Homebuilt ROVs Forum

I see that you are coming along quite well with your experiments. Congratulations. I love it when people think outside of the box and try new things.

I read some talk about bearings and I was wondering if a silicone lubricant wouldn't do the same thing and eliminate the issues of weight which might effect or have a diminishing return. Just a thought.

But anyway. WOO HOO. Keep up the good work.

ErieWreckDiver

Thanks for comments.

I'm really psyched about the new developments.

$10 DC motors with boatloads (ouch!) of torque!

https://store.rc4wd.com/mobile/home.asp ... ubCat_26_1

Garagescience wrote:$10 DC motors with boatloads (ouch!) of torque!

https://store.rc4wd.com/mobile/home.asp ... ubCat_26_1

I just checked out some of them. They're all listed as 'out of stock'. Thanks for the link though, I'll check in that direction as well.

I just checked on the status of the motor drivers I ordered from, ahem, overseas and they should be at my house when I get home from work today!!

Woohoo.

I've been waiting for a way to power my mag thrusters with adjustable PWM signals and enough punch to power it without burning something out and until now it wasn't possible. When I get home I'll be able to get started on the coding and hopefully by this weekend I'll have another thruster test to report on.

In the meantime I've come up with some cool ideas for the thruster housings so I can make them available as add-on units if anyone is interested (and it works. ).

This way you will just mount and wire up the self-contained two-wire thruster to your motor driver and PWM (or use the ones I used) and you'll have your own sealed mag-coupled thruster. No more wet motors.

Stay tuned...

OK, I've mentioned some progress in other threads, but I wanted to update this one with some recent test results and video.

First video is a demo of it in the tank, second shows a bit about the current design of the thrusters.




I'm only getting about 100 grams of thrust out of this thing right now (at .5 amps) but someone mentioned something in another thread trying to offer suggestions for a lack of power and it hit me: I've been using really thing speaker wire that I had laying around. I wonder if some heavier gauge wire would help?

I have a lot of ideas for further design mods like using two thrusters in the same 1.5" pvc 'housing', one in front of the other for a 'twin engine' kind of configuration. I think I can put two electric motors in a 3" piece of PVC in such a way as to both turn the same inner hub to add some power to the thruster prop turning on the outside. I have to circle back and try that geared motor again too.
Different 3D printed parts could make it work for PVC from 1.5" (like I am using in the vids) to 2", 3" even 4".

OH, PS: I got the ethernet comm working really well. Switched to control using Netduino. Not sure why I kept resisting it, the platform is really good and looks like it will work perfectly for me. Time to start setting up the tether and finalizing the design...

So many ideas, so little time...

Looks good!

I would definitely try a heavier gauge wire and maybe connect the thruster directly to the power source just to see if there is any difference.
Do you have any estimate how deep that setup can go? any psi rating of the pipe and plugs you used?

olegodo wrote:Looks good!

I would definitely try a heavier gauge wire and maybe connect the thruster directly to the power source just to see if there is any difference.

Hi Ole,

I always appreciate you feedback and insight. I was thinking the same thing about 'hotwiring' the thrusters to eliminate some variables. One problem I was afraid of (that may not be warranted, not sure) is the motor spinning up and breaking loose of the magnets. Essentially my setup involves 4 magnets in one longitudinal line, all facing the same way. It forms a very powerful 'shear pin' of magnetism (which btw would be a great name for a rock band ). Anyway, it acts as a kind of built-in clutch that would allow the inner hub to spin while the thruster is not. Quick changes in the RPMs could do this too (in theory, though it hasn't happened in practice yet). The initial design called for four magnets inside and four outside but the powerful ones I'm using seem to be enough. If I switch thrusters and have more power to deal with, I will have to revisit the additional magnets in an array of 3 or 4 pairs rather than 2.

I will definitely test with heavier gauge wire today though and report back. I'd love to see how much I can squeeze out of these motors at say, 2-3 amps of draw. That would be my target based on the other requirements I have for my design, any more than that and I think I'd need additional batteries and that's a whole new ball of twine.

Do you have any estimate how deep that setup can go? any psi rating of the pipe and plugs you used?

I did test the housing as you see it with the plugs in it in my home made pressure tank (homebrew beer keg ). I wanted to push it up to 100psi (about 200ft or so) but the regulator I have only goes to 50ps which would be about 80 feet or about 25 meters.

When I tested at that setting for some 3D printed parts at 30% density and also the thruster housing it showed no sign of leaking or any damage to the 3D printed parts at all.

I know that's not much of a test for either one, but my max depth around here is only going to be about 35 meters or so (100'). I think I'm going to be fine for that.

Will post back after the 18 awg wire tests...

UPDATE: 10:30am
item 1: confirmed that wire gauge was a factor. I'm getting much more power now.
item 2: confirmed that applying full power to the motor will break the magnets loose IMMEDIATELY.

Then I connected it to the system with the new wiring and it did draw a lot more, showed more power, but then my battery died rather quickly. I hadn't charged it in a while so I think that's just because of that, hopefully it's not drawing so much that this will be an issue. I didn't really get any amp draw numbers yet, hopefully that will be next.

I guess I need to recharge and re-run the last few rounds of tests because I did all of the prop iterations with the previous wiring.

This is GOOD NEWS though.

The thruster is looking really good, I'd say you proved the design on the coupler anyway. You might be able to get more thrust by just redesigning the prop. While the straight blade prop probably allows for the same thrust in forward and reverse its probably not that efficient. I'd look into something like the Bluerobotics prop, it has some really small blades but puts out great thrust because of the shape. I think olegodo designed his prop based off theirs with great results too. I think you can find the cad file on their site too so you can see what it really looks like.

-Steve

Thanks Steve,

I'm sure you're right about the prop blade and I will probably try something in that direction.

I learned some really good stuff today.

First of all, you know how they learn what value of fuse to put in a circuit?

Well, it's possible I toasted a LiPo battery and very likely I cooked a bilge pump motor. I'm not the least concerned about the motor but the LiPo stings a lot. That was a Christmas gift from my son last year and it's the only one I have.

I also learned that my friction-mount motor install needs a bit of work. When the motor heats up it starts to spin the entire motor in the PVC pipe. (YIKES) so that was interesting...

Here are my results from this afternoon before things started blowing up and heating up too much to use:

Input throttle (0-255)/amp draw/thrust (grams)
65 1 80
75 1.25 90
85 1.41 93
100 1.63 105
110 1.80 110
120 1.96 112
130 2.12 123
140 2.29 115?
150 2.46 130
155 2.64 130
175 2.88 137
185 3.06 137
200 3.31 135

At that point things started getting hot and I imagine that 3 amp limit they recommend for the bilge pump motors kicks in.

I think the results show that the prop blade efficiency quickly became an issue and somewhere in the 2.2 amp range (only about 1/3 throttle) the amount of extra thrust gained was incremental and not linear to the amount of input amperage. I think at that point it was just heating up.

So I was hoping to keep the motor draw under 3 amps and that still looks possible with a (much) more efficient prop design. I should probably limit the throttle range in the software so that I don't send any more than the motors can handle and hopefully I won't burn up anything else that's expensive...