This is an PTW thread

[mcguyver]

Well, there is only 2 possible ways to do it. One, is to get a shortened EL-003 board and extend the control and motor leads and stuff it all the way to the rear, then insert your battery via the buffer cap. I don't like this approach, it takes too long and leaves lots of room for error, especially concerning the wiring.

The other approach is cut open the buffer tube to allow the battery to be inserted. But, the entire stock must be off, and the retaining bolt must be removed. I'm working on a solution to this that will allow for quick removal of the stock and still be strong enough to use a sling. It is a work in progress but is definately a viable option.

As well, you need to install a set screw into the takedown pin spring and guide hole to retain those if you install the UBR and plan to remove the stock for battery change. This is dead simple with a tap and a set screw,

[mcguyver]

OK, nobody is going to die, so I will show you guys one way of doing the UBR on a PTW so that you don't have to pop the buffer cap and you have access to the battery in mere seconds.

Now, here is the gun, and the stock fully collapses:



Now, a closer view of the stock:



Now, here is how I chose to fix the stock on the buffer tube. It is a brass knurled nut ($1.29 at Home Depot) that I drilled out and tapped for M6 x 1 for a clone UBR (you didn't think I was going to try it first shot on a real one, did you?). A real one is Imperial threads, and that is easier to find parts for. I cut an M6 x 1 screw to allow me to access the buffer tube with threads to screw the stock on. The nut is going to get painted black, but I left it brass to see easier in the pics:



Now, in order to accomodate the nut and still be able to fully collapes the stock, I needed to drill a hole through the butt. This is nicely hidden by the rubber butt pad:



It takes mere seconds to unscrew the nut, and then you simply slide the stock off. This was a clone, and the fit and finish is not like the real deal (but it is 1/5 the price), so I needed to sand the buffer tube some to get the stock to slide nice and smooth.



Once the stock is off, you have access to the battery and the electronics. I cut a notch with a Dremel into the buffer tube to be able to slide a battery in place. You see the stock EL-003, and realize right away that you need a shortened board, the stock one is about 1" too long. Mine is still on order, but I proceeded with the mods pending its arrival.




Also, to get to this point, you need to deal with the takedown pin spring and detent. Normally, these are floating and are held in place with the stock. However, this stock comes off, so that would not do. I opted to tap a small set screw in place, cut a little bit off the spring and screwd it and the detent in place. Now, there are no issues, and it does interfere with any stock installation, be it UBR or not.

[ThunderCactus]

What size of LiPo can you fit in there?
I'm going to be looking into this as well (yeah yeah, buying a PTW), but your method is pretty well perfect.

If your going to leave the compartment doors on the UBR, do you think it's possible to hollow it out and just have your battery in the sliding section of the stock, with access through the buttplate?
I'm not at home to look at mine right now, but at first glance it seems like there's enough room to slap a small square LiPo in there....

[mcguyver]

Originally Posted by ThunderCactus

What size of LiPo can you fit in there?
I'm going to be looking into this as well (yeah yeah, buying a PTW), but your method is pretty well perfect.

With the shortened board, the Firefox 11.1V 1100mah 15C battery fits nicely. I have another one coming this week with is a little bigger, so we'll see.

Originally Posted by ThunderCactus

If your going to leave the compartment doors on the UBR, do you think it's possible to hollow it out and just have your battery in the sliding section of the stock, with access through the buttplate?
I'm not at home to look at mine right now, but at first glance it seems like there's enough room to slap a small square LiPo in there....

I thought of that as the first option, but 2 immediate problems arise. How do you route the wiring so that it does not get damaged and keeping the stock movable and how much can you hog out of the stock to keep its integrity and still get a battery in and out. I took the stock to a hobby shop and went through dozens upon dozens of batteries, and I could find nothing that would fit, give me the voltage and discharge capacity I need.

I opted instead to stay within the confines of the buffer tube, and avoid some other problems.

[ThunderCactus]

Hobbyking has a monstrous variety of packs of all shapes and sizes, but I've done it twice now, it's a major pain to go through them all looking for a specific size. I don't know if they have anything narrow enough to fit in a stock tube though.

Luckily my UBR is always in only one position, so I personally don't have to worry about the wiring moving around to much. But I'm gonna say I probably won't be able to get anything bigger than a 3S 1600mah in there anyway... Even if Rhino made me custom triangular LiPos...

Does anyone know anything about micro-fusion cells? lol

[Rookie Ab]

That is slick. I've put the UBR on a KJW but the PTW had me stumped till now.
Hope your parts come in soon.

Thank again for the how to and letting us live

[Drunk_Albertan]

I think I judt found myself a winter project, thanks Mac.

[mcguyver]

Originally Posted by Drunk_Albertan

I think I judt found myself a winter project, thanks Mac.

If you have a Dremel, you will need to find multiple projects. Now that I've done one, it only takes an hour or two to flange that sucker up.

Next up is CNC lower. I know who could do it, it is just a matter of talking them into it and how much it will cost.

Also, if you don't have an adjustable motor, think MIAD. It takes some time and a Dremel.

[Rookie Ab]

Hey Mac, any updates on your UBR project? I got mine done but had a bitch of a time with the battery connectors (Deans). Tight fit with the Firefox 15c but I made it work with different connectors.

[iMak]

Originally Posted by mcguyver

Next up is CNC lower. I know who could do it, it is just a matter of talking them into it and how much it will cost.

I'll take 2.

How much are prime lowers going for now?

[mcguyver]

Originally Posted by Rookie Ab

Hey Mac, any updates on your UBR project? I got mine done but had a bitch of a time with the battery connectors (Deans). Tight fit with the Firefox 15c but I made it work with different connectors.

Micro-Deans are the ones to use.

I'm still waiting for the shortened board along with some other do-dads, so it hasn't progressed really beyond that.

[ThunderCactus]

Do you know the exact dimension that is available in the buffer tube?
Would it be possible to use a Turnigy nano-tech battery, or LiFePO4 cells?

[Rookie Ab]

I only have 115mm of room for the battery.The 15c I have is a 106mm and with the balance plug oriented at the end it is 111mm.So it's snug.

[mcguyver]

Tackleberry's Super-Mini board is 34mm long and is the shortest one out there. I'm not sure if you could fit that, the connectors and a 20C battery in a UBR, but you can fit a 15C.

I measured Jonas' G&P 20C and it is 138mm long not including the connectors.

[ThunderCactus]

What about width? What's the max?