There are several custom ebike builders who have been featured here more than once, but…this is a new record, since this is Matt Schumakers fourth custom build that we’ve written about. He decided that he wanted to produce his vision of the ultimate light-weight off-road full-suspension ebike.
As you can see, Matt is no stranger to high-powered ebikes, but…he recently got the itch to make a light full-suspension off roader. This next build has plenty of power, but it’s main focus was having enough power in a bike that was as light as he could make it (without going to exotic carbon fiber). Matts company is “DaVinci Drives” and you can find his website here.
Here’s the story in Matts own words:
“…I have been thinking about this build for a very long time. Those of you who know me, know I tend toward extremely powerful bikes with long range. These two traits dictate high weight and relatively bulky shape and size, even with the use of Lipo cells. However, this build is focused in a different direction.
I decided to pull the trigger on this build at this time because I made room in the stable by selling the Motoped. I also realized I have a motor, drive unit parts, a controller, lipo packs, and misc odds and ends lying around. What I am missing are brakes, forks, and a frame. At least I WAS missing a frame until now…
This is a frame I have lusted after for a long time. I remember when this bike was released in 92. I was transfixed by it. Since then I have always wanted one… The San Andreas frame has begun going up in value recently. So, I figured if I want one, I better get it now before the prices go up even higher.
I looked for a frame that was heavily used (I did not want to alter a perfect frame), yet still looked good. This one seemed to fit the bill. I also wanted to find a bare aluminum frame. This way I could weld to the frame without having to have it bead blasted first. This bike will remain bare aluminum, at least for the forsee-able future. This is for looks, and also I can weld to the frame at any time…”
Cutting and welding the frame
Matt made a jig out of “8020 T-slot extrusions”, and there are a variety of jig plans on the internet if you want to copy something like this.
“…You can see the black line on the right side of the frame just below the shock. This is the cut line for the new frame section….”
I cut off the front section of the frame and fabricated the new section. This new front section is a twin spar design. However, it is not a side-by-side twin spar like a motorcycle. It is an over/under twin spar. This allowed easier access to the battery packs. It was also a touch easier to fabricate with good left/right symmetry.
I plan to use four Nano-Tech 8-Ah 6S packs for a 12S / 16-Ah pack (44V nominal). That will give me over 500 WH to work with. That should be good for 20 miles of street cruising, or 45 to 60 minutes of trail riding. I have these packs in stock. So, I want to go with them. They are perfect for this build.
The Motor and Drivetrain
I am using a 3 turn motor, a 3220 terminated in Wye. That makes around 10,000 RPM with this battery voltage. About starting on a steep hill from a dead stop, we all know these sensorless motors and RC controllers start up with a little bit of a stutter when they are under load. I don’t start from a dead stop when aimed uphill. I would always give one pedal stroke then hit the throttle. On a flat surface, these systems start up just fine. However, even then it is best to give one pedal stroke then hit the throttle. It is much easier on the controller that way.
Limiting torque is handled two ways on this bike;
First, the controller is programmed with a low throttle response. This effectively gives a throttle ramp up a delay, thus softening the throttle “Hit”. Second, there is an adjustable mechanical torque limiter (slipper clutch) inside the large belt pulley on the drive unit. This will be adjusted to slip a small amount under only the harshest conditions. This will protect the driveline.
You can see the chain management I designed. The swingarm pivot is above the chain. This necessitated tucking the chain up very close to the pivot to reduce torque jacking of the rear suspension and to minimize chain growth under compression.
The chain management for left side drive was extremely complicated. So, I wanted to set it up this way first. The chain idler wheels are modified skate-board wheels. I have found these wheels perfect for this application.
Freewheeling crank setup (sprocket and spacer). This is a Rebel Gears sprocket with a custom spacer on a double bearing WI freewheel (expensive). The main reason for the freewheeling crank is because I want to try this bike with crank drive too. I want it to be convertible from a “left side drive” to right side drive relatively easily. Beyond that, I like freewheeling cranks. I back-spin my cranks periodically and the freewheeling cranks have a better feel to them when doing that.
The Finished Bike
“…In these pictures you can see the handlebar arrangement. I prefer using a twist grip shifter mounted on the left bar when using a twist throttle. This allows a much cleaner control center for the rider and reduces the amount of work being done with the right hand. You can see the controller and the throttle PWM interface box mounted on top of the frame…”
The tiny controller (Electronic Speed Controller, ESC) is an Edge HV-160 controller from Castle Creations. 44V X 160A = 7,000W
The left side chain guard is finished as well. This is made of 3mm thick carbon fiber and is held in place with titanium nuts. I have MANY titanium screws and nuts on this bike. In fact, nearly every nut and bolt is made of Ti. I think there may be 4 or 5 that are hardened steel. The rest are titanium.
