29 October, 2014

DIY: Turn your bike into an e-bike for yourself - Step 2/5: Mount the engine and disc brakes on it

2: Putting the engine on the bike
In this post I will explain how I placed the wheel with the engine kit on the bike, but before going into the details of the assembly, we will expand the information in the first inning on motors that we use for our bike. 
In theory you could use any engine from 150 to 1000W (or more, but I think putting more unnecessary and dangerous), with or without brushes, etc, but if we use a lot of bike, it is better to spend more on a good motor brushless dc (B rush L ess D irect C urrent BLDC) that will last us as much as the bike itself (while we burn not overheat), since the only mechanical parts, bearings, they last almost a lifetime and may be changed if necessary. 
Brushless motors have the advantage of being easier to handle (not require an electronic controller), but require increased maintenance to bring wear parts (brushes, and gears if available).
Legally you can put a powerfull motor and limit it to 250W in certain countries; it is the output which is limited.
Among the small BLDC motors have 250 / 380W with gears to increase torque, the gears are usually made ​​of nylon and after a few thousand miles. often fail (although you can get partsof metal). These motors are recommended for people using the bike for rides, and have a little help with hills; they are small and inexpensive. 
It is always preferable to a direct BLDC motor bike without gears for the following reasons: 
  • They are the most efficient (up to 97% efficiency).
  • Very good power / weight ratio.
  • Very low maintenance.
  • High acceleration (nothing mechanical that limit, the limit is usually electronic).
  • Precisely controllable rate.
  • Low operating noise (soft rrrr only at low revs).
As I already mentioned , if we want to climb steep slopes need 500W at least one so you can go loose and does not overheat; on hot days the engine of my bike can become hot enough to climb a hill of 500 meters and 10% incline. 
As I said, I recommend reading the blog of Sebastian Reyes , especially this entry to choose the right kit for your needs. On this page of Golden Motors is a good comparison of performance and recommendations of the various engines.
I chose the 901 Prokit a kit consisting of rim GoldenMotor brushless motor that can work at 24/36 / 48V (500/720 / 1000W), controller knobs (with the right type motorcycle throttle), and a pair of switches for the horn and cruise. 
This engine runs about 38 km / h with a battery of 36V and 20Ah (I checked), and according to specifications can feed the Prokit 901 with up to 60V; I can not imagine how fast you could go with that voltage! 
An American editor has managed to put it to 120 km / h! . Yes, theorists in vacuum at 1050 rpm. and running at 72V, I guess.
Riding the rim with motor bike 

The Prokit 901 brings a BAC-281 controller 50A peak (30A continuous) which is fine, it can also operate without hall sensors (in case one fails), besides bringing cruise control, horn, anti-theft system etc, but your program setup by PC brings few changeable options: 

But let the subject motor kit, because we need to test it to its proper place (or attach the shaft securely to prevent damage to the wiring).
IMPORTANT: First of all, you have the manual assembly of this kit at this link (English) , that all details listed consider.
First I put a presentation to see where they could come the drawbacks that were seen coming from the washer and shaft size, and check the remaining distance. 
Note that the wheel does not come with gears, so you need to buy a set of gears 7 changes (thread); in the store so you can be placed in a second, just screw the whole and now is fixed.
It also comes ready to put brake disc, but very little room for him, as we shall see. 

The shaft is flattened to fit and can not rotate (if it did would be damaged cables because the stator where induced is staying still or while rotating the outer rotor, which are magnets and attached to the spokes), and had a little more as the hole of the support, so I used the dremel craft with a small cylindrical grinding stone to wear a bit expensive where I was stayed pending the entry well.

Bring lock washers put aside to tie the axle to the frame, but as in this table do not coincide with either the modified flattening and welding a small squadron of steel. This continues to fulfill its role, which is that in case of loosened the wheel nuts, not out of place.

Given the strength that it can get this engine, all security is low.

And that would be on the side of the brake disc (even loosely):

Place camera and tire
First of all it is convenient to put the camera and the old tire wheel:

We will introduce the camera in place first valve sticking in his hole. This is a reinforced rim (to hold the horsepower you can have, in addition to ours), so that the valve protrudes only 1 cm, and can not even put a stopper without cut in half. Is advisable to put a washer to secure the valve in place and can not be twisted if the tire pull to one side (as usually take close valves as cycling chamber). Anyway, to avoid this we must keep always well inflated wheel as it could only happen if there is little inflated and exert a lot of force on the wheel (with a motor can happen). We will avoid any problems if we put a valve chamber more long, available on request.

A lack of adequate tools, I used spoons to fit the tire, since the songs have killed and pose no danger to the camera or the tire:

Finally we will inflate in half and slip the wheel on the ground to ensure that all sides of the tire are properly seated on the rim, and finished inflating to the correct pressure.

