New here, and a crazy project!
vk2fro
Posts: 3
Gday
My names Ben and I am new here. I've played with a basic stamp and fiddled with an arm9 eval board that was overkill (and over my head in the coding for me) for my project. However I will scavange its 3.5 in touchscreen and use it in my project...
I have read the specs on the propeller chips and figured one of these are ideal. I've not read up on how they are programmed yet (spin + pASM), but will do some reading over the next couple of days. First of all I'd like to know if the propeller will be suitable.
My project is a ECU unit for a home built gas turbine engine. Also known as a whomping big home made noisy smelly jet engine! *lol*
The engine isnt even built yet, as I want to get the ECU built and tested first. It will act as one giant interlock and status display, along with user interface, to protect the engine (and the operator) from adverse situations.
Heres a list of items the propeller will need to monitor and control:
Inputs:
Oil pressure sensor
Exhaust gas temperature (EGT) sensor
RPM sensor (optical only here!)
Fuel flow sensor (liquid flow sensor)
Combustor boost pressure (air pressure valve 0-20psi)
Clutch engaged (micro switch)
Touch screen (for user input)
Throttle (potentiometer)
If any of these exceed certain values, a watchdog must sound an alarm, and if ignored for more than 3 seconds, cut off the fuel.
I presently have one sensor so far, the EGT sensor. This is a K type thermocouple linked to a max 6955 T/C to SPI chip.
Outputs:
Starter motor (RC car/heli BIG ESC - basically appears as servo to the propeller)
Throttle (Servo)
Clutch Solenoid (engage and disengages the starter, kinda like a clutch)
Fuel Solenoid x 2 (turns fuel on and off. 2 for redundancy)
Combustor dump valve (prevents fuel pooling in the combustor)
Ignitor (relay)
Gas solenoid (for initial starting propane)
Fuel pump (relay)
Oil Pump (relay)
LCD display (user feedback)
Siren (emergency feedback) (relay)
Strobe lamp (bystander warning) (relay)
BIG RED STOP BUTTON (TM) (switch)
*phew* big list eh!
Now for the actual running of the machine. This is how I figured the system will run.
At power up the system reads in the variables from eeprom for the safe conditions for the engine. Once the operator enters a pin code (to prevent unauthorised operation) they are presented with the initial screen with 3 options.
Full auto start
Manual start
Configure <-- if blank, default to this screen and provide generic values)
The first one is self explanatory, i'll get to it in a minute. The second allows external switches to run the various systems, to gather calibration data for the engine, so the configuration can be set. The third allows the user to enter configuration data.
I'll explain the configuration data first, as its kind of needed to understand the rest of the modes.
The configuration data contains several fields that are required to be filled in before the engine will start in full auto mode. Thats because the computer doesnt "know" the engines parameters, and the last thing we want is an over speeding or over heating engine. They tend to turn into giant hand grenades when they over speed. No one wants hot fragments of metal flying around at near supersonic speed (worst case - exploded turbine wheel)
These are:
Minimum oil pressure (usually 25-70 psi)
Maximum Safe EGT (exhaust gas temperature) (around 600-700C)
Minimum idle rpm (Speed at which to shut off starter motor and disengage it) (usually 45,000 rpm)
Min fuel rpm (absolute minimum rpm before fuel is turned on and ignited) (about 3000-6000 rpm)
Preheat time (time to use gas fuel until switching to diesel) (usually 10 seconds)
Over speed (depends on the turbo charger used. Lets say 120,000 rpm)
Ok now we have some parameters entered, and assuming they are correct for our engine, we can return to the initial screen and try the manual mode to get more accurate values.
In manual mode the screen changes to a screen showing the following:
RPM
Oil PSI
EGT
Boost PSI
Fuel type and pressure.
