High Powered Cycles recently began retailing a frame kit called the HPC Revolution. We’ve been looking for an excuse to write about it, and endless-sphere member Leeleeducati just finished building a powerful mid drive out of one of these great frames. Most Revolution frames have been built with a rear hubmotor, so this mid drive is very special.
Let’s start with the frame
Something like this frame was overdue for the ebike world. It has similar features to the Qulbix Raptor Q140, or the Q76R, but…it’s made from aluminum instead of steel. There are several frames that either have a concentric swingarm pivot (Greyborg, Stealth Bomber, etc), or have the bottom bracket (BB) located on the swingarm (Vector, Stealth Fighter, EEB, etc). Doing that simplifies “chain growth” issues when the rear suspension is cycling, but…it also eliminates the option of using a conventional mid drive (Lightning Rods, Cyclone, BBSHD, etc).
The majority of Revolution frames have been built up as a rear hub ebike (we have been keeping our finger on the pulse of the large DD rear hubmotor world for a while), but…one of the things that grabbed my eye as soon as I saw the Revolution frame, was…it can take an available mid drive as an option.
The frame is made from 6061 T6 hard anodized aluminum. The weight (as shown above) is 12.5 lbs (5.7 kg) for the full frame, including the carbon panels.
The head-tube is a heavy duty tapered 1-1/8″ – 1.5″ with extra-thick walls, 44mm top/56mm bottom. The current model Revolution uses an 83mm BB width, but…they have informed me they will be upgrading soon to 100mm to provide customers with more of the downhill crankset options that are currently popular (buy the frame first, before ordering any mid drive kit, so you can order the right kit).
In the pic above, you can see a fully-outfitted “turn key” HPC Revolution on the HPC Dyno (located in Southern California). Even before adding the weight of a rider, the head tube angle is raked enough to show that it is clearly made for downhilling, and…that same head-tube angle also provides extra stability at high-speed for anyone who might want to build up one of these frames for street use.
Our friend Lee (endless-sphere member “Leeleeducati”) lives in Toronto Canada. He decided that he wanted to adapt a new motor from Revolt (made in Israel), and make it into a mid drive. Alexey is the guy to talk to at Revolt. All their contact info is on their website but here’s how Lee contacted him; firstname.lastname@example.org. Pricing depends on how you configure it, but…the RV160Pro Short is in the $400 USD range. Alexey can give you a firm price based on any mods that you request.
At the time, Alexey at Revolt was working on “short” version of the RV100/120 and also a new 160 pro. The 160 is approx. 165mm diam. x 85mm wide (6.5 X 3.4 inches), the stock default shaft is 20mm diameter, kV’s can be custom-wound, but…min/max is approx. 35-45 RPM/volt. Lee wanted an RV160Pro-“Short”, with added hall-sensors, temperature sensor, and custom shaft. Weight is approximately 5Kg (11-pounds).
Lee’s goals might have been easily met by the smaller RV100 or RV 120 motor, but…since the RV 160 was available, he figured there’s no problem getting the same power from a larger motor (which would run cooler at the same power levels). The RV 160 Pro-S is just about the biggest motor that would fit inside the Revolution housing.
Since this motor is an “outrunner”, it provides the maximum “torque per input watts” when motor volume is the issue of concern. Heat from the stator is shed by air-flow, and also by any physical connection to the stator end-plate. So…the end-plate motor-mount is made from aluminum, in order to make the entire aluminum frame of this custom build a “heat sink” for the motor. Since the motor is slightly oversized for this application, it would not experience much heat, but…whatever heat is does generate will quickly be “wicked away” by by this configuration.
In the pic above, an additional bearing was added onto the end of the drive-side of the power shaft. A sprocket will be driven in-between this bearing and the motor, and the space provided is just barely wide enough for a chain.
The motor will be mounted (of course!) right next to the bottom bracket.
Single-Speed Rear Cassette
Edward decided that he wanted the strongest rear hub that was possible, even if it was “overkill”. This led him to researching splined cassette hubs that use a “through axle”.
A cassette hub has a bearing at both the innermost location of the splines, and also the outer-most tip of the splined driver. Even when using only a single-speed, a cassette is stronger than a freewheel hub.
