Chronographs to measure projectile speed?
Quantum Singularity, Fri Feb 24 2006, 01:31AMI was wondering if anyone here uses chronographs for coilguns, railguns, or ring/disk launchers? Since I am a hunter I wanted to buy a chrono, especially for my bow. If I can use one also for an EM launcher than I'll probably buy one for sure. What I wasnt sure of is if a stong magnetic pulse would mess them up if spaced close? For a railgun, I was thinking the muzzle blast might mess it up as well as they are an optical device? Any other suggestions? I saw one plan online for building a chrono using the freq meas of a dmm but it didnt appear to be easily scalable atleast for firearm and bow applications.
Re: Chronographs to measure projectile speed?
..., Fri Feb 24 2006, 05:19AM
Chronographs can be used for coil guns (I doubt the emp will be too bod, but if it is just move it further away), but the muzzle flash from a rail gun seems to mess them up. Some people have good luck just putting a piece of cardboard in front of the gun to stop the blast (the projectile just punches a hole thorough)...
The easiest way to build one yourself is to take a a pair of IR led's and a pair of photodiodes, power the LED's, and hook the photo diodes into a flip-flop logic gate, which then feeds an and gate with the output of a 1mhz self contained crystal oscillator which is divided by 10 to give 100khz, which then goes to a counter. Or if you are into programming PIC's there is some code floating around that uses a pic to do all of the hard work. With the PIC model you can change the code to make it work for most anything, and by using different clock speeds you can adjust the range for the discrete one.
Good Luck!
..., Fri Feb 24 2006, 05:19AM
Chronographs can be used for coil guns (I doubt the emp will be too bod, but if it is just move it further away), but the muzzle flash from a rail gun seems to mess them up. Some people have good luck just putting a piece of cardboard in front of the gun to stop the blast (the projectile just punches a hole thorough)...
The easiest way to build one yourself is to take a a pair of IR led's and a pair of photodiodes, power the LED's, and hook the photo diodes into a flip-flop logic gate, which then feeds an and gate with the output of a 1mhz self contained crystal oscillator which is divided by 10 to give 100khz, which then goes to a counter. Or if you are into programming PIC's there is some code floating around that uses a pic to do all of the hard work. With the PIC model you can change the code to make it work for most anything, and by using different clock speeds you can adjust the range for the discrete one.
Good Luck!
Re: Chronographs to measure projectile speed?
Bjørn, Fri Feb 24 2006, 05:38AM
http://sciencezero.org/electronics/speedtrap.htm
This one has been built by many people without any reported problems. If you look around for cheap parts it can be made almost for free.
Bjørn, Fri Feb 24 2006, 05:38AM
http://sciencezero.org/electronics/speedtrap.htm
This one has been built by many people without any reported problems. If you look around for cheap parts it can be made almost for free.
Re: Chronographs to measure projectile speed?
FastMHz, Fri Feb 24 2006, 06:26PM
I use a Shooting Chrony, which can measure up to 7000fps...works for my ring launchers and coilguns and costs about $70.
FastMHz, Fri Feb 24 2006, 06:26PM
I use a Shooting Chrony, which can measure up to 7000fps...works for my ring launchers and coilguns and costs about $70.
Re: Chronographs to measure projectile speed?
Yohan, Fri Feb 24 2006, 09:08PM
I also use a Shooting Chrony. (on number 4, only had to pay for 1
)
We've toasted 3.
2 to EMI and 1 to stupidity in interpretation of projected trajectory.
In our design, we experienced interruptions as far as 10 feet from the last coil.
See the archives for the design.
Yohan, Fri Feb 24 2006, 09:08PM
I also use a Shooting Chrony. (on number 4, only had to pay for 1
)We've toasted 3.
2 to EMI and 1 to stupidity in interpretation of projected trajectory.
In our design, we experienced interruptions as far as 10 feet from the last coil.
See the archives for the design.
