Teemu chose to build his own battery pack, and his construction methods are something I found to be very interesting. The connection to each 18650-format cell is a spot-welded nickel ribbon, which also carries the small balancing current across the paralleled cells when charging. The high amps of the series current is carried by pure copper bars.
The battery pack is 96V, 26S / 54P. The battery weight is 84-kg (186 lbs), and the power is programmed to cut when the smallest-capacity cell voltage drops to 3.1V.
Teemu reports that his motor is drawing 30-kW (30,000W), and divided by the systems’ 96V, that makes the amps roughly 313A. This means the peak amp-draw is 313A / 54P = 6A per cell. Some of the 18650 cells appear to be my favorite, the Samsung 30Q, using the Lithium-NCA chemistry on the cathode (Nickel, Cobalt, Aluminum). Most likely harvested from cordless tools, and rated for 15A peaks. Approximately 30% of the pack’s cells are new.
The total weight of the entire completed motorcycle is 200kg (441-lbs). The biggest sponsor of the project is Turun Ekotori (located in Turku), where Teemu got most of the battery cells, and also fans to cool the battery.
Teemu reports that the controller still needs adjustment to obtain the max performance that it is capable of. However it now produces a maximum torque of 124-Nm, and the power is 30-kW (roughly 40-HP). The 40-HP figure may seem low, but it is deceiving to gas-bike enthusiasts, because…the 124-Nm of torque is the same rating as a Ducati 600cc at 8,700-RPM’s.
The Duck weighs 408-lbs when loaded with four gallons of gasoline. This means Teemu’s electric motorcycle has the same torque as the Ducati 600cc, with only an extra 33-lbs added. That being said, the E1 doesn’t use any titanium or aluminum in the frame, it’s all steel.
The Custom Frame
This bike has very few purchased parts, and the few that he did buy were used. The forks are from a 1000cc Aprilia, and the rear shock is from a Yamaha of the same size. The wheels are from a Husqvarna supermoto
By using an elevated stay on the swingarm, the chain does not need to have any links broken and re-fitted to swap a chain out. The lattice-style side-frame members are time-consuming to make, but they are light and strong. By focusing the loading-forces onto these side-frame elements, it frees-up the battery box to be made from light aluminum sheets.
”After I created the concept, I used google to see if there was anything similar out there. I didn’t want people to say my bike is a copy. For example, I made the triangular structure of the frame irregular so that it would not be the same as Ducati’s.”
The 30-kW electric motor is a gift from sponsors, and it was mounted onto the front of the swingarm. For home-builders, this is a solution I am seeing more often, and it is one of the features on this build that caught my eye. The ideal location for a motor is in the frame itself, but…doing that is complex and much more difficult. Also, mounting a motor in the frame intrudes into the space that is the most desired for locating as large a battery as possible.
The easiest solution would be to use a large hub motor in the rear wheel (perhaps from Quan Shun / QS, in China), however…that puts all of the weight of the motor into the unsprung mass of the wheel. Locating the motor onto the front of the swingarm (near the pivot) is a great solution to minimizing the weight that the swingarm has to move when the motorcycle hits a bump, while freeing-up as much frame-space as possible for the largest possible battery.
The original article
Here is the link to the original web-magazine article on the RMK E1 for our readers who understand Finnish. The website is called “tekniikka talous” which Google translates as “technology & economy”. A quick scan of their other articles seems to indicate that this site is focused on green energy news.
The Finished model
The professional look of this custom build really impressed me. I have seen some that performed well, but they looked like a garage-built Frankenstein. This one had the extra effort put into it to make it something that I would be proud to own.
Based on the huge response Teemu received from showing the E1, Teemu formed a company called RMK Vehicles. Below is a graphic showing their new design, the RMK E2, which features a hubless rear wheel. Of course, hubless wheels have been around before (especially on custom motorcycles), but…this is the first hubless electric hubmotor I’ve seen.
I am not a fan of the hubless wheel for a production vehicle because I feel it places too much unsprung weight in the wheel. However, I understand the eye-catching appeal, and I wish RMK luck with their new business.