Need motor pressures

Salutations
I have a question. I want to use the engines pressure to detect when burn out has accord. I have e-mail Cesaroni asking what is the max pressure for there L265 an M1545 motor, an have not got a response from they. So I was wondering if any one might have a clue what the max pressure would be? I have design a pressure switch that will arm the staging/recovery delay outputs. Right now I have the switch set for 150psi for at lest 1.5 (chuff timer) to arm the firing circuit. Then when pressure drop below 75psi and G load is .5 or lower the firing circuit will turn on (after a delay for recovery deployment or no delay for staging). I need this info to ensure the pressure switch can handle max pressure of the engines.

Thank You:grin:

Rocket Nut 9

I have no idea what CTI runs at, but I've always heard most commercial motors run 400 to 600 psi. That could be way off.

I've seen several research motors on the test stand that ran at 1,200 to 1,300 psi. Frankly the maker was surprised they held together.

How do you expect to tap into the internal pressure during flight?

If I'm understanding correctly... You want to detect the drop in motor "pressure", to arm staging or recovery. This seems like an overly complex idea. Why not just use an accelerometer (Raven altimeter for example) to achieve the same end result?

The attached screen shots shows how plan to it. Basically I will install a threaded stud (with 1/4" center bore) to the engine case. This stud screws into the bottom of a isolation unit to shield the sensor from the hot engine gases. This isolation has a aluminum base with cooling fins the extend 1/8" outside the airframe for cooling. Attached to this base is a 3D printed isolation block that has a internal spiral duct that interfaces to a pressure sensor. The computer can read the sensor an determine when burn out has accorded.
That's why I need to know what the max pressure is so I don't blow the sensor because of over pressure.

This not at all complex. With the computer it's makes a very flexible system that has many uses. The computer is also a GPS locator for recovery. The computer is a Arduino Pro Mini made be SparkFun.


Rocket Nut

I tend to agree with scsager, this seems like a very complicated solution to a very simple problem. An acceleration sensor attached to the computer board in the direction of flight will go from a positive thrust when the motor is burning to a negative value equal to gravity plus drag when the motor burns out. The timing might not be exact, but it shouldn't be off by more then a few hundredth of a second.

I'm not surprised that CTI will not give you that information as you would have to modify their motors to employ your method. Modifying a certified commercial motor to perform these measurements decertifies the motor, and that's not a permitted topic of discussion in the forum.

The use of an accelerometer is a universal standard method of burnout detection. It works and requires no motor modifications, and it is simple to add to an Arduino Pro Mini since Spark Fun makes accelerometer breakout boards.

Bob

Message received, an dropping this pressure method. I will use the accelerometer method.

Sorry for any trouble that I might have caused

Rocket Nut

RocketNut9 said:

Message received, an dropping this pressure method. I will use the accelerometer method.

Sorry for any trouble that I might have caused

Rocket Nut

Click to expand...

No problem. You appear to be new to the forum and new to rocketry. While your device is clever, it is extremely complicated and difficult to implement, and the accelerometer method is very simple and requires no motor modifications.

Bob

My old trip number is 1001. I have not been flying because of personal reasons. I am thinking about getting back into things (since it's so long I will have to start out at level 1 with is no problem), with a 3 stage bird. The pressure method was a way of know which stage was up an running.

Old timers might remember the Light Stager. Which my partner an I made.

Yes I'm new to this forum.

Rocket Nut

bobkrech said:

I'm not surprised that CTI will not give you that information as you would have to modify their motors to employ your method. Modifying a certified commercial motor to perform these measurements decertifies the motor, and that's not a permitted topic of discussion in the forum.

Click to expand...

So, you can't modify a commercial motor and turn it into a research motor?
You can't discuss something like this on RF?

Richard Dierking said:

So, you can't modify a commercial motor and turn it into a research motor?
You can't discuss something like this on RF?

Click to expand...

This is a long dead thread, but modifying a commercial motor makes it a EX motor, and as such that means any discussion of it is in the Restricted Research section of TRF.