Re: Chronographs to measure projectile speed?
aahz, Fri Feb 24 2006, 11:37PM
Yohan, you mentioned in the archives (in regard to your excellent efficiency) that you did several things atypical of most coilgunners. Would you care to explain some of the 'very significant differences' in your design? Pleeeaaaasse?
So far, I see the following contributing to high efficiency: High-capacitance coupled with variable pulse times (Not depleting the stored energy of the capacitor, keeping 'on' time current high), Slotted armature, half-bridge design, Non-conductive barrel, multiple stages...... I'm sure I missed some obvious things....
aahz, Fri Feb 24 2006, 11:37PM
Yohan, you mentioned in the archives (in regard to your excellent efficiency) that you did several things atypical of most coilgunners. Would you care to explain some of the 'very significant differences' in your design? Pleeeaaaasse?
So far, I see the following contributing to high efficiency: High-capacitance coupled with variable pulse times (Not depleting the stored energy of the capacitor, keeping 'on' time current high), Slotted armature, half-bridge design, Non-conductive barrel, multiple stages...... I'm sure I missed some obvious things....
Re: Chronographs to measure projectile speed?
..., Sat Feb 25 2006, 12:49AM
I believe the main thing that gave them good efficiency is how they used the half bridge to recover the excess energy from the coil and feed it back into the cap bank (instead of dissipating it in a diode)...
..., Sat Feb 25 2006, 12:49AM
I believe the main thing that gave them good efficiency is how they used the half bridge to recover the excess energy from the coil and feed it back into the cap bank (instead of dissipating it in a diode)...
Re: Chronographs to measure projectile speed?
aahz, Sat Feb 25 2006, 05:06AM
Not quite.... he reported around 14% efficiency with a non half-bridge design (using all six stages), as well as a 'horrible' 5% efficiency when shooting for higher speeds.
After the half-bridge implementation, he reported 13% efficiency with a single stage. But still... prior to being a half-bridge design, the efficieny was excellent.
aahz, Sat Feb 25 2006, 05:06AM
Not quite.... he reported around 14% efficiency with a non half-bridge design (using all six stages), as well as a 'horrible' 5% efficiency when shooting for higher speeds.
After the half-bridge implementation, he reported 13% efficiency with a single stage. But still... prior to being a half-bridge design, the efficieny was excellent.
Re: Chronographs to measure projectile speed?
Quantum Singularity, Sat Feb 25 2006, 07:09AM
FastMHZ, Yohan, and others who use comercial shooting chronos, do you have any difficulties using the chronos indoors? I know some I have seen had optional low light/indoor hoods that incorporated a light into the hood. Will they work indoors without these or can you build your own indoor hood?
The only problem I have with DIY is that most use a photo trigger which requires the projectile to break the beam. If I am to use this with my bow also, it would be kinda difficult to be precise enough at distance or even up close for that matter to pass my projectile within 1" of the center of the beam or so.
About $70 you say... is that new/retail? Most new ones I have seen (example-cabelas) are $99.
I think its great to talk about cg efficiency and such but we might want to start a new thread for that so others who arent interested in chronos might notice it.
Quantum Singularity, Sat Feb 25 2006, 07:09AM
FastMHZ, Yohan, and others who use comercial shooting chronos, do you have any difficulties using the chronos indoors? I know some I have seen had optional low light/indoor hoods that incorporated a light into the hood. Will they work indoors without these or can you build your own indoor hood?
The only problem I have with DIY is that most use a photo trigger which requires the projectile to break the beam. If I am to use this with my bow also, it would be kinda difficult to be precise enough at distance or even up close for that matter to pass my projectile within 1" of the center of the beam or so.
About $70 you say... is that new/retail? Most new ones I have seen (example-cabelas) are $99.
I think its great to talk about cg efficiency and such but we might want to start a new thread for that so others who arent interested in chronos might notice it.
Re: Chronographs to measure projectile speed?
