July 21, 2018

Blue Robotics T100 Bilge Pump Conversion

This is another idea was toying with… it’s a Blue Robotics T100 Thruster converted to use a Mairfair 750 GPH Bilge Pump for the motor. If it works out it might be a cheap alternative for some MATE teams on a budget. (or anyone for that matter.) The idea is all of the parts would just be 3D printed to make for a cheap thruster. I originally hoped to just use the Blue Robotics props because they are cheap and would hold up better than a printed part but unfortunately I had to scale the design up a little in order to fit the bilge pump so the prop will have to be printed also.

After scaling up the cad files Blue Robotics provides on their web site I joined them with the bilge pump thruster I designed awhile ago so the pump cartridge just easily twists locks in place while still having a nice clean look.

Rear View

Front View

Exploded Views

I still have redesign the prop to be able to fit it to the pump. I I think a simple inserted sleeve with a set screw should do the trick. After that the next step is to see how well the parts will print and then see if the Bilge pumps will actually produce enough thrust to make these worth using.

The first piece printed, this is the mount for the actual bilge pump.

It’s a little rough but being a prototype I use some cheap Chinese filament and just used some generic print settings because I have never calibrated this stuff yet.  I printed it pretty fast with a high layer height and with only 10% infill so there’s no way it will be water proof but this is just for proof of concept so it doesn’t matter.

The good news it the pump slides right in without any sanding as I made the tolerances greater in this design.

For the prop I just hollowed out the rear section and added a riser in the center for the shaft. I will be secured to the shaft with a 6/32″ set screw for the testing.

I gave the prop a try with the same crappy filament and ran into some issues. (I had a feeling printing this would not that easy or straight forward because of the angles of the blades)

The blades are so thin that the edges are tending to warp when printed in PLA. (Things would probably be a lot easier with a duel nozzle printer that could print with water soluble supports.)

I could probably heat the edges up and bend them back to the correct positions if I wanted to but I thought I’d try a different material. (PLA isn’t the best choice for outside items anyway.)

I next tried to print a prop in PETG and while it came out a lot better….

… the blades are way too flexible.

At this point I decided to make the blades thicker and see if that would help with the printing. I really don’t have the CAD skills to redesign the angles on these blades so for now I basically just stacked several copies of them to make them thicker. The weird edge details will be ignored by the slicing software because they are so thin.

I printed this thicker version in both PLA and PETG and they came out a lot better. (In these pictures I rough sanded the PETG one but not the PLA one yet.)

I don’t know if it will affect the thrust out put of the prop but it definitely came out better being thicker. The PETG one is still a bit flexible so I’m going to test it first with the PLA version.

Next it’s on to printing the nozzle which might present some challenges but I think I know how to get around them….. We’ll see.

To make printing easier and to preserve the leading and trailing edges of the nozzle I cut it in two pieces before printing it.

I added a few alignment holes in the design and used short pieces of filament for the pins.

I then used superglue to glue the two piece together.

The seam was then given a quick rough sanding to smooth out the joint.

I used a couple of 8/32″ heat set inserts for the mounting points. (2 for now for testing should be enough)

The nozzle is held to the pump mount base with (4) 6/32 screws. (I tapped the holes in the base first)

It’s a little rough but should be good enough for a thrust test to see if this is even going to be worth it.

Here are a few finished pictures before the testing process. I have to dig out the test tub and find the mount I made for testing out the Original T100 I tested a long time ago. (of course the mount might be off a bit because of the scaling on this one but I’ll modify if I have to.

I had to make a new test mount because the other one was to short.

Back in the test tub….

I didn’t take any pictures of the meters during testing or get any real accurate numbers because the results were a little disappointing.  Roughly…. this setup put out about 2lbs of thrust but at about 8-9 amps in forward. (reverse was about 1lbs at 5-6 amps I think ) I didn’t really do any post clean up after printing besides some minor sanding but I  it would be a lot more efficient if they were smoother.  I thought about also trying the 3 blade prop off the T200 but that would probably only increase the amp draw.

Overall it might work as a budget thruster if you have a 3D Printer… I know people are printing the stock versions modified to fit other Brushless motors but this might also be a option for those people just looking for a basic on/off control of a brushed motor. My only concern is the amp draw might be a little to much for these pumps in the long run.  Anyway It was a fun project to try though.

 

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