Switch positions for starter, oil, fuel and ignition
At this point the computer is only monitoring. but will sound the siren, if any of the maximums are exceeded. If ignored for more than 3 seconds, control is taken away from the operator, the fuel pump shuts off, and the cooling cycle begins. The screen will display the reason for the emergency shutoff, with an OK button. It will also not allow an incorrect manual start (e.g. trying to spool up the engine without the oil pump on). The strobe lamp will also come on once the oil pumps are running and at correct PSI, and the ESC is armed. During manual start, the operator controls the engine via a series of switches below the screen.
Finally we get to the good bit, the full auto startup procedure.
First a status check (on the manual controls):
Throttle: Idle
Fuel pump: Off/Computer
Oil pump: Off/Computer
Starter: Off/Computer
Ignition: Off/Computer
First, the computer turns on the oil pump and waits for oil pressure to come up.
Next it sets the clutch in the engaged position and see if its locked. if not, the ESC is brought to 10%, at which point the hex drive should engage the starter nut. Provided a "clutch engaged" signal is recieved, the system goes into full on start mode.
The ESC is wound up to the ignition RPM of 3000 rpm (for arguments sake). At this point the gas valve opens and the ignitor is switched on. At the same time, the combustor dump valve opens, as a saftey vent in case the gas doesnt ignite to prevent a very loud bang
. Assuming a succesful light off, the EGT will rise. This tells the computer to start ramping up the ESC at a ferocious rate until the running speed is reached. Around 15,000 rpm the dump valve closes as enough air is being rammed into the combustion chamber now. Once idle rpm is achieved, the ignition is turned off, the fuel pump turned on, and 10 seconds later, the gas supply shut off.
At this point the engine is idling and controllable by the potentiometer, being watched by the watchdog for any unsafe conditions.
All data of the engine is displayed on screen - RPM, EGT, Oil, combustor and fuel pressures. A shutdown button is provided onscreen, and can be tapped to initiate a shut down
Shutdown:
Fuel is switched off, and the turbine allowed to spool down to 5000 rpm. At this point the clutch is constantly engaged and disengaged until it locks. Then the starter is ramped up to 7000rpm and allowed to drop to 3000rpm in a cycle until the EGT drops below 300C. At this point the starter is shut off, and following a drop to ~0 rpm, so is the oil pump.
The shutdown procedure is also carried out if the big red button is pressed. (nice big target for a panicing operator to hit!)
*phew - again*
I think I will be using 7 of the uP's in the propeller:
RPM sensor (this is a pain in the butt and needs its own uP)
Display (user feedback)
Control (relays, solenoids, pumps etc)
Touchscreen, switches (user input)
Watchdog, variables, big red button
EGT Oil and fuel pressure (these can be monitored simultaneously by one uP? - 3 sensors)
I've been writing for an hour now - So I thought I'd introduce my crazy project that I am SURE my neighbours will love (not), and see what you guys have to say.
I may in future ask for idea for the different bits of code, but I prefer to get as much as myself done first.
Thanks for your input, and once again, hello [noparse]:)[/noparse]
My names Ben and I am new here. I've played with a basic stamp and fiddled with an arm9 eval board that was overkill (and over my head in the coding for me) for my project. However I will scavange its 3.5 in touchscreen and use it in my project...
I have read the specs on the propeller chips and figured one of these are ideal. I've not read up on how they are programmed yet (spin + pASM), but will do some reading over the next couple of days. First of all I'd like to know if the propeller will be suitable.
My project is a ECU unit for a home built gas turbine engine. Also known as a whomping big home made noisy smelly jet engine! *lol*
The engine isnt even built yet, as I want to get the ECU built and tested first. It will act as one giant interlock and status display, along with user interface, to protect the engine (and the operator) from adverse situations.
Heres a list of items the propeller will need to monitor and control:
Inputs:
Oil pressure sensor
Exhaust gas temperature (EGT) sensor
RPM sensor (optical only here!)
Fuel flow sensor (liquid flow sensor)
Combustor boost pressure (air pressure valve 0-20psi)
Clutch engaged (micro switch)
Touch screen (for user input)
Throttle (potentiometer)
If any of these exceed certain values, a watchdog must sound an alarm, and if ignored for more than 3 seconds, cut off the fuel.