Bjørn, Sat Feb 25 2006, 07:47AM
If you place aluminium foil on each side of a sheet of paper you get a fairly reliable trigger that can take a lot of shots berfore it needs to be replaced.
Bjørn, Sat Feb 25 2006, 07:47AM
If you place aluminium foil on each side of a sheet of paper you get a fairly reliable trigger that can take a lot of shots berfore it needs to be replaced.
Re: Chronographs to measure projectile speed?
FastMHz, Mon Feb 27 2006, 08:11PM
I have no problem with my chony indoors. I simply put on the plastic diffusers and position a desklamp above it. Works perfectly.
I got mine brand new from
FastMHz, Mon Feb 27 2006, 08:11PM
I have no problem with my chony indoors. I simply put on the plastic diffusers and position a desklamp above it. Works perfectly.
I got mine brand new from
Re: Chronographs to measure projectile speed?
Yohan, Fri Mar 10 2006, 08:14PM
I'm sorry aahz I wasn't trying to ignore you. I didn't think we'd have any follow up questions here.
You've pretty much listed the major points.
The significant difference is the energy usage. We had a huge capacitor bank but we only used a few tens of joules at a time as opposed to the 2kj dumps that our competitors attempt. It's extremely wasteful to just full-charge and dump.
We didn't look at the capacitors as "capacitors". We looked at them as a power supply capable of delivering several thousands amps with a minimal voltage drop. (If you have enough of them)
Now, the smaller your capacitance (keeping I constant) the larger your voltage drop on the bank. And vice versa. We were attempting to create the ideal low-esr constant voltage supply.
And yes, you will have problems with a Chrony indoors if you don't have the light fixtures for it.
FYI: Just to pour salt in any wounds....when we finished the project in December 05' we were at 22% Efficient tossing a 133gram armature about 100fps with the 6 stage TTF design. It's a good thing we graduated or someone would be dead.
Yohan, Fri Mar 10 2006, 08:14PM
I'm sorry aahz I wasn't trying to ignore you. I didn't think we'd have any follow up questions here.
You've pretty much listed the major points.
The significant difference is the energy usage. We had a huge capacitor bank but we only used a few tens of joules at a time as opposed to the 2kj dumps that our competitors attempt. It's extremely wasteful to just full-charge and dump.
We didn't look at the capacitors as "capacitors". We looked at them as a power supply capable of delivering several thousands amps with a minimal voltage drop. (If you have enough of them)
Now, the smaller your capacitance (keeping I constant) the larger your voltage drop on the bank. And vice versa. We were attempting to create the ideal low-esr constant voltage supply.
And yes, you will have problems with a Chrony indoors if you don't have the light fixtures for it.
FYI: Just to pour salt in any wounds....when we finished the project in December 05' we were at 22% Efficient tossing a 133gram armature about 100fps with the 6 stage TTF design. It's a good thing we graduated or someone would be dead.
Re: Chronographs to measure projectile speed?
Quantum Singularity, Sat Mar 11 2006, 12:50AM
The sportsman guide I beleive is surpluss type stock and varies and unfortunately doesnt look like they have any chronos right now. As far as indoors I know there will be problems, thats why they sell light fixtures for some of them - but I should have asked if anyone has just tried to use thier own lighting (fixtures I have seen were like $30-40!). Seems like FastMHz did this succesfuly with common lamps... has anyone else? Anyone else have any sources for new units much less that $100?
Quantum Singularity, Sat Mar 11 2006, 12:50AM
The sportsman guide I beleive is surpluss type stock and varies and unfortunately doesnt look like they have any chronos right now. As far as indoors I know there will be problems, thats why they sell light fixtures for some of them - but I should have asked if anyone has just tried to use thier own lighting (fixtures I have seen were like $30-40!). Seems like FastMHz did this succesfuly with common lamps... has anyone else? Anyone else have any sources for new units much less that $100?
Print this page