Copy that. Thank you.

Richard Dierking said:

So, you can't modify a commercial motor and turn it into a research motor?
You can't discuss something like this on RF?

Click to expand...

OK sorry about that. I will not ask any other questions dealing with modifying a commercial motor. I did not mean to brake the rules.

BPS has a decent system for detecting Apogee.

No reason you can't get a solid RMS bulkhead and thread it to hook into a pressure monitor. No need for the Heat sink fins. Just make sure that the entire section to the pressure gauge is filled with grease. It does not have to be gas, heat will not propagate thru the grease. Pressure is pressure, gas or liquid does not matter. Years ago I used a simple piston system that pushed a momentary switch when pressurized. It was set to trigger at about 50-100psi. The piston was 1/4" diameter inside a 3/8" diameter tube (2024T3 aluminum, could withstand up to 3000psi. no possibility of a commercial motor over-pressuring it.) Super simple circuit. SPDT switch at rest shorts an igniter across a 1000µf Capacitor, thus safe at all times until motor comes up to pressure. Then the thrown switch decouples from the igniter to a 9v battery to charge the capacitor. (You could also use a 12v a23 battery) At burnout the switch closes and discharges the capacitor thru the igniter. Totally independent of burn time. I used this method to do a 2 stager at Black Rock 1 K300 Blue thunder 1800ns staged to a K250 2560ns, minimum diameter Laser LOC. est alt 42,000'

bobkrech said:

I'm not surprised that CTI will not give you that information as you would have to modify their motors to employ your method. Modifying a certified commercial motor to perform these measurements decertifies the motor, and that's not a permitted topic of discussion in the forum.

Bob

Click to expand...

I think you are a little broad on with that statement.

The TRF rules, #9 says
9. Research Rocketry (making your own motors, igniters, etc) is an advanced topic that is restricted to certified flyers from the United States. The specific details are not to be discussed except in an area specifically designated for such topics. These topics include propellant and igniter compositions and techniques for processing propellant. Posts on the topic of Research Rocketry containing information not widely available in published materials are limited to the access controlled area.

I think the last two sentences are the key ones. As long as you are not talking about compositions/formulas or processing techniques, or secret squirrel stuff, it isn't banned. If it's not specifically banned, it should be allowed. I would rather error on the side of freedom of speech than censorship.

Just talking about using a threaded closure which makes a commercial motor a EX motor so you can take pressure reading doesn't violate any of those rules that I can see and I think should be allow. EX isn't a dirty word.

I came up with another sensor to determine when the booster has burned. It works by sensing the amount of force the engine is pressing against the bird's thrust bulkhead. It uses a spring that gets fully compressed (appx. 5LBS) it pushes a slide breaks the light beam of a photo-interrupter. Which tells the flight computer along with the G-load sensor that the engine is firing. Then when the engine burns out the spring pushes the slide back down, which allows the light beam to provide a logic 0 which fires the next stage (or what every the flight computer is programmed to do).

It uses the threaded upper bulkhead attachment thus there is no need to modify the RMS engine case.

Handeman said:

I think you are a little broad on with that statement.

The TRF rules, #9 says
9. Research Rocketry (making your own motors, igniters, etc) is an advanced topic that is restricted to certified flyers from the United States. The specific details are not to be discussed except in an area specifically designated for such topics. These topics include propellant and igniter compositions and techniques for processing propellant. Posts on the topic of Research Rocketry containing information not widely available in published materials are limited to the access controlled area.

I think the last two sentences are the key ones. As long as you are not talking about compositions/formulas or processing techniques, or secret squirrel stuff, it isn't banned. If it's not specifically banned, it should be allowed. I would rather error on the side of freedom of speech than censorship.

Just talking about using a threaded closure which makes a commercial motor a EX motor so you can take pressure reading doesn't violate any of those rules that I can see and I think should be allow. EX isn't a dirty word.

Click to expand...

Bob Krech's statement was made 5 years ago, and this thread was recently necro'd, the OP also has returned to answer, probably notified via the notifications.