Saturday, 18 April 2015

LiPo Mods: Elite Rayven and Rapidstrike PDW

So far in my electrical modding history, I've done several rewires and a few (minor) motor replacements [usually just Barricade motors], but I have never delved into the world of LiPo batteries. After experiencing some blasters that don't work too well even with the higher current IMRs, I decided to save up and jump in.

These are the two LiPos I currently have, with a Koosh dart for scale.
The top LiPo is a 1s (a single LiPo cell, with 3.7V nominal), 750mAh (capacity), 35-70C (discharge). It can continuously supply a current of around 26A (current = discharge * capacity), and burst supply nearly 53A. Compare this to two parallel IMRs that put out at most 20A in burst. This LiPo is for running the Tamiya Mach Dash Pros in my E.Rayven.
This particular 1S had a different connector, so I had to cut the wires to solder on the new connector, hence the e-tape insulation. It is incredibly important when doing such a modification to only cut one wire at a time, as shorting out a Lipo can have severe consequences, such as a fire.
The bottom LiPo is a 2s (two LiPo cells in series, with 7.4V nominal), 800mAh, 40-60C. It can continuously supply 32A, and burst supply 48A. Compare this to two series IMRs that put out 5-10A at most.

I chose these particular LiPos to start off with because they will power the blasters most in need of LiPos. The E.Rayven's Mach Dashes can pull quite a lot of current, and though parallel IMRs put out a decent amount, the extra resistance from the battery tray terminals (among other extra parts) meant that they didn't receive as much current as needed, resulting in a slower-than-ideal spin-up time, and noticeable loss of range in rapid fire.
The Rapidstrike's design means that it effectively has 3 motors in parallel as opposed to most flywheelers, which have 2 in parallel. This causes it to draw significantly more current than say a Stryfe. Because the two series IMRs can't put out enough current, when the flywheels are revved while the dart pusher is moving (as when you're firing), both receive a noticeable drop in speed. As a further issue, the low current put out by IMRs means that the loss of range in rapid fire is very significant, a major problem for a full-auto blaster.

Trustfires would do nothing but amplify the problems IMRs have. Unlike IMRs which can put out 5A or more, Trustfires are typically stuck with at most 1-2A. While Trustfires are typically much cheaper than IMRs, they are significantly worse for our purposes. Likewise, while IMRs are better than Trustfires, they are still not the best as just about every viable replacement motor draws more current than IMRs can supply.

Let's look at the Rayven first.
Externally it looks no different. While blasters need further modification beyond just a standard rewire to accept LiPos, it's not difficult or particularly space consuming.
The battery tray holds the major alterations.
Instead of housing 1-4 AA-sized batteries, the battery tray now houses the 1S LiPo and a LiPo connector, in my case an XT60 (male end, the battery has the female end). As shown above, the LiPo fits neatly in the tray without the connectors connected, so the battery is kept safe while the blaster is kept inert.

Naturally the battery tray had to be significantly altered, with holes made for the wires for the connector, and the ribs removed for the LiPo and connectors to fit.
Connected up, the stiffness of the wires keeps the LiPo in place along with the ribs.
 The bottom of the tray has some foam to cushion the LiPo, as well as to keep it from sliding around.
The battery tray cover also has cushioning foam, andhad to be shaved down a little to allow for the height of the XT60 connectors.

Let's look at the RapidPDW.
Again from the outside nothing looks different to what it was last time.
 Like the E.Rayven, the RapidPDW also has an XT60 (male end) for its LiPo in place of its old 2AA holder.
Unlike the E.Rayven's tiny 1S that fit in easily, the 2S for the RapidPDW only just fits. And by "only just", I mean that some grinding was needed to make the LiPo removable and insertable without opening up the whole blaster.
With some careful grinding though everything fits in nicely. The loose wires that are sticking out fold in behind the battery door, and are not exposed at all.

One other change was made to the RapidPDW, though not a LiPo-related one.
 As we know, the Rapidstrike's stock can be retracted...
 ...or extended. However I had a slight problem. Even with the stock retracted the RapidPDW would be *just* long enough such that when put in my Uni backpack the muzzle would *just* stick out.
Solution? Make the stock removable. It's very basic, it just involves shaving down a few plastic protrusions to allow the stock to be pulled out. The metal pin also needs to be removed, though as that particular piece is free floating, chances are you've dropped it a couple times already if you've opened your Rapidstrike.
A not insignificant amount of force is required to remove or reinsert the stock, but for the average teenager or adult, it should be pretty easy with a single smooth motion.
I personally think the RapidPDW looks pretty cool without the stock, it still feels reasonably well balanced and is still easy to handle.
With the stock removed the RapidPDW now fits into a shorter space, and is now short enough to fit inconspicuously into my backpack.

