Matt Shumaker really made a name for himself a few years ago by developing high performance electric bikes that used the high-end Astro Flight RC motors. The distinctive feature of his drives were the chunks of billet aluminum that were cut into beautiful and well-designed brackets, which mounted these motors to various bicycle frames. You can see his monster yellow trike here.
Matt had calculated out a lot of variables and optional configurations during the first year he was developing hot rod RC drives for E-bikes. The high-end Astro motors he used have the ability to run at very high RPMs, and to access the extra power that is waiting there, you have to use quite a bit of reduction to get the RPMs back down at the wheel speed.
Something that Matt did on his monster yellow trike is to use a smaller 20-inch driven wheel,which simplified several aspects of the design process, concerning the amount of reduction needed. Since he likes to stick with things that have proven to work well for him, the following bikes also use a 20-inch driven wheel.
I really enjoyed reading through the history of the development of these bikes in Matt’s own words, so I am including a lot more text than I normally would. The process of dialing-in the performance is a lot more subtle than just making the calculations on paper and buying the parts to assemble.
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The PK Ripper, April 2009
A few years ago, Matt built up a twin Astro bike that used 20-inch wheels. This bike was an “over the top” hot rod, and he used a PK Ripper frame. It ended up weighing only 45 pounds, and with 14-HP on tap (10,000 watts…not a typo), the bike was very “wheelie prone”.
Matts twin-Astro PK Ripper.
” That [PK Ripper] bike was far more fun than any other bike I have built. However, it was too short (wheelbase) and had no suspension. I have had many requests for another 20-inch build and I began moving in that direction“
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Diamondback X6, March 2012
“I had this Diamondback X6 frame sitting around (built by Intense Racing back in 1999). This frame was bought for its perfect frame setup. There is room in the triangle for LiPo and a high, round downtube for drive unit mounting. It also has a great swingarm for left side chain clearance. I began doing some calculating and figured out that my X6 frame would work if I used a longer shock (I had one lying around) and flipped the shock linkage upside-down. This would drop the swingarm to the correct level for a 20-inch wheel (to have the proper crank height). So, I took my beat up X6 frame to the powder-coater for some gloss black.
When I re-configured the frame for a 20-inch wheel, a couple of cool things happened. First, the rear end is plenty long, and this is great for a forward CG. It also rotated the frame forward, thus steepening the head tube angle. This sets up the geometry for proper road riding. I think the head tube angle looks a bit too steep. But, the bike handles phenominally like this. The wheelbase is also longer than my Hooligan. This makes the bike far more stable while retaining sharp steering with the steep head tube angle.
A Diamondback X6 modified with 20-inch wheels and longer forks, also with a longer shock to rotate the swingarm down.
The forks are White Brothers Groove 180’s shortened to 4-inch travel for me by White. The brakes are Hope 2-piston units. I may to to a 4-piston up front. We shall see. The wheels are Industry Nine custom items using my 47mm wide rear rim. I have another set of wheels like this that use standard spokes and hubs. I may use those. and save these to put back on the red Hooligan as a pedal-only bike. I have to see how things go with these wheels.
You can see the HUGE amount of room under the down tube for the drive unit and plenty of room for lipo. Four 6S packs will reside inside the frame triangle while I am considering a bunch of 3S packs (configured in 12S layout) on each side of the frame with side covers to protect them. That will keep the overall width reasonable and give me plenty of range.
“The drive will be a [single] 4-turn 3220. This is the most powerful motor I have run that is absolutely 100% reliable. I could go to higher power like a 6-turn Delta, but…that would be a bit too much power and would be a hard on the controller at partial throttle. This setup will be good for a reliable 9,000 watts without any reliability concerns.
I honestly think I will need to dial out the wheelie tendency with the slipper clutch as it is. The bike actually rides wonderfully. I think part of that is the rigidity of the frame, forks and wheels allowing the steep head-tube angle to work. The wheelbase is also longer than a typical 20-inch bike, and the forks are a bit heavy. This slows the steering down a touch. I have ridden it fast no-handed without a problem. My mountainbikes can get the headshake wobbles when I do that, but not this bike.
