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steppers on an engel tank ?

R/C Submarine modelers

Postby raalst » Sat May 31, 2003 5:49 pm

Hi all,

I am planning to put a stepper motor on an engel tank.
I will insert a new controller behind the old tank controller
to convert from normal motor control to stepper signals
did anybody try something like this before ?
Regards,

Ronald van Aalst

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Postby Ramius-II » Sat May 31, 2003 8:20 pm

Hi Ron:
I was wondering what the purpose would be for using a stepper? It would seem like you would be jumping from one amount to the next with no inbetween. ??? This would be good in an "all digital" approach where you could "dial" in a number for a given depth and consistantly repeat the setting. Is this the plan?

Best Regards, Ed
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Postby raalst » Sun Jun 01, 2003 1:01 pm

The main reason is, I do not like the lack of feedback
from the normal motor :
the tank apparently got stuck, the motor stalled,
the limit switches fried, the relays got stuck and the
controller fuse melted.
I had a true fire on board, and I was lucky the
hull was undamaged.

with the stepper, the limit switches are not part of the
circuit feeding the motor, so they do not have to carry
whole amps.
second, with a training mode I can determine the point
between sinking and surfacing and repeat filling the tank
to this point.

lastly I want to be able to get input from the level and depth
controller which now only actuates the rudders, not the
tank.

only problem I see is maybe the speed of the stepper
compared to the normal motor. it might be very slow.
Regards,

Ronald van Aalst

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Postby KOEZE » Sun Jun 01, 2003 3:58 pm

Hallo Ronald,

I think that working with a stepper motor poses a number of serious problems in modelling. I've contemplated the use of steppers in stead of servo's (much more flexible with angles and power) by using a more powerfull power stage on the driver.There's much more flexibility in power etc. The thing is you'd need a microcontroller to control the stepper controller that remembers the position of the stepper (the task of the feedback pot) and that can be programmed to your required range (servo has a standard deflection). Furthermore you would still need position switches and a homing procedure.

Of course it can be done but you would have to done quite a lot of designing and programming (AFAIK).

Speed would also be an issue. The controllers I know give up to 3000 pulses per second. At 200 steps per revolution the max speed is 15 revs per second.

If you get is to work I'me very interested but I tink it would be MUCH simpler to hook the position switches to relais and let the control the motor.

EJK
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you get older because you stop playing.
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Postby ThierryC » Sun Jun 01, 2003 11:57 pm

Hello

I am pretty surprised that you had a fire onboard, last summer the tank got stuck because one of the gear seized from lack of lubrication. The problem that happened is that the fuse blew. It took me a while to find out that the problem was coming from the gear and I tried a few times to get the piston working by powering the piston, and the fuse blew again and again until I localised the problem.
If you removed the fuses from the setup, it is to be expected that you would risk burning all the electronics !

Using stepper motors sounds like a pretty cool idea though !
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Postby raalst » Mon Jun 02, 2003 3:27 am

guilty as charged :(
Regards,

Ronald van Aalst

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Postby Sub culture » Sat Jun 07, 2003 2:20 am

Why not fit a proportional tank controller?

Norbert Bruggen produces those, and they aren't a whole heap of money either.

Failing that, there is a circuit published in 'Model submarine technology', which will probably cost as much to build actually, but if you like to DIY....!

Any power circuit in a Sub should be fused.

Also I wouldn't consider using a speed controller of any kind on a sub that wasn't thermally protected against overload.

Andy
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Postby raalst » Sat Jun 07, 2003 11:24 am

Thanks for the tips !

I am aware of the proportional tank controller, but
the problem I want to fix is stalling the motor.
the proportional tank control will not prevent
the stalled motor to burn out
(using proper fuses will, that point is taken into the
design)

a stalled stepper will not disintegrate or blow a fuse,
it will simply try again.

anyway, you are right, it is a hobby in itself. I like to
make my own mistakes before "giving up" and buy proper
equipment in the shop.

Regards,
Ronald
Regards,

Ronald van Aalst

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Postby Ramius-II » Sat Jun 07, 2003 3:50 pm

Hi Ronald:
Another possibility for you is a resetable circuit breaker. It will trip during an overload (due to heat) and when it cools down, it trys again! Just a thought.

Ed :)
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Postby raalst » Sun Jun 08, 2003 11:16 am

Yes, a circuit breaker is also a good idea,
although I would not want it to trip when
blowing the tank... (and provided there is space)

The stepper meanwhile made it's first steps with
my Atmel AVR 90S1200 processor and a bit of code.

The functionality now is :
- initialize
- check training jumper
- normally
- poll two pins which represent dive/surface
- act on it but only fill tank up to trained
maximum
- training :
- empty tank
- fill tank until surface command is recieved.
- mark this position in EEprom

The idea is that while training i can sink the boat
until it has minimum buoyancy. the rest (keeping the
boat a fixed amount under water) is done with
another controller (by N. Brueggen) acting on the
dive planes.

things to do :
- testdrive this
- add sampling of servo channel encoding
dive/surface command (removes need for BTS unit)
- add sampling of commands from the depth keeping
board for fine tuning the tank position.
Regards,

Ronald van Aalst

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Postby Sub culture » Mon Jun 09, 2003 5:41 am

raalst wrote:Thanks for the tips !

I am aware of the proportional tank controller, but
the problem I want to fix is stalling the motor.
the proportional tank control will not prevent
the stalled motor to burn out
(using proper fuses will, that point is taken into the
design)

a stalled stepper will not disintegrate or blow a fuse,
it will simply try again.

anyway, you are right, it is a hobby in itself. I like to
make my own mistakes before "giving up" and buy proper
equipment in the shop.

Regards,
Ronald

Erm, like I said in my post- thermal protection!

If the controller is thermally protected against overload, it should cut the power before you ever get into a fuse blowing situation.

Mike Stothers controllers have that built in as standard-

www.modelcontrollers.com



Andy :)
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