The below is what we came up with, with much starting advice from the band director. I'm documenting it here in case some other band needs something similar, or some street performer or busker can use some help with how to do this.
Here's what it looks like:
It is essentially a hand truck with an amp strapped to it, and the thing above that is the battery unit. The keyboard rests on 4 magnets that are attached to two shelf brackets.
We started with a hand truck. This is one of the cheaper ones we could find, and it is definitely strong enough for all we're doing. It is a bit short, though, for a 6' person standing and playing, so if you are a taller person who will also be standing, you may want to find a slightly taller hand truck, or use some different way to mount the brackets/magnets up higher (which is difficult on this one because the handle bends backward at the bottom of the keyboard here).
We initially spray-painted the hand truck black, but it turns out that doing that, over nice shiny new painted tubes, doesn't work very well, it tends to rub off on hands. So we ended up wrapping everything we could with black electrical tape.
- self-contained: one box that contains the battery, the inverter, and the charging system.
- The UPS we chose (a CyberPower CP1000PFCLCD PFC Sinewave UPS) was chosen especially because it has pure sine wave output, which is important for more sensitive electronics (such as a synthesizer, and the other amp we have that has effects built in). Using these devices with a regular "stepped approximation" inverter can result in poor performance, lots of noise on the audio output, things heating up, and reduction in lifespan of the device, if not outright breakage.
- UPSes have intelligent charging systems: just leave them plugged in when not out in the field, and they'll stay perfectly topped up, and will never overcharge.
- This UPS has a discharge gauge and other displays that help you know how it's doing.
- It is light and small, I still can't believe how much play time we get out of it. (The amp you use and how loud you play it will have everything to do with how long it lasts, so I can't even begin to guess what success you'll have, but we are using here a 50-watt Crate bass amp, turned up mighty far, and at band camp it was used several times a day without issue... at home we tested it about 50% loud, playing demo drum tracks from the synth, and it played continuously for 40 minutes until we couldn't take any more dancing, and it was still at about 80%.)
- This use is definitely means the warranty doesn't apply, so please don't expect (or try to get) any help from that direction if it fails.
- It ships in a fault state (for shipping safety), and must be plugged in before it can be turned on. This is important to know because if it ever faults out in the field, you'll need to plug it in somewhere in order to turn it back on.
- It did fault out a few times when we first started using it, and we found out that it really doesn't like to be laid on its side. Once we turned it upright as you see here, all was well and it had no further problems. No idea why, it doesn't have any moving parts except maybe a relay. We did put feet on it, as you'll see in other pictures, to keep the vents clear on the then-bottom. Hmmm.
- In its default state it beeps every x seconds when it's on battery power... but using the software that comes with it loaded on a computer one time lets you disable that. It does still beep when it's turned on and off, but that's not too bad. You can also disable the beep from the onboard control panel each time you start it up if you wish.
- It will charge when it's plugged in whether it's on or off, so it will spend most of its life off and plugged in in the high school band equipment room.
The Korg Microstation uses just teeny little sips of power compared to the amp.
The straps we used to hold everything together were possibly the hardest part of the whole thing to get right. The system was supposed to be all black, so that immediately limited things. I ended up using:
- lashing straps to keep the amp on the hand truck
- ladderlock straps to keep the UPS on the hand truck
But I don't like them: in this installation (possible because of the small lengths involved) they don't stay tight (especially as this whole thing rattles over bumpy fields and into equipment trailers and over door thresholds, etc.), and I can't even get them as tight as I want in the first place. In one of the first versions of this system we used a ratcheting tie-down, and it worked great, they can get very snug, and stay that way, but it was not black. (I only just now found that one, and may get a couple of those... that one is especially nice because it doesn't have hooks, it's an "endless loop" tie-down, which is better for this short-length use. I will use two for the amp, and one for the UPS.)
Yes, the keyboard is a bit crooked, but you probably would't have noticed it if I hadn't said anything. :-) It's because either the handle is uneven, or the top cross-support (behind the UPS) is crooked, and that's what I used as the guide for where the shelf brackets were installed.
The coil cord in the instrument cord that connects the keyboard to the amp. All the other cords are behind the foam. The foam is there to keep all the cords in, and it seems to work very well even on bumpy ground (and when in motion, the hand truck is tilted back and everything really wants to fall out and throw itself under the wheels). In this image you can also see that I cut the extra length off of the straps, and used a flame to seal the ends of the straps (as per instructions). Then a simple knot was applied to keep the ends from dangling.
The keyboard is held onto the hand truck by two shelf brackets that are screwed to the upright tubes of the hand truck (a screw each in the top and bottom of each side). This was easily done with a standard drill, although drilling holes into 1" diameter tube can be a bit of fun. Then the magnets were bolted to the horizontal section of the brackets. The small ones at the back used the existing holes in the brackets; I had to drill hols for the magnets closest to the hand truck, but it is thin metal and easily done. I used bolts with lock nuts to keep them from shaking loose.
We started with 16# magnets in all four spots, but we bumped up the ones closest to the handle to 25# to provide better grip (one of the things my son must do is pull this on to and off of the field while he's also wearing his quints, so having the keyboard stay on for sure while he pulls it one-handed is important.
 |
| Keyboard leaning against amp with back facing this way |
To give the magnets something to hold on to, we taped big washers to the bottom of the keyboard. I used Gorilla Tape, which is very strong and the right color.The bigger washers for the bigger magnets on the back side of the keyboard needed some extra tape on the left there... if I need to redo anything I'll move the magnets away from the handles a little bit more so the washer fits on the bottom without the tape crawling up the back. Magnets are very much affected by distance... even just putting a layer of tape between the magnets and the washers decreased their strength quite a bit. For example: the 25# magnets held the washers so strongly, when directly applied, that you can't pull them off, you have to slide them until enough of them are sticking out that you can leverage them off. With the tape holding the washers in place, the keyboard can be removed from the mount (with all four magnets in play) easily enough. You've probably noticed this yourself: holding one sheet of paper to the fridge is easy for a given magnet, but add a few more sheets, and gravity wins the battle.
That little strip of tape on the top (back) of the keyboard is to let me son know where to put down the keyboard: when you have that tape right at the upright tube of the hand truck, the washers are directly over the magnets, for maximum strength.
We found that the whole thing was initially a little wobbly when played, so we screwed a piece of wood (painted black) on the very front bottom of the amp, and it props things up enough that it's stable now.