In the pic above, Lee sourced a red adapter from “Origin 8” that will allow any sprocket with a 6-hole ISO “brake disc” pattern to be used on a cassette. He then machined an aluminum disc adapter that connected that to a standard 104-BCD chainring. In this way, he could have a robust cassette hub, while using a wide variety of tooth-counts at the rear wheel. I have seen 104-BCD chainrings with tooth-counts from 30T up to 48T.
Lee designed his custom drop-outs for a standard 150mm wide hub with a 12mm diameter through-axle.
A “through-axle” rear hub is probably stronger than needed, but…Lee wanted this ebike to be as strong as possible in every possible way.
The Bottom Bracket Freewheeling Crankset
Edward chose to drive the motor through the BB using a freewheeling crankset. Instead of buying an available kit, he chose to make his own aluminum adapter-disc that mates a White Industries “ENO” flanged freewheel to a common 104-BCD chainring.
Trials bicycles launched a million mid-drive DIY builds when they began producing right-side crank-arms with freewheel mounting threads on them. By making the BB crank-set freewheel (instead of the rear wheel, meaning the rear wheel has a fixed sprocket), they could use the smallest possible rear sprocket, and still have an acceptable sprocket ratio with a fairly small chainring on the front (for ground clearance).
If you’d like to see an absolutely INSANE trials jump (bicycle parkour?)…put your beverage down and click on this.
You may wonder why…if Lee only wanted a single-speed, why didn’t he just get a rear hub-motor? It’s the same reason he wanted to pay extra for an aluminum frame. Its lighter. The gearing ratio between the motor and the rear wheel means that the motor can spin many times faster than the wheel (and larger-diameter wheels are good for tackling holes and bumps).
By having a motor that was geared to the rear wheel (instead of direct drive, DD), a smaller and lighter motor can have the same wheel torque. Also, using a mid-mount motor moves the weight of the motor to the center of the bike, which means the motor is no longer “unsprung weight”. Nimble off-roaders like to keep the wheels as light as possible
Three years ago, I would have said that the HPC Revolution’s battery housing was too small, but…now? there has been a dramatic improvement in battery cells about two years ago (which we wrote about, here). Lee wanted a battery pack using a specific cell, and he wanted it in a custom shape and configuration. That meant…he had to make his own, so…he bought the cells and a spot-welder that was made for 18650’s
If you are wondering what this entails, we wrote one of our most popular articles about our friend in France, Damián Rene. Click here to see him building his own battery packs for customers in the European Union (EU).
We can now get high performance and also long range from a fairly small battery pack. Lee had a particular cell that he wanted to use (The Panasonic-Sanyo GA), and he also wanted to have a battery pack that was a specific size and shape. So…he decided the only thing for him to do was build his own pack.
If you look at the pic above, the cell-groups (once the bus-plates are spot-welded on) will be four cells in parallel (4P). Since the cells are Panasonic GA cells, they have 3500-mAh per cell and provide 10A each, so this small and light pack will have 14-Ah of range and can provide 40A of current, with 60A temporary peaks.
The 4P groups form 18 cell-groups in series (18S). The average “nominal” voltage across the duration of the ride will be 3.7V per series group, and 4.2V when fully-charged. That means this 18S pack will be 75.6V when fully charged, and 66V for the majority of the ride.
The average performance will be 66V X 40A = 2640W, and this bike provides that in a very light, balanced, and nimble platform.
The Final Product
I must confess, I am not an active off-road ebiker, but…if I was going to build one, this frame is in my top two picks. The Qulbix Q76R is less expensive, but its also heavier. If you’re going for a street build, get the rear hubmotor, and doing that leaves the the entire frame housing for as much battery as you could possibly want.
But, for off-road?…light weight and having the motor and battery mounted to the frame is the ultimate configuration.
The brakes are Hope V4 floating 203mm rotors (from the UK). Ventilated dual-disc, which provides heat dissipation at it’s best. The Hope X12 spacer kit worked perfectly. The 157mm hub fits just as it should have, right from the start.
The swingarm is designed to accept 26-inch and 27.5-inch wheels, with tires up to 3.25-inches wide.
You can find Leeleeducati’s build-log here
If you like this configuration of mid drive ebike, you might also like:
HPC Revolution with a hubmotor
For off-road, the trend has been towards lighter frames using a mid drive. However there are still many enthusiastic off-roaders who like the simplicity of a rear hub, plus they love how the rear hub leaves the entire frame free to accept the largest possible battery, for more time in the saddle, having fun.
Written by Ron/spinningmagnets, July 2016