The original plan was for a single 3220 Astro motor, but a customer bought this bike and moved up to a twin-motor system.
Like I said, it rides wonderfully! The steep head tube angle sharpens the handling that would normally feel sluggish. Whenever I build a bike with wide tires and heavy forks it steers heavy. Not this bike!”
I am getting used to looking at it like this. I wish it was one degree shallower just for “the look”. Remember, small wheels put far less twisting load on the frame and fork. They also flex less by their very nature. Beyond that, disc brakes are far more effective with smaller wheels. Also, small wheels allow much more room in the frame for electric components. This makes small wheels and ideal choice for a dedicated electric bike, or at least a dedicated electric agressive streetbike.
The rear was raised three inches and the front was dropped six inches. That rotates the frame forward. That being said, the head tube angle was far too relaxed for a streetbike previously. I may go to 24-inch wheels in front…and rotate the frame rearward just a touch. But, I really want to stay with the 20s if at all possible.
I need to do some 30+mph testing. It rides awesome at 20-MPH. It corners like a freakin 125cc sportbike. The bike is so freaking stout, that I cannot help but move it in that direction. I want to see how “motorcycle like” I can make it while remaining under 70 pounds. If I have to, I will go up to 80 pounds. But, that would be [battery] pack size dependent. I will start with 1-kWH of battery and see if that is enough for my riding. If not, the weight will go up to add range. But, I am committed to making this a true light streetbike/motorcycle.
I want the chassis, wheels, brakes, electric system, etc to all have headroom I.E. I want to make sure nothing is overstressed. I want to know I can beat on this bike, hit rough pavement or small potholes, do some trail riding, aggressive street riding, and have the bike survive. The wheelbase is about 1200mm (3′ 11″). The head angle is around 71 degrees.
Here are Astro Flight’s most popular RC motors for E-bikes.
This is my new flagship build…[and then a little bit later:] this bike is sold! It was sold to a high-end client who wants it built up with TWO 3220’s. This bike will be built as a wheelie prone 50-MPH monster! The buyer is a crazy, high-powered sportbike guy who wanted the ultimate in an overpowered, yet light weight, wheelie machine. The drive will be two 6-turn Delta 3220’s with as much LiPo as I can fit in the frame. The LiPo will be flanked by large carbon fiber panels on each side. This will be somewhat of a Super-Motard bike. My guess is an overall weight of about 70 pounds or so, with CRAZY power.
The gearing will be set for 65-MPH top speed. The customer only weighs 135 pounds and has a turbo charged Hyabusa. I think his light weight and familiarity with high power will make this a perfect bike for him. His specific request was for 60+mph with insane wheelie capability. He already has this exact drive system geared for 60-MPH on a KMX trike. So, he knows what he is in for.
Big hub motors are capable of huge power too. They also cost less, but…there is a weight penalty, though. Two [Castle Creations] 160s with two of these motors is plenty reliable. I have sold many twin motor systems. The bike is capable of over 20,000 watts total assuming the rider is not thrown off. Honestly, I think about 12,000 watts is the limit before violent wheelies become a problem. The bike will weigh in at under 75 pounds with 24 horsepower. That is a 3 to 1 weight to power ratio. This is the most powerful bike at that weight I have ever built.
A close-up of the twin Astro’s powering the left side of the rear 20-inch wheel.
That [battery cover] is 4mm carbon fiber. It has 25-Ah of LiPo.
Twin motor drive with controllers, frame mounts, etc $3,000
Forks $1,100
Brakes $700
Shock $300
Carbon Fiber $400 (and that is a discounted price)
Wheels $1,100
Bike? (I bought it used, and then stripped and powder-coated it) I have about $600 in the frame alone.
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Cannondale Hooligan, May 2014
“I was in the shop the other day after finishing a bunch of work on customer’s bikes and drive systems, and I began looking at various parts I had laying around the shop. I realized I have a drawer full of LiPo packs (brand new). I have a couple battery boxes, a brand new fan-cooled 5-turn Delta 3220, controllers, throttles, drive parts, frame mounts, sprockets, chains, etc. Then…I glanced at my red (Cannondale) Hooligan that I had setup for mild trials riding {but rarely ride} and I decided to build myself a bike as quickly as possible, and…this is what I came up with!”.
