5 replies to this topic

[arfink]

EDIT: for those who see my informative block text and give it a TL/DR, here is a quick summary:
Auto-tommy 20, a few simple mods, now gets 2 shots per second ROF and 45-50 foot ranges. Read on for the how and why.

OK, before I begin with this post I just want to say that I have already been trying some of these ideas out, and they seem valid enough. I know many people here dislike flywheel guns for the reasons that they are obnoxiously loud, not terribly accurate, and get poor ranges. I have been experimenting with an automatic Tommy 20 for a bit just to see what I could do to it, since it was laying around collecting dust. Here are some things I came up with:



First, the over-voltage trick that everyone knows about: I selected about 7 volts for my modification because I had a 7.2 volt cheap-o RC car battery laying around which was also collecting dust. When installing it I noticed some interesting things about the internals of the Tommy 20. On the negative terminal of the battery holder there are a pair of capacitors. These are used for two things: soft starting and over-drive protection. Now, at 7 volts the capacitor for the flywheel motors seems to eventually go into a "thermal runaway" state and limit current to the flywheels, slowing them down. So I removed that one. But I left the capacitor for the carousel-advance mechanism because it doesn't seem to have over draw problems when running at 7 volts. Also, the capacitor helps to prevent having the motor jerk so violently when the trigger is pulled all the way down and the firing mechanism is engaged. The added jerk of not having the capacitor in there seems to be doing bad things to the mechanism, and can jar the carousel and cause darts to get unseated, jamming the gun.



I tried using 9 volts, as many people here do, and found that while the flywheels did indeed spin faster, the firing mechanism was simply being put under too much strain. 7 volts is more than enough for me, and seems to put much less strain on the mechanism. At 7 volts the rate of fire increases to almost 2 shots per second, and everything seems to work comfortably. 9 volts has an even better ROF, but can have problems with the carousel mechanism skipping forward too quickly for the darts to be removed from the carousel by the flywheels, resulting in massive jams. If I were to use a 9 volt power source I would probably add some kind of simple resistor pack or potentiometer to reduce the speed of the firing mechanism while getting the advantage of the higher speed flywheels.

Speaking of jams, I noticed that in the entry to the flywheel area there is a small rubber tab sticking down. I did notice that at 7 volts with the tab still in there I would sometimes get jams, and without the tab there were no jams. However, the tab seems to be intended to help center the dart and make sure it enters straight. Without the tab jams don't ever occur, but accuracy seems to suffer significantly.



I also noticed that, for a dart to fly straight when picked up by the flywheels it is critical that the head of the dart be gripped by both wheels at the same time. The wheels, however, are covered in ridges. These might help improve grip, but it would seem that at higher speeds all it does is make it so that if the ridges are un-aligned then one wheel or the other will grab the dart head first, resulting in darts which fly out of the gun at strange angles. I have been experimenting with covering the flywheels in various things, including rubber bands, e-tape, and duct tape. I may experiment with "plasti-dip" as well. Adding a conformal coating of that kind seems to help accuracy a good deal. (straight darts with properly aligned heads are more important) I have noticed that adding enough thickness to the wheels allows them to grip the shaft of the dart as well as the head, vastly improving accuracy and the speed at which the dart exits the flywheels. However, this also can result in the destruction of darts with normal heads, since they get violently crushed and pulled by the flywheels.

Perhaps the best performance I have gotten so far is with darts with low profile heads and solid shafts. A streamline, cut down slightly and with a straw inside for more stiffness, seems to fire very nicely with thicker flywheels, and a long stefan fires very well too. Regardless of what kind of flywheel/dart combination I use, at 7 volts I am getting an average of 45-50 feet flat with an ROF of around 2 shots per second. Stock darts seem to be highly erratic, and will basically go everywhere except where you point the gun. Modded streamlines and stefans with a thicker set of flywheels fly much straighter.

Since I was having problems with side-to-side deviation of darts I decided to experiment with re-aligning the flywheels. Re-centering them on the stock motors is nearly impossible, as removing them and putting them back on tends to only make the alignment problems worse. However, I noticed that there is little angular deviation up or down. (though some up/down variation is caused by the varying speeds that the darts can exit the flywheels.) So I decided to try rotating the flywheel assembly 90 degrees. I haven't permanently attached the flywheels in that fashion as it's simply too cumbersome to do right now, but did notice it decreased the side-to-side deviation significantly, while making the range of each shot more uncertain than before.

