This months custom electric bike build is from the city of Linz (in Austria, central Europe), and the builders name is Martin. He has put together an absolutely beautiful E-bike and documented it with very well-done pictures (ES username “madin88“). Martin sometimes has to ride in traffic, so he needed something that could keep up to speed safely, and he readily admits this is more of a street moped, rather than a electric bike.

During the research phase, he chose the Votec VR150 DH (Down Hill) frame, because he felt the beefy upper swingarm would handle a lot of torque, and also because it would easily accept custom torque-plates to hold the axle of whichever hubmotor he chose. He was able to find one of these frames in Germany for 600€. This frame is not listed in their public catalog, and it is made from AL7075, which…although it is made from light-weight aluminum alloy, it is almost as strong as some steels. Others who were lucky enough to get a test-ride have said that it feels more like a very light motorcycle, rather than a heavy bicycle.

Martin briefly investigated the well-regarded Crown motor from Crystalyte, but in the end he decided to go with the Cromotor, and he is very happy that he did because of its higher power capability, and its greater ability to absorb large heat-spikes safely without damage. This E-bike is capable of 75-k/h (47-MPH). The Cromotor was designed to do this at 72V, but since Martin uses 90V, he can achieve this with lower amps, so…when he is simply cruising through traffic, the massive Cromotor barely gets warm.

In the spring of 2014, Martin will attempt to get his E-bike to pass the state Moped inspection (in Austria, it is called the TÜV), which will allow him to legally ride in the street all the time, with a license-plate, insurance, and registration.



It’s not light, but it has the high-powered street performance that Martin needed for his commute.


The wheels are double-wall 20″ BMX rims with 2.5-inch wide  / 16″ Moped tires. Spokes are 13-Ga front and 12-Ga at the back. The back rim is custom-drilled to make the steep spoke angle possible, so the Cromotor could be fitted in a very beefy GSPORT Ribcage 20-inch rim while still having a cross-lace pattern (94mm-95mm length spokes, with 4.5mm nipples in 5mm holes, 12-Ga stainless steel Sapim spokes from Volt Riders in Missouri, a partner with Holmes Hobbies).


The Cromotor has proven to be an efficient, powerful, and reliable product. Also, using a heavy-duty 20-inch BMX rim with a moped tire (like Martin) is becoming very common on hot-rod E-bike builds

The Cromotor has proven to be an efficient, powerful, and reliable product. Also, using a heavy-duty 20-inch BMX rim with a moped tire (like Martin here) is becoming very common on hot-rod E-bike builds


Martin specifically chose a full-suspension frame that is very strong, but he also made certain it was a frame that would easily accept custom drop-out adapters. He designed these, and had them CNC-milled to allow the Cromotor to fit perfectly.



Martins custom drop-out adapters made on a CNC mill.


These custom drop-outs were needed to fit the Cromotor onto a

These custom drop-outs were needed to fit the Cromotor onto this frame.



Here’s a close-up of the left-side drop-out, along with the excellent Shimano Saint 4-piston hydraulic disc brakes.



The brake discs are 203mm front and back. The Rock Shox Boxxer fork provides 200mm of travel, and works quite well. Although, he now wishes he had gotten a dual-disk fork so the front brakes would run cooler, such as the  DNM-USD8, or the Kowa GF



Martin could not find a battery pack that he liked, so he decided to build his own, using the finest available components. He selected the excellent Sony VTC4 cell, in the 18650 cylindrical format (18mm diameter, 65mm long). When fully charged to the recommended voltage of 4.10V per cell…this 22S / 9P pack provides 90V and 18.9-Ah. The US18650VTC4 cells have 2100mAh capacity each, and are rated for a max output of 30A, which is an incredible 15C current-rate.



I much prefer spot-welding tabs to individual cells, since there is a danger of damaging one or two cells in the middle of a pack when you are using the high heat of a soldering iron. Soldering a pack together is a delicate balance. You must have a large-tipped iron (100W minimum) with enough mass so that it does not cool down quickly as soon as it touches the connection. But…if you touch the connection for just one second too long, some of the internal electrolyte will be damaged from the heat.



Here is what the naked sub-packs look like.



