Chronographs - Measure velocity or energy?

di11on

Hi folks,

I'm just wondering do the chronos used in airsoft measure the energy of the projectile or just the velocity. I.e., is the mass of the projectile considered?

Just had a look at the wikipedia entry on chronos. Quite interesting. The first type of chrono was pendulum based. This is perfect as it considers the mass of the projectile as well as the velocity. You fire a projetile at a pendulum and the height the pendulum reaches gives you the energy.

Should be nice and easy to make a home made version of this? Using this site you can work out the energy of the projectile based on:

• Length of pendulum string
• Mass of pendulum
• Angle at maximum deflection

Must give it a go!

Stercus Accidit

You would lose energy through deforming the projectile, and deflecting it, so it would not be accurate.

The Xcortech cronos calculate energy and speed once you type in the weight of bb used.

Puding

The legal limit is a measure of energy, as you say this is worked out by knowing the speed and weight of the bb

chronos used to just give speed but modern chronos will allow you to enter in the weight of the bb being used and it will work out the joule output

as long as you know the weight of the bb used and the chrono is set up correctly you will get an accurate reading, the problem comes when people chrono using a differant weight bb to what the chrono is set for this will give you incoorrect readings

di11on

Thanks guys - so chronos are just measuring speed. You can enter the weight but it isn't measured.

@Stercus Accidit: Since you will always be measuring in the region of 1J, you can quantify this error and calibrate the device - should allow for a decent measurement then.

If your pendulum was something like bluetac and your bb gets embedded, then you can safely say that all the energy has been trasferred to the pendulum.

Stercus Accidit

di11on wrote: »

@Stercus Accidit: Since you will always be measuring in the region of 1J, you can quantify this error and calibrate the device - should allow for a decent measurement then.

If your pendulum was something like bluetac and your bb gets embedded, then you can safely say that all the energy has been trasferred to the pendulum.

Again, deforming the bluetack would take energy out of the system.

By all means try it out and and check the results versus a chrono, and see how close the readings are.

Stonewolf

The problem is though chronos give varying results depending on ambient conditions and brand.

Puding

Two points there...

Chronos can be wrong , site should really have two chronos ideally two differant models to cross check if needed

conditions can effect fps but if fps go up due to atmospherics then that's is still the energy oyput at that point , the bb is traveling at that speed and is a set weight, if the chrono is accurate and chronoing done correctly then that is the joule output at that point, set your aeg up for 310 with .20g and you will not really have a problem with any ups and downs

di11on

Stonewolf wrote: »

The problem is though chronos give varying results depending on ambient conditions and brand.

That's ok... I'll do it all in space.

Sugar... that won't work... what will my AEG compress to fire the BB? :-)

Tactical

If we want consistent and accurate readings then the chronograph would need to be calibrated and a calibration chart for the instrument available to allow us to add in any calibration factor to obtain an accurate reading.

BioHazRd

Tactical wrote: »

If we want consistent and accurate readings then the chronograph would need to be calibrated and a calibration chart for the instrument available to allow us to add in any calibration factor to obtain an accurate reading.

Not forgetting a repeatable controlled testing environment. As this is not practical between shop and site, it would be advisable to build the error correction into your guns output power. (ie - have your gun set to 0.9 Joule as Puding suggested)