Buying a frame that accepts the Bafang Ultra Max Mid-Drive Motor, and 3 builds

Back in April of 2019, we wrote about an electric fatbike where the owner wanted the new powerful Bafang Ultra Max G510 drive, but…the few frames that came from the factory with it were either too expensive, or didn’t have the features he wanted. So, what’s a man with an angle grinder and a TIG welder supposed to do in that situation? Hack up a perfectly good frame, of course! (click here for that article).

Well, the factories in China that make ebikes with these drives have caught up with the production orders, and first-year exclusivity clauses in the contracts have expired, so now the factories are selling every frame they make direct to the public. One builder in Belgium decided to order a frame that would accept the Ultra Max, and fortunately for us he documented the process.

_____________________________________________

Titanium?

The builder is “Daxxie” in Belgium, and the ebike we are featuring just below is his 7th build. He wanted a titanium frame, so he went to a Chinese website that allowed him to chose the dimensions of the frame, and they built it to order. He bought it on Alibaba, which is the Chinese “Ebay”, so buyer beware. That being said, the factory he chose was BJCSTI (and there are other titanium frame factory options)

Dax: “Parts I ordered for the bike:

Magura MT5 + MT5e (I only want a brake sensor on the rear brake)
203mm and 180mm brake discs. I also found a nice “cheap” secondhand wheelset from DT-Swiss with Fatsno Pro-4 hubs. Sizes 150×15, and 197×12. The wheels came with 4.0-inch wide tires, and I ordered some 4.8’s…

…I borrowed the Bluto fork and SRAM X9 derailleur from my Scott fatbike, and later, I will find another Bluto fork in a different colour…”

A lot of details on this electric fatbike are very eye-catching

OK, it’s time to start crawling down the rabbit hole and see where it leads…Why go to so much trouble to use the Bafang Ultra Max G510, you ask? When it comes to the amount of copper mass in the stator, the G510 is the reigning king of power potential (to see our article on the G510, click here). On top of that, Bafang included a smooth and sophisticated torque-sensing PAS (Pedal Assist Sensor). This allows you you program-in a seamless transition of power being added when you pedal.

Off-roaders really like this so they don’t need to manipulate a hand-throttle. There would be a more abrupt power-on pulse if they had used the less expensive “speed sensing” style of PAS (that’s the common type that’s found on most kits). Torque-sensing is an upscale feature when you are precariously tackling a difficult technical obstacle up on a mountain trail. This way, your hands are completely free of any throttle duties, so they can concentrate on braking and steering.

Take note in the pic above of the three fat Blue/Green/Yellow (BGY) motor phase wires.

Daxxie wanted the option to use 72V on this drive, so he pulled out the stock controller to see if he could fit something inside the case. If that didn’t work out, of course he could have mounted a controller on the outside, but in this case, he found a solution that worked for him.

The skinny-wire bundle. Red and black are the 5V positive and negative power wires to the Hall sensors, and the skinny Blue/Green/Yellow wires carry the signal from the three Hall sensors back to the controller. The sixth white wire is an auxiliary, which can be used as a tachometer signal or sometimes for a temperature sensor.

To see our article on the wires and connectors for Halls, throttle, and motor, click here.

Dax was already familiar with the Phaserunner controller, so he wired it up to see if it ran with the Ultra Max, and it did.

You can’t really see it from this angle, but Dax had to trim a few millimeters off of the controller to get it to fit inside the Ultra Max case. He also had to grind away some of the aluminum in the case-body to be able to get the cover closed.

The Bafang Ultra Max G510 unit was purchased from Luna Cycles in Southern California, and the 72V Phaserunner controller is from Grin Tech in Canada.

_____________________________________________

The Battery

Daxxie wanted a 72V battery pack, and since he didn’t find anything that appealed to him, of course he decided to make his own. Below, you can see the 3D-printed side panel to the battery case that he designed and made.

To get 72V, Dax is using 20 groups of lithium cells in series (20S), and the higher voltage means that he might be drawing fewer amps…if he can take it easy on the assist level!

I was surprised to see he went the “high volt / low amp” route, because one of the places where the G510 really shines is in how many amps it can take without overheating.

To see our article on designing and building an ebike battery pack, click here.

“…Been driving it for over a year now. I love the frame and the Bafang Ultra…”

_____________________________________________

Daxxie’s Ninth build

Based on his experience with the previous G510 frame, Daxxie decided that he wanted another one, and he decided that his next frame would be aluminum. He shopped around and ordered a frame from the brand Seroxat, based in Shenzhen, China. The retailer was salto-bike.com

It took a while to arrive straight from China to his driveway, but here it is, fresh out of the box

Dax received the frame, and immediately sent it off to be powder-coated a light gray color. Power-coating is a process that covers a given part with a very hard ceramic, and it comes in a wide variety of colors. I’m told it’s much tougher than paint.

Dax was surprised at how cool the previous Ultra Max ran, so this time he decided to use 52V and six “high-amp” cells in parallel (6P). Using 52V is 14 cell-groups in series (14S)

“…Frame was $350 USD + $250 USD shipping (to Belgium)
I ordered two frames for the same shipping price:
$700 USD + $250 USD = $950 USD and then I sold one as soon as they arrived. So it cost me $475 USD…

…Changed the chainring to 46T, and I also got some shorter Miranda cranks. Officially it has 144mm rear travel if you use a 190/51mm damper. But, by installing a 200/57 damper you will get up to 160mm. I changed the air springs on the front shock. They are now also 160mm...

…I posted some pics in the Facebook group, and someone asked if it was for sale. I have some ideas for a new project, so I sold it…”

_____________________________________________

Dengfu E06 Carbon Fiber Frame

The first two Bafang Ultra frames were titanium and aluminum, so I looked around for a build using carbon fiber, and…I found one by forum member BeachRider2016, from North Carolina

If you want to search for these, it’s E-Zero-Six, not E-Oh-Six (why do they do that?)

“OF course” BeachRider 2016 wanted to build a custom battery with cells that he had selected (for high amps), so the pic above and below are his 3D-printed cell holders.