The drive system is 6 to 1 ratio from the motor to the jackshaft. The output freewheel on the drive unit is 16 tooth (White Industries) and the rear sprocket is 60 tooth. This should give me a 30mph top speed.
I manufacture a sprocket adapter that sandwiches between the disc and hub. It offsets the sprocket 3/4 inch inward to provide room for the caliper. The chain always moves with the wheel. The drive unit freewheel is on the drive unit output shaft. I use normal chain lube. But, I have never had lube hit the disc. Remember, it slings outward away from the disc. I am working with Rebel Gears right now to make one piece sprockets with the correct offset. Those complete sprockets will cost less than the adapter alone.
Last I checked, no load power consumption was on the order of 300 watts at full throttle on my other bike (with identical drive system). I have not checked it on this bike yet. The drive side chain is a simple BMX bicycle chain. For extremely high power systems (20kw or more) a trials bike chain is best. But, for this application, a normal BMX (single speed) bicycle chain works great.
It rides fantastic! It is extremely stable, and the suspension is perfect for my intended use. It rides almost exactly like the Motoped from a cornering perspective. The riding position and seat to bar relationship is very similar. This bike will be geared about 20% lower than the Motoped and weigh about 60% less. That should make this bike (one motor as opposed to the twin motors in my Motoped) ride nearly identically to the Motoped. We shall see.
It has absolutely, positively TOOOO much power! The data logger shows I have only pulled 7,900 watts. But, this thing is a friggin MONSTER! Geeze, one motor…So, I turned the throttle end point down (simple potentiometer) to 60% and it is a joy to ride now. The bike handles wonderfully and is pleasant with just enough power (at 60% end point), to lift the front wheel without a problem. I will have to weigh it. But, it is really light. It feels like a typical mountain bike, more-so than any E-bike I have personally ridden. The trail manners are awesome as well.
I have been trying various setups, looking for the ideal performance versus controllability. The bike was built with a 3 turn 3220 at first. That is too much power (though admittedly it is fine with the throttle end point turned down a bit to soften the output). Then I tried a 6 turn 3220 (1/2 the RPM) and geared it up to a similar top speed. This cut the torque way down. But, the torque was cut too far. It ran like a pooch. I think a 4 turn 3220 would be great or a 6 turn 3215. I may move to a 6 turn 3215 and do some testing. But, for now, I am going back up to the 3 turn 3220 with throttle end point adjustment and I will be extra careful with it.
I went back to the 3 turn 3220 and have been riding it a lot. It looks like the range at 25-MPH is around 20 miles without any pedaling. That is right in-line with my black bike (around 33 to 36wh per mile). Bear in mind, I have done zero hypermiling on this bike. I just ripped on it. So, that range is really great from my perspective.
The complete bike weighs in at 54 pounds. Bear in mind, that is WITH the pack. This is not a back-pack battery bike. The pack is inside the frame. That is a touch heavier than I was trying for. It also has more motor and more battery than it really needs. I could easily shave 6 pounds off the bike by reducing pack capacity and running a smaller motor. But, I like the pack capacity I have.
If I pedal on the flats I could increase my range 10 miles easily. Oh, that brings me to the next point; This is a truly great pedal bike as well. In fact, it is a great hybrid. It pedals just fine and the electric drive is well integrated into the bike. It is a joy to ride by adding pedal input and/or motor input as I see fit. Just wonderful to have an E-bike that is still a functional bicycle.
On the subject of weight, I have been messing around with weight and I have found that for high power and high speed, a bit of added weight adds stability, and a solid feel to a bike. So, reducing weight too far may be detrimental to the handling of this bike. One other item I want to mention is the anti-squat layout of the rear suspension (swing arm pivot above the drive chain). I really like the way the bike responds to throttle input with this setup. The rear end stays nice and level when feeding in throttle, rather than squatting like other bikes I have ridden. This anti-squat geometry makes chain management a bit more difficult, but the ride quality seems to more than offset that.
Also, I GPS-tested the bike. On a full charge it runs 34mph. That is too fast for this application. Ultimately it should be no more than 30-MPH (actually 28 feels like an ideal top speed for this bike). More testing and validating. After a long ride I am happy to report the WH [Watt Hours] per mile is 25.5 at 20-MPH! That is over 23 miles of range from my 12S / 16ah pack. That is considerably better than I anticipated.
So far, I have about 100 miles on the bike without any problems. It is great being able to hop down curbs, run through trails and overall have bashing-around fun on an ebike.
I am 100% happy with the bike.
Written by Ron/spinningmagnets, August 2016