Banner Ad 1

Reversing Polarity on One Motor for Tight Turns - Or maybe a bow thruster?

R/C Submarine modelers

Postby safrole » Mon Sep 01, 2003 3:25 pm

I know, a submarine with a bow thruster, anathema! But it could be discretely placed in some permanently open torpedo tubes.

I just want my Robbe U-47 to pivot around in my 20x40x20 pool, so I thought I would have a bow thruster activated at the limit of rudder servo travel.

Alternatively I thought about reversing the polarity on the motor to the inside of the turn, also at the limit of servo travel. The main downside would be that the inside motor would be slammed into reverse at full speed, with only a minimum latency between the normal and pivot modes. This would also require two double pole double throw switches rated for full motor amperage. (I'm 12v) I'm having trouble envisioning it without using relays. (ugh)

I also found a sharp Brit to whom I've already sent an email. He has exactly what I'm looking for, though the execution of it is lost on me because it requires mixing hardware with which I am not familiar. His link is listed below.

Anyway, your thoughts and/or advice are appreciated.

--Jason Overhulser
http://www.kleefeld.freeserve.co.uk/model....m#Mixer
User avatar
safrole
Registered User
 
Posts: 274
Joined: Wed Aug 06, 2003 9:22 am
Location: Elkhart, Indiana

Postby KOEZE » Mon Sep 01, 2003 4:54 pm

Mixing hardware is simply a microcontroller that calulates mxing ratios. You attach the servo cables for the rudder and the speedcontroller and and its outputs are attached to the rudder servos and the 2 speed controllers (one for each engine)
As you give rudder the speed of one of the two speed controllers is reduced proportionally to the rudder signal. I don't know this specific piece of kit altough I already pointed somebody else towards it. I use a mixer to drive my x-rudders (Walrus class submarine). Many mixers use dipswitches or jumpers to make adjustments to the standard settings. It may even be possible to reverse one of the engines at full rudder. Remember that tanks and other tracked vehicles also use this technique.

Hope this helps.

EJK
You don't stop playing because you get older,
you get older because you stop playing.
User avatar
KOEZE
Registered User
 
Posts: 230
Joined: Thu May 22, 2003 5:55 am
Location: Leeuwarden, The Netherlands

Postby Ramius-II » Mon Sep 01, 2003 6:14 pm

Hi Jason:
I was faced with the same problem of tight turns for a Typhoon. I chose to use a speed control tied to the rudder servo feed thus creating "power steering". As you increase the rudder angle, the speed control increases the thrusters power. This is independent of motor control. I haven't tried it yet and I believe you could turn the sub in it's own lenght.

Ed
Just one more wire!
SC# 2268
WB6NSN
User avatar
Ramius-II
SubCommittee Member
 
Posts: 394
Joined: Tue Apr 01, 2003 6:35 pm
Location: Lomita California

Postby Art Broder » Mon Sep 01, 2003 7:12 pm

Jason,
I faced the same problem; turning my 5ft, 1/72 688I, in a similar size pool. I installed a Graupner bow thruster, on a 'Y' connector with my rudder servo. It is operated with an ESC (speed control), instead of a reversing switch, to give proportional power to the thruster as the rudder stick is moved proportionally in either direction. I didn't notice too much improvement in turning radius while running forward, but I can turn the model at the far end of the pool while it is stopped, with just the bow thruster and no forward speed. It turns slowly, but at least I don't have to walk to the other end of the pool and turn it manually, or go back and forth in forward and reverse, to turn it around. You can see the model on my web site atArt Broder's Models. Just click on PICTURES in the left hand column and choose the L.A. San Juan album.
Art Broder
SubCommittee#0060
RCABS- It's easy to control your own bladder!
User avatar
Art Broder
SubCommittee Member
 
Posts: 487
Joined: Sat Feb 22, 2003 4:35 am
Location: MA

Postby Skip Asay » Mon Sep 01, 2003 8:01 pm

In most cases, "the tail wagging the dog" is not a good thing. But in the realm of vessels that travel on or under the water, it is the tail that determines the direction that vessel will go in. Think about it. After thousands of years of trial and error, it's been determined that the best way to turn a boat is by moving the stern sideways to point the bow in the direction you want the boat to go. Hence, the rudder is in the stern. If you want your boat to turn better WHILE UNDER WAY, put the thruster in the stern and control it with a speed control connected via a "Y" connector to the rudder channel as Art Broder described.

