Assembly: Battery Centering

Assembly: Battery Centering

The final step in the assembly of my Crazyflie was mounting the battery. It’s a simple thing, the battery mount, a square of double-sided mounting tape, a small 170mAh LiPo battery and a short two-wire connector. Easy as pie. But… The battery needs to be centered for a perfectly balanced airframe. The question is, how to go about achieving that quickly and simply? I thought I’d found an answer, but maybe it was just a pipe dream.

In my “vision” I pictured a device capable of allowing me to center the battery just right and achieve exceptional balance. In my reality I created a contraption that seemingly worked, but it may have just been dumb luck. Who was I to question results?
level oneI thought about using levels to set up a jig and then using the jig to balance the Crazyflie as I fine tuned the battery placement. I tried to put together a tool like I’d thought about it. What I made was probably more of a contraption than anything else. I did use levels though and I was able to verify with them that the surface I was using to balance the Crazyflie was quite level. Before I put this contraption together, I’d thought of a few different approaches. One of them was to use thread to hang the PCB by the mechanical mounting holes at the corners of the Crazyflie. I’m not really sure how that would have even worked actually (like a plumb bob maybe?). It was an idea I didn’t pursue. I’d also thought about trying to balance the PCB on a point of some sort and then striking a good, balanced battery position from that. It was another idea I had no clue how to execute on so I gave it up. The final stroke of genius is what’s pictured here. My balancing jig.

level twoIt’s set on a marble countertop that’s fortunately quite level. The “mount” is a standard woodworking level and I have two wood dowels (I guess they’re straight and true) taped (hey, it was good strong duct tape) to the level. I verified the dowels were level by using a miniature picture hanging level and I verified the “mount” level was level using that same level (I don’t sound very “level” headed here, do I?). Finally, I set the Crazyflie on the dowels, making sure the curved underside of the motor mounts were in contact with the wood. This made it quite hard to maintain balance and it was what I had intended — my thought process being that: if the Crazyflie doesn’t tip to one side or the other, it is balanced. I made the measurement on two axes and it actually seemed to work.

When time came to “set” the battery, I simply stuck a piece of the provided double-stick mounting tape to the battery and lightly set it on the PCB. I kept moving it ever so slightly until I could achieve (and maintain) the balance I’d verified existed without the battery. It didn’t take long and the results seemed to be pretty accurate. When I was confident the battery was centered, I pressed it down on the PCB to “seat” the mounting tape.

balance jigGiven that I didn’t need to adjust pitch or roll trim at all during my first flight seems to have confirmed that I got it right! Looking at the contraption I made however, still makes me wonder if it wasn’t just dumb luck though. Oh well, whatever works!!

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