The technical data for this Sony cell claims it does not need to be balance-charged, but Martin included the balance-taps (the white plugs with blue wires) so he can check the voltage of each individual parallel string if he wants. The 5.5mm bullet-connectors worked well for him on other projects, but for this amount of amperage, he chose to double them, rather than use a larger connector.


Martins initial battery pack was a large single unit mounted just in front of the handle-bars. It worked well, but…he was told by an experienced friend that if he mounted the pack to the frame, it would improve the handling of the bike. He had also decided to increase the size of the pack, so…he ended up with the two water-proof Pelican cases in their current location. Says Martin: “Overall it’s now about 28cm (11″) wide…I have to spread my knees a bit, but its not uncomfortable. Better this way than one heavy case at the handlebar I think…”


This battery case configuration is unconventional, but it works well for Martin

His first battery pack is shown on the left in one of the well-regarded water-proof Pelican cases. The final battery case configuration on the right is unconventional, but it works well for Martin. It provides the large battery volume needed to get the volts and amp-hours needed to achieve the top-speed and hard acceleration he desired.



With the side case open, you can see the ends of the cylindrical cells, the balance-taps (if he ever wants to balance charge the packs), and also the foam blocks that keep everything firmly secure, so the parts don’t jostle around,



Martin started out with a Lyen 18-FET controller. It was set to 100A phase-amps and 60A from the battery (about 5-kW), and it was limited by the Cycle Analyst V3 from Martin was beefing up the internal components of the controller to allow it to run high amps as cool as possible, but…a fatal mistake by him caused a catastrophic short.

About this time he had become interested in how sine-wave controllers can operate a system with more efficiency, while also allowing a hub-motor to run more quietly. He decided to experiment with the new Max-E sinewave controller from Adaptto, a Russian electronics company.



Here is the Max-E sine-wave controller from Adaptto in Russia. It does not require a laptop computer to program, but the included proprietary control panel is a requirement. It is capable of temporary power peaks of 12-kW.


We are impressed by the feature-set of the Adaptto controllers, but we are waiting for more builders to report back before we make any claims about them (also used by ES member andreym), however…the initial reports are good so far. They currently make two models; the Min-E 65A 12-FET, and the Max-E 140A 18-FET using  TO-247′s.

They both are rated to operate 24V-100v systems, and they are currently developing upgraded models to run up to 150V. Their respective prices are listed at approximately $450 and $750 (depending on the exchange rate to the Ruble), and are only available right now through (here is the Google-translate version of the controller page in English). These controllers have a desirable torque-throttle mode, and they can run sensored or sensorless, plus they can auto-detect the hall sensor sequence (among many other features).

These controllers also have an anti-roll option, which shorts the motor phases to make it unable to be pedaled. You might be able to lift the E-bike to steal it (and it is quite heavy), but you cannot ride it away. You can find more detailed information about these controllers in this discussion thread.

This controller allowed him to program-in 100A battery, and 200A phase-current, and as a result…when he disables the throttle-ramping, his E-bike easily wheelies if he wants.

Martin was pleased with the affordable price, open-source nature, and easy ability to modify the Lyen controller, along with the excellent Cycle-Analyst, but once he used the Adaptto controller system, he feels the higher price is worth it to him, for this application: “…With the sine wave and torque throttle mode, its a dream and a very comfortable and silent bike, I like it!…”



The multi-function electrical junction box.


Between the battery packs and the controller, Martin made and installed an electrical junction-box with a anti-spark circuit (high voltage systems create a large spark when you plug them in), which was designed by long-time ES member Fechter. He also included four low-ESR capacitors to smooth out any voltage spikes and voltage ripple. The socket on the side is the port for the charger to be plugged in. It also houses four FET’s (IRFP4468pbf’s, four of these can easily handle 100A continuous) which turn on the power to the whole system, and are activated by a low-amp keyswitch on the handlebars . The bullet-connectors shown are 7mm.



Here you can see the perspective of the rider, with the 11-inch wide battery cases (28cm). The two red switches are for the moped horn, and the lights. The gray rocker switch is for the turn signals.



This mounting clamp is from a fender Martin found, he liked it and used it to mount the tail-light, red reflector, and the turn signals.


The original build thread can be found here

Written by Ron/Spinningmagnets, January 2014