Hi guys, we have just read your discussions about our e-truck and that there is maybe a lack of information. Thus we will give you more details about the technic.
We know that the whole truck indicators sounds too crazy, so it is difficult for us to demonstrate the benefits. We try to explain the whole truck with calculation examples and support it with videos - if our truck is back from an exhibition in Berlin.
First about the batteries: Fundamentally the energy and the power of a cell goes opposite. So for range we need energy, and for acceleration we need current. To combine range and acceleration (especially needed at the drive up) in one cell, we develop a serial / parallel switch to have 2S2P for high torque and acceleration at low speed and 4S1P for high speed. Four batteries are integrated in each hanger of the truck. So we have in two trucks 8 cells in sum. We use the new industrial cell size 2170(0) to get almost the latest and best cells for the truck. At the beginning we tested our trucks with the LG HG2 (18650, 20A continuous, 3 Ah) and had very good results regarding acceleration and good regarding range. Now we test the Panasonic NCR20700B (2070(0), 15A continuous, 4,25 Ah), cause the focus is to increase the range. With this cell we generate a conservative calculated capacity of 100 Wh with a moderate cycle life. At this point we haven’t consider the new 2170(0) cells, which will be available very soon.
EMC The cells are directly mounted on our PCB inside the truck. So we have a very short distance between cells, EMC and Motor and have only one plug between the PCB and the motorphases. So the wire losses are minimal. We use a four layer PCB with 70 µm cooper, so there is for every single motorphase a own PCB layer with lowest resistance. We tested the PCB successful with 30 Amps (temp rise at 20 A is about 7° C). We have at both ends our motormosfets with a low RDSon of 1 mOhm and a QGD of 13,5 nC for highest efficient. We have never made a compromise between cost and quality, we almost take the best for the best result (OK, no silverwinding ;)) The PCB includes:
- for each motor a mosfet circuit with driver, a back emf measurement, current measurement and capacitor bank
- a balancer circuit for each cell with voltage measurement and total current measurement
- a cell switch 2S2P <-> 4S1P, to have till about half of speed high torque or if the torque is not required a quarter of the cell losses. example, 10 km/h and 10A for each motor, 20 mOhm cell resistance 4S1P: (20 A)² x 4 x 20 mOhm = 32 W cell loss 2S2P 2 x (10 A)² x 2 x 20 mOhm = 8 W cell loss so the controller switches if possible in 2S2P to reduce internal losses.
- an automatic on/off switch with self holding (using the voltage from a rotating motor to switch the circuit on at about 2-3 km/h)
- a DC powerline communication, to communicate and power the PCB in the baseplate with only one power pogopin (mass connection goes through the housing like in a car) so you can mount the hanger in the baseplate without plug a cable.
- a high-performance, low-power 32-bit controller with 50 MHz to manage all the tasks
- and other stuff like voltage regulators and temperature measurement. All parts are under 1 mm height and so the total PCB height with parts is max. 1,8 mm.
Motor We use an ironless permanently excited synchronous machine. This kind of motor has following benefits:
- no cogging and very less eddy currents, cause of the less iron in the stator and the thin lamination. We want to use the e-truck like a normal truck, so we don’t want to use electric energy for freewheeling. This is the only permanently excited synchronous machine who can do this. Other possible motors for freewheeling are without magnets, like reluctant- or asynchron. But these types are heavier at the same power and have no ideal powercurve for our application.
- best ratio of weight to torque (in hub configuration without gearbox) cause of the less iron which is needed to close the magnetic circuit.
- high efficiency, in our manufacturing process we press the cooper winding with high pressure on the stator and get a coil resistance of 50 mOhm of each phase! In one motor we generate a torque of 0,06 Nm / A. The three motorphases would be automatic connected by putting the stator on the truck, so you haven’t connect the motor with a cable.
In sum we get a very high system efficiency, which generates less heat and more range!
PCB Baseplate In the baseplate we include a second PCB. This small PCB includes the following features:
- powerline communication with the hanger PCB, cause the hanger PCB is inside a faraday cage and can’t send via bluetooth.
- communication via Bluetooth with the second truck, the remote and possible with a smartphone or -watch
- handle the USB PD protocol to unlock the PD charger. We can charge the e-truck with profile 4 and 5, this means 3 A @ 20 V or 5 A @ 20 V (look for further Information at USB Power Delivery)
- Charge inductively the e-truck. We integrated in the cover a primary Qi coil. With this coil the board could be charged inductive. The holder is under development, but other tasks have actual higher priority.
- As gadget you can charge your qi-able phone if the truck is drop through mounted, otherwise you can charge via the type C connector. Both connections are limited with 5 V @ 1 A. We see this connection as a emergency charge station, to take a call.
- NFC chip for fast Smartphone connection and fast Truck profiling
Truck housing The truck itself is made of a high quality aluminum alloying, which is normally used in automotive axis. Unsuccessful we tried to break it with a 2 t car jack. The truck is housing and cools the rest of the motor and electronics.