I recently picked up a set of Rotor Riot’s Hypetrain Freestyle 2306 2450Kv motors for my freestyle quad build. Rotor Riot designed them and T-Motor manufactured them. They offer a unique and elegant design and claim to have a good power-to-efficiency ratio. You can get the hypetrain motors for $25.99 USD each from Rotor Riot’s store or GetFPV. That price makes them one of the more expensive offerings on the market: Let’s take a deeper look and see if they’re worth it!
(UPDATE: Rotor Riot recently released version 1.1 which claims to increase the strength of the bell. No change in price.)
The motors ship in an unassuming black box containing 1 motor, a nylock nut, a set of mounting hardware, and an orange Rotor Riot sticker. The motors themselves are stunning. The black and gray brushed-finish bell looks really sharp against a carbon frame, and the red accents against the silver windings make for a high-end look. The three support arms are a nice nod to the Rotor Riot logo, but I wonder how they’ll hold up in a crash. (UPDATE: Rotor Riot recently released version 1.1 of these motors at the same price, which claims to increase the strength of the bell. You can also purchase replacement bells here).
The motors feature an open-bell design and have a hollow shaft. Both of these features share a tradeoff: weight savings vs durability. Every fraction of a gram matters on motors, especially for freestyle. The weight out at the arms must be as low as possible to minimize angular momentum for flips and rolls. However, a hollow shaft is more likely to get bent, and the windings are more vulnerable without the protective bell on the bottom. The benefits are obvious, but we’ll have to wait and see how durable these motors are over time. On the other hand, the stator attaches to the base with an actual threaded screw (not a c-clip) which will make repair and maintenance much easier. Be sure to Loctite that screw if you ever have to take a motor apart.
They’ve got a 16x16mm mounting pattern, which is different from the standard 16x19x16x19mm on other similar sized motors. The oblong mounting pattern originates in the days of fixed wing props on airplanes, and there’s really no reason to keep it rectangular on miniquads. The argument here is that a smaller mounting pattern allows for smaller frame arms. Most frames out there today will support this 16x16mm pattern just fine but you may want to double check yours.
Finally, the silicon coating on motor leads is high quality and feels great. And they ship pre-tinned: Doesn’t really matter because they need to be cut to length, but I’ll never complain about attention to detail.
The Hypetrain motors have a 2306 stator (23mm wide, 6mm tall). Generally speaking, motors with larger stators can push larger loads (larger props, props with more blades, or props with more aggressive pitches) because the windings can be thicker and current more efficiently. 2306 is pretty large, but becoming more and more common these days.
The Kv constant is complicated. (over)simplified: it’s a measurable constant that relates to motor speed (it is not RPM per volt – it has to do with back EMF produced that opposes the power source voltage. Check the links below for details). The higher the value, the higher the top RPM but at the cost of reduced low-end torque. Freestyle flight typically favors torque over top-end speed. Higher torque means higher rotational force and faster response times to quick changes in throttle. Many freestyle motors come in around 2300Kv (for example Armattan OOmpfs @ 2300Kv or TBS Steele motors @ 2345Kv). A value of 2450 on the Hypetrain motors says to me that these motors will have a bit more top end and a bit less torque than others.
That’s not the whole picture though. Current produces torque. While the Kv constant gives a picture of the motor’s current draw profile, it’s not the whole story. There is resistance in the motor windings that causes current loss. The Hypetrain motors feature thick solid windings coated with silver – both of these properties ought to reduce overall surface resistance. More current makes it to the motor instead of getting lost as heat in the windings. In other words, there’s reason to believe the mechanical design improves power delivery enough to keep torque just as high at the higher Kv. If that proves true, these motors might have similar freestyle properties with a lot more top end power when you need it.
There’s a lot to say on this subject and someday I’ll write a post on how motors work. For now, I’ll refer you to a couple outside sources to read more about torque/Kv/current/RPM:
- Brushless Motor Kv Constant Explained (learningrc.com)
- The relationship between Kv, Resistance, RPM, and torque in BLDC motors – explained! (rcgroups forum)
So, should you buy these motors? Are they worth $26 a piece? It’s a hard call, but I think they are. I was looking at the Armattans pretty seriously, but I ended up picking the Hypetrain motors because I simply loved the design and visuals. Plus, on paper, there’s a good chance they outperform the competition. I’m worried about the damage risk (and the risk to my wallet when I break one) but we’ll see how it goes. In the grand scheme of things, $26 isn’t that much more expensive per motor – I’d say the Armattans (again, on paper – I haven’t flown them) are your next best option and they’re $22 each.
Finally, before you make a choice, go spend some time over at MiniQuadTestBench by Ryan Harrell. He’s compiled a wealth of motor information. The website presents this data in a highly interactive way. I’d suggest you go read his reviews and compare the Hypetrain data against similar motors (like the TBS Steele and the Armattan Oompfs). You can drill down on the parameters you care most about and decide from there.
If you’ve got any experience flying these motors or any similar ones, please share your thoughts in the comments below!