driving multiple mortors

[FlyingPenguin]

Hi people,

So, I'm completely new to this kind of stuff, and got myself into this crazy project of building a small submersible ROV.
One of my biggest problems right now is what hardware to use. I need to control 6 motors (probably around 5 v brushless RC boat motors) forward and reverse, and get video feed using a raspberry videoboard.

How do I get 6 motors running on 1 Raspberry pi?
I read something about controller borads and other things, but I'm still not sure what to get.
Would the breadboard fit all motors?
Would I need a battery for the Pi and another for the motors? can it all be on one?

Also, will the video fit on the Pi along with the 6 motors?

Thanks in advance
Seb

[joan]

Read through issues of http://www.raspberrypi.org/magpi/ and search for projects which may have relevance to yours.

[MeanderingLaser]

Hi Seb!

I'll take a stab at trying to help -

How familiar are you with electronics? I'm pretty new to the RPi, but I think I can help with some other questions.

I read something about controller borads and other things, but I'm still not sure what to get.

If you only want a motor to go one way, you can power it using a transistor. If you want it to be able to switch (like you say you do), then what you're looking for is an H-Bridge (half H-Bridge is good for DC voltage supplies if I remember correctly). The power for the motors won't come from the Pi, it'll go through the bridge, which is what you want.

Would the breadboard fit all motors?

I think I remember the H-Bridge being 8 pins long... and each one contained 2, so you would need 3 of the IC's.

Would I need a battery for the Pi and another for the motors? can it all be on one?

As long as the battery can handle the load, then you can use one battery. You may want to put something between the motors and the Pi to protect the Pi, though.

You'll have to be careful with the motors. When the motors switch off they'll want to induce a current on your circuit, which could cause problems. I dealt with this in one of my projects by putting a 10 ohm resistor (that can dissipate a lot of power) in series with the motor. There's probably something else you need to do, but you at least need to do that

Hopefully that helps!

[BMS Doug]

Hi Seb:

I hope this suggestion doesn't sound rude, it isn't intended as any sort of insult.

I would suggest starting out with a small wheeled robot, Magician Chassis kits are really quite cheap (I bought mine for £10) and come with 2 wheels.

Once you have developed a program to control a 2 wheel robot you can improve your program to control a 6 motor submersible with the confidence that a basic programming error isn't going to lose your ROV (an advanced programming error on the other hand....).
To control 6 motors I would use three L298N boards, they are cheap and easy to use (but check back with us first, there is one bad video floating about that makes a fatal error in its application).

[morphy_richards]

First, I agree completely with Doug. First make a simple rover bot using something like a magician or even see if you can cannibalise some old motorised toys to sort out the concepts.

But I love the idea! Ever since I was a kid making little motorised model ships (that invariably capsized and sank) to push out onto Wedgewood lake where I grew up I always wanted to do something like this.

One thing I always wondered about was what to do about water and motors. Do you just let the water in, in which case they will get damaged sooner or later or somehow waterproof the drive mechanism. I never really worked out an answer to that. Anyway, good luck!

[FlyingPenguin]

Hi guys,

Thanks for the helpful replies.
I have teamed up with a friend who knows a bit more about electronics, and we will look more into all the suggestions.

Hi Seb:

I hope this suggestion doesn't sound rude, it isn't intended as any sort of insult.

I would suggest starting out with a small wheeled robot, Magician Chassis kits are really quite cheap (I bought mine for £10) and come with 2 wheels.

Once you have developed a program to control a 2 wheel robot you can improve your program to control a 6 motor submersible with the confidence that a basic programming error isn't going to lose your ROV (an advanced programming error on the other hand....).
To control 6 motors I would use three L298N boards, they are cheap and easy to use (but check back with us first, there is one bad video floating about that makes a fatal error in its application).

no problem with your suggestion about starting small. I agree it would be a good idea, and I plan on simply working it one small step at the time as you say, 2 motors, get the code right and then upgrade. And do lots of testing. And then one magic day have everything working together
I will make sure to be careful about the motor error.

One thing I always wondered about was what to do about water and motors. Do you just let the water in, in which case they will get damaged sooner or later or somehow waterproof the drive mechanism. I never really worked out an answer to that. Anyway, good luck!

We have bought a couple of these bilge pumps for testing. They are cheap and somewhat waterproof.
http://www.instructables.com/id/How-to- ... bmersible/


As for the body we are looking into 3D printing something like this (if the material can be waterproof and hard enough), and somehow add the motors either by making some sort of sockets attached to the body, or strap them on. Printing this design gives us the possibility to run cables inside down to the landing gear and add lights in there.
Basically trying to avoid too many holes.

http://www.diyrov.net/files/front_1200.jpg

Our big plan is to make it work down to 30 m. and look at shipwrecks

Thanks again,
I'll keep you posted about it all.

Seb

[BMS Doug]

Those motors will need a particularly large h-bridge, the L298N isn't capable of handling the 5A those motors need.

[FlyingPenguin]

The post about the bilge pumps was just to show the general idea. We have 12 V, 2 Amps pumps. L298N boards should be fine right?

[BMS Doug]

The post about the bilge pumps was just to show the general idea. We have 12 V, 2 Amps pumps. L298N boards should be fine right?

2A is the rated max for the L298N, I'd be slightly concerned that changing the prop may increase the load on the motor and thus the current.