ML DH Comp Cromotor Max-e Build


10 kW
Jul 8, 2009
South Dakota
I'm excited to be working on my 2nd build this summer- the DH Team! My first bike has taken me 3,500 miles in 4 years - it's time for round 2! :)

I bought a large DH Team last winter. Then bought a Cromotor, and worked on getting an Adaptto Max-e.

I've been trying since May to get a set of dropout adapters! Frustrating! I'll probably take a gander at making my own soon because I need the bike to be done in a couple weeks. I'll be taking a trip out to Brammo...

I have built the Cromotor into a 19" motorcycle rim, from DCinGC's thread here -
I used 12Ga Sapim spokes 129mm in length with a 19x1.4" pro wheel rim. Spokes were pretty cheap and they had extremely fast shipping from Holmes Hobbies. The rim was about $100 from EBay, tire was $30, rim stip $10, tube.. $15?. It was easy to put the spokes in, and truing the wheel wasn't too bad. I just put the wheel on the bench, cut some cardboard and used pieces as gauges, and trued the wheel like that.

My Max-e adventure was long, but shipped July 21. It left Russia on the 23rd, so hopefully it shows up in the next couple weeks! I also ordered the charging coil and BMS.

The plan is to run 20s 15Ah turnigy hardcase packs. I can fit 25 into the triangle without too much trouble. The battery enclosure is going to be about 6" wide.

My rear swingarm was 135mm, so I followed Obiwan007 and sent it to Quality Heliarc out in Nevada. He cut and welded my swingarm to 155mm. It is still a pretty tight fit for the brake disc; looking back I maybe should have gone with 160mm. His thread has a bunch of pictures/info on the welding process-

I had the frame sandblasted. I want to powdercoat the frame and handlebars white to match my fork.

Things left to do:
-Battery Enclosure!
-Freewheel - single speed or 3 speed?
-Charging PSU
-Powder Coat Frame

The bike

The batteries came in a huge box! 45lb!

Two of them have a maybe weak cell? I got 2 extra so that's good. Waited until the popup thing appeared and paid mid $23/ea from US warehouse.

25 in the frame, just have to take one out of the case to fit 9 in the bottom row. My frame is a large.

The box will be about 6" wide, which will hopefully accommodate for the wires/bms

The welding job from Quality Heliarc

After getting the frame sandblasted, and the target white color

The Layout

Lacing the rear wheel

I think yours is only the second of the swingarm mods done by Robb at Quality Heliarc but I'm sure it is going to be good for you. I know mine is. I just sent another ES member to him the other day. Let us all know how the MC wheels and tires work out for you. I did mine with bicycle components this time and they have been good so far except that it appears to be going through tires pretty fast. Get kiwi adapters if you can. It looks like he is trying to license them to someone here in the states. Obiwan
Weird - this is virtually identical to the build that I'm starting shortly! Hopefully the fact that we arrived at basically an identical spec list means convergent evolution is finding the best bang for buck :)
Cool build :)
Obiwan I know you sent me the info
I'm still planning on having them do the swingarm mod, but maybe later in the fall
having too much fun riding (even with a bit of a spread and not much useable gears) and almost done changing over to the minie with bms
I may be starting a new project soon. I just acquired another Cromotor from an unlikely source. It's probably in the mail already. So I think I will be looking for a new DH team/comp frame in the near future. That said, I may be both the first and the third person to get a swingarm mod done by Quality Heliarc. I guess this means the acquisition phase has begun. I started both of my last builds with a frame and a fork. This time it looks like a motor and brakes are the starting point. From day one I have been jonesin for a true full suspension fat bike. With new products on the market like the Risse Racing fat-bike-ready dual crown forks it may be possible. Since I now have a Heliarc welder that I trust and is willing to do just about any modification I can dream up...hmmmm, who knows. The hamsters are running.
Hey! I've got a picture of my lacing stand. I just clamped the axle to my workbench!


To true the wheel, I just set cardboard pieces on the edge. It is easy to true the wheel with this setup.


When I previously had to true a wheel on my other bike (after I broke a spoke), I just used squeeze clamps to clamp cardboard to the frame. Easy way around an expensive stand!

I am hoping to soon get kiwi dropout adapters. They are in the process of getting quoted for production now.

Once I have the adapters I'll have a better idea of whether to recommend a width; 160mm? I'm guessing.. However Obiwan probably knows more about a Cromotor in a DH comp than anyone in the world! :) Quality Heliarc is a really great resource for us ebike builders!

Thanks for the heads up Scott!! I'm thinking about a White Industries ENO freewheel, but it seems unnecessarily expensive? single speed, 2 speed? 3 speed? I'll have to do my research.