Perhaps the biggest problem I have with this gun is how temperamental it can be with different types of ammo. With properly formed stefans of the correct length it's a joy to use: an inaccurate, noisy monster that can lay down a short to medium range wall of foam in a big hurry. Of course in a war situation it's almost impossible to ensure you'll always have stefans of exactly the right length. So if I ever used it in a war at all it'd be used as a somewhat bulky secondary (perhaps with a sling?) for when I'm getting rushed or with integrations. The shell has a decent amount of space that could be used effectively for an integration. Given that I paid nothing for this gun, I find that it does improve significantly with the 4 simple mods I did: increasing voltage, removing only one of the capacitors, removing the rubber tab in the flywheel entry, and thickening the flywheels.

Edited by arfink, 20 December 2010 - 05:23 PM.

[FriendlyFireNH]

Ammo wise, do you think perhaps using stefans with tape on the end covering 1/3rd to 1/2th the dart? That way it is never pushed by the fly wheels, only pulled. Seems to me like that might help accuracy (and dart life?).

I was considering one of these, but with all the lack luster reviews of the gun I'd just buy another barricade instead.

[arfink]

Ammo wise, do you think perhaps using stefans with tape on the end covering 1/3rd to 1/2th the dart? That way it is never pushed by the fly wheels, only pulled. Seems to me like that might help accuracy (and dart life?).

I was considering one of these, but with all the lack luster reviews of the gun I'd just buy another barricade instead.

Well, considering what the gun has going for it, I'd get one only if it's dirt cheap and available. I did this mod simply because I had one that was literally not going to get used for anything ever again if I didn't do something to it. You can almost certainly get better performance out of a barricade, and it's more suitable as a sidearm than this. So I would say, if you have money to spend, spend it on a barricade if you want a flywheel gun. If you have a Tommy 20 around, play with it for a bit before you decide to spend more money.

EDIT: one thing to note- this gun is fully automatic, while the barricade is not IIRC. If you were adventurous and wanted to change the orientation of the flywheels in the auto-tommy 20 you could probably get nearly identical performance to a barricade with full auto fire. But it's a good deal of work. How badly do you want full auto? That's the question.

As for e-tape on stefans, that's an interesting idea. I find, however, that if all the flywheels do is pull the dart it won't fly as straight. I don't know this for certain as I haven't done extensive tests and can't see inside the flywheel chamber easily while firing, but it seems as though having contact with the shaft of the dart is needed in order to make sure they fly straight. I have been wrong before though, and this might warrant some more tests.

Edited by arfink, 20 December 2010 - 09:38 PM.

[Exo]

It seems like AT20's and most other flywheel guns are killed by noise. I think that if you actually care about the noise enough as to not buy a gun, then you are trying too hard to be a ninja. Ranges, stealth, and accuracy aren't as important on these guns, just because they are so fast, and they often carry a lot more ammo.

I think accuracy could be improved by a skimmer barrel, one that doesn't actually touch the darts, but would guide them if they went of the wheels at a wild angle, maybe with something like a foot or so of 3/4" to 1" pvc. Power is also upgradeable, as shown in this mod. 45'-50' isn't bad for just voltage and flywheel mods. Changing out the motors should be relatively easy if you have a soldering iron and can find suitable motors, which might also improve "stealthiness" if they are quieter, should also prevent against burnouts, as they should have a higher voltage allowance, which means, even move voltage.

Nice job, arfink. One of few mods I've seen to this gun, and one of few mods I've seen on a BuzzBee gun.

[mysterio]

The voltage upgrade, flywheel thickening, and rubber tab mod also work on the Ultimate Rapid Blast, the semi-automatic cousin of the AT20. This is a very nice mod, and I will be sure to try rotating my flywheels to a vertical position in my Ultimate Rapid Blast, to mimic your results.

[arfink]

Yeah, making the flywheels vertical instead of horizontal actually makes the Tommy 20 a little more nice than a Barricade simply because the capabilities are about the same and it's fully automatic with the Tommy 20. If/when I get around to permanently mounting them that way on mine (as opposed to just wiring it up and holding it on with duct tape) I'll post pics and results.

One other thing to note about flywheel blasters- keep in mind that eventually you can and will reach the physical limit at which you can simply shove darts around with flywheels. Tearing, abrasion, and mangling of darts, especially ones with distinct heads (IE, stock darts) can happen when you get the flywheels going fast enough. They will always be limited in range because the darts simply can't survive getting pushed/pulled really hard.

As for the idea of a skimmer barrel, it's not a bad idea but in my experience the darts that really fly askew would probably swerve enough to jam in such a barrel, and as my mod suggests, I'm willing to sacrifice accuracy to eliminate jamming.

Edited by arfink, 24 December 2010 - 12:37 AM.