Mass is the constant ...weight varies with gravitational pull..and helium balloons .

You could reduce the weight of the robot with helium balloons but not the mass.
That's what I said wasn't it?.........

To get lift from helium balloons you need volume ...

Helium has a lifting force of 1 gram per liter. So if you have a balloon that contains 5 liters of helium, the balloon can lift 5 grams.

1000 liters = 1 kg of lift ...etc
So 200 balloons for 1kg..... Hhhhhhmmmmm.

Could make a robot like a Zeppelin! Then I would call it Lead Zeppelin!

Thanks,