Double Pedals allow you to hit the bass drum twice as fast as you could with just one foot.
A double pedal setup has a normal looking pedal and a second pedal that can hold two beaters. However only one is moved by pressing down on the pedal. The other has to be moved by connecting it to the first one and thats where a solid, extensible drive shaft comes in.
Normally you would buy the complete package of two pedals with beaters and the drive shaft as one thing.
In my case I got two Tama double bass drum pedals second hand as part of a second hand Yamaha drum kit and the connector rod was missing.
Having spent about AU$600 or about US$430 (Feb 2016) for the Yamaha kit, I didn't want to spend the same again for a connector. I found some good looking new ones for about US$200 and second hand for maybe US$80 but wasn't sure they would fit.
Thinking about it a but more, I felt I could make one for much less. It kind of became a competition.
I first started planning to use a chrome vanadium 1/4" universal joint (used for spark plug removal and other tight working environments). But due to the cost of buying 2 (about $10-15 each) multiple cobalt tipped drills and drilling oil and fuss, I felt there had to be a better way.
This method is cheap, reliable, and only takes a few hours max, including trips to the hardware store, if you know what you are doing and have the right tools.
As I had the tools and I valued my time at $0/hour, it only cost me about AU$7 (US$5). That's a bargain folks, and there's few in music like that.
Step 1: Check and Measure Your Pedals and Plan the Distance Between Them
This is critical. The nodules on the side formed by the axis sticking out of the side of the pedals is where you are going to join these boys together.
Measure the diameter of them, notice the shape (mine were round but had two flat edges at right angles and it was clear these were used to clamp onto the drive shaft. Mine stuck out 1cm (about 0.4 of an inch).
Move stands out of the way to allow you to put the pedals down. Imagine them connected and make sure you have enough room. Measure the approximate distance between them. Allow about an extra 5cm (2 inches) more, especially if there isn't a clear straight path between the pedals due to the snare drum stand etc.
A big benefit of this approach is that you have much more flexibility than the hard shafts normally used.
Step 2: Buy the Parts You Need
Buy a flexible water pipe made of braided stainless steel.
If in the US you can buy this in home depot:
Model # 7223-16-12-1 Internet # 203082343 Store SKU # 405221
I bought mine at a national chain in Australia called Bunnings.
You can buy them in a range of sizes. I bought one at 450mm. The US one above is 500mm (20 inches).
The length you buy is based on your measurements in step one.
In addition to the connector, you need two brass adaptors that reduce the large pipe connector ends down to the be just larger than the diameter of the nodules that stick out of the pedals.
In my case they were about 8mm in diameter. The threaded brass adaptors I bought reduce the ends of the connector from 15mm diameter to 10mm diameter.
You also need some 4 small screws designed for metal work with flat ends (i.e. not with a point on the end). Probably length is not critical but allow the internal diameter of the pipe is a good rule.
For tools you really need a drill press to drill 4 holes nicely in the threaded brass adaptors. I found I just couldn't do this by hand drill as the brass is so soft. You will need metal/wood drill bits. An adjustable wrench comes in handy to screw the adaptors onto the ends of the flexible pipe.
You will also need a thread tapper set to tap threads in the holes you will drill. These will hold the screws. The screws will hold the connector on tight and will be drilled at 90 degrees to each other.
I bought some PVC pipe as my concern was the flexible pipe contorting when in use. If it did do that, pedal driving the connector would not be effective, and the beater wouldn't hit the drum. In the end I didn't need it, and it looks much more steam punk without it. If I did need it now, I would actually buy some thinner diameter metal rod cut a little shorter than the flexible pipe, and I would put that into the flexible connector, allowing enough room either end for the pipe to maintain the flexibility. In this way, it would still look steam punk, and also be quite a lot straighter.
Step 3: Tapping the Threads
Once you have drilled two holes at right angles in the smaller end of the adaptors, its time to tap the threads.
My screws were M3, a standard Metric designation that simply means they have 3mm diameter.
I drilled with a 2.5mm drill bit, allowing for the tap to do the rest, cutting away what is needed.
Be careful with this, as brass is so soft you can stuff up the thread. If you do, you still have two or more attempts drilling new holes (as necessary) in the same adaptor without having to buy another one.
I was able to tap by holding the adaptor in a vice, and turning the thread tapper by hand. Of course I am using a 3mm thread tapper.
Just remember, if you have never used a tapper before, you need to use the screw pitch tool which looks like a small pen knife at first, and has a lot of weird teeth that swing out. You run through these until the right one fits snugly into your screw you plan to use. That tells you the pitch of the tapper to use. Mine was 0.5 (or, 0.5mm distance between the threads), so I had to pick an M3 x 0.5 thread tapper.
Step 4: Screw the Screws Into the Adaptors
This should hardly need a step to explain, but watch the softness of the brass. Put the screws in until flush with the inside of the adaptor surface. Screw the adaptors onto the connector pipe and use a wrench. You don't want those guys coming off during a song.
Step 5: Attach the New Drive Shaft to the Pedals.
If you have, as I did, two flat surfaces on an otherwise round nodule at 90 degrees to each other, now is the time to look at where those are and tighten the screws hard and make sure if doesn't move with one hand when holding the pedal down with the other.
Step 6: Placing the New Drive Shaft Into Position
Now is when you realise you didn't measure in step 1 properly, or that you didn't quite have the equipment in the right place in Step 1. Hopefully if you drive shaft is long enough this shouldn't be too much of a problem.
If a longer (or shorter) one would be better now, take it back to Home Depot/Bunnings and swap it.
Now make as much noise as you possible can hitting the pedals one at a time. And relax. You just saved yourself maybe hundreds of dollars.