Monday, 20 August 2012

1kg of thrust!

Here are some pictures of the thruster in the tank in the reverse direction, now to be known as the forward direction ;)

First a solid 1.9kg of thrust ......

And then a fleeting 2kg!

So taking into acount the ratio of the lengths from the pivot point to the thruster and the fishing scale that's 1kg of thrust, or 2.2 lbs in old money, in re-circulating water!

Saturday, 18 August 2012

Thruster with shroud and filled with oil

As the title of this post suggests my thruster design now has a shroud and also the motor and control PCB housing is filled with low viscosity oil.

The cowl has an ID of 125mm and my thruster prop has a diameter of about 115mm, so it's not perfect due to the rather large gaps between the prop and the cowl, but not far off really for something that I found on the internet.

The mounts for the cowl are just 1.5mm stainless steel that I cut on the band saw, drilled on the pillar drill and bent with a good old hammer in a vice!

You can just about see the oil in the tube coming out of the back of the thruster.

My test tank is struggling with this size of thruster in there as it stands but I still managed to get some good runs and readings.

I was seeing over 1.5kg every now and again, which equates to about 750g of thrust in a far from ideal environment for the propeller, from a water flow perspective, so I'm pretty happy with that :)

I'll do some further tweaking and maybe see if I can find a bigger plastic container to use as a tank.

I'll also turn the thruster around in the tank and see what thrust I get in the opposite direction too.

Sunday, 12 August 2012

Motor shaft extension

Posts are now coming thick and fast (relatively ;)).

After investing in some stainless steel hex bar and a few drill bits, taps, grub screws etc. I now have a motor shaft extension (courtesy of my lathe) which means I won't have to drill my new motor shafts when I make up the rest of the thrusters for my planned ROV.

Here's a clearer picture of it outside the tank.

The added benefit, as I've just found out in the tank is more thrust too, due to better water flow (presumably) around the propeller. Here's a picture of the thrust measurement.

I'm now having to weigh down my test jig as it now lifts up due to the increased thrust! I saw 1.4kg on the fishing scale at one point, divided by 2 to give around 700g, and the recircualtion of the water in there detracting from the true thrust should put it up near 1kg ....... hopefully.

Just the propeller shroud to try next (although I'm not sure how I'm going to mount it) and maybe fill it with oil too as this increased the thrust before, probably due to lubrication of the shaft seal.

Exciting stuff ....... for the ROV geeks among us :)

Saturday, 4 August 2012

Slow (but sure) progress

Well, it's been a while but I've finally got a bit of news to share regarding my new ROV thruster design.

Over the winter I've been doing some re-design on the pressure tolerant brushless DC motor controller. I now have RS232 (TTL) coming out of the PCB and a couple of new tantalum capacitors on there. Unfortuantley the capacitors cost nearly 10 pounds (UK) each! in small quantities. You can't use (cheap, relatively) electolytics if you want a pressure tolerant design unfortunately.

I've also bought 6 brand spanking new motors from Anaheim Automation in the US.

Not cheap but cracking little motors. I've managed to flood my old thruster design a few times and they just keep on working and they're quite powerful for their size and rpm.

I've just been doing some tests with the thruster again, but in the reverse (to the one I tried before) direction and I'm getting a bit more thrust out of it. I saw 1.3kg (divided by two again to give 650g) at one point.

Here's a picture of the setup I used and the new control PCB I prototyped recently, with a potentiometer for the speed, a switch for the direction and level translator for the RS232 so I can use it with my PC.

I am now going to concentrate on getting a kort nozel on there to see if I can get a bit more thrust out of it. I may also make a prop shaft extender because I don't really want to drill holes in my new motor shafts and connect the prop directly to it, which I have done with the old motor.