Wednesday, 9 September 2015

DIY Long Tail EBike - Chapter 3

DIY Long Tail EBike - Chapter 3 - Electrics and Drive System


It would appear that building the frame and doing the normal bike stuff was the easiest part of this DIY Long Tail EBike, when you go off piste trying to think about an ad-hoc drive system the project becomes tricky, but certainly not impossible. In Chapter 1 we saw the concept and beginning of the frame. Chapter 2 saw the frame being welded and first test ride. In this chapter I will explain how I fitted the electric drive system.

Rear Wheel Drive - Things can get complicated even without gears.

First off for your own sanity I would advise a front wheel drive system, this allows for standard configurations at the rear of the bike, were you may need gears etc. and lets face it the rear wheel hub area of the bike is complicated enough as it is.

So for those of you looking for guidance at this stage I would suggest a front wheel drive set up for simplicity.

DIY Long Tail EBike - Chapter 3 - The Law


In the UK you are allowed 250w for a normal bike or 300w for a tandem.

This kind of power will propel 200kg of rider and passengers at around 10 mph on flat terrain, perhaps a bit faster dependent on gearing. But you WILL need to pedal quiet hard on a moderate hill, and you will be pushing up a steep hill. One bonus is that if you a carrying a load the bike will push itself up the hill, you can run along side it if you like!

Please Ignore the Color Scheme.


The law state 15.5mph as a maximum speed which is fine, as this feels quite brisk. But if I were to be asked for my opinion I would ay that the wattage could be raised to 1000w (or removed all together) to allow for hill climbing with a load, so long as a max speed limit of 15mph was maintained. After all you can pedal a lot faster than that on the flat any way! Also speed is a lot easier to measure (by the police) than wattage. To measure peak wattage of a setup, the policeman, policelady or policeperson would have to ride the bike up a steep hill whilst looking at the results from a amp meter and then work out the results based on the voltage. Based on the above it is unlikely you will ever get caught for riding an over power e-bike so long as you do not go over 15 mph.

The regulations also state that you should have a metal plaque on your bike stating the manufacturer and wattage and voltage. As my daughter made up the name for the bike (The Happy Uphill Bike) she is elated at the thought of having the bike labelled as such.

This bike is what is known as a "twist and go" I the throttle in independent of the pedals. After January 2016 bikes like this will not be legal, and all e-bikes will have to be pedal sensor type.

DIY Long Tail EBike - Chapter 3 - Voltage


Most motors aviable are 24 or 36 volt with some being 48 volt. The most obviously advantage to my untrained mind with a 24 volt system is that you only need 2 x 12 volt batteries. Which keeps things simple.

However this leaves you a bit stuck if you want to up your voltage.

A Wide Seat = Plenty of Room for Batteries.


I chose two 12 volt 22ah Panasonic Sealed Lead Acid (SLA) batteries. I am still unsure if this was the right choice. Most SLAs require that they are run at 50% discharge as a maximum, meaning a 22ah battery will only give you 11 ah. Looking at the manufacturers specs however, hundreds or cycles are achievable at 100% discharge, which is similar to the alternative that is lithium ion batteries. Expect to pay 3 times the amount for reputable lith-ion batteries of the same capacity.

You see as you increase voltage the required amp hour capacity of a battery decreases. A 36v motor running at 250 w will require a lower current than a a 24v motor doing the same work.

So if you decide to embark on a project such as this choose 4 x 12v batteries at around 10ah. These can be configured as two sets of 12v in parallel to give 24v or all in series for 48volt.

DIY Long Tail EBike - Chapter 3 - Wattage


It would appear that the wattage written on the side of any motor is a made up figure. A 500w motor may be labelled as a 250w motor so it will sell better in an country (like the UK) where 250w is the legal limit.

For testing I have been running my 250w motor with a 500w controller. And that seems to work fine, and gives much more power than when using a 250w controller.

 DIY Long Tail EBike - Chapter 3 - Fixing the Motor


For those of you daft enough to be considering a chain drive motor solution. You can mount using per-manufactured mounting brackets or build a mount with metal, hacksaw and a welder. In may way fixing the motor is quiet easy. the main problem is how to keep the pedals (required by law) and introdcue a motor without having to pedal "through" the motor.

When mounting the motor, try to place some rubber blocks between the frame and motor mount to reduce vibration noise. I used a chopped up bike tire. The motor mount has to be solid, even a small motor produces a strong twisting motion when under load, so the mount should be securely attached to the frame. I initial bolted the motor to the underside of the wooden deck, but this was not good enough and had to weld a mount in place.

Run Two Chains - Note Chain Tensioned for Pedal Chain

Chain Tension - Only One Side can be conventionally tensioned.


