Its ironic that in the same month that Specialized announced the release of their first electric bike and touting it as the “fastest ebike ever” (read Specialized Turbo article here), a DIY electric bike builder, Simon Howarth out of the UK converted a Specialized downhill mountain bike frame into one of the best (and fastest) full suspension ebikes ever created. Specialized spent hundreds of thousands of dollars, had infinite resources, and took 4 years with a secret team in Switzerland to create the Specialized Turbo.
Simon converted his Specialized Big Hit into an electric bad ass in under 3 months time and on a tight budget. In all, Simons development and build cost him less that the $7,000 price tag of what a single Specialized Turbo would cost the consumer to buy. What is ironic is what Simon built out of his garage is probably more desirable to most consumers (and much faster) than the expensive big company creation the Specialized Turbo.
Where as the Specialized Turbo burns a measly 250 watts (to make it marketable in power-limited countries), the Specialized Super Charged Racer puts out over 3000 watts (yowsers!). Here is Simon’s Specialized Big Hit DH bike that he started with to start his conversion. For an article on which bike to base your own DIY build check out this article here.
And this is how he finished:
One of our favorite things about this electric bike is that it is not a simple hub motor conversion. Building a full suspension mountain ebike is tricky enough (where to put the battery in the small triangle etc), but building one which the frame must also fit the motor and controller is an insanely difficult task. Also hub motors, which are generally weak at low RPMS are notoriously weak mountain climbers and off road riders. The ultimate solution for trail riding and mountain climbing is a motor that goes through the pedal gears, allowing the electric motor to reach its optimal rpm even at a low speed while climbing.
Also most performance hub motors are heavy, and that unsprung weight in the wheels makes the bike feel heavy and unbalanced, and not as good for jumping. Simon solved a lot of these problems by actually mounting his hub motor inside the frame, centralizing the weight, and running the motor through the pedal gears, giving him a much more effective climbing abilites. With this type of set up he can climb a steep grade effortlessly at 5mph, something a hub motor built into the wheel could not do.
Simon started with a high performance hub motor he was familiar with..the Crystalyte HS3540, a motor known for being bullet proof, cheap, and capable of putting out a lot of power when overvolted.
Simon decided to run this motor at 40A with a standard ebike controller, and power the controller with a maximum of 75 volts of Hobby-King LiPo.
Here is what Simon’s batteries looked like, strewn together to form one 66 volt pack:
Simon was able to accomplish this amazing build with no fancy CNC equipment etc to pull it off. He used mostly basic tools to form his creation. But Simon is a gunsmith by trade, and capable of some extremely skilled work.
To begin the project, Simon stripped the bike of all her components and then bead-blasted her until raw. The Specialized Big Hit is a favorite candidate for electric conversion because of its massive full suspension and the light weight of its aluminium frame construction. Check out the alloy welding skills to transform this ordinary bicycle frame into a carriage to lovingly cradle the above electrical components:
This amazing E-bike frame was made in a garage-like work shop without fancy CNC equipment. Here is the frame with its custom fabricated pieces bolted on:
The Crystalyte HS3540 is normally a hub motor that weighs a bulky 18 pounds, a lot of weight to carry in the back wheel. In this build, the motor has been fitted with larger bearings and machined down to shed 3 pounds in weight and will be situated just above the bottom bracket, so the rider and the motor can both share the same driveline in tandem.
Here is a beautiful pic showing you how the hub motor interfaces with the human pedal drive line:
And the big picture of the Big Hit:
In the below picture you can see how the E-bike’s custom altered frame hides all the electrical components in a neat and tidy shell. This bike is using a total of six Hobby-King 22V / 8-Ah packs, combined to make a single 66V /16-Ah pack…a gigantic pack capable of taking a bike like this for an honest 50 mile range giving 75V when fully charged (66V average). To give you a comparison the Specialized turbo has less than half this amount of battery, and is less efficient because it has only one gear:
One of the most challenging aspects of building a DIY Lithium-Polymer powered ebike is battery management. Hobby-King LiPo packs can be dangerous if not handled properly. Simon chooses to use an on board Cycle Analyst to make sure his batteries do not go beneath the critical minimal voltage….the cycle analyst made by ebikes.ca has become a “must have” on most serious high performance E-bike builds because of its ability to help tame the rage that is lithium…notice how well the CA mounts to the handlebars, as if made for the bike, and a perfectly integrated power switch for the built in LED headlight:
A view of the custom light wired to the battery pack of the bike:
He uses a sophisticated RC charger in a custom box to make sure the cells are charged properly, and do not go over their critical maximum voltage. This box consists of a power-supply that converts household 120VAC into DC, and a Hobby-King programmable charger that takes an input of DC between 6V up to 36V (so RC toys can be charged from a 12V car in a remote area, or higher voltage when available). It has LED readouts and data-logging so that Simon can monitor the health of his battery pack. This model charges the massive pack in 4 hours.
This charger, made for field charging and adapted to be used as a safe home charger, is a perfect example of how DIYs use a mainstream mass produced technology (R/C) and adapt it to fit their hobby (high performance E-bike building).
Like all E-bike builders using RC technology, Simon has to cleverly adapt a technology not perfectly suited for his application. RC motors, controllers and batteries are designed for lower voltages than what is typically run on high performance electric bikes.
The charger in this box is made to charge a maximum of 22 volts (6 cells in series). High performance bikes usually run a minimum of 48 volts. Simon is running 66V on this bike (22V x 3) , but the charger is only made for a pack one third of that voltage. To deal with this Simon made the following battery interface port. What this does is effectively separate the main battery-pack into three sub-packs in parallel for charging. The blue socket is for parallel charging, and the gold-pins are for series “run power”:
And then when it is time to ride, this custom removable bus-bar effectively connects the sub-packs in series again to triple the voltage. The six pins on the left are the pos/neg from the three 22V sub-packs, and the two pins on the right are pos/neg out to the controller. This device also acts as an on/off key, and a battery-kill switch with a simple pull-cord.
Here is a picture of ebike and charger in perfect unison…a high-tech high-voltage crescendo when the bike reaches full charge:
DIY’s have been learning from each other, and technology has been building on itself. This bike is a perfect example of a myriad of ideas that have been exchanged on the technical E-bike forum endless-sphere, and a bike has ensued that has wowed E-bike builders everywhere. This is without a doubt, one of the cleanest conversion E-bikes ever created. Every detail of this bike has been meticulously thought out:
So here is the bike in action….a bike capable of 40-MPH in top gear, and also able to crawl with awesome climbing torque at only 5-MPH:
Congratulations to Simon Howarth for making one of the most spectacular DIY E-bikes ever:
January 7th 2014 update –
This bike is currently for sale as a used bike with the added feature of a $1400 Rohloff as a transmission. Currently the bike is only being offered to European buyers at a cost of $6500 Euros. It will be available this spring.
If you are seriously interested track down user Courcheval on Endless Sphere. This is a rare opportunity for someone to own a one-of-a-kind build, and one of the better electric bikes ever built.
__________________________________________________________
Written by senior editor Eric, April 2012
