YZ250F 2014 Build With QS 138 70H V3 Motor and 450A controller Part #1 and Part #2


Well-known member
I was asked for information on this build so I thought I would share it with everyone. Let's start with the end Product, a picture (IMG2785) and a video of it at the track yesterday.

I started with a 2014 YZ450F donor bike (IMG2571). This bike had been modified as another electric motor bike so I removed all the new lower tabs to start fresh. You can make non welded in mounts to do this also, but I elected to do the weld in method. I am only showing the main pictures here, but I have a ton of images of the build.
I use 6061 Aluminum 1/4" x 1 1/2" across the down tubes, and for all the motor mounts, and the battery supports.
I built the mount for the swing arm bolt, ( i will explain that in Part #2) that would be going down to the main frame center, and up to support the back of the battery tray. This battery tray could be built with a quick change battery system if wanted. XEMX1.com will be selling a kit very soon. Ask and I can get you more info .
I mounted the motor, and alignment with the rear sprocket is very important, and hard to get an alignment point. I find a straight edge to come from the rear sprocket is good. ( make sure the rear wheel is true in alignment on the swing arm) and to wear marks on the chain guard on the swing arm. You want also to position the sprocket center to as close to level with the swing arm bolt and as close to the swingarm to allow bigger sprockets to fit. I am using a 520 13T sprocket, and it barely fits on the motor, to were it will hit the nub on the motor, and it already has..., (I have to move it out by 2 washer/spacers, since it is touching/wearing) The motor and it's brackets kind of limit how close you can get to move it back and down, so do your best. You are splitting hairs, if you are close it is good, just make sure the sprockets is true to the rear sprocket.
Next is the Controller mount. You will see a special bracket that mounts to take the weight of seat and mount the controller. I can make you these if anyone wants them. You spread the sub frame outward 1/4" on each side. Very easy. You can see it in IMG1604. Then I make a tray out of 1/8' soft aluminum, so I can bend it to what I want, and open the middle up for a future water cooler if you want to go to 450A ( the controller does heat up at the higher currents). I can supply these brackets and coolers too if you need them.
At this point , Motor mounted, and Controller mounted, I plugged the built wiring Harness from Electroandcompany.com onto the bike with the throttle and switches also included. Added a 72V battery, that I had, and it ran.
Here is a short YouTube
Now we are going to make the battery tray. The battery is the battery I am going to use, but this was just a temporary box for road tests. The mounts were the same. First off I cut off or mill off , remove the upper mount on the motor. We need the battery space. We have 3 solid mounts on the lower part of the motor, and I want the battery separated from the heat of the motor, so no direct connection with the top of the motor. I used a Sawsall to remove it , draw or mark lines to keep it straight, , but you want to keep a few of the fins for cooling. ( I also opened up the webbing between the fins where the mount was. IMG2621) Then I made mounts that bolted to the main mounts on the down tube in the front, and mounted to the rear like the pictures show. (IMG2622 thru IMG2627)
I am going to stop here , and I will continue in another session. I am limited to 20 Images.






















Well-known member
Part #2 of the Build

As I mentioned in the first part, I forgot to talk about the Swing Arm Bolt Mount. I used 1" od Aluminum tubing with 1/2" id. I cannot measure the width, but it is approximately 3 1/8". I then used a drill press to drill out the center with either a 17mm drill or a 11/16" drill ( both are available on Amazon) Make it so it is snug on each side, wide enough, not less than. This is one of the 3 major foundation points
There is a 3d printable file for the QS 138 70H V3 motor if you are interested. You get both with the top mount or without.
I know I mentioned it before, but the controller and programming the controller to your motor, can and could be your biggest hurdle.
Eliminate that issue with a preprogrammed kit from ElectroandCompany.com. You will be really happy, and the cost is not that much more to order it from ElectroandCompany.com, as compared by ordering it direct from Alibaba. If you own a Sevcon controller, you know how much trouble and cost it is to get it working. This bike before I rode it at the track, I made 4 simple adjustments, and drove it. But none of them would have stopped it from working.
1.) Changed the % of max power for each of the Modes 1-3 ( from 25%, 50%, and 100% to 33%,66%, and 100%)
2.) Changed regen from an automatic 15% , upon throttle release to 8%. A little less.
3.) I changed the throttle to a SurRon type Hall sensor from the the Lite version, so I needed to reset the Throttle Start Voltage.
4.) I changed the max Current for Boost from 350A to 400A. My battery only has 370A, so that is my max, for now

