Search This Blog

Friday, June 4, 2010

Magnetohydrodynamic Propulsion Drive

Cool name, right? Magnetohydrodynamic drives use a crossed electric and magnetic field to propel ions, such as salt water ions. That simple. Think the caterpillar drive from the Hunt for the Red October, or the Japanese boat, "Yamoto". I first came accross this idea at "Evil Mad Scientist Laboratories" 3 years ago. I found this article shortly afterwards and decided to build one! I apologize for the cruddy pictures-it's a cell phone camera.

The gray strips on the inside are aluminum electrodes. The big bricks on the left and right side are 1" x 1/2" x 4" NIB magnets. The magnet field on the inside maxed out my sensor, which goes up to 1000 Gauss. I'm guessing the inner gap is around 1T, considering the size of these things. The middle box is made of fiberglass; it needs to be to hold the magnets apart.

The black coating is "Plasti-Dip", possibly one of my favorite things. It's a liquid rubber that drys to form a rubberized coating on pretty much any surface. It's used by R/C hobbyists to waterproof electronics, such as servos and receivers. I used it to coat the MHD drive.
It comes in both a can and a spray. See the big spill on the can? Funny I bought this thinking it would be easy to just dip the magnets in one at a time and get a nice coat on them. Turns out the can is steel. The magnet just jumped into the can and made a huge mess- my hands were black for about a week. (That's when I bought the spray.)

My setup was a tub of salt water and a 13.8V 25A DC power supply. Here are some videos of it in action:

The effects of electrolysis are pretty obvious; I can't think of any way to counter this. The aluminum electrodes wear out pretty quickly. Reversing the electric field (and thus the flow) every now and then seems to help with electrode wear. Titanium or platinum electrodes would probably help a lot, but are also expensive. It was a cool project. Future work will include:
1. Incorporating a similar (probably bigger/longer magnets) into a custom R/C boat or submarine.
2. Using onboard power. I'm thinking LiFePO4 power cells- the high discharge rate would be very beneficial. I think I'll stay away from LiPo's this time. Considering all the H2 and O2 produced, I think there will be enough flammable stuff around.
3. Experiment with ways to reduce the electrolysis and increase electrode life.


  1. Yeah, this has very little to do with my ELB project, lol. Just trying to catch up on some stuff while not working on the longboard.