rhino-aus

Wasn't that the MTB group or something?

This one? (Links to Youtube.)

Edit: I actually noticed another engine in the post jwasko made, in the guide by rhino-aus, the NSR 3005 Shark, crazy specs that one has! My only concern is with engines that reach such a high RPM (40,000), do get that torque of 210g/cm over a wide range or only at that RPM? If the latter is true, wouldn't an engine achieving 30K-35K RPM and 210g/cm torque be better suited than one that does 210g/cm torque at 40K RPM?

Ohi! It's me; that flywheel obsessed guy from MTB!

The trade off between RPM and torque is the stored energy and the stored energy recovery rate. The difference between Shark 40Ks and the MTB Rhino motors we are about to start distributing is practically minimal. The MTB Falcons are designed to handle 15 darts per second which is way more than any pusher motor can possible fire out of a Rapidstrike. The higher RPM of Sharks could allow for a sustained ROF of 18 darts per second but even the old ultra high RPM Ranson motors in the pusher only get about 12.

Using the maths and simulation i developed for that paper you get the following results:

A Shark will spool up to its stable 18 DPS RPM in 0.21 seconds
A MTB Rhino will spool up its stable 15 DPS RPM in about 0.22 seconds

The soonest you can fire a 120fps dart out of a Shark is 0.19 seconds
The soonest you can fire a 120fps dart out of a MTB Rhino is 0.2 seconds

tl;dr Sharks are "better" but the performance gain is absolutely minimal; particularly for motors that will cost about 4-5x as much.

I had the idea to make my own out of polycarb where the motors are closer together and the flywheels are smaller. Will smaller flywheels help or hinder performance in any way?

So a few things happen with smaller; closer together flywheels:

- The flywheels have a smaller radius so the edge velocity is lower. This may be problematic if they are so small to the point where the edge velocity is lower than the potential maximum velocity: the dart will never travel faster than the flywheels.
- The smaller flywheels will likely have reduced inertia which will cause more slowing during the shot; however this may be offset by the higher density. For reference the moment of inertia of a stock flywheel is 805g.mm^2.
- If inertia is reduced your spin up times will be reduced, otherwise they will be increased.
- Flywheel RPM will be mostly unaffected; the max RPM is based off the no load speed. Assuming nothing is rubbing on the flywheels, they should always eventaully reach this max RPM.
- If the flywheel gap is reduced you are likely to get more normal force applied to the dart which may improve performance assuming the other previously mentioned factors dont limit maximum velocity
- If the surface roughness is higher than the stock flywheels you are also likely to get better performance due to a higher friction coefficient; again as long as your surface velocity remains high enough.

All in all I feel that great care will need to be taken to avoid hindering performance; smaller, lower inertia flywheels will most likely perform worse with the same motors.

I'd definitely suggest upgrading the motors instead of building the suggested control system. Stock motor performance is just too low to justify that.

though i've found brushless motors that could work for around 15 each motor. there's things you can do to change how it moutns into the blaster and how the flywheels are attached.

I have tried to swap the shafts on some of the micro brushless 1220, 1230 sized motors from hobbyking. Ended up breaking 3 of the 4 magnets I had trying to get the shafts out. If you do get those, the shafts at 1.5mm at the attachment, but have been lathed down from 2mm so a shaft from a stock motor will fit nicely inside. I will retry when I can make a jig to press out the shafts; hammering them out is a terrible idea...

If it helps I run these motors in my RapidPistols on a 3S LiPo. They \love\ to burn out. You really need to burn in the brushes otherwise they will die almost immediately at 12v. When you do get them working you can get 13 darts per second which is absolutely glorious. In the flywheels you will get the standard 120 FPS ceiling since they turn more than 25K RPM. I wouldnt use these for flywheel motors tho; there are better options. If you want to use them put them in the pusher!