Here are the specs;
Schumaker Technologies V4 drive
5-turn Delta, fan cooled 3220 (12,000 RPM motor)
10-Ah of 12S / 25C LiPo inside CNC-machined battery boxes
Drive unit frame mount clamps used to mount the boxes
Castle Creations Edge HV-160 controller
Simple PWM throttle
18 to 1 ratio from motor to rear wheel
One of my 47mm wide rims on the rear
45 pounds exactly
Seatpost: Thudbuster Long-Travel
If you let a single Astro run up to 10,000-RPM’s, even a motor this small can pop wheelies. Here, the crankset has been upgraded to a larger 5-arm 110-BCD.
I set to building the bike, and all of the wiring, component mounting, and machining a couple small parts. I had spent only 4 hours on the bike and it was finished. I have around 15 miles on it so far. The range is around 10 miles on a charge, with my wheelie riding style.
So, I programmed the controller for throttle response setting of “one”. This reduced the violence of the response, and drastically smoothed out the low speed control.
The bike rides great and is EXPLOSIVE! I have pulled nearly 10,000 watts, according to the data logger. I can run at 30-MPH and then snap-wheelie violently. It actually has way too much power for such a small bike. But, with the throttle response at 1 and a bit of care taken with the throttle, it rides wonderfully.
This bike is very similar to the PK Ripper I built 5 years ago, but it is lighter, faster, and more refined. I cannot believe how easy this bike was to build.
So, I decided to mount a lower set of trials forks, to drop the nose of the bike. This lowered the nose two inches and the bars one inch. Now it is a bit less wheelie-prone and much better handling. It does pull more wattage now…
The stock Hooligan has a lefty fork, but the 1-1/8 inch head tube will accept a variety of suspension forks.
I am getting used to the crazy power. 10,000 watts is a bit on a wild side on a 45-pound 20-inch bike. But, I am settling into it and having a LOT of fun.
Right now it is geared for just shy of 40-MPH (about 38-MPH). I feel like the bike needs to be geared for at least 45-MPH, or maybe 50-MPH to realize its full potential. It is capable of 15,000 watts peak (battery watts, so maybe 12,000 watts at the rear wheel).
Right now I see only two volts of sag at 10,000 watts. So, that is pretty good. These 25C cells rock! Oh, 10-MPH to 35-MPH takes only two seconds if I literally lay over the bars.
It would pull harder if I could keep the front wheel down. Hmm, maybe I should lengthen the wheelbase and add more cells up front, along with lowering the seat. I bet that would make this thing a sport bike.
I geared the bike up a touch. It is now geared for 43-MPH according to the math (I have not timed it yet). Anyway, with this gearing, I was able to increase the throttle response a bit and I am seeing far less wheelie tendency. The bike pulls a consistent 11,700 watts under acceleration now and winds out at (ironically) 11,700 RPM under full load according to the data logger.
The increased gearing was accomplished by changing the pulley ratio on the reduction unit. The problem is, the only way to do this with pulleys I have in stock was to move from 5mm pitch up to 8mm pitch (again based on pulleys I had in stock). I am wondering if this larger pitch is affected by the extremely high RPM the motor pulley is turning. Generally, larger pitch is not as tolerant to high RPM. The belt gets a touch warm, but not hot.
Anyway, the bike is no longer a violent nightmare. Now it runs like a sport bike. It has strong acceleration and is very willing to wheelie, but it is not frightening.
The Castle Creations controller is so small, it’s hard to see. The black boxes hold additional LiPo batteries, and the controller is the small square shape just in front of the seat-tube mounted auxiliary battery pack. The wires from the motor go directly to it.
Oh, the wheelie tendency is prevalent when the throttle is opened hard with the bike at or below around 60% of its top speed. Anything above that speed, I can hit the throttle and the front end get a touch light, but does not automatically wheelie.
