20
Jun

Day 5 begins with a structural dilemma.  Well, not really a dilemma, we just have a lot of building to do.  We begin by building upwards behind the whipped cream canister holder.  We also add a weight in the back, since we know we will somehow have to balance out the extreme heaviness of a full can of whipped cream.

Next, the other holding ring is attached.  This will ensure the canister stays upright and doesn’t move around when its nozzle is pressed.

When the canister is loaded, the whole structure still falls over.  More scaffolding is added…. so it holds a full canister of whipped cream, just barely.  As you can see below, we also moved the weight to table level—it is more effective there because it brings the center of mass of the structure down, closer to table level.  This means that it takes a much heavier can of whipped cream to tip the structure over.

Not so sturdy…

The structure is still bending though, so something has to change.  We are thinking of building more up the back, and then using rubber bands to pull the tallest part back to the square position.

Much better.

That idea seems to be working fantastically.  It looks a little…..less than perfect, but it is definitely more square.  The rubber band can also be switched out for a stronger or weaker one based on the amount of whipped cream left in the can.  We also added some rubber grip material onto the arm that presses the whipped cream nozzle, to prevent slippage.

1 hr later…

We’ve figured out, after another series of disappointments, that the last problem lies with the strength of the NXT motor.  Even at full strength, there simply isn’t enough power to make the nozzle bend sufficiently, dispensing the whipped cream.  This means we will have to add another motor to the same axle and use them both simultaneously, to simulate a stronger motor.

Two motors are better than one.

Great news; the dispenser finally dispenses!  After the addition of another NXT motor, we finally created a system that could push the whipped cream nozzle with enough force.  The only remaining problem is that the second motor tends to be ripped out of the structure by its own strength.

20 min later…

Not to worry, we’ve now attached it more securely.  Unfortunately, the can still wiggles :(

Not

But with a small adjustment….

Note the extra beam between the can and the edge of the contraption.

Success!

success!

Here is the code we used to test out our whipped cream dispenser:

Day 5 Conclusions:

  • LEGO motors are still not known for their power.  Surprise!
  • Sometimes integrating non-LEGO material into a LEGO project can do great things (rubber bands, grippy stuff…)
  • Likewise, the NXT LEGOs are not always exactly what you need.  Sometimes the more traditional bricks can help you out.
  • In design projects, a small change can really help you out.  When your project doesn’t do quite what you want it to, you don’t always have to tear it down and reconstruct–try adding or changing one small detail.

To Do for Day 6:

  • Begin the combination process: line everything up and make some decisions about how this thing will work.
  • Bowl-Bot!

One Response to “Day 5: More Power, Please!”

I loved the idea of the blog as a working in progress register for the project. Very nice!

Marcelo Molina
June 22nd, 2011