INSTALLING AN EXTERNAL VOLUME CONTROL IN A TAMIYA PANTHER

If I were in charge, all RC tanks would be designed with a volume knob somewhere on the exterior of the tank, cleverly disguised as a detail. You shouldn't have to open up the tank, flip it over, or use tools just to adjust the volume, especially if you decide to power up your tank at 4 a.m.!

I expected this to be a no-brainer, so I didn't bother checking it out until it came time to deal with it. I saw the two round doo-dads on the back of the hull and figured that one or the other would be the ideal place to mount the 20K potentiometer. After all, that's how it went with the King Tiger. I didn't count on the fact that the Panther is smaller, the speaker is closer to the hull's ceiling, and there isn't much space between to fit a small pot. Once I realized this, I looked at other options. My second choice had been the turret, but I saw that it would probably interfere with the gun's elevation. It's also preferable for fewer wires to be run to the turret. Plan C would be to place the knob beneath a hatch. That would be an admission of defeat since my philosophy is that when you need to turn the volume down quickly, you don't want to be messing with no stinkin' hatches! Back to plan A, in last-ditch salvage mode. (Mind you, this may not be the best way to install a volume pot-- it's just what I had on hand!)

Tamiya 1:16 RC Panther tank volume control To do this mod, the pot's shaft has to be trimmed so that the detail part can mount on it and look like it's supposed to look. Ideally, you can install the pot recessed in the hull and trim the shaft with a tiny bit poking above the hull for the detail part to attach to. In this case, the speaker box was in the way and overlapped half the pot. I knew that I'd have to cut into the speaker box, but I thought the less, the better. To recess mount the pot, the recessed mounting should be substantial enough to support the mounting shaft and ideally, the face of the pot-- but the more substantial it is, the more the speaker box would have to be cut. I realized that I'd have to trim more than just the pot's shaft, but also the threaded barrel for the shaft. This was tricky.

I don't like to mod pots because I consider them (and switches) to be consumables and should be replaceable with off-the-shelf parts, without a lot of hassle. Trimming the shaft length isn't too unreasonable, but beyond that is probably going too far. Still, we do what we have to do to make stuff work, and learn along the way...

Construction of pots varies, but I learned that with this particular knurled shaft pot (20K replacement for an Ibanez Tube Screamer-- an electric guitar gizmo) I could not just pop the back casing off and remove the shaft and wiper. Nope, the wiper was held in tension against the carbon trace by the wider knurled part of the shaft retaining it within the barrel. Huh? (Don't worry. Few will understand what I'm talking about.) So, the upper part of the shaft had to be cut off exactly at the junction before the shaft could be removed from the barrel, so that the barrel could be cut. You're probably wondering, "Uhhhh... Wasn't the wiper held against the carbon by the shaft-barrel tension?" Yepper. That means that the ass-end of the wiper had to be pushed in by the casing. I used a ball-ended hammer to tap/dish the center of the casing inward. That wasn't quite enough, so I added the washer that had come with the pot (hey, recycling!). Whew! It worked, with no snaps, crackles, or pops.

The other steps were much easier. A half-circular rod section was cut out of the speaker box, taped over and covered with putty. The hull opening was ringed with putty to make a fitted mounting for the pot's face, and the exterior part (knob) was fitted to the pot's shaft. The height was close to perfect. Both the knob and the pot were affixed with contact cement. This forms a strong elastic bond, that can be pried apart so that parts can be removed. Unlike Superglue, the bond stands up to shear forces and if the bond is stressed or stretched so that the part pulls away, there are usually strands of the stuff that keep the part from completely falling off and getting lost. In this case, the pot is probably secure enough since its putty mounting is molded to the shape of the face (so it won't twist) and there's very little downwards pressure from the knob since the knob is plugged into the hull's original mounting hole and flush with the lip.

The other part of this operation requires surgery on the DMD unit, which is inadvisable if you ever intend to sell it. This is pretty straight-forward: The top cover is removed, the volume trimmer is snipped off and three stranded wires are soldered to what remains of the snipped off tabs. There's not a lot of working space there, so don't attempt this if you're bad at soldering.

Tamiya 1:16 RC Panther tank circuit laser volume controlThis is also a perfect place to use one of those 3-pin plugs and sockets you've been hoarding. You should use a shielded 3 conductor wire for this, or you may get buzzing if you handle the wires; as usual, the ground should be connected to the shield wire. (In the pic, I used a short run of ribbon cable which is spliced to the shielded cable.) The wiring is routed around the side of the hull towards the center, with a plug or socket, and the DMD wire gets the mating hardware. It's worth planning out wire runs so that the tank can be disassembled easily and logically, without putting stress on any of the electrical connections. You also want to make it easy to figure out what plugs into what without error.

While you're busy devaluing the DMD, you might want to shunt R18 so you can run a laser machinegun. it's also a good time to enlarge the opening where the flash plugs in. This will give you more room to grip it when you have to disassemble the tank. As is, it's very hard to unplug-- the plug itself is quite flimsy and you run the risk of accidently yanking wires out, and then trying to figure out where they belong. (Of course, never unplug anything by pulling on the wire or cord!)

--09/11/09

 

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