Intro: Solar Powered Festival Cart
The bulk of my festival experience is at Burning Man, which is really quite a unique animal in many respects - not the least of which is you get to drive to your camping spot, complete with whatever trailer or monstrosity you can attach to your vehicle. It's also long, and big, and centered around creating huge and outlandish things... so I'm used to bringing a LOT of stuff to party with. In 2016 my wife bought us tickets to go to the Lucidiy-Crossroads festival, which is much smaller, was sold out of car camping passes, and would require us to haul everything we brought from the parking lot to our camping area. Clearly I needed to minimize what I was bringing; but I have some very cool festival toys that I really didn't want to leave behind. I needed a way to charge batteries, and haul my easy-up and some heavy, bulky costumes. I needed a secure place to lock up my electronics at night, and ideally it would look sweet and be fun to make.
Enter the festival cart. This is basically a wagon that's been hitting the gym, and has some cyborg upgrades that currently include a solar panel, USB charger, Inverter, and a 12v lighter socket. Future plans are to upgrade with a wheelchair motor so it drives itself, but we'll cross that bridge when we get there.
Project cost was about $350, but could be done much cheaper with some craigslisting, or omitting some features.
Step 1: Things You'll Need
I imagine every builder putting their unique spin on this, so I won't be too prescriptive. The basic elements you'll need:
Chassis: I used a Gorilla Carts 1200lb dump cart. I initially was going to build my own from scratch to suit the purpose, but this cart is $130 on amazon, and it's got all kinds of sticky details already figured out for you like ackerman steering, and the dumping bed (which I didn't think I wanted, but ended up taking advantage of). I did end up modifying this cart by lengthening it about a foot, but you could just build a smaller cart if you don't want to do this.
Box: I wanted an enclosed space I could lock at night to keep my battery chargers, lithium cells, camera, wallet, etc. in rather than just an open bedded wagon for hauling stuff. I made the box from 1/2" sanded pine plywood and 2x2 studs from home depot.
Batteries: One of the main functions of my cart was to provide power to charge my phone, camera, and the batteries for some of my other frivolous toys like my 75w led coat (instructable to come). As such I needed some pretty decent batteries. Weight not being a major concern, I went with sealed lead acid batteries designed to power electric wheelchairs. These are WAY cheaper online than in a mobility store - mine were $40 each from amazon for 20Ah cells, and I went with three of them (though there's room to expand later).
Solar Panel & Charge Controller: I didn't have faith that the three batteries alone would bring enough juice to keep me going all weekend, and I didn't want to be fiddling with charging the batteries up between events and so on, so I put a 50w ALIKO panel on top to keep the batteries charged (and it worked like a charm, despite the cloudy weather). You'll also need a charge controller with a solar panel.
Hardware Etc: The stuff that always seems to hold up a project right at the end because I forget to buy it or assume I can get it at the hardware store and then can't. Things like:
- Bolts to hold the bumper on
- Electrical Connectors
I really wanted to replace the back wheels with wheelchair motors. Some manufacturers of electric wheelchairs make their motor units a simple bolt-on block with a 10" tire already mounted to the motor shaft, so that building a drive train is as simple as making a bracket to bolt this unit to. Pairs of these are available on ebay from $60-$200. Add in a motor driver and a throttle and you could sit on the front of the cart and drive it, rather than pulling it around like a chump!
Step 2: Assemble Your Chassis
For this project, I started by assembling the gorilla cart out of the box and scratching my chin for a few weeks. I liked how easy it was to put together and how rugged it was, but the bin on top wasted a lot of space as far as I was concerned, and sat way up high. I wanted more weight down low, I wanted it to be longer, and I thought a rectangular cuboid shape would give me the most internal space.
So, the bin had to go, and I cut the main frame rails and welded a section of 1" box iron in place to lengthen the chassis out to accommodate a 48" box. Doing it this way left the dump mechanism intact, which I would have to figure out how to take advantage of later, I just didn't want to ruin it yet if I didn't have to.
Step 3: Build a Box
This is really quite self explanatory and simple; I didn't really spend much time designing this up, which is really unusual for me - I usually draw for weeks before I build. Anyway this step was really just about as simple as it sounds. I laid a roughly 2' x 4' board on the chassis and went from there. Because I was using 1/2" plywood, which doesn't really lend itself well to holding screws driven into its edges, I put 2x2 dimensional lumber on the insides of all the corner joints and screwed to that with a healthy dose of wood glue mainly because I like to overdo everything.
I re-used the mounting holes that the original bin had used, which are all at the back, so that the box is only attached to the small sub-frame at the back of the cart. This is done because that sub frame is the dump mechanism. The front attaches to a locking mechanism (You can see the tops of the bolts in one of the photos above. The underside is shown further down in the photos with the battery box) that latches to the frame, so when the box is down it is secured at the front and back, but when you release the locking mechanism at the front, you can lift the box up, exposing the chassis. At this point this probably seems kind of useless, as the box is fully enclosed and can't really be dumped, but remember I need to put some heavy SLA batteries somewhere, and there is quite a bit of room in the chassis I can use for this.
