Thruster build

[darrenervine]

Thanks for the analysis..
Where did the 4-5lbs "goal" come from?

maybe there is a way to adjust the goal by adjusting other things, like weight/design/# of motors??

Just trying to think outside the box...

[darrenervine]

BTW, does that prop come in both left and right versions?

[DavidF]

The prop does come in left and right versions, its a Raboesh 63 mm 7 blade. Im probably going to switch to prop shop of England props because they list the pitch as well as the diameter and this could be very beneficial when testing. Im thinking a smaller prop would make more thrust, I have thought from the beginning the 63 mm was too big but was pretty surprised with its output.
There is no real reason for wanting to make the 4-5 lbs of thrust other than its there if you need it, but Im also planning on using the rov in a creek that has a little bit of flow to it and might need the power if I put out alot of thether. Ugg I should just go back to my crawler Idea to make my life easier, but there is places where a crawler just wont work and this is a good starter rov that I can actually afford to build. Then I can take what I have learned and apply it to a larger rov.

[darrenervine]

I was thinking of 4" wheels on the skid frame so when you are on the bottom and it is flat you can just scoot ahead and not worry about -/+ buoyancy.

Probably an after idea though...

[bikerbones1968]

What is the internal resistance of the motor? Should be able to calculate the current draw with different voltages applied to the motor easily. Of course under load it will increase from a calculated value.

[DavidF]

Increasing your voltage will increase your speed and thrust, In turn this should lower your current draw not increase it! Higher voltage = lower amps

Scratching head and thinking........
That's why I hate electronics, it just doesn't seem right. You would think the amps would go up as well, unless its because the motor is rated 20v and I'm running it on a lower voltage? Or maybe as the voltage goes up the rpms will go up and in theory the prop spins faster and the load goes up increasing the amp draw due to too large of a prop? I ask because when running at 8v it was only drawing 3 amps but the thrust was way down. There must be some curve in there somewhere???
That's why I like the mechanical end of things, I can see and feel things...

[DavidF]

What is the internal resistance of the motor? Should be able to calculate the current draw with different voltages applied to the motor easily. Of course under load it will increase from a calculated value.

How go I check it? Ohm the commutator?? Need a spelling check on that one lol.

[bikerbones1968]

Quite a bit to read but very well written and detailed information on brushed motors. It includes various types of DC motors, testing, current, volatge and speed formulas etc..

http://www.anaheimautomation.com/manual ... -guide.php

[DavidF]

Brushed 555 motors

[DavidF]

Thanks for the link Bones, its a good read. Unfortunatly Im not capable of performing those equasions and even if I was there are some variables that I would need to try and figure out before I even could. What would really be nice is if I had some sort of a load cell that I could use to dyno the motors and a tachometer, then I could really test out the motors and find thier sweet spot to prop it to thier maximum ability. Hmm wonder if they make something for r/c car motors??? Going to do some surfing on that one....