As far as individual control of the screws is concerned, in most submarines (Typhoon is probably an exception), the screws are too close together relative to the length of the boat to really give effective leverage for turning purposes. I tried that on a relatively short sub a bunch of years ago. Ahead on the port screw/astern on the starboard screw. Put the transmitter down. Head for the head. Talk to a couple of guys along the way. Take care of business. Talk to a couple other guys on the way back. Stop for a sandwich. In that amount of time, the boat had not yet reached 90 degrees! As soon as I got home, I pulled the extra speed control out and built an operating periscope system controlled by that now extra channel. Much better use of a channel!

Skip Asay
SubTech
The U.S. of A - Land of the Free BECAUSE of the Brave
Skip Asay
Registered User
 
Posts: 255
Joined: Fri Feb 21, 2003 11:04 pm
Location: Sanford, NC

Postby safrole » Tue Sep 02, 2003 10:12 am

I do believe wholeheartedly that leverage would be an issue, so I'll scrap the idea of independent reverse rotation. The twin screw U-boat has rudders immediately behind each prop, which serve to vector the thrust to a limited extent, so I'll put the bow thruster up front. It's more easily hidden there and will hopefully yield the necessary leverage in conjunction with the semi-vectored engine thrust.

Thanks for saving me a lot of time. I'm trying to get her in the water before Indiana freezes over.

Thanks,

--Jason Overhulser
User avatar
safrole
Registered User
 
Posts: 274
Joined: Wed Aug 06, 2003 9:22 am
Location: Elkhart, Indiana

Postby Ramius-II » Wed Sep 03, 2003 11:23 am

Hi Jason:
Here's an idea for you, how about two thrusters? One on the bow and one in the stern! Thus you could "parallel park" easily! Skip has a lot more knowledge and experience than I do and maybe it's a result of taking thing literally when the pump is called a "bow" thruster. To my mind, the stationary fin in the stern would seem to be the pivot point when the sub is not moving. When it is moving, a stern thruster would be better.

Ed
Just one more wire!
SC# 2268
WB6NSN
User avatar
Ramius-II
SubCommittee Member
 
Posts: 394
Joined: Tue Apr 01, 2003 6:35 pm
Location: Lomita California

Postby safrole » Tue Sep 09, 2003 1:57 am

The Graupner bow thruster arrived today. It looks like it will be tough to install without getting ugly. I had hoped to have some permanently open bow torpedo tubes, but I'm not able to see how to hide them well enough. Maybe I can cover each outlet with a little flap door, except then the opposite side could not take water in properly. Any opions are appreciated.
User avatar
safrole
Registered User
 
Posts: 274
Joined: Wed Aug 06, 2003 9:22 am
Location: Elkhart, Indiana

Postby KOEZE » Tue Sep 09, 2003 3:05 am

I've made a bow truster myself for use in a target (surface ship) that didn't have a thruster originally. So I faced the same problem.
I built it using 2 pvc pipes.
I'll try to descibe it as I don't have pics.
The thruster consists of two pvc pipes. One from one side of the ship to the other (Normally the prop would be in this one).
This pipe is given a halfround cut at the top (or bottom for all I care) so that the other pipe fits into it at a right angle.
Make sure that the bottom of the second pipe is halfway ino the first pipe.
Open the second pipe so that the water can flow freely from one into the other.
Now take a piece of brass rod and cut a slot in one end. Take a piece of brass plate and solder this into the slot.

Add bearings and a seal to the shaft and slide it into the second pipe. You can imagine that only one blade is visible every time. This functions as a pedal wheel.

Seal the entire unit with caps and add a motor. This can be quite a big one compared to the rest of the prop. I used 32mm (1 1/2") pvc and put a 540 type engine on it.
Place the entire unit into the ship and drill two small holes in to hull for the prop.

A friend of mine used this principle in his sub and the thing could turn within it's own length. A bit too strong but with some speed control very usable as yo can imagine.