I presently have one sensor so far, the EGT sensor. This is a K type thermocouple linked to a max 6955 T/C to SPI chip.
Outputs:
Starter motor (RC car/heli BIG ESC - basically appears as servo to the propeller)
Throttle (Servo)
Clutch Solenoid (engage and disengages the starter, kinda like a clutch)
Fuel Solenoid x 2 (turns fuel on and off. 2 for redundancy)
Combustor dump valve (prevents fuel pooling in the combustor)
Ignitor (relay)
Gas solenoid (for initial starting propane)
Fuel pump (relay)
Oil Pump (relay)
LCD display (user feedback)
Siren (emergency feedback) (relay)
Strobe lamp (bystander warning) (relay)
BIG RED STOP BUTTON (TM) (switch)
*phew* big list eh!
Now for the actual running of the machine. This is how I figured the system will run.
At power up the system reads in the variables from eeprom for the safe conditions for the engine. Once the operator enters a pin code (to prevent unauthorised operation) they are presented with the initial screen with 3 options.
Full auto start
Manual start
Configure <-- if blank, default to this screen and provide generic values)
The first one is self explanatory, i'll get to it in a minute. The second allows external switches to run the various systems, to gather calibration data for the engine, so the configuration can be set. The third allows the user to enter configuration data.
I'll explain the configuration data first, as its kind of needed to understand the rest of the modes.
The configuration data contains several fields that are required to be filled in before the engine will start in full auto mode. Thats because the computer doesnt "know" the engines parameters, and the last thing we want is an over speeding or over heating engine. They tend to turn into giant hand grenades when they over speed. No one wants hot fragments of metal flying around at near supersonic speed (worst case - exploded turbine wheel)
These are:
Minimum oil pressure (usually 25-70 psi)
Maximum Safe EGT (exhaust gas temperature) (around 600-700C)
Minimum idle rpm (Speed at which to shut off starter motor and disengage it) (usually 45,000 rpm)
Min fuel rpm (absolute minimum rpm before fuel is turned on and ignited) (about 3000-6000 rpm)
Preheat time (time to use gas fuel until switching to diesel) (usually 10 seconds)
Over speed (depends on the turbo charger used. Lets say 120,000 rpm)
Ok now we have some parameters entered, and assuming they are correct for our engine, we can return to the initial screen and try the manual mode to get more accurate values.
In manual mode the screen changes to a screen showing the following:
RPM
Oil PSI
EGT
Boost PSI
Fuel type and pressure.
Switch positions for starter, oil, fuel and ignition
At this point the computer is only monitoring. but will sound the siren, if any of the maximums are exceeded. If ignored for more than 3 seconds, control is taken away from the operator, the fuel pump shuts off, and the cooling cycle begins. The screen will display the reason for the emergency shutoff, with an OK button. It will also not allow an incorrect manual start (e.g. trying to spool up the engine without the oil pump on). The strobe lamp will also come on once the oil pumps are running and at correct PSI, and the ESC is armed. During manual start, the operator controls the engine via a series of switches below the screen.
Finally we get to the good bit, the full auto startup procedure.
First a status check (on the manual controls):
Throttle: Idle
Fuel pump: Off/Computer
Oil pump: Off/Computer
Starter: Off/Computer
Ignition: Off/Computer
First, the computer turns on the oil pump and waits for oil pressure to come up.
Next it sets the clutch in the engaged position and see if its locked. if not, the ESC is brought to 10%, at which point the hex drive should engage the starter nut. Provided a "clutch engaged" signal is recieved, the system goes into full on start mode.
