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Brushless Stryfe Project


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#1 shardbearer

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Posted 27 October 2016 - 12:06 PM

Hey NerfHaven it's been a while, but I just got to college and there's a decent HvZ scene here so I'm getting back into Nerf.My first project, a custom flywheel cage for a Stryfe with brushless outrunners as the flywheels.

I've seen a couple people do this before, but none of them have any documentation, so I'm mostly starting from scratch. I'm starting off with these 26x27mm motors, which are rated for 47k rpm and 300W on 3S, as well as some Simonk speed controllers and a Zippy Compact 1Ah pack I have laying around. The other, more powerful, motor options are this one, which is 56k and 365W at 4S, and this one, which is 44k rpm and 755W at 4S, but I'm not sure they'll fit without cutting the shell as they're both 36mm long. I also don't have a 4S pack of the right size on hand, so we'll see if the first motors have enough power. If they can spin up fast enough, I'd love to put the rev switch behind the trigger like the FDL-2 and eliminate the separate rev trigger.
 

Another question is the flywheel surface. I have about 3mm of thickness in my current design to add another material with better grip to the outside of the motors. I'll do some tests with the stock steel cans, then with polished steel, before moving onto gluing on rubber tubing, like Mcmaster's 35A and 50A hardness silicone tubing. I'm surprised nobody's tried anything like this before, I think it would give a significant increase to the friction against the dart, and therefore the velocity, but I'm not sure they'll stay glued on properly. It sounds like a silicone based adhesive like E6000 or silicone caulk is my best bet.

 

And of course, flywheel spacing has a big impact on dart speed, but I haven't seen more than a few anecdotal numbers, so the motor mounting holes are slots so that the spacing is adjustable and it will accommodate different sized flywheels.

 

As you can see, there's a lot of things to experiment with, and I haven't even gotten into barrel guides or canted flywheels. I'm super excited to get back into this community. Here's what I have so far for the CAD model, I'm currently debating whether to 3D print it or CNC it out of aluminum.

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Edited by shardbearer, 12 March 2017 - 07:09 AM.

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#2 Draconis

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Posted 27 October 2016 - 02:22 PM

While I don't think anyone has tried that particular tubing, many of us have tried other types.  Some of them, like bicycle inner-tubes, flex so much that sometimes they well come loose from a press-fit when spun up, and walk off of the wheels.  It would certainly be worth a try, but I would not base a whole build around the possibility.


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#3 shardbearer

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Posted 27 October 2016 - 11:07 PM

Yeah, I wasn't sure how long the rubber would stay on. Those slots are long enough that it can use the bare motors, or I can turn some concave hard plastic rings and glue them on.

Eli Wu just posted a video of his amazing 3 stage brushless Rayven, and I asked him for some more details in the Reddit thread. He has two sets of outrunners running on the bare steel cans and one set of inrunners with Worker wheels. There is also a cooling fan on each motor too, which is a bit concerning.

 

My Stryfe arrived this afternoon, and I spent the night doing some basic mods to make it usable this weekend. 3S Lipo, no locks, new wiring, barrel chopped off though it's rather ugly for the moment, and the top opened up for refilling mags on the fly. Still need to cut an opening for the voltmeter but I don't want to wake everyone up with more dremeling. The main battery connector can't be reached without opening up the blaster, so it looks like I'll be making an adapter to charge through the balance leads. And it looks like the smaller motors will fit in the shell, but it's going to be extremely tight. And my hand's too big for the handle so I'm definitely getting one of these grip covers from 3D Printed Solid and either a Worker stock or one of their stocks.

 

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Edited by shardbearer, 12 March 2017 - 07:10 AM.

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#4 shardbearer

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Posted 12 March 2017 - 07:07 AM

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It's been a while since I last updated this, but I finally got this project working. I scrapped the CNC aluminum cage and 3D printed the cage and wheels. I modified the Simonk firmware to be able to monitor the speed as the motor spins up, and saw significant spinup time benefits from turning up the low speed power, detailed here and here. I haven't tested it with the latest version of the wheels, but with these motors, high power settings, and no wheels, I was getting spinup times of around 0.15s, similar to 130 brushed motors, and with the flywheels attached it is significantly slower. The torque is much greater than brushed motors, but the inertia is also much greater.
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It took me 3 attempts to fit the Stryfe perfectly, over which I also significantly reduced the amount of plastic required for the cage and flywheels. I tested a 3D printed rubber concave flywheel, but the rubber expanded at high speed, hit the wall of the cage, and stalled and burned up the motor. I got some magnet wire and rewound the motor with what I believe is the same as the original setup, 10 turns of 5 strands of 32 gauge wire in DLRK. It took way too many hours, and I do not recommend anyone do this for relatively cheap motors like this one. I need to do some testing to verify that the speed of the new motor is the same as the other one, however the ESC I had modified for speed monitoring is not working, along with another ESC, both of which I flashed with the firmware version meant for a different board. I'm currently using two different types of ESCs, which means they hang out the side of the battery compartment. Once I get another Afro 30A Race Spec Mini, that should be able to close properly, and the battery is stored in the Modulus Storage Stock. I also had issues with a 1000mAh 25C pack charged to 11.3V sagging under startup enough that the ESC's 10.5V undervoltage protection kicked in and they shut down. With a higher power pack, my newly rewound motor let out the magic smoke after a few spinups, though it seems to be working afterwards so I think that was the super glue I used to hold the wires in place. Either way, I turned down the power on the ESCs to a more reasonable power level.

Long story short, it works! I have yet to chrony it, but it's shooting fairly hard and straight with both Elites and Men-gun darts. Strangely, USC darts seem to hang in the flywheels for a fraction of a second before firing, leading to a massive amount of dart wear and a large cloud of foam dust and smoke. I would share the files if anyone wanted them, but at this point I cannot recommend anyone build an outrunner flywheel blaster. Perhaps we'll see inexplicably good chrony numbers like the FDL-2, however the inertia of the outrunner motors is simply too high to get spinup times competitive with 180 brushed motors. However, I do see there being possible advantages to an inrunner system, and designed a modified Open Flywheel Project Stryfe/Rapidstrike cage for the XK2040-4500kV if anyone wants to try it. My brushless code for the Teensy 3.2 is on Github here, including the Python scripts to capture and graph the speed data.

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Edited by shardbearer, 12 March 2017 - 01:08 PM.

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#5 shandsgator8

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Posted 12 March 2017 - 08:19 AM

How comfortable is that stock?


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#6 shardbearer

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Posted 12 March 2017 - 11:34 AM

It's decent. It's convex so it tends to slip on your shoulder a bit, and I've been thinking of gluing some grippy foam or rubber to the back. Length is pretty good, I locked it to the longest setting by putting hot glue behind the ratchet nub. It still collapses under a lot of force, but this isn't a springer so that isn't an issue. It's a pain to get open because the hinge pin is permanently attached to the orange piece on both sides, which means you can't permanently glue the tube to the body and still be able to reassemble the stock. I took some pictures so I can write a guide for opening it up and putting battery wires through.

I also have a grip extension from 3D Printed Solid on this blaster which I forgot to put on for the photo, and I really like it.

Edit: Stock mod guide is here.


Edited by shardbearer, 12 March 2017 - 01:06 PM.

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#7 NerfGeek416

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Posted 12 March 2017 - 12:10 PM

Very nice! The big advantage of outrunners is that it's much easier to design 3D printed frlywheels for them. I'm looking forward to chrony data!


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