I added 15-Ah more LiPo this morning. That makes a total of 25-Ah. This should be good for a 40 mile range if I nurse it, or 30 miles of fun.
With the added weight up front, the bike corners better. It feels more planted. It was far too light before, and that made the handling quite skittish.
I was hoping the added weight would tame a little more of the wheelie tendency. It does a small amount. But, the bike is still very willing to wheelie. However, it is far more controllable now. It feels lot like riding a 600cc class sport bike in first or second gear. If you hit the throttle hard enough, it is very willing to wheelie, but not freakishly so anymore. The weight is 58 pounds at this point.
Well, I can verify the range. I just went for a 10 mile ride averaging 25-MPH and used less than 25% of my pack. So, it looks like 35 miles is my range (leaving a safe margin of capacity in the packs).
I can tell you this thing absolutely NEEDS suspension forks! My hands fell asleep and my wrists took a beating. It is fine for general bashing around, but for any amount of commuting, suspension forks are needed. Also, I need a less insane motor. Every little bump made my wrist turn the throttle a tiny bit and that translated into motor response. That made bumpy road riding require too much concentration. So, I will remove this 12,000-RPM motor in favor of a 7,500-RPM motor and gear it up. That should tone down the craziness.
Of course, the power IS fun.
Matt used two motorcycle mirrors, and a Garmin GPS.
P.S. I just got back in from a fun blast. I pulled 13,200 watts on that run. Also, I only saw 0.7 volt (7/10 of one volt) sag under load. I think I am at the limit of this controller.
My hands do not fall asleep when riding smooth roads. I had the bars three inches higher before. But, the wheelie tendency is far less with them lower. It also corners far better with the lower bars. It is not very comfortable for long rides, though…
…Yup, 13,200 watts now. It is a freakin MONSTER! But…it is still ride-able at this point. I ordered a fan-cooled 4-turn wye for it. That should make it possible to wheelie, while being extremely rideable and more efficient.
I am pulling 14,000 watts with it at this point, while geared for 45-MPH. If I cruise at 25-MPH and hit the throttle, it will power wheelie even if I lean forward.
I have a Garmin automotive GPS mounted to the bars and I love it. I have around 100 miles on the bike totally problem free. I have really gotten used to the power, too.
Oh, also, I am using a Meanwell PSC 1000 as a charger running through a Watts Up meter to monitor the charge. This is the best charging solution I have run yet.
I have the throttle response set very low (#2 at this point). That dampens out sharp throttle peaks while retaining ride-ability.
What is funny is that I can achieve 23-WH per mile if I am careful, and still have huge power when I want it. Actually, when I ride the bike without thinking about my range at all, I see 32-WH per mile consistently. That is riding with the occasional power wheelie, a bit of full throttle 45-MPH riding, and some general cruising ending with an overall average of 22 to 24-MPH for the entire ride.
I love this thing…
The large 224mm diameter Hayes front disc, with a Hope hydraulic caliper.
At this point I installed a MRP fork (White Brothers), 224mm Hayes front rotor, Garmin GPS, and motorcycle mirrors. I also have the motor setup to be easily reconfigurable from Delta to Wye. In Wye I see 23-WH per mile. In Delta it is 28 to 32-WH per mile.
I also installed [shorter] 140mm cranks to provide greater ground clearance, and I installed one of my torque limiters to minimize the wild wheelie tendency. The bike has several hundred miles on it so far without a single problem…”
Matt has had good luck with Maxxis Hookworm tires, and the jackshaft output is using a heavy-duty White Industries ENO freewheel.
The original discussion thread for the red Hooligan can be found here.
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If you like the idea of a 20-inch street fighter, but the Hooligan isn’t quite what you are looking for…I found a frame that has a big rectangle in the main frame for mounting a big pack made from 18650 cells. This bike is called the “Yooniq”
For non-suspension frames, I highly recommend a suspension seat-post.
The Yooniq also uses 20-inch wheels. The head tube might be too long to swap-in a suspension fork, but the long head tube also allows a very large rectangular battery pack to be mounted in the center of the frame.
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Written by Ron/Spinningmagnets, July 2014