The ESC is wound up to the ignition RPM of 3000 rpm (for arguments sake). At this point the gas valve opens and the ignitor is switched on. At the same time, the combustor dump valve opens, as a saftey vent in case the gas doesnt ignite to prevent a very loud bang
. Assuming a succesful light off, the EGT will rise. This tells the computer to start ramping up the ESC at a ferocious rate until the running speed is reached. Around 15,000 rpm the dump valve closes as enough air is being rammed into the combustion chamber now. Once idle rpm is achieved, the ignition is turned off, the fuel pump turned on, and 10 seconds later, the gas supply shut off.At this point the engine is idling and controllable by the potentiometer, being watched by the watchdog for any unsafe conditions.
All data of the engine is displayed on screen - RPM, EGT, Oil, combustor and fuel pressures. A shutdown button is provided onscreen, and can be tapped to initiate a shut down
Shutdown:
Fuel is switched off, and the turbine allowed to spool down to 5000 rpm. At this point the clutch is constantly engaged and disengaged until it locks. Then the starter is ramped up to 7000rpm and allowed to drop to 3000rpm in a cycle until the EGT drops below 300C. At this point the starter is shut off, and following a drop to ~0 rpm, so is the oil pump.
The shutdown procedure is also carried out if the big red button is pressed. (nice big target for a panicing operator to hit!)
*phew - again*
I think I will be using 7 of the uP's in the propeller:
RPM sensor (this is a pain in the butt and needs its own uP)
Display (user feedback)
Control (relays, solenoids, pumps etc)
Touchscreen, switches (user input)
Watchdog, variables, big red button
EGT Oil and fuel pressure (these can be monitored simultaneously by one uP? - 3 sensors)
I've been writing for an hour now - So I thought I'd introduce my crazy project that I am SURE my neighbours will love (not), and see what you guys have to say.
I may in future ask for idea for the different bits of code, but I prefer to get as much as myself done first.
Thanks for your input, and once again, hello [noparse]:)[/noparse]
Comments
You'll have a great time, as the Propeller sounds perfect for what you are shooting for.
I'd recommend breaking this monster down into small tasks, but it sounds like you've got
some experience with other micros under your belt. Take the time to do the PEkit tutorials,
as they will give you a good understanding of .spin that you might now have cracked open yet.
Welcome to the group! It's addicting fun! Keep us up to date on your progress, photos, videos, etc. [noparse]:)[/noparse]
OBC
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New to the Propeller?
Visit the: The Propeller Pages @ Warranty Void.
1) A Propeller can certainly do all of the monitoring and controlling. For some of the sensors (EGT, oil & fuel pressure), you should probably use an external ADC. The cog that handles the sensor readings can use one of its cog counters to count RPM pulses.
2) You will need some fail-safes. This will be external logic that will shut everything down if certain specific things aren't working (including a programming bug in the Propeller). It'll be a couple of gates and an external watchdog timer that'll "pull the plug" if the Propeller doesn't respond within a certain period of time or critical items are absent. The Propeller can provide a more sophisticated watchdog and emergency shutdown, but you need a primitive hardwired one too.
3) Programming bugs happen and hardware failures occur despite the best of planning and design. Assume that you may have a giant hand grenade and build an appropriate test cell. Use redundancy for sensors and the control processor (maybe two Propellers, one primarily for redundant watchdog-type processes and emergency shutdown, so it can override the main controller and independently shutdown things).
Thanks for your input. Yes I have just been reading some primer code in the stickies, and the propeller looks totally suited to the job.
Mike, I would never rely on a microprocesor to handle the operation of such an inherently dangerous contraption, I will be building in failsafes and backup failsafes.
I have already decided that the big red stop button will instead shut off both the supply to the fuel valves and pump. This will trigger an error condition, and if the propellor doesnt automatically go into shutdown/cooldown mode, some simple timer logic will take over.
Mabye I can do away with the touchscreen and keep to switches, that way I can shut it down correctly manually, by hitting the kill button and then manually operating the starter to cool it down, and then turn off the oil.
The EGT sensor already has its ADC, the MAX 6675 IC, and the others are analogue (as most of these pressure guages are, from my readings about them), and simply require an ADC. The rpm sensor is simply a photo transistor and a lower powered (1mw) laser diode., detecting the compressor nut spinning. Its half painted white, and other half green (green absorbs red laser light).