The battery I used in this build is a 20S14P VTC6 Sony cells, 42AH, and 2.8KW. It is divided into 2 packs for quicker charging on 120V, 2 10A 120VAC chargers. I disconnect the batteries for charging with a dual battery switch , so the BMS's don't fight each other, during Charge. I use normally ANT 300A Smart BMS's so I can watch the packs integrity , but these 2 packs have Daly BMS's, not smart, and only for Charging. You don't want the BMS shutting you off suddenly in the middle of the ride.. The Votol Controllers have Soft undervoltage, usually set at 65V and Undervoltage set at 59V. This will slow the bike down at 65V but let you keep moving until 59V.
I had the 2 packs in a temporary box for test riding (the gray plastic box) , and then I built a new box ( the black plastic box so that I could make it water resistant IP65, so you can at least pressure wash it, But not submerge it, like if it was IP67. The Motor and Controller are both IP67
Here is the top of the bike with the meter and the Master ON1,ON2,Both,OFF switch, and the Voltage and Current Meter, IMG2680, and then the underside.( IMG2862) 2 #6 wires from each battery pack and #4 to the controller. I have an Antisurge resistor across either pack lead and output. It is a 1K 10W resistor.
I make my own Plastic boxes to hold the battery. I am using 1/8" Black ABS. It is easily bent and welded. Plus you can weld certain pieces with ABS pipe glue. I make the connections with Black NYLON 6MM flathead Phillips screws. For more security, I can also close it up with .060 Aluminum sheet, but I haven't on this one yet. The battery box is 6 1/2" x 9 1/4" x 13 1/4" tall. The packs I have are 20S14P, but I could get a total of 20S16P in the box, with the BMS. That would be a 48AH battery and 3.4KW. Here are some pictures of the battery build.
The battery is held down by the bracket on top of the Battery (IMG2772). It is bolted to the middle mount under the seat, and a turnbuckle in the front.
I use an inexpensive sheet metal brake and a Harbor Freight Plastic welding gun to get nice crisp bends of the ABS. You can see the corners of the base bucket are ABS Heat welded using a soldering Iron and ABS welding monofilament. I had not cleaned up the plastic welds yet in the picture IMG2741, yet. I used the same system on the top.
4'x8' Sheet of Plastic Port Plastics (cut and shipped 2'x4') $148
1/8" Black ABS Welding Rod (approximately 170' per lb. coil) Price: $15.31

Welding GUN ( Harbor Freight) 1300 Watt Plastic Welding Kit with Air Motor and Temperature Adjustment $79
18 in. Mountable Bending Brake Harbor Freight $45
Any soldering iron to Weld Plastic. It will ruin it for Solder.
M6 x 1.0 6mm Black Nylon Phillips FLAT HEAD Machine Screws Black Ox Countersunk 100 $659

We will stop here for now. If you have questions, feel free to ask. I will include the sketchy schematics and pin outs that I have hand written. The Schematic is with a DC to DC converter to run a water pump if you want to go 450A on the controller.
















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Bob Casper

Active member
There is a great deal of very useful info in this build. Don has been instrumental in helping with my builds. If you enjoy tinkering, these are very fun, great performing bikes.


Well-known member
way over my head but I am glad there are people like you sharing this knowledge. maybe someday I will understand my toys better but for now I am happy to stand on the shoulders of giants like yourself and reap the rewards. thanks so much for being part of this community and for all the help and advice you give and have given


Well-known member
way over my head but I am glad there are people like you sharing this knowledge. maybe someday I will understand my toys better but for now I am happy to stand on the shoulders of giants like yourself and reap the rewards. thanks so much for being part of this community and for all the help and advice you give and have given
Thanks B.Frank. I enjoy building these toys, riding them, and sharing them. Another person who is really sharing the electric Bike Experience and info is the Administrator of this Forum Phillip Glazatov. He will let almost anyone ride one of his Alta's. I let a young kid ride my YZ at the track last week, and the kid said wow yes, I road a guys Alta out here a while back, and it was Phillip's Alta. And he keeps this forum alive for all of us. We can thank him for this sharing location.


Well-known member
I give credit where credit is due. I am the electric biker in my area, I have a Schwinn stingray 48v rear wheel drive, a 72v surron, alta mx, alta sm and a zero sr. all my friends who ride ask "why electric?" and I say"ride it" I don't have tracks near me so it's all woods and street riding for me but everyone loves my bikes. the mx is the coolest, I tell people to ride in mode 2 or 3 for the woods but they always start in 4 and it's fun to hear the wheel spin and then the laughter...zzzz. ha ha. haven't converted anyone yet but maybe as these get more available I might be the Johnny appleseed of electric bikes in my area. I would love to try to build one someday but right now life is moving along too quickly to take on another big project but I do love reading about yours. I didn't know Phillip also built bikes just that he was one of the many helpful people on this forum.