Making the disc brake 
With the weight that takes the bike, and the speed could be as high, it is best to replace at least one of the brake shoes on the other disc and pads durability and reliability, if we want to stop in walking distance.
I opted for one of the cheaper cable, but if you can, place one better with hydraulic disc without perforations (wearing pads and more I see unnecessary unless we engage the descent ).

The downside of this engine is that it occupies part of the space normally reserved for mechanical disc brake, and after placing the box on the brakes, it hit me in the hood (maybe it's just this model, which takes rapid change pads on both sides), and I was obliged to cut the shaft to press the inner pad to the limit without preventing normal operation, but the rapid change of pills may be nullified (forcing release the brake for it).

With sandpaper or grinder with cutting disc, cut carefully piece shaft protruding
In the next picture you can see just what's left brake cover.

Also the position of the pads was so foreign that barely brushed the outer disk, so I had to eat one side of the washers positioning (internal) to make contact pads all possible braking surface:

The brake already installed and working; with black nut regulate the voltage
On the other hand, leave excess cable to the engine, so that in case of a puncture, not left us so fair that when released (in my case cutting flanges electrician with that subject) left us no space maneuver to take the wheel of your site and access the camera.
I recommend putting a little silicone on the pier where the cables come from inside the shaft so that no water can enter there.

Technical details and performance
The Prokit 901 brushless is from 20 0 to 1000W (depending on amperage and voltage); operated from 24V to 60V, and has 46 neodymium permanent on the wheel (rotor) with 51 poles in the shaft (stator).
In the example photo, the poles are copper and magnets are small gray rectangular outer segments, with 3 Hall sensors that detect wheel position monitoring a magnet passes near the sensor.

Image of a similar engine without lid (change number of poles and magnets) Source
As shown in the lower image, the poles are in groups of 3, with the central pole winding in the opposite direction to the other two. The magnets alternate in polarity, so that when current passes through the first set of poles in one direction, the next magnet attracts and repels the above, resulting in the movement, which is perpetuated by alternating phases.If you will look closely at the colors, red, green and blue, each color is a phase, current flows in the opposite direction in each phase, and the driver, according to the position indicated by the Hall sensors (placed at 120 most of the time ), alternating current phases, faster the rpm spin the wheel, and activate only two phases at all times (you can see it better in this video ).

MOSFET driver transistors control the direction and amount of this current, so regulating the power and rotation of the wheel according to the position indicating the Hall sensors.Depending on the controller, there may be two or more controlling MOSFETs each phase (depending on the power thereof), controlling the positive half and the other half negative. One of the hall sensors detect when a magnet is near, sending a signal to the microcontroller to enable the power transistors (MOSFET), controlling the flow of electricity and address.
A more electricity the magnetic field is stronger, so the strength and speed increases.
Higher voltage means more power, that's why higher voltage means higher top speed (RPM).

Hall AHall BHall CRed PhaseBlue phaseGreen Phase

There are drivers (as included with the PROKIT 901) that can also operate with damaged or non-functional sensors determine the position measuring electricity inducing magnets on coils with movement. This way of working requires the engine is in motion, so we have to start moving to use force, unless the driver is of quality, accuracy decreases with Hall sensors at low speeds, so the power and slightly lower maximum speed.

This motor obtains its improved performance and operating at 36V 11A (81.4%); here the efficiency curve .

Getting more power out of your engine without frying
The Public Enemy No. 1 of any electric motor is temperature. Furthermore, the power of these motors is only limited by the heat generated . There are controls such as Kelly including engine temperature sensor, but to place this kit require open and modify it, adding a pair of thin phase to the hall and a probe cable and sticking into the stator.
When I go up the hill to my house the engine temperature is healthy, will have about 30, but I worry that in a path of endless slopes can fry it, so I will raise this modification should make similar paths with her.
A 1000W motor as mentioned could overfeed with 60V and 25A, 1500W opteniendo with which run more than 60 km / h, and could give the power for a while, but not all the time because it could overheat and burn his wound, and the main drawback engine bike is poor ventilation from being unable to place any type of fan (although it could have resulted place some type of aluminum heatsink, a disk around the inside so that when you turn removes heat from the rotor, cooling the assembly work).

In yesterday morning summer storm dropped a bike being on the street (34 l / m2 in minutes), a real shower for the bike. Luckily I had already sealed with silicone those places where water could sneak in, and left the box well sealed at the top and open at the bottom so the little water that might sneak out freely and not accumulate.
It is situations like this that do not recommend vents for the engine covers but well sealed with silicone, which can be removed for maintenance.
Although an engine with an oily liquid ventilation and corrosion protection could give good results, as we will use it rarely rain.

Well, that's all for now on the engine; in the next posts we will see how to mount the battery box and light resistant form, analyze the different drivers available (depending on what you want to complicate life) and program a Kelly, to finally analyze better things and general feelings of this project. Have some fun!

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