# Help with calulating a cyclic rate

• Senngenn

#### Senngenn

Hello, sorry if i do not ask the question correctly but any help would be great.
i need to find the speed of an item and I'm not sure what i need to find this out?
well a cyclic rate of this item?
Thanks

Hi Senngenn. Welcome to PhysicsForums.

I see about 40 people have read this but no one offered an answer. It might be that we are not understanding your question.

Are you asking about a certain situation? Can you describe that situation?

You said "cyclic". Is this something rotating?

It might help to post a drawing.

I hope i can explain better,
the item Wt. is 210 grams the maximum travel is 2 1/4" it travels in a strait line.
We are a Firearms Mfg. we have a semi auto bolt when fired it travels the 2 1/4" we are trying to regulate the speed of our sub machine. when we do not regulate the cyclic rate it has a speed of 2500rpm we are trying to slow that to about 900 to a 1000 rpm. so i think I'm really looking for is to determine the speed involved with his moving mass? because when the round is fired the explosion is what drives the bolts speed.

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the item Wt. is 210 kilograms the maximum travel is 2 1/4" it travels in a strait line.
We are a Firearms Mfg. we have a semi auto bolt when fired it travels the 2 1/4"
210kg sounds a bit high for a firearm bolt, no?

210kg sounds a bit high for a firearm bolt, no?
sorry 210 grams

What drives the bolt on the return segment of the cycle?

What drives the bolt on the return segment of the cycle?
Springs.

we are trying to regulate the speed of our sub machine. when we do not regulate the cyclic rate it has a speed of 2500rpm we are trying to slow that to about 900 to a 1000 rpm. so i think I'm really looking for is to determine the speed involved with his moving mass?
Can you explain what this means? What is spinning at 2500 RPM and how is this involved in the firing of your gas-driven firearm? Can you upload a couple pictures or a diagram? Thanks.

What is the spring rate, installed preload and, if you have determined it, the maximum deflection during firing of your spring set?

Can you explain what this means? What is spinning at 2500 RPM and how is this involved in the firing of your gas-driven firearm? Can you upload a couple pictures or a diagram? Thanks.
Nothing is spinning 2500 rpm is in a strait line motion

Can you explain what this means? What is spinning at 2500 RPM and how is this involved in the firing of your gas-driven firearm? Can you upload a couple pictures or a diagram? Thanks.
also our firearm is designed not on a gas system but a delayed roller system it uses the pressure from the round going off to drive the bolt back words.

What is the spring rate, installed preload and, if you have determined it, the maximum deflection during firing of your spring set?
i"m not sure what the spring rate is but we preload the springs about 3/4" and they are compressed 2 1/4" due to the firing. if this helps the spring is 6 1/4" long .275 OD and the wire diameter is .035

Another spring characteristic that is required to determine its spring rate is the "number of free coils" which is the sum of all of the coils excluding the two partial end coils. With that plus the above information it should possible to determine an approximate spring rate; but, I haven't done that particular spring analysis before.
If you know your spring manufacturer and their part no. for your spring would it be possible for you to contact them to get the spring rate because if your spring is one made specifically for your use then that is the only way to determine the true spring rate for your spring?

Alternatively, with that same information, if they are a principal manufacturer and your spring is a stock item for them, I may be able to find an online catalog that will give me the spring rate for your spring.

This information is important because with the installed and compressed spring lengths you have given it is possible to determine the average spring driving force and, from that, the average bolt closing acceleration; and, subsequently, the bolts' travel time during closing. With that information, then the gas powered opening time is equal to the time of one rpm minus the calculated bolt closing time (and the average bolt opening driving gas pressure can also be calculated).

Another spring characteristic that is required to determine its spring rate is the "number of free coils" which is the sum of all of the coils excluding the two partial end coils. With that plus the above information it should possible to determine an approximate spring rate; but, I haven't done that particular spring analysis before.
If you know your spring manufacturer and their part no. for your spring would it be possible for you to contact them to get the spring rate because if your spring is one made specifically for your use then that is the only way to determine the true spring rate for your spring?

Alternatively, with that same information, if they are a principal manufacturer and your spring is a stock item for them, I may be able to find an online catalog that will give me the spring rate for your spring.

This information is important because with the installed and compressed spring lengths you have given it is possible to determine the average spring driving force and, from that, the average bolt closing acceleration; and, subsequently, the bolts' travel time during closing. With that information, then the gas powered opening time is equal to the time of one rpm minus the calculated bolt closing time (and the average bolt opening driving gas pressure can also be calculated).
Sorry there are 52 coils and the lead is .125 on each coil

I need a bit of clarification on spring's total compression. Is the 2.75" travel in addition to the .75" installed deflection for a 3.50" total max spring compression?

I need a bit of clarification on spring's total compression. Is the 2.75" travel in addition to the .75" installed deflection for a 3.50" total max spring compression?
We preload the spring 3/4" and the travel of the bolt is 2 1/4" for a total compression of the spring of 3"

Thanks, I just got offtrack on decimal part of the travel length

Thanks, I just got offtrack on decimal part of the travel length
no problem thanks

Using those spring specifications and some circular load at 3" deflection trial values in an online spring calculator from Newcome Spring Corp (see below) it appears your spring rate is 3 lb/in. and its load at the 3" in deflection is 9 lbs. and results in an installed preload of 2.25 lbs at 3/4"

Edit: Which results in a 5.625 lb average closing force.

https://www.newcombspring.com/springulator/compression-spring-calculator

Now, with that information, after a bit of a break, I will take a run at my above described calculations for the closing time, etc.; unless you would prefer to do those yourself.

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No please have at it but if you could explain how you came up with the final numbers I would appreciate that thanks for all your help.

Nothing is spinning 2500 rpm is in a strait line motion
we are trying to regulate the speed of our sub machine. when we do not regulate the cyclic rate it has a speed of 2500rpm we are trying to slow that to about 900 to a 1000 rpm.
Okay, I guess "rpm" is rounds per minute of machine gun fire, and you'd like to slow that down to 900-1000 rounds per minute with some control mechanism or damping. Is that correct?

What are you using for the control of the firing pin? The initial release of the firing pin is via the trigger sear, and after that the firing pin is locked in place proud for the automatic fire? If you had control of the delay for the firing pin release for each cycle in automatic fire mode, that would be the easiest way to regulate the fire rate, IMO.

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I have done a quick calculation and I am running into an immediate conflict in that the travel time for the bolt closing based upon the bolt mass and the average spring force is greater than the total cycle time at 2500 RPM.

In that respect, what, if anything, prevents the bolt from traveling more than your specified 2.25" other than the the resisting force of the spring at 3" of compression?

Edit: Attached below is a screen print of my initial analysis:

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• Sceen Print of initial bolt return time analysis.JPG
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• Sceen Print of initial bolt return time analysis.JPG
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Is there someplace where the spring diameter and spring material is given, or did I miss it?

See Post #13 for spring OD and wire diameter. The spring material has not been specified but I used the chrome-silicon selection in the spring calculator

Tom.G
With respect to my question about what limits the bolt travel, if you have a backstop that determines the 2.25" bolt travel, some percentage of the energy from the bolt opening is going to be added to the spring energy and that is going to increase the bolt's closing speed and reduce the bolt closing time.

Determining the bolt opening energy requires knowing the bolt's opening terminal velocity which requires knowing the maximum gas chamber firing pressure and the shape and dimensions of the chamber and the bolt diameter in the chamber.

Estimating the percent of energy returned from the bolt/backstop impact requires knowing the material hardness of the bolt and backstop components. The harder the materials, the higher the percent of energy return.