd it around the battery. BUT! I stuck it on with the sticky side outwards!

This way I was able to take it off later, and also I could slide it all the way to the top of the battery:

Then I added a piece of (white) double density tape - and made that stick on both sides.

On top of that, I stuck my clips with wires.

Now, if you can find some long flat copper or the like, it would be better. Like I wanted to in the first shot above. (And second video)

Last I took a little piece of stick, and stuck it to the other side. This is to lift it a little when doing vacuum moulding, so the plastic can get under and lock the battery.


Now, watch the videos. If you live in china or cannot see videos for other reason there are some pics here. All there is to say is that I have made a box that holes the object to be moulded. And into this box I placed the end of a vacuum cleaner.

Then I heated 2 plastic plates - I could have used just one, but 2 makes a thicker layer, and they stick together when moulding.

When I use plates, I have a sheet of cardboard that I place over the larger square with holes in, so vacuum is around the plates edges.

You can heat in an oven, or make some apparatus with a grill. And any plastic seams to work. Only thing is that when the plastic gets hot enough, it goes completely soft, and also it wants to pull itself together.

So, if you want, you can make a frame (just some wood) and clamp on your plastic, all the way around. The wooden frame then goes into the oven, just give it almost full heat, and then you can take out the frame, and smash it onto the thing to be moulded, while sucking underneath. There are trillions of videos on this out there. My "grid" fits to a frame I made, so I can use the complete area when doing larger stuff, using other sheets than plastic plates.

However, I found plastic plates to be a nice source of flat sheets of plastic for small parts, and the smart thing is that if you use an electric heater like I do on the video, you wont even have to make a frame; The plastic plate has it for you, as long as you only heat up the centre part.

Other good sources: if you buy something that is inside transparent plastic, that can be easily used as well. Even if it has a shape to hold the item you where buying.

Because when heated, all plastic turns into the same flat membrane. Any bumps dissapear. This also means that you can use plastic plates with patterns, and if a mould did not go well, you can just re-heat the plastic, and it will turn into membrane again (unless you made holes in it).

Another source is when my butcher sells me a beef, he puts it into these nice black plastic cases, with transparent lid. Tear off the lid, and the plastic is ready to become robots!

Finally, you can of course jut go to any hobby store and buy large flat pieces. Oh, just remember; In the supermarkets they also use big flat pieces to signs! I stole some, and they are perfect!

When done, cut out the piece. Because the way the tape is put on, it just goes off when the band is cut.


You can take out the battery, and fine cut the shape that you want:

Now you can also bend the clips in towards the battery a little, to make sure they will make nice contact. But the plastic has also made it tight, as it shrinks when heated / cooled down.

Cut holes to pull out the wires or what ever you used.

And you are done :)

This one was done while video was rolling. So It was not made too well, and I re-heated it, causing edges to be thin and in general it all became a little more melted in the look :)

But it works fot the purpose, and the battery sits very tight. You can take it out with a flat screw driver, or if it is too tight, you can cut off some more of the edges of the holder.

Here is the original one, the style I recommend you do go for, only use metal that sticks to solder:

Mind you this is very close up, so everything looks a little melted, even on this fine and crisp mould :)

See how vacuum has made a hole in the plastic. If you want to avoid this, use more false air / let the vacuum cleaner have other holes / turn it down to less power if your model can do that.


Now, if I wanted, I could place some wheels on each side of this, and mold the whole thing one more time. Then I would have a steady shape that holds 2 wheels and motors and a LiPo. And if I wanted, i could even add some more stuff there, and make a complete chassis :)

Or make extra shapes to be put on the robot.

A final tip is; if you make 2 sides of an object, you can cut each one out, tape it along the edges, and fill up the chamber with PU-foam. That will then harden, and you have made a complete 3D copy of your item - weighing almost nothing, and extremely durable and hard to break.

Old toys, parts from a joystick, anything can be used as "positive", to create a shape from.

And it looks really good when spray painted!

Oh; One final tip: You do NOT want to use hot glue on your positive / shape. Heated plastic makes it stick. I made some really nice shapes with different materials, including hot glue. And was not able to get out the original from the mould :)

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Fritsl, you da man!

Cool tip. Even with hot plastic plates!

Great idea using the plastic plates. awesome.

Yes, that's a realy great idea!

Do you think that a simple hair dryer would make the work?

I know for a fact that a hair dryer would not make it work!

Yes, I admit I have tried, just as I have tried with an open flame. (Seamed like an interesting idea at the time).

If you look at the topmost video, from 0:38 to 0:52, you will see that even my heatgun did not work. It has a thermostat, and is only "on" some of the time. at 0:54, you can actually hear my vacuum cleaner go a little down in pitch.

This is because all power in my little workshop goes through one cable. And at that time, the heat gun thermostat is turning on the heating elements in the gun. And only at that time does the thing melt plastic. At this time, your hair would be gone, for even when thermostat is closing for the heater, you would get a very, very funny look from it ;)

You need to get around 160 degrees celcius / 320 degrees Fahrenheit on in the plastic core before it turns into wobbling membrane.

That's a real shame. I was looking up plates on eBay last night, and they are really cheap.

Unfortunately, I don't have a heat gun, only the wife's hair-drier :(

Vinyl gramophone records? Not even if I taped up the hole?

I will try for you, one moment..

Hmm.. First challenge; There is a huge piece of paper in the centre.. Heck, will just heat it all!

Hang on..

Records / vinyls works fine!

Only the paper is irritating; Where it is, the plastic does not like to stretch. And it is relatively thick, so I recommend to make a frame and put it in the oven. Because when you have to heat something that thick with the heat gun, it can be hard to regulate, and then I had to heat too much on a spot, and it "tipped over" (changed structure/"burned"), resulting in holes.

But if you can find an easy way to get the paper off, and will make a frame that can hold the round shape, they should work fine.

The plastic is breaking when beaten or bend hard though.

Only question: How will I get my scissors out from that record again?