My thought, is a 2 speed freewheel really worth it? Not a huge jump in gearing with the two. Single speed I could probably get away with no derailleur, which is probably the weakest spot on a bike. For a 100lb, high-powered bike, pedaling is just for getting started, or going slow. Limping home. No way to go fast. Commuting to work, I never need to add my 300W pedaling assist while I pull over 2000W continuous.

Obiwan, didn't you try out the cheap 3-speed freewheel from Amazon? Doesn't look like you want to stick with it.. :)

Also I got something fun today! :)


Oh my!


The Max-E!! :D Wasn't impressively packed in my opinion, but it all looks like it's in good shape! (this picture I put everything back in from memory; wasn't packed exactly like this, but close)

The controller is very small. A little longer, but not too much more than my 12fet Infineon.



Pretty small screen.


It is just 2.5" compared to the 4" Cycle analyst screen.


I'll have to figure out how to mount the controller, I'll probably put it under the downtube.

I have some really fun plans for the bike! First variable regen with my max-e.

Then, I ordered 1000 addressable RGB LEDs.
Why? because they're awesome!! I've used these in the past (in adafruit strip form) to make a sweet lamp really similar this one -
I want to make a table like this -
and something called an ambilight- like this!-

For the bike, I want an array for a tail light. I could make it a brake light and blinkers. I could add an accelerometer so the blinkers automatically turn off after a turn.. It would be pretty easy to implement. I'd use either a Teensy 3.1, or for simplicity's sake, a 5V Arduino. Really fun stuff to do!
Scott said:
Be careful when buying a freewheel. I bought a Shimano 16 tooth single speed freewheel but the removal part sticks into the threads and it only screws on 1/2 way onto my cromotor.

View attachment 1

There is a way round this, which is what im doing with the White Industries one to make it fit and thats to get a machine shop to mill 5mm off the mounting threads on the motor so it sits lower down on the spindle.
Just literally got back from the engineering company, they have milled off 5mm for me and now it fits perfectly.
I have a bunch of new pictures! I spent some time making my battery enclosure. It is made of aluminum tread plate. My plan is to epoxy some rod connectors to the inside and bolt plastic side panels to it.



I am going to have beefier plates to put on the inside of the box so I don't bend my tread plate over time.

I've got two more packs to squeeze in, I have to take them out of their cases.


Original max-e mounting idea

This might be easier and better tho (yet asymmetrical!)

It sticks out less and is more protected from the wheel throwing stuff at it

I ordered a throttle and freewheel from

I also ordered a couple power supplies from ebay. I paid $45 shipped for two DPS-1001AB-1 E Series server supplies. They are 48V supplies and push 700W at 110V and 1000W at 220V.


Instructions to turn on the supply are here -


I'll probably put them in parallel and feed 48V 27A into my max-e. I have a 30A charging inductor. They are pretty heavy but the fans aren't too loud. There's a way to slow them too.


Aaaaaaaaaand my dad and I made a cornhole set :)


They turned out perfect!

Needs a trip on the belt sander and paint still. Ripped the 2x4s to 2.5" and used 3/4" dowels to hold the legs on.
Metalover you are on a roll. I can't wait to hear how the max-e works out for you. You are in a perfect position to compare it with the CA V3. You are right, I will likely try something else with my 3-speed free wheel arrangement. I have been looking at options to get more gearing. Problem is all the good options are really spendy. So at this point I think I'm going back to trying to get all three gears of this freewheel working properly. I figure it would be a shame not to explore the full potential of it before I move on. I was worried about getting it off since the freewheel removal sockets are a joke. But I laid hands on a similar 5-speed and experimented with methods for removal and found that it's pretty easy to disassemble and then remove using some of the inside geometry to get ahold of. So after my big north coast trip I will likely shim this one out and try to get all three gear working. Report later. If I don't like it I will likely go with a dos eno and see how I like that. I might be able to get a used one on ebay. In other news, it looks like I may have gotten my hands on a set of Risse Racing "Trixxy" dual crown forks. These have 4 3/16" between the tubes. Big enough to fit a vee rubber Vee8 26 X 4" fat bike tire, here:
I also talked it over with Robb at Quality Heliarc and he is up for doing some extensive swingarm surgery to make a custom fat-bike Giant DH Comp swingarm that will also fit a 4" wheel. So, let's see,...Cromotor..check, fat-dual crown forks..check, aluminum surgeon..check,...I think I have stepped onto the slippery slope. Now that I have thread jacked you I better start a new build thread. Obiwan
So the bike runs. Unbelievable!!

First pictures.

Parts back from powder coat. Sand Blast was $60 and powder coat was $165. I like it!

I got kiwi adapters from Scott. Sweet parts!! Scott did a lot of work to get me these in time for my trip- thanks Scott!