The way I got around this was to buy a flip-flop BMX rear wheel, which as a thread for a freewheel on both sides. However, these hubs are not intended to be used both sides at once as the threads will be opposite when mounted on the bike. One freewheel must therefore be glued ( I used strong LOCTITE) in to position to stop it coming undone when in use.

Most flip flop BMX hubs have two different thread sizes for the 2 freewheels so make sure to get the right size freewheels. One is normally standard size the other will be 30mm size.

On tension of the chain. Whilst you can tension the chain by moving the rear wheel as is normally the case. It is unlikely you will end up with a tight chain on both sides. So I have opted to tighten the chain via moving the back wheel on one side (motor side) and with a chain tensioner on the other side. This works fine, but you will need a rear mech hanger welded on the frame some where so as to attach the tensioner. You can buy a steel mech hanger on ebay for £1.50 so don't go hack sawing one off of another bike!

 DIY Long Tail EBike - Chapter 3 - Gearing


The motor chosen is the Unite Motors MY1016Z2, which is a 24v 250w motor with 10:1 reduction gearing. You will need reduction gearing if you intend to run a chain drive motor. Most motors will produce a bout 3000 rpm, if ungeared and so if you "do the math" multiplying rpm by wheel circumference you will get an answer some where in the region of 150mph as a top speed, which is not realistic.

With a 10:1 reduction I ended up with an rpm of 315rpm, further reduce at a ration of 9:16 by the drive sprocket and freewheel gearing. The tire circumference for a 20" wheel is approx 157cm. A simple excel spread sheet is handy, as you can tweak the numbers and watch the results change.

Excel Spread Sheet to Calculate Speed in Relation to Gearing
I have opted for low gearing as I live in a hilly area, to assume that a 250w motor will pull 200kg up a hill, at 15mph incorrect. In fact it will not even pull 200kg at 10 mph as geared above. An increase in the rear freewheel size to 24 teeth gives a top speed of 7 mph. With more torque for hill climbing.

DIY Long Tail EBike - Chapter 3 - Chains and Sprokets


Who knew!? Did you now there are different sizes of chain? I did not. The most important measurement is the pitch this the the length of each link. Most motors come with a #420 sprocket, this to fit #420 chain, this is a heavier grade chain than normal single speed bike chain, the rollers are larger, although the pitch is the same.

My motor sprocket comes with a sprocket that fits normal BMX chain, and that made things easy.

DIY Long Tail E-Bike - Chapter 3 -Wiring

 The ampage involved is considerable.  A household kettle draws a current of 13A, and even a small e-bike motor will draw the same current albeit at a far reduced voltage. For higher powered motors say 500w the current will increase to 25A and you should start to think about the sizes of the wires you use.

Wiring for a brushed motor is relativity simple. Note doubled up wiring. Switches for lights and "Ignition".

I was using bits from the garage and so I have chopped up an old extension lead, which is 13A. I have then doubled up on these wires, using to parallel wires for each high amp connection. If you wanted to do a proper job then head down to your local motor factors and buy some 25A or even 50A wire.

The thick wire need only be used for the follwing connections:

  • Motor to the controller.
  • Controller to batteries.
  • Battery to Battery Connnections.
You can use thinner stuff for the other connections. The controller came with plug in style connectors, I have cut these off and soldered all of the joints.

The complexity of the other wiring will depend a lot on the controller you are using. Some have more "tails" than others. If you have an ignition switch tail then this will need to be sorted out with a toggle switch, so you can turn the controller on and off. However other tails such as brake lights, can be left unused if you want to.

DIY Long Tail EBike - Chapter 3 - Lights


Joy! With a normal dynamo operated push bike you are limited to 6v systems, but with a huge battery to power the motor and the new generation of LED lights you can have some serious fun with the lights. For the rear light I got some cheap LED side lights for about £6. For the front light I purchased a 12V 27W LED flood light, which is just awesome.

A Front fork with V Brake Mounts is preferential over U-Brakes (as pictured)

A Massive front head lamp will be great to use this winter.

In time I will fit a low power "be seen" light and switch the main front light independently so as to effectivly have a dip and main beam. Alternatively you could fit a hood over the front lamp to direct beam away from drivers eyes.

DIY Long Tail EBike - Chapter 3 - Lessons Learned

  1. 250w will not get you up a hill without pedalling.
  2. Don't buy purple pedals. Even if they are cheap.
  3. SLA batteries are fine. 
  4. A bank of smaller batteries is more versatile than two larger ones. 
  5. FRONT WHEEL DRIVE is easier. Perhaps opt for a hub motor.
  6. You need a geared motor.
Did you miss Chapter 1 or Chapter 2.

Read on in Chapter 4

Please leave any questions or comments below.

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