Piston Tanks - proportional control
If you are interested in developing or building proportional piston tanks, I am pleased to give some details here:
A basic description of the controller follows:
- Proportional means that a stick movement produces a proportional movement of the piston in the tank.
The electronics to proportionally control a piston tank needs to have the following functions:
- A method of counting the revolutions of the screw thread which drives the tank. (A Hall effect sensor, in this case.)
- A microprocessor (In this case a PIC) to process the receiver output and remember the number of screw thread revolutions and to control the motor control board (The H bridge.) The software includes proportional and derivative control functions. The counter can be reset by powering off the TX. The software includes lost signal routines.
- The H bridge is a driver chip and 4 MOSFET transistors which control the piston tank drive motor in forward and reverse. The H bridge is to a Microchip design and includes the protection suggested by John R (Electrolytic capacitors fed by Schottky diodes to prevent any problems with current surges.)
-Limit switches are needed to provide security against any drive overruns. I favour a completely independent circuit using microswitches with diodes to allow reverse. (See Norbert Bruggen's schematics in "Model Submarine Technology) In normal operation only one microswitch is triggered and this only on first power up.
The design is very reliable and I have used this every 2 weeks or so in one of my 3 submarines for the last 4 years with 3 different tanks. I have used it with both 40Mhz and 433/458 Mhz r/c equipment as developed by Tim Senecal. It works with both but the lack of interference on 433/458 makes the piston tank work more smoothly.
The software is made available under an open license for people to use and modify as they wish on the basis that their software continues to be available to others. So it is not for commercial gain.
The software is written in assembler for a PIC micro.
An Arduino version written in C would be very welcome!
The mechanical construction of piston tanks is covered elsewhere in the AMS Forum but some tips include:
- threaded M5 stainless rod works well and matches the "screw turn data" from the controller.
- don't try to move the piston too quickly - current draw and electrical surge problems. I use gearbox ratios of about 1:30.
- the magnets for Hall effect sensors have a habit of flying off and sticking to steel items! They can be attached to suitable gear wheels etc using hot melt adhesive.
Have fun with the design and I hope you find it useful and please say how you have used it and suggest (and make public) any software improvements.