I threw on the rear wheel and had a little dishing to do. I think I ended up with about 2 1/2 turns on every spoke to dish cleanly. The wheel build isn't what I'd consider quality, however it isn't too bad for my first motor built from scratch.

Bike put together

Got it to spin up!

Autodetect with the Max-E was a fun experience! The first time it jerked slow at the start, then smoothed out for a couple minutes. Then it went into a higher speed and I swore everything on the bike was about to give out! I let up and tried again and it worked better. :) Easy process overall!

Another aspect with the controller was charging. I was a little worried about my power supply, connections, software, etc., however it went really well! The first time I wired up my motor I didn't put the second plug on a phase wire, so I did that.

What still confuses me, and is a little concerning, is there is a floating voltage through my frame when I'm charging. It's like a phase wire is shorting to the frame. I still need to investigate.

However, I'm happily charging at 650W with my $22.50 charger! :)

The BMS was easy to set up! Thought my fourth module wasn't working, but then I figured out I needed to program it in the display. Really, really awesome BMS! I'm still not going to lose diligence with my lipo, but I feel a little better now. :)

I have 25 packs in my frame. I had to take 2 packs out of their hard cases for them to fit. I left all the original connectors on so I can replace them if needed. I locally did 5 packs in series, then paralleled those groups with a 5-p adapter I made. After that I hooked up all the 0-4s balance taps in parallel, 5-8 in parallel, etc. Each pack is labeled so I didn't mess that up, ha!

I still haven't weighed the bike, but it's definitely over 100lbs. I used two bike racks. The top rack pulls straight up on the bike/bottom rack to hopefully not pull laterally on my hitch. It made it 400 miles with this.

Now we have it in our pickup 1400 more miles going to Ashland, OR. :) :)

The motor temp sensor didn't work, so I tried changing the setting for "internal thermometer". Later I noticed the wheel would hardly turn, I thought what!? I saw fet temp showed about 225*F. Woha it clicked I changed that back and everything worked again. I thought I'd burned my controller!

Then I rode it. Wow!!! Woww!! The first thing was the noise. Quiet as a whisper! I had a 9c with a 12fet infineon before, and that sounds like a jet taking off compared to the Max-e. It really sounds like a hybrid vehicle inching out of a parking space.

I was riding in normal mode. I turned it to boost. I expected a lot of power. What I got blew my mind! Huge wheelie down the street, lucky I didn't flip it! After that, I found I can do power wheelies! 20s lipo with a 19" MC wheel and max-E is wild. I think I'm about a 40mph top speed. I need to play with the timing advance still, I might get more out of it. 45mph would be nice so I can go on highways.

Still to do is rear brake and freewheel. The freewheel I got from has the lip you guys warned me about and doesn't thread all the way on. :/. No chain for now! ha. Rear brake is regen for now. I put a switch on an old brake lever. The Max-E made me happy here where you can invert the switch polarity for regen :)

I'll power more later. Bike runs but still a ton of work left before it's really ready. I am really happy!
Nice build!
Is that a cromotor with 3 or 4 turn stator?
Powerwheelies, what kind of phase/batt amp are you set up with?

Keep in mind that autodetect can be a bit off if you do it with bike up side down, your wheel could be out of ballance and during detection the bike can jump around. In this case have it lying on the floor, works better.
Not sure about turns on the motor. I bought it spring of 2014 from the main for sale thread. I'm guessing it's the slow wind. Maybe some day I could upgrade/trade to the fast wind :) ;)

I'll get back to you on the phase/battery amps, the bike is tucked in the back of our pickup right now. I really just threw it together and didn't play with it much yet. It's set for the default boost mode on the Max-E. I think I saw 13.5kW peak, idk if that's calibrated right, but 12kW at 80V is 150 battery amps. It does power wheelies when I'm leaned over the bars, granted I only weigh 150lbs.

I used the same spokes throughout, 129mm Sapim spokes from Holmes Hobbies. :)
Fantastic that everything works. Ironing out the details is the fun part. I'm really happy for you Metalover you're gonna love this bike. Obiwan
Big/cool update today!! We're on our way back from Brammo. We got to see their facilities and learn a little bit about their stuff! I also brought the new ebike to show off a bit.

I didn't have my motorcycle license in time, so I didn't get a test drive! But the bikes were really sick! BTW they just opened up a huge price drop to their 2013 bikes; you can buy an Empulse for about half off!!

I was blown away at the support of electric bikes in the area. We walked to two shops, as well as met a handful of Brammo guys with their own bikes, including PaulD! :D Another guy took me out one night for a ride through the mountains. What a blast!! He took his custom-built Electromoto Blade out with my bike and we jammed. He could really ride! Thanks so much for the fun trip! Our bikes were both really fast. Top speed was about the same, and they would both flip you over the handlebars with a twist of the throttle! The big difference was weight; His was 148lb and my bike is 107lb.

