So, I set out to reproduce the project using a more readily-available mold material: LEGOs! The plus side is that means the project no longer requires a 3D printer. The down side is that the smallest 1x1 LEGO "brick" unit is considerably larger than the resolution of even cheap consumer 3D printers - meaning the entire robot mold has to be scaled up, so the cost for silicone rubber will be higher. You'll also need a much bigger air supply than the tiny squeeze bulbs or syringes used in the first Instructable - but luckily a bike pump, generally readily available, will work nicely.
In this Instructable I'll go over the basic procedure to build a single, manually-powered "gripper" robot. If you'd like to try something more advanced like a walking, electronically-controlled, or even autonomous robot using these methods, you should check out the publications of the Microrobotics Lab and the Whitesides Group at Harvard, where this technology got started.
- Ecoflex 00-30 for robot's top layer. Trial kit should be enough for 1-2 robots depending on the size of your mold, gallon unit is more cost effective if you're doing a camp, makerspace activity etc. and need to make lots.
- Ecoflex 00-50 for robot's bottom layer. Same notes apply about quantity.
- Bicycle pump with needle attachment (for inflating footballs, soccer balls etc)
- 1 or 2 large LEGO base plates (see picture above). 2 plates means you can make 2 molds and cure each half of the robot simultaneously, so the project will go faster.
- Assorted small LEGO bricks and plates (see Step 2). Exactly what you need depends on the shape of the mold you want to build. You can get individual bricks from the LEGO Pick a Brick shop.
- Recommended: small level, to make sure the mold is level when curing
- Optional: plastic tubing with an inner diameter that will fit over your bike pump's needle. This makes it easier to attach the pump to the robot, but is not required (see step 12). I used 1/16" ID polyethylene tubing.
- Plastic cups and popsicle sticks for mixing ecoflex
- Highly recommended, especially if doing this activity with kids: paper towels, disposable rubber gloves, and plastic cafeteria trays or a disposable table cloth. Ecoflex is non-toxic* but can be messy and kids tend to spill it everywhere.
Step 1: Build the LEGO Mold
1) A bottom mold that just has the outer perimeter of your robot. Use standard LEGO bricks (3 units high) for the outer walls.
2) A top mold that has the outer perimeter and interior air channels. Use regular bricks (3 units high) for the outer walls, and smaller plates (only 1 unit high) for the air channels.
Make sure the outer perimeters of the two molds match. You can follow my design above to make a four-fingered "gripper," or come up with your own.
Step 2: Mix Ecoflex 00-30
Note: it can be hard to pour the Ecoflex without dribbling some down the sides of the containers - have some paper towels handy for cleanup.
Step 3: Pour Ecoflex 00-30 Into Top Mold
Now, slowly and carefully pour the Ecoflex into the mold until it is just starting to spill over the top edge. It's much better to over-fill the mold than to under-fill it. You can always use scissors to trim away excess material later if the Ecoflex spills over the edges. However, if you don't use enough, the robot could be too weak, and is more likely to pop or develop an air leak.
Watch the Ecoflex for a few minutes - you should see air bubbles slowly floating up and working their way out of it. You can accelerate this by popping the bubbles with a pin or toothpick. Ideally you would do this with a vacuum chamber, but that type of equipment isn't typically available at home.
If you only have one LEGO base plate available, now you'll need to wait 4 hours for the Ecoflex to cure at room temperature. Ecoflex will cure in only 10 minutes at 150 degrees Fahrenheit, but I did not want to find out what happens when I stick my LEGOs in an oven.
Step 4: Mix Ecoflex 00-50 and Pour Into Bottom Mold
If you only have one mold, you'll need to remove the top half of your robot from the mold first (see Step 6), then remove all the interior air channel pieces from your top mold to convert it into a bottom mold.
Step 5: Let Ecoflex Sit for 4 Hours
Step 6: Remove Top Layer From Mold
Important: do NOT remove the bottom layer from its mold yet.
Step 7: Apply "glue" Layer of Ecoflex 00-30
Mix a fresh batch of Ecoflex 00-30, the same way you did in Step 2. The quantity can be much smaller - you just need enough to apply a "glue" layer, not to fill an entire mold.
Keeping the bottom layer in its mold, carefully pour and spread a thin, even layer of fresh Ecoflex onto the top side. The thickness of this layer is critical. If you use too much, you will clog the air channels, so your robot will not inflate. If you use too little, the top and bottom layers will not bond well, and are much more likely to peel apart or develop an air leak. It's difficult to measure, but experience indicates that you should use a layer about 1 millimeter thick. So, make sure you have a complete, even coating with no gaps; but also make sure that you don't go overboard and just dump on a ton of Ecoflex. If you accidentally use too much, you can always use a paper towel to soak some up.
Step 8: Place the Top Layer Face-down on the Bottom Layer
Step 9: Apply Glue Around the Perimeter
Step 10: Let Sit for 4 Hours
Step 11: Remove Robot From Mold
Step 12: Attach Air Supply
Step 13: Inflate!
Unfortunately there's no good way to fix this if you have de-bonding issues inside the robot. If you have an air leak though, all you need to do is mix up some fresh Ecoflex and patch it up. Remember that this technology is still a work in progress, actively being developed by scientists at a major research university - so don't feel bad if your robot doesn't work perfectly on the first try! I don't have better pictures because I used all of my Ecoflex on this rather large mold (I actually only used 00-30, but would have gotten much better results with 00-30 and 00-50), and didn't want to spend the money on a second batch. If you manage to do better, please post pictures in the comments!
If you run into any other issues or have questions about this or any of my other Instructables, please don't hesitate to leave a comment below.