Thursday, February 2, 2012

Nerf Rayven - Electronics Guide


This is an electronics guide for the Nerf Rayven. For a mechanical interns guide reference SG's guide.  

The following image, courtesy of SG, shows all the electronics inside the Rayven.  The four yellow things are inductors (or chokes) that are insulated.  The black component under the trigger is a diode, and the component next to the diode that looks like a capacitor is really a PTC (or thermistor).  


The following is the circuit for a stock Rayven.  There are a few SMD capacitors on each motor, but they are left out for now.  One thing to notice is that if your jam door is open, and/or your clip is not loaded, then the motors are shorted and the left side of the circuit is not present.  Shorting the motors will make them stop very fast, so this is obviously a safety feature.



As far as modding, removing the diode will be like increasing your battery by 0.8 volts, and the only downside is that if you put your battery in the wrong way, the fly wheel will spin backwards.  The PTC (thermistor) was put in as a safety mechanism.  If something in the circuit causes a short, and a large amount of current starts flowing, then the PTC will become an open circuit.  Unfortunately the current which causes an open circuit varies greatly.  I recommend taking the diode out to get better performance, but leaving the PTC in, unless the blaster stops working when you increase the voltage.

The chokes are an RF/EMI suppression component, as are the small SMD capacitors found on the tiny PCBs soldered to the motor terminals (thanks to torukmakto for pointing that out).  They should not hinder performance, unless you are using a very high voltage or current, in which case you might be going over the max voltage the capacitor can take, or the max current the inductor can take (I have no idea what those limits are, but they are probably more than high enough for us).

The last thing to note is that the wires used in the Rayven are very thin, and although they are probably fine for even a high voltage mod, it never hurts to replace them with nice thick wire. 

Now, if you are someone like me who wants to use a rechargeable battery, but the only ones you have are battery packs with a fairly high voltage, and you are afraid of putting too much current through the motors, then read the following.  I personally use an 8.4V NiMH battery (commonly used in Airsoft guns).  After voltage modding my blaster, I noticed a faint burning smell coming from the motor, and the motors (combined) were drawing 1A at start-up and 0.5A full-speed.  In order to effectively reduce the voltage I was giving my motor, I put a power resistor in series with everything.  I realize this means a huge chunk of power is being dissipated into heat, but I rather have that than buy a new battery pack (or burn out my motors).  I also realize most people aren't going to bother using this trick, because they don't have power resistors sitting on the shelf and don't feel like buying one.  However, if you want to use a power resistor to lower the current, then just use a mix of ohms law, a multimeter, and testing.  In a future guide I will discuss using PWM to fix this issue.