Just like a big gas laser (like an agron I used to own) this thing will also be interlocked to hell and back, any system failure will result in an immediate shutdown, controlled by either the propellor or the logic backup board. (or as you mentioned, second propellor)
edit:
I also forgot to mention how I will test this system.
Oil pressure will be a closed loop test system. A regular oil psi guage will be placed inline to verify correct operation.
Fuel pressure will be tested in the same mannor, but not with fuel (obviously) but with water.
RPM can be tested with a dremel and cutoff disc, painted the correct colours and connected to a variac to control its speed. A signal generator and frequency counter can also be used in this case, a 0-200,000 hz counter and sig gen would be fine.
Solenoids are pretty easy to test. If they pull in, they work, if not, theres a problem.
In conjunction with the sig gen / frequency counter, or dremel setup, the correct operation of the entire system including all fault conditions can be conducted. The EGT simulation can be handled by providing the correct input to the unit, or by a seperate thermocouple and multimeter and a small hand blowtorch I own (use it for heatshrink - much better than the soldering iron barrel!)
Post Edited (vk2fro) : 10/14/2009 4:46:13 PM GMT
In a post to a different forum just this morning a rocket engineer I know wrote
If you watch the video and imagine the motor to be a giant hand grenade, you'll see what this guy meant.
·
Kept the cooling (in this case a big blower) running, but removed power to the excitation circuit and filament).
This way the oil pump keeps running, to prevent the bearings in the engine failing.
The blast sheild on that rocket thing looked far inadequate.
I agree what he'd videoed was insane.
I will need to design in sheilding for the engine, and a seperate "bomb proof" cell for the fuel supply, preferably with one of the fuel valves on the inside.
The engine is going to be small, but small ones are still as dangerous as big ones. Some of the websites that detail making these engines have plans for blast sheilds and max rpms along with suggested top rpms for different models of turbos.
I might not even be able to build it yet - still need to research the local authorities into the legalaties of building a gas turbine. I may find they have very stringent rules for their construction, or possibly not allow them at all.
P.S. I live in Sydney, Australia. I'll go update my profile now.
I built a controller more for monitoring my engines the EGT,s 3 of them feed into a circuit that ran to my prop board and then to an LCD display everything worked fairly well at first in the garage but as soon as I brought it outside +10 to -20 degrees everything became a problem
Either the heat or cold raised cane with my project and I could never work the bugs out, also the high frequency output from my magnetos ruined so many chips I wanted to cry My question have you had any luck using a controller "home built" to work on a running engine in the real world to measure or control fuel based on EGT readings?
Mike
I second what is said about security. The hardwired security devices MUST operate this way: only if EVERY dammed detail is OK let it run. If ONE single detail is wrong SHUT DOWN imediatly
This includes: fuel supply is only opened when power is present
very simple and redundant temperature security sensors. As long as everything is OK the contact of the sensor is CLOSED
if it opens SHUT DOWN: this way you catch failures like cutted or disconnected wires.
ALL security devices have to be redundant and are all lined up sequential. This means if any device has a failure the signal-loop is opened and the engine shuts down.
Two temperature sensors in serial, two gas-detecting sensors in serial, etc. etc. All these sensors are DIRECTLY hardwired to the engine-shut-down-device
These sensors HAVE TO BYPASS the propeller. If you have a software-bug or a damaged propeller the shut-down-device must still work !!
If you imagine all this: do you own some square-miles of desert where you can put your teststation in the middle of it ? Having still enough money to setup
remote-controls and cameras to stay away from your gas-bomb ? - eh - sorry gas-turbine ?
What do you think about a much more secure project ?
How about a WIND-turbine with adjustable blades for optimizing efficiency to different strong wind ?
Or a combined electric power and heat-engine realized with a modified car-motor or small motor designed for long-run (20.000 hours)?
best regards
Stefan
Post Edited (StefanL38) : 10/14/2009 5:28:46 PM GMT