If you have any questions ask.

EJK
You don't stop playing because you get older,
you get older because you stop playing.
User avatar
KOEZE
Registered User
 
Posts: 230
Joined: Thu May 22, 2003 5:55 am
Location: Leeuwarden, The Netherlands

Postby SubCom#2021 » Tue Sep 09, 2003 8:21 am

Try this link;
http://www.astecmodels.co.uk/
go to "Product Listings" then select "Electronics" from pull-down menu.You will find a product called "Amix".It will also reverse inside motor when you command full rudder.

--------------------------------------
<product manual>

Amix - Multi Motor Mixer

Thank you for buying an AsTec Product. With a little care it will give you hours of good service and enjoyment. To ensure its reliability we have used nothing but the best parts available.
HOW IT WORKS

The heart of the unit is a micro-controller chip (combination of microprocessor and memory unit all in one). The runs an embedded program that dictates what actions it should take and when. When the unit is first turned on it checks the incoming pulse signals from the receiver. The length of these signals is stored and used as the null point. Once the controller is set up it enables it's output lines and starts the mixing process.

The process follows certain rules:-
Motor output is a combination of speed (S) and rudder ® settings following rules LM= S-R RM=S+R
S and R are measured with respect to the Null point.
Motor speed can be no greater than normal output (I.e. pulse width is limited to normal RX output) at full speed and full rudder the inner motor will stop at half speed the inner motor will reverse to half speed in the opposite direction and the outer motor will run at full speed
Null point is set a switch on by measuring TX output

There are also pass through ports that provide access to the receiver signals without any processing, these can be used for the rudder servo and for centre motors on triple motor arrangements ( only the wing motors will be mixed). The unit has been programmed to work correctly with most modern two channel outfits. It does expect to see the rudder signal first (channel 1) and then the Speed signal (channel 2). It will work if they are reversed but response may be slowed. If this occurs we can provide and fit an alternate micro-controller. If the returned mixer is brand new and in pristine condition then the cost will be covered by postage. Otherwise please ask what the current charge is.
SETTING UP.

Check the receiver plugs for polarity by matching them up with one of your existing working servo plugs Changes to the wire positions can be made by gently depressing the metal retainer and removing the necessary wires. They should automatically lock in place when re-inserted in the required positions. The supplied plug fits modern futaba equipment with no changes, the plug tabs can be trimmed to fit other models - we recommend the gentle application of a file for this.

Plug the unit in to the receiver sockets as specified ( a servo can be used to check that you have the correct ports - receiver are configured differently so we cannot be of any more help). Plug your speed controllers in to the unit. (Servos can be used for initial set up's if preferred). Turn the transmitter and receiver on in that order. The unit will perform a set up sequence to read and store the null positions etc. This only moments.

Now go through the following steps - do not continue to the next step until the one that you are on is correct. To prevent confusion when you make changes only make one change at a time .

Check for correct rudder operation. Stand behind the model facing the bows. Move the rudder stick to the right. The rudder should move to the right (Starboard). If it does not turn off and correct it's movement by using the other side of the rudder arm or using the servo reverse on the transmitter. If you user servo reverse make sure that the mixer is reset by turning it of and back on.

With no rudder use the throttle stick to check the basic motor operation. If the motor(s) run in the wrong direction correct this by swapping the motor leads on the motor terminals.

Set the speed to say 1/4 ahead. Slowly introduce right rudder. The right motor should speed up and the left motor should slow down and eventually reverse. If the left motor speeds turn off and either swap the MOTA and MOTB connections on the mixer OR swap the motors between speed controllers.

If you have got here it should all be working correctly.

The unit will theoretically work in any set up?but it prefers to be connected as directed. It is also sensitive to too short RX pulses in combination. If you experience strange results try swapping the rudder and speed inputs.
--------------------------------------

I am using it in my r/c tank and works great.

Hope this helps.




Edited By SubCom#2021 on 1063110680
SubCom#2021
Registered User
 
Posts: 7
Joined: Sun Feb 23, 2003 11:49 pm
Location: Tokyo Japan


Return to R/C Modeler

Who is online

Users browsing this forum: Yahoo [Bot]

cron