It’s time to show you guys what we’re working on. We’ve changed the DiffTrike a little bit, put a new seat back that is more comfortable and robust. And it even has the feminine touch of macramé ropes. 😉 (click to view original size)
The seat back is a freecycled automotive child seat. The back is attached to the structure of the Trike by a couple of hinges, so that the angle of leaning can be adjusted by adjusting the length of rope. This helps us manage not just the comfort of the rider but also the mass centre placement in relationship to the main axle. We’ve also integrated the joystick into the right hand side of the Trike after a few ergonomic tests. It’s actually quite comfortable! 🙂 You can also see the battery pack box (long black thing in the middle), the main controller box (dark gray thing with an antenna sticking out, right in front of the seat), and the GPS antenna at the front end of the Trike.
Now a close-up of the battery pack insides. We’re using the lithium-ion battery pack from an electric bicycle. The pack died a somewhat sudden death after about 8 months of normal usage, it just refused to let me use its charge. It turns out that the charger that was supplied with the bicycle has a charging voltage of 42V, but the cell chemistry (NCM) only allows a maximum of 4.1V per cell. And since there are 10 cells in this pack, each got 4.2V at the end of each charging. Talk about planned obsolescence!! I don’t know who screwed up, the Chinese supplier or the Portuguese integrator. Of course, the guarantee for lithium packs nowadays ends at 6 months (and now you know why). 😦
Anyway, you can see the 3 first cells on the left side are slightly bloated; these no longer hold any useful charge (I tested them). So, I’ve wired the pack to be charged through 10 cells just the way it was, but to be discharged from only 7 cells, yielding full power at 25.2V (3.6×7) instead of no power at 36V (3.6×10). Which is close enough to the rated 24V of the motors (lucky bastard). I removed the part of the BMS circuit that cuts the power supply when some trouble criteria is met, and I left in the voltage-balancing part to help during charging. One of these days we’ll have to hack the charger down to 28.7V (4.1×7) too. The over-current protection will be implemented in software – which is just fine in this early stage proof of concept.
So now, on to the main dish: the controller. We freecycled a cable modem case and glued and screwed-in the following items: one Neo Freerunner GTA02 motherboard, one 5V DC-DC switched converter made by NJay, one Wifi antenna freecycled from a wifi router, one USB female plug, one big-ass retro-style power switch, and a handful of spaghetti wiring. Oh, and an external GPS antenna.
Here’s a close-up for you. It looks messy, but that’s just looks. It’s actually very well organised. 😉 The external wifi antenna improves wifi remote monitoring from the laptop by several orders of magnitude, so it is a very cool addition.
On the top left corner is the DC-DC 5V converter; on the lower right corner is the GTA02 board with 2 cables coming in at the top edge: a USB power supply / connection to the joystick, and a coaxial from the GPS antenna; On the top right you can barely see the butt of the wifi antenna and its thin cable; and at the top centre, hidden behind the GPS cable, you can see a few solderings that hold a couple of pull-down resistors on the USB data lines, as well as the 5V power distribution from the DC-DC board to the GTA02 and to the Joystick. The GTA02 has also a few wires sticking out (brown, brown/white, red), which are the current implementation of the I²C bus connection to NJay’s power controllers (not in picture).
And now, a sneak peak into the much anticipated power controllers NJay is building for the motors:
This baby has been in labour for almost 5 months and over 38 hours of development and testing have been logged to this task. Why buy something simple when you can build something complicated?! 🙂 Anyway, we’re all sitting at the edge of our seats while waiting for NJay to finish preliminary fire-up tests so that we can get to real-life testing with all the gear on the Trike.
And then, it’ll be like the other guy said: “I feel the need… the need for speed!!!” 🙂