Note: I made the sides of my box hang down about 6" past the "floor" of the box, to hide the battery box I was going to put in the chassis; also I thought it looked better to have fairing around the chassis. This fairing rubbed on the wheels though, and I needed to cut out fender wells for the wheels to clear. I think it looks better with the wheel wells anyway.
You can see I was also getting excited about the solar panel and had to mock it up just for giggles.
Step 4: Build the Battery Box
I don't have a lot of pictures of this , because it's kind of boring and simple. The chassis frame rails sit about 15" above the ground, and the batteries I chose are around 7" tall, so I reasoned I would make the box 7.5" tall (inside) and 14.5" x 14.5" square, because that's about all the room I had in the chassis to fit between the rails, and stay forward of the dump mechanism.
To hold the batteries in place, I glued a 2x2 lip to the bottom of the box just the right size to prevent the batteries from sliding anywhere, and then I took some metal strapping and tightened it down over the top of the batteries until snug. If using this method take care not to tighten it too much or you could damage the battery casing.
Note: It's not shown in any of the photos, but I bent some steel straps into brackets to support the bottom of the box. These batteries are heavy and I didn't want to take any risks, so I welded these straps to the frame where they go down around the bottom of the box and back up and are fastened to the wood with screws.
For wiring, I'm blessed enough to have a ton of leftover heavy gauge wiring from my old job and a couple of decades of old projects, so I used 6awg stranded wire with heavy duty crimp terminals. If I was buying materials from the hardware store I probably would have used 8awg and standard terminals to no ill effect. The three batteries are wired in parallel (+ connected to + connected to +, - connected to - connected to -).
In one of the photos above I'm using the batteries to power my Lithium Ion charger... that's unrelated to this project but I used the photo to show:
- The 12V ATX "Maxi" fuse holder. I used a Maxi fuse holder because I had one, and also because if I do put motors on this thing, there is the potential to need a lot of current and I wanted the expansion capacity. WARNING - Don't skip this. Each of those batteries can put out over 100A if shorted. That kind of power will cause you to have a very bad day if discharged accidentally.
- How I routed power out through the plywood. There isn't room to just run a cable over the lip of the box, and I wanted to put terminals on the outside of the box, so I can connect this and that to it easily. For example the lithium battery charger shown above connects with alligator clips. Having terminals on the outside of the box allows me to connect the charger to the terminals and leave it without leaving the box in the upright position. I've also included a sketch of how these terminals are made. I've done this on a number of projects and it's one of my favorite ways to create simple, cheap terminals on the side of a power box that can carry a lot of current in a pinch. WARNING - These terminals are exposed on the outside and susceptible to being shorted! This is another reason it's very important to have a fused connection at the battery. If I touched a wrench across these terminals with no fuse, it would create a dangerous arc flash and possibly a fire.
Step 5: Fit Up & Wire Solar Panel & Outlets
Mounting Solar Panel: The solar panel turned out to be exactly the right size to be framed in by 2x2's, which provides a nice bit of extra protection for it. I used a 2" hole saw to make a hole for the wires to drop into the box (make sure the hole is near the hinge side of the lid, so the wires don't get in the way when you open the lid). To hold the panel down, I clipped 1/4" UNC U-nuts over the aluminum frame of the panel where there were already mounting holes drilled. I then carefully pushed the panel into place, pulling the wires through, and screwed 1/4-20 bolts in from the underside (obviously after drilling holes for them).
As an added protective feature, I stacked scraps of wood under the solar panel to snugly fill the air space between the lid and the back of the PV cells. I did this so that if someone puts a heavy object (like a human derriere) on top of the glass, there will be some support underneath instead of the full load going on the thin glass.
Power Outlet: The outlet I used is a 3 in 1 unit with a slick voltage readout, 2x 5v USB charger outlets, and 1x 12V lighter socket, available here. To mount the outlet, I actually recessed it by making a cutout slightly larger than the outlet bezel, and then glued another piece of plywood to the inside. This protects the outlet a bit, and saves me the frustration of getting it caught on things. Also I'll admit here that I screwed up the original cutout for the sockets to go through, and so I had to do this to make it work - but it worked out better this way anyway so - serendipitous sweetness.
Solar Charge Controller: I used a cheap waterproof 5A unit from Amazon. Unfortunately it doesn't come with any mounting hardware, so I just spliced it in and told myself I'd mount it later... which is an adorable white lie.
Wiring: I didn't want wires running all over the place, so I put the solar panel wires and the outlet in the same corner of the cart, and spliced all the wires together in that corner so I would only need to run two conductors back to the battery box. Running these wires back to the box was a bit of a sticking point in itself and I'll cover it in the next step - suffice it to say you don't want to run any more than you have to.