So how have the LiPos affected the performance of these two blasters? Very, very well in fact.
The E.Rayven now spins up much faster than before, reaching max speed in just over half a second. Thanks to the extra current, the motors can now spin stock Rayven flywheels seemingly as fast as the lighter Stryfe flywheels, where IMRs spun the Rayven flys noticeably slower than the Stryfe flys. The E.Rayven is now easily one of my favourite and best performing blasters, and would be my go-to for most purposes.
The RapidPDW now shows no issues with revving the flywheels and cycling the dart pusher simultaneously. Additionally, the flywheels seem to spin up faster and the dart pusher seems to cycle slightly fast than when it was being run on IMRs.
I feel like getting a 40C 2S was pretty overkill for the RapidPDW, I've seen people run upgraded motors that draw heaps more current with 2S LiPos with lower discharge rates and comparable capacities. On stock motors you could probably get away with the slightly smaller and cheaper 20-25C.

The two biggest problems with LiPos that are can see are as follows.
Firstly and most obviously from my pictures, LiPos require a special connector to hook up to the blasters, unlike Trustfires/IMRs which are AA sized and so slot right in. Furthermore, due to their non-AA size and shape Lipos typically require some sanding/grinding/cutting/sawing of internal parts to have them fit internally, especially if you want them in an AA battery tray. However with a soldering iron (which you should already have if you're doing rewires and are considering LiPos) and a rotary tool (which is a universally useful tool, not just in Nerf), these problems are easily fixed.
Secondly and most economically important for entry into the LiPo world, LiPos require a special charger. While you can get a versatile, good quality Trustfire/IMR charger for about 20AUD, a reputable branded LiPo charger with power supply can cost upwards of 50AUD. It was this initial cost barrier that has prevented me from entering the LiPo world for the period I was considering LiPos during, and is likely the main cost that will repel many people from switching to LiPos.
Ironically however, LiPos themselves are quite cheap compared to IMRs and Trustfires, considering their capabilities. A pair of IMRs required to run just a single blaster typically costs about 20AUD, while my two LiPos cost less than 15AUD together, and the LiPos have much, much greater current output capabilities. Trustfires can be had for very cheap, let's say around 2AUD per Trusty. To match my 2S Lipo in current, which cost about 12AUD, you would have to string together about 32 pairs of Trustfires in parallel, which would cost 128AUD for all 64 Trustfires required. Simply put, LiPos completely outclass Trustfires and IMRs in current output per dollar. For that reason, after overcoming the initial cost barrier LiPos can become surprisingly cheap, and are incredibly good at their job.

All in all, the switch to LiPos I think is a good choice for me. They put out the current required for higher spec flywheel builds, which is far beyond the capabilities of IMRs or Trustfires, and are also cheaper (after the initial cost) than IMRs.

And in other non-Nerf related news, Star Wars Battlefront! *much excite*
Also second Star Wars trailer, IMO much better than the first.


  1. Glad the Lipo worked out for you! I would never use anything else now.
    40C is a good rating for a Rapidstrike pack. Never go below 30C for even stock motors. They draw a peak of around 7A EACH on startup/stall.
    Other things to note- try XT30 or Deans connectors for tight fit trays, they are smaller overall than the XT60. It's also worth buying a cheap mixed set of heat shrink tubing for insulating connections, it flexes more than E-tape and is neater. EBay has lots of options or a good auto parts store will have several sizes.
    If you are going over to packs permanently in a blaster, remove all the springs and metal arts from the tray in case a wire ever comes loose, as they can short the pack, which is bad. Also it's worth removing all the ribs from the tray, as you can fit a higher capacity pack in then.
    Nice work though. I hope all those blasters are properly wired inside, as your new high current batteries need 18AWG wire to take the loads without getting hot.

    1. Thanks FDS! Your advice was a big part of me moving to LiPos.
      I got XT60s because most of the packs I'm looking to get in the future use them, but I might look to XT30s or Deans if I find myself really squishing packs in. I'll look to get heatshrink too before I do my next rewire/pack implementation.
      I'll get to removing all of the battery related stuff in the tray. I left the partial ribs in for now as the Rayven currently runs exclusively that particular 1s, and the ribs remain in place to help keep the 1s in place. That particular 1s was the highest capacity pack I could find on HobbyKing that would fit in the tray, and I think it'll be enough for casual/short game use.
      Wires are 17AWG I believe, microswitches I'm fairly sure are rated to at least 10A, so they should hold up ok.

    2. That sounds like a very solid set of components. Glad Lipo has worked out well. Have you had a chance to war test yet? If you want more capacity from 1s then you can get a parrellel connector, that allows you to plug in two packs to give you double the capacity at the same voltage.

    3. No war experience yet, I've been too busy to get friends around since the LiPos came in. Seeing as I've got a bunch of assignments due soon and exams after that, they probably won't see war use until mid year.