31 replies to this topic

[stix]

Hey guys, I'm wanting to put this little project together. It's to do with testing rocket motors, but it could be for anything.

 

This is the specs and components required:

 

I'm ok with everything except for the PN2222 Transistor and the 1N4001 Diode. My local online electronics store offers the 2N2222A NPN Transistor and the 1N4004 1A Diode. My understanding of electronics is very basic. What I'm asking is that are these suitable replacements?

 

My gut feeling is that they should work fine, but I don't really know.

 

Thanks for your time. Cheers.

Edited by stix, 30 August 2021 - 06:54 AM.

[davidh]

I'll bite. how do you use an electric motor to test a rocket motor?

[stix]

Well thanks for your interest David. It goes something like this.

 

I'm trying to sort out a safety issue, a point of failure. I'm creating a rocket motor test stand that others may use.

 

The point of failure is on purpose for safety reasons. It's hard to explain. This is the first prototype:

 

 

The bottom of that blue vertical V structure (rocket motor holder) is a weak point - in case the rocket motor blows up on the test stand, the load cell and the rest, will not be destroyed - but nevertheless, it should be strong enough for "normal usage".

 

-----

 

So, what I'm wanting to achieve is to make a simple device that tests the strength of that (on purpose) weak point. Attach a small motor on the V-mount, spinning with an off-centre device like a really big vibration. Until the point that it fails.

 

It's a process of testing until it fails.

 

---

 

I can do the physical part. With the Arduino, I can direct the motor to spin up and put force on the structure (sideways) - like a real rocket motor out of control - until it fails.

 

It's important for me to know this.

 

 

how do you use an electric motor to test a rocket motor?

 

This is how.

 

I guess you wished you never asked.

Edited by stix, 30 August 2021 - 08:50 AM.

[stix]

So it still becomes:

 

I'm ok with everything except for the PN2222 Transistor and the 1N4001 Diode. My local online electronics store offers the 2N2222A NPN Transistor and the 1N4004 1A Diode. My understanding of electronics is very basic. What I'm asking is that are these suitable replacements?

 

[Richtee]

I’d say yes to the components. The transisitor is a generic NPN, and the 1N4004 only has a higher PRV (peak reverse voltage) rating. Even better than the 4001 I’d say.

[stix]

I’d say yes to the components. The transisitor is a generic NPN, and the 1N4004 only has a higher PRV (peak reverse voltage) rating. Even better than the 4001 I’d say.

 

Thanks Richtee. I'm going further than I probably need to with this. Thanks for the info, much appreciated.

Edited by stix, 30 August 2021 - 09:41 AM.

[stix]

I now purchased the electrical components.

 

So I must follow this through, make some contraption that spins off center.

 

Should a be good experiment.

[stix]

My thanks, is your reward. Oh dear...

 

https://soundcloud.c...2020-yes-master

[SeaMonkey]

It all depends upon how much current the motor will require to develop sufficient stresses for the testing.

 

The PN2222A Transistor is a Small Signal Transistor which doesn't have the capability to switch more than about 600 milliAmperes.

 

You may need a Power Transistor to safely switch the motor current if the PN2222A doesn't last.

 

The Diode is there to protect the Transistor from any Inductive Kickback Spikes which may be created and to increase motor efficiency when Pulse Controlled.

 

Let us know how the testing goes as it progresses.

 

The Motor Control Circuit is quite basic and is designed to demonstrate a principle.

 

You may need to "beef it up" if more power is required to operate a motor large enough to do the job.

 

If so you'll want to replace the PN2222A with a Power MosFet and use more than 5 Volts to energize the motor.

 

The basic circuit would not change a great deal.

[Richtee]

My thanks, is your reward. Oh dear...

 

https://soundcloud.c...2020-yes-master

I wanna see the results, sir.

[Richtee]

Yes indeed. As II mentioned the PRV of the 1N4004 is a good call. But yes  I wonder about mortor current.

 

The Diode is there to protect the Transistor from any Inductive Kickback Spikes which may be created and to increase motor efficiency when Pulse Controlled.

 

Let us know how the testing goes as it progresses.

 

 

[Arthur]

Can anyone explain to me why it's necessary to use an arduino to control the speed of a DC electric motor? Wouldn't a moderate variable resistor do the same job and so much cheaper.

[Richtee]

Can anyone explain to me why it's necessary to use an arduino to control the speed of a DC electric motor? Wouldn't a moderate variable resistor do the same job and so much cheaper.

It COULD. But you’d lose motor torque due to current drop doing that. I dunno if that would matter or not. I do have some old wire wound 50 ohm 25 watt pots. It would work.

[SeaMonkey]

A couple of videos which demonstrate the versatility of Pulse Width Modulation Motor Control and other applications of PWM:

 

Circuit Skills - PWM - Pulse Width Modulation

 

How PWM works - Controlling a Motor

 

Commercially made Pulse Width Modulation circuits can be found on Ebay and Banggood quite inexpensively.

[stix]

Can anyone explain to me why it's necessary to use an arduino to control the speed of a DC electric motor? Wouldn't a moderate variable resistor do the same job and so much cheaper.

.
Thanks Arthur. Yes, I'm happy to explain. Please take your time (and others) reading my explanation.

 

Using the Arduino allows me (via programming) to ramp up/down the motor speed and also reverse the direction - therefore giving a more "random result". That is to say, giving more natural/random forces applied to the "failure point" being tested. Also programming the Ardy allows me to test over a period of hours without any intervention on my part. In other words, the test can/will continue for hours to the point of failure, or non-failure???.... I'll be trying my best for failure.

 

Thanks SeaMonkey for all that info, much appreciated. I ended up changing the circuit to this:

 

 

It uses a L293D Motor Driver IC. Also, I've gone to a more robust motor. A geared 12VDC motor that has more torque - it seems that this may be the solution.

 

Now I have to come up with a physical contraption that puts the forces where they need to be. I'll keep you posted on the progress. Cheers.

 

[EDIT] Also, I already have some Arduino boards in hand, @US$5 a piece when I bought them. I also have some reasonable programming experience, that's why I'm going down this path.

Edited by stix, 03 September 2021 - 12:58 AM.

[stix]

Just a bit of an update.

 

The biggest pain so far has been trying to find a mounting hub for the 4mm motor shaft. I found some, but postage is getting really slowww.... (4 weeks+ between States) which is really sh*t for us here in Oz.

 

So I made my own mounting hub. The mounting hub connects to the motor shaft which is a D type shaft. The hub is attached to the "Arm". Gotta do some more cutting of the main arm piece. Maybe the whole idea will fail. Dunno. Lots of fun though. Cheers.

 

[stix]

Almost getting there. Not too far off to do the "stress test". It's stressing me out!!

 

[stix]

Using the DC motor this way (PWM) seems gutless. Maybe a stepper motor is the best way. But stepper motors are way to expensive just to prove this almost pointless test.

[SeaMonkey]

Firebreather,

 

Your workmanship, your attention to detail are really quite impressive!

 

For those with an Engineering bent, testings are never "pointless."

 

It takes a special appreciation of forces and failures to devise such tests and there are always lessons learned.

 

Those of us who are more interested in the mundane often scratch our heads as we enjoy watching the show.

 

As we wait patiently for the part where parts go a'flying.

Edited by SeaMonkey, 10 September 2021 - 04:37 PM.

[Richtee]

 

 

As we wait patiently for the part where parts go a'flying.

Heh  ain’t that what we wanna do best?  Oh  and brightly!