We have been working on a few things here at Defiant lately. We’ve already mentioned the AT wheels and the belt drives we’re working on. But we’re also working on a much less expensive alternative to the Davega dashboard we use for our boards. Currently these dashboards are feature rich and display a ton of different information, with speed, trip, and battery level on the first screen just to name a few things. But these devices add significantly to the cost of the boards and our retail price is something we hear a lot about.
With that in mind we thought we’d see what we could come up with to display just the most important info you need: your battery level. Obviously our boards have a level of polish that we’d like to preserve, so whatever we designed needed to fall in line with that. We wanted something elegant and simple, but we also wanted compatibility not only with the motor controllers we’re using but any VESC based motor controller, and at almost any cell count. We use 12S packs at the moment, but we may decide to go higher in the future. We also want to make these available to DIYers and have them work reasonably well out of the box and provide some kind of firmware update process for when we have to make adjustments.
What we came up with was a simple and bright eight LED display integrated into the x-plate over the front truck that shows charge level right on the front of the board where the Davega would be. It’s a small PCB that attaches to the bottom of the plate and shines its LEDs through light pipes that are flush with the top surface. It connects to the VESC based motor controller via UART and reads the battery percentage data, then converts that data for display across the eight lights. When all the lights are on the pack is full, and when they’re off or it’s blinking the pack low or within cutoff range and the board is about to turn itself off to protect the battery from over discharge.
We’ve been working on this idea for a few months now, and it’s great to finally see a prototype working. So what were some of the challenges we faced? Well first of all we needed this to work well in spite of all the variance between VESC based controllers and other variables. Different controllers read slightly different battery levels, meaning we had to work in some reasonable margins of error. On top of that, the math in vesc based controllers is based on 4.2v cell charge maximums, which nobody sane uses. Most BMSs will cut the charge off around 4.15v for safety and cell longevity reasons, so with that math the pack will never be full. In addition, a fully charged pack may read slightly different voltages day to day anyway because of things like air pressure and temperature, and due to tiny drains some ESCs put on the pack while sleeping a board might read full off the charger then not so full some time later before its ridden.
We’re continuing to work through these issues and adjust the display accordingly. Fortunately firmware updates are a straightforward process via USB, so we’ll be able to adjust further after production based on feedback and user experiences across different ESCs and cell counts.
In conclusion, we’re very excited about this fuel gauge and hope to have them in production very soon. We’ll keep you updated. In the meantime, happy riding!