Well-known member
I took it out to Glen Helen Tuesday. It was the first time I rode on the REM track. What a fun track. I got about 10 laps on it and then on the charger. If it wasn't moving it was on the charger. With all of us riding it we did about 30 laps. There were at least 5-6 others that took it for a few laps. What a blast. This youtube is 1/2 a lap, my sighting lap, and the memory chip was full on my GoPro. So no more video. It ran flawlessly all day.
I got to ride a friends brand new KX250 for some laps, and the power wasn't much different, but man you had to shift and clutch, an throttle it...man the electric is so simple drive, twist the throttle and go... And I was in mode 2 most of the day, next time I want to try mode 3 with a full battery.
Here is the pile of mud I had to remove.


Bob Casper

Active member

It was a very fun day at GH with you and the group. Thank You for the ride on the YZE. On the REM track, the power and bike was so much fun to ride. Had a kid on a 450 Husky that talked with me and said he couldn't pass or even stay close. Definitely a fun 5 laps.


Well-known member
Incredible work. Thanks for sharing!

Friend of mine converted a Honda CRF250 to electric, using a QS motor and Votol controller.
We ride together (with my Alta). These high quality conversions are great.



Well-known member
The power on my YZ is only about 35hp ( 370A at 72V = 27KW=35hp) There are pluses and minus's to that power number, but the torque is the fun part. I ride most of the time in 81 to the 72V range. If my battery was larger, like the KTM 2017 150SX I built , 63AH, It can provide 450A at 72V for longer ( it has a max of about 700A). 72v x 450A = 43HP . I have not ridden it at 450A, it needed a cooling system on the Controller. Manny Guerrero has built a few with this combo, 450A and a Controller Cooling system. He owned an Alta , and he said the QS motor at 450A, is all of Mode 3 (40HP) on the Alta. And over 20lbs of less weight. The KTM with 63AH or 4.8KW battery weighed 245lbs. My YZ with 42AH or 2.8KW battery weighs 221lbs.
Check out this new build by Manny Guerrero of a YZ (20S12P P42A Molicels, 540A and 3.9KW battery) and 3 modes , 1.) 250A , 2.) 350A , Mode 3 or Ludicrous, 450A, and I think he said it weighed 230lbs. The new owner of this bike should riding it soon. I hope my calculator didn't make any gross mistakes, lots of numbers... What I know is this QS 138 70H V3 and the EM260 controller makes a fun bike.






New member
Killen, Al
Don that clears it up a pretty good bit. Do these motors hold up well to the extra amps ok? I currrently have a KTM 300XCW and I ride single track in the woods. I like the idea of a 150, seems it would be a good size for single track non-race bike. 63AH @ 72 volts, do you have an idea how many miles on the track that is good for? I don't want too heavy but I also don't want to have to push it out of the woods. I've not ridden electric yet but I think it would be great, no stall, no clutch slipping, would be able to crawl if needed and if you go down in the middle of a good size hill being able to take off mid-hill without having to worry about atalling and wheelies would be great.

I'm 64 so a 25 mile day is a big day for me. I hope when I'm 77 I'm still able to ride.


Well-known member
The person I built the KTM for, loves single track and is super jazzed on that bike, so he built another CRF150 for his kids. With the 63AH battery, he gets about 40 mile of single track riding on the KTM. So far so good, on the motor holding up. At 350A on mine , I have put over 100 laps on it on the Moto track. They don't get hot, and it just works. My battery on the YZ is 42AH, and I did a 12 mile desert loop with pretty aggressive riders, and the battery was at about 40% (67V) when we got back, I could have probably gone another 5 miles. Out of a 34AH battery on a smaller bike (KX100), we have 2 of those, they get routinely over 20 miles of single track. Same motor, smaller controller, and a 175lb bike. Yes there are a lot less moving parts and things to go wrong with an electric bike, you need enough battery.


New member
Killen, Al
If gets 40 miles single track it would be more than enough for me. I love riding but I'm not fast, I don't try to be. I just go to have fun. Do you have info some where on your battery builds?

Check this out. at the very first of this vid you can see me working the start of a test at one of the National Enduros we used to have at the club I've been a member of for years. I'm on the right, the short fat guy in the blue on the right side in the picture of a taller gray haired guy. You can watch this vid and see what I'm riding but as you watch, understand these guys are racing and I'm no where close to their speeds. Same single track though.



Well-known member
you go don! you don't stop riding because you get old, you get old because you stop riding. I really want to try building my own electric bike but I already have 10 bikes (5 are electric) and I really don't have time to ride all of them like they should be ridden. ps I'm 64.


Well-known member
Thanks Frank. Sounds like you are deep in the electric bike world. It sure is fun. I'm not going for the quads on a SX course, but this has plenty of power for my riding. Your statement about riding is so true. I've always ridden in some way , crashed enough, but kept riding. I sure was sore after the Cahuilla ride above. I cased the double at the end, to many times, but I got it some of the times. All fun. I'm well today and ready for more. The soreness from riding is almost a drug , it hurts but your better in a day or 2.
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