The only problem I encountered, well, big problem! Was at the end of our ride I believe I overheated and the epoxy holding my magnets gave out. Ouch! I have ordered some epoxy and will attempt to fix this weekend. If all the magnets are OK I think I'll have it done. I didn't have my temp sensor working at the time, so I probably deserve this! :? ha!

Also, does anyone like a little dyno action!? :) This is me in the video; I got the chance to do a couple quick runs.


9.54HP is what the bike made! The dyno was set for a torque load of an original Brammo Enertia. There are two runs on this graph.

Settings for the adaptto max-e and cromotor were boost, shown here. 202 battery amps, 301 phase amps

IDK how to interpret my 9.54HP, or if it was even accurate or not! I think we had it set up alright, although the torque load may have been too high? I guess I really don't know how dynos work. Let's say 80V @ 200A is 16kW or 21.5HP. The display has always read readings well above 12kW, I think I saw 19kW after this dyno run. 12kW is 16HP.

I guess if the dyno read right, that makes my "battery" power of 21.5HP running down to 9.54HP means 44.37% efficient. Take that with a grain of salt, I'm not too sure about my numbers. :)

I guess looking at this simulator (random graph, I don't know how to put a cromotor in), that could be about right. I guess I may have not really been pulling 202A either.

Huge thanks to all at Brammo who helped make our week great!! And a huge thanks to the man who hooked me up with some new custom crowns for my bike! No pictures yet because they're in our pickup, at the shop. He has a pretty awesome bike started an says he'll try to post it up here when it's further along. :D

Bad thing is, our state vehicle broke down last night! The fitting on a power steering hose cracked, and the dealership can't get one in until tomorrow. One more night in Oregon for us! 8) And one more missed day of class. :? 1400 miles and we're home :)

On the list now:
-Epoxy Cromotor magnets back in place (hope none are broken/not more damage)
-Finally make side covers for the battery enclosure (have parts; need time)
-Fix brakes; install magnet/hall sensor
-Think about a startup system; contactor, key switch, precharge, etc. (mosfets?)
Awesome job on the bike!

That's really cool to see your bike on the dyno I have wanted to get mine on one for a long time now.

I really hope your magnets are ok, what were you doing when you think it happened? I have only done street riding so far and hills gets my motor hot but I have been careful and almost always used a temp sensor, except when I killed a hall when I did not have it connected. :roll:
We were aggressively riding on the mountain bike trails. Flying up steep grades and regen all the way down. Doing that for an hour straight got the motor really hot. My friend's bike was fine because it was a mid drive, in runner motor. I was doing things I know a hub motor probably shouldn't do; my old bike wouldn't have made it up a lot of the hills I flew up with my new bike. I knew the motor was getting pretty hot towards the end, but I guess I didn't know what the limit was. I could never smell the motor.

I was able to ride a couple miles later that night, but after the motor warmed up a bit and I hit the throttle really hard the magnets slipped loose again. The following day I tested it again and they slipped on hard acceleration. I'm almost certain the issue and the only issue is the magnets coming unglued. Count me #2? 3? :)
Thanks Paul! We did make it home, although a day late.

I am now in a frustrating loop of issues! I took apart my motor and glued the magnets back. That went well!

Some were broken!

I got them all out; all the pieces too

The last few

I used a scraping knife to scrape off all the old epoxy.

The pile of fried epoxy

Then goo gone and rubbing alcohol to clean it all up.

I don't have a picture, but I took the other side cover off when gluing the magnets back into place. I quickly realized if I had not, I would have epoxied the cover right on to the wheel! I used Doc's favorite DP460 ("3M Scotch-Weld Epoxy Adhesive DP460")

Work time was 1 hour, it took me about an hour to get all the magnets in and positioned. I used probably about 1/4 of the tube of epoxy.

Then I put them all back in. I got all the pieces back all nice

When I plugged it all back in, I was so excited to go for a ride! However, I got !HALLS!... :(

I checked for bad connections, and it all looked good. Then I switched to the second set of halls, and it still didn't work! :(

So I've spent at least 10 hrs trying to troubleshoot and replace halls. I'm using honeywell SS41 sensors I had around.. I think they would be compatible with the Cromotor? I used them in my 9C great.

One scary thing happening is I think the hall sensor is working, then when I hook it up to the max-e, it dies. Is it possible there's an issue with my Max-E that's killing halls?? :(

I'll keep at it :)
So many batteries! Nice work fitting all those in.

I trust you've fixed the !HALLS! error now?

You must have the unlocked firmware for the Max-E, is it still strong?

I bet you'd have a hard time keeping the front wheel on the ground with this setup :D