PSA - Turnigy XK20 inrunner shaft diameter change NOW 2.3MM. DO NOT BUY

Ordered two Turnigy XK2040-4500kv motors from HobbyKing US warehouse recently. I had planned to use these to run the HBC Riot Cage, as well as reviewing them as a 20mm inrunner option for SSS flywheel systems.

However, there was a complication.

Specs on listing (note 2.0mm shaft, in agreement with the 2.0mm shaft these motors had in the past):

Motors received:

2.3mm nominal with a flat. God damnit Hextronik you have failed me.

I am RMA-ing these things. It's a shame, they are nice motors with what should be perfect specs for this application, and I really wanted to give them a go.

Instead I am going either with another pair of GWS GWBLM005, which will hopefully have better bearings than my last noisy pair of them, or maybe I will give the Hobbywing EZRun 2030 18t (5200kv) a try. After a lot of digging I have had a hell of a time finding any other 20mm motors with 2.0mm shaft ends. A real shame about these Turnigy.

Overview/General Build Log: Prometheus

Prometheus: an electropneumatic, magazine-fed, fully automatic, open-bolt, 12.7x36mm, high-velocity capable dart blaster development project. Or you may know it as an HPA engine design, or as one of those new "NIC" blasters that isn't technologically stuck in 1995.

This is Prometheus.

Combat Tested: Hooligan Flywheels

(Disclaimer: I was sent free samples.)

This is Hooligan Blaster Company's first flywheel product.

This is a CNC machined, Delrin, smooth, mild-concave (Artifactoid profile) superstock-standard flywheel in the 35mmOD class.

Project Hy-Con: A flywheel geometry development effort [Part 1 of who the hell knows]

One of the many recent discussions of flywheel physics sparked a realization about the design basis of a flywheel profile most elemental, and in hindsight, plainly obvious at least in theory. It involves concavity. So let's talk about concavity and ask the most basic question there is.

What the hell is the purpose of a concave flywheel profile, anyway?

(Be warned, theory ahead, but there are some cool things later on!)

Brushless Inrunner AR Cage Continued, and Project T17

Where did I leave off with Project ACR? Here, I believe.

So the last image showed what was about to happen, more or less. Well, it happened. But not after a bit of bug hunting.

Mini-Review Raytheon Waffle Dart

I received one sample clip of this dart from dkdavid721.

Tip diameter: 0.460" front, 0.490" rear
Foam OD: dart 1 0.488 - 0.502", dart 2 0.485 - 0.503"
Length: dart 1 2.892" (73.64mm), dart 2 2.875" (73.02mm)

For reference:

• Mengun Red, tip diameter 0.405 front/0.462 rear, foam OD 0.487 - 0.513", length 2.884
• Gen3 koosh (yellow foam), tip diameter 0.483, foam diameter 0.510 - 0.519", length 2.877

Chrono shots: T3.1, full length RS inner barrel (straight flute), Hooligan flywheels: 120.0, 129.8, 123.6, 125.1, 127.4, 120.1, 114.4, 123.1, 117.9, 123.5

Notes: A very, very accurate dart, easily killing the koosh hands down. These things are lasers with groups under 18" at 45 feet range and 120fps. The newer version of tip that Raytheon sells has a shorter core than the original waffle tip and is made of a slightly stiffer compound. Also, the tip gluing is improved over the "Ekind" era waffle dart.

Tip failures should not be an issue with these and flywheel performance and consistency is improved over the Gen 1 waffle dart. These shoot as clean as Mengun red. However, the foam is still small bore, coarse celled and not that great of quality and velocity retention is still a bit poor.

Verdict: Good stuff. I'm buying several cases of this dart right now. However, I do recommend using it with at least a modern SSS flywheel gun equipped with a high crush flywheel system and a short barrel.

Also, even Hooligans/other Artifactoids and similar class of flywheels (like Worker and CC Cyclone) in 43.5mm cages, which work well for fatter-foamed darts, may not give the correct crush ratio to be optimal on these, due to the small bore foam. They are worth a shot with a combination of same flywheels and a crush-boosting cage.