Step 6: Connect the Electrical Stuff to the Battery
Now, the trick here is ye olde dump mechanism. There is relative movement between the main box and the battery box when the dump mechanism is used, so I had to run the wires where they wouldn't get pinched, stretched, or otherwise messed up. The way I did this was to run the wires out the bottom, and along the underside of the floor, looping around to fasten them in the middle of the sub-frame. All these pieces are bolted together and do not move relative to one another, so we're fine so far. The reason for the weird routing was to get to a point that only moved a little bit when the dump mechanism is used. This point on the floor moves the least with respect to the battery box, and so it was the ideal place to fasten the wiring to the box before it makes the free air leap over to the battery terminals.
Step 7: Make It Sexy
Flame Finishing: I really wanted the grain to stand out, as it had a cool pattern. I started looking around for ways to do this and instantly hit on flame finishing. This is a very cool and very easy way to put a very cool finish on your woodwork projects. This pine plywood is not very dense, and the difference in density between the spring grain and autumn grain is significant enough that if you expose the wood to flame for a brief moment, the soft grain carbonizes but the harder grain does not.
Basically you take a propane torch and slowly run it over the wood. It takes a little bit of practice to get the technique and work out how long to expose each section. I suggest starting with quick, brief exposure and going over areas that don't get dark enough for you. Doing the whole box took me a couple of hours, and I think it was well worth it.
Stain: I really wanted a fire engine red stain. Like I would have been willing to go over the whole cart with a big red sharpie if I'd had time, but I settled on this wine colored stain I found at the hardware store, and I think it came out pretty well.
Paint: The thing about plywood is the edges look like crap, unless you get very expensive ply and spend the time to properly seal and sand the edges. I didn't have this kind of time on my hands, so I took some black spraypaint and feathered in all the edges. I think it goes well with the overall "scorched" color scheme, and it hides all the screw heads and imperfections in the edges. While I was at it, I painted the steel where I'd welded it.
Lights: OK, the lights were a step too far perhaps. I had some red strip lights laying around and I thought it would be cool. I stuck them on in such a rush though and it shows. I didn't have time to mount a switch or anything so I haven't even ended up using these. These adhesive backed strip lights are also kind of garbage because as they warm up, they expand and wrinkle, pulling off the adhesive and falling off.
Step 8: Hardware Etc
Hinges: I used a router to flush mount the hinges as you can see in the photo showing the solar panel connectors - this is optional but it gives you a nice firm contact around the rim of the lid when its closed.
Locks & Hasps: I wanted to store valuables in here, so I used some cheap galvanized lock hasps from the hardware store, and a pair of master locks from a set I have that all use the same key. Protip - I used a carabiner to hang a spare key under the chassis, inside the battery box in case I lost my key to the padlocks.
Bumper: When I lifted up the box, the way this cart is originally designed, the chassis touches the tires right around when all the dirt or yard waste or whatever would be sliding out of the original top bin. Because I mounted a large, ungainly box on the cart now instead of a dump box, the frame touching the back tires was now the end stop for standing up the box. This was kind of unstable, and squashed the tires to the point of being a concern. I added a 1.5" thick bumper to the back to the cart so when I lift up the box, the bumper hits the ground before the tires get squashed too badly.
Lid Stays: Opening the lid and letting it flop over to be held up by the hinges works, but it damages the paint, and eventually will tear the hinges out. I wanted to be able to open the larger lid with the solar panel on it to various angles to catch the sun if I wanted to, but also to open all the way over to be a table of sorts while I was messing around with the contents of the main box. To do this I just cut a steel bar and welded a nut and bolt to one end, and a big washer to the other end. The washer end got bolted to the main box with a lag bolt, and then I drilled several holes along the edge of the lid, so I can open the lid and push the bolt into one of the holes and it will hold the lid open there. I just made sure one of the holes was in the right place for the stay to go when the lid was closed, one was in the right place for it to be open at 180 degrees like a table, and a few in between.
The front lid doesn't need a stay, as I can open it and use the wagon pull handle to prop it on.
Step 9: Future Improvements
Motors: As I mentioned earlier I would really like to motorize this with some electric wheelchair motors. This may require adding a couple more batteries, and I made sure to only use screws (no glue) in the front part of the box. This is so I can take the front off and rig up a drivers seat in the front 18" of the cart. I have some grand plans to use the trailer hitch that's built into the pull mechanism to hook this up to my tricycle, and get the cart to push the trike. This may be reeeaaally unstable, but you never know unless you try, right?
Lights: I like to light my projects up. The red lights shown were a serious midnight afterthought before Lucidity. I'd like to put some RGB strip lights under the box and hook in a cheap music reactive controller so the lights flash and change color with any ambient music. It's worth mentioning that I have a portable solar powered stereo system I also like to bring out to festivals, so the two working together would be great!