Another friction drive project

[kosilica]

Hello to you all!
I am so glad that forum like this exists, it confirmed my idea that low-cost e-drive for bicycle can be made. I searched the forum, used wiki, but before spending money on parts, I would like to get confirmation from someone who already made one or more friction drives that this combination I have in mind will work.
What I expect from my project is:
-Speed anywhere between 30-40 km/h
-Range up to 15 km flat ground, (only pedaling when starting, drive would be engaged at the speed of about 10-15 km/h).
-Have in mind that both me and bicycle weight about 100 kg, and tire dimension is: 700x38C).
What I have in mind that will do the work:
-Motor: http://www.hobbyking.com/hobbyking/store/__36407__Turnigy_Aerodrive_SK3_6354_260kv_Brushless_Outrunner_Motor_EU_Warehouse_.html
-ESC: http://www.hobbyking.com/hobbyking/store/__10331__Turnigy_Brushless_ESC_85A_w_5A_SBEC.html
-Battery: http://www.hobbyking.com/hobbyking/store/__8590__ZIPPY_Flightmax_5000mAh_6S1P_30C.html
-Speed control: http://www.hobbyking.com/hobbyking/store/__18309__Hobbyking_LED_Servo_Tester.html

Thanks in advance to anyone who is willing to help. I will keep the topic alive and post progress of the project along with pictures.
Looking forward to it!

 

[kolby]

Friction drives don't seem to be that popular around here anymore. Here is what I built recently:
http://endless-sphere.com/forums/viewtopic.php?f=28&t=63553&p=952009

I used the G160 motor (My eflite 160 seems to be the same motor):
http://www.hobbyking.com/hobbyking/store/__14408__Turnigy_G160_Brushless_Outrunner_245kv_160_Glow_.html

The motor you linked has a very narrow bell housing, and not a lot of mass to dissipate heat, although for your speed it might work.
I use the same ESC but I bought some cheaper Multistar batteries (only 10C, but enough for the motor with 2 in parallel).

What is your bike? Where and how do you want to mount your motor? I'm happy to give you the details of my bracket if you want.

My setup is very simple, but I had to ditch the servo tester. After using it for a while, the potentiometer loosened a little and I had the motor run at full speed in my apartment. Not that great. It burned a lot of rubber before I could switch it off.
I've since purchased a programmable servo controller from polulu.com (the Mini Maestro), and did some custom programming to ramp up the motor nicely and set a speed dependent motor rpm.

After many test rides, I finally found a good wear layer for the motor housing.
I wrapped the can with a layer of Scotch Outdoor Mounting Tape (very sticky on both sides, slightly cushioned) and then mounted a piece of an MTB inner tube over it. It gives excellent grip on the rear tire without wearing it down too quickly. I'll update my build thread with more details.
I really love my friction drive with my current setup.

Good luck with your build,
kolby

 

[kosilica]

Hi kolby and thanks for reply.
Sorry for my lack of knowledge, I am little bit confused right now. What is exactly the difference between friction drive and the setup you built recently? I actually had very similar design in mind, with same motor placement as yours.
I intend to use a piece of old inner tire as a grip between the motor and a tire.
I choose that motor because I saw one setup successfully built with that motor and I am aiming on low cost for my first project. As I can see the rotor is wide enough to provide grip on the tire.
I will use a Wheeler Cross 6.4 bike. Take a look at the pictures of where I want to put the motor.
And yes, details of the bracket would be great to have. Actually, getting the correct position and pressure of the motor on the tire when engaged and disengaged is the only problem I have with this build. All the other things are very familiar to me.
And about that servo tester and incident you had: Safety first, first thing when done operating is to disconnect the battery, just the habit I have from flying R/C models. I also intend to install the fail safe switch so I can disconnect the power if anything goes wrong during the ride.
http://imgur.com/u4jasdP
http://imgur.com/6Vop0qu
http://imgur.com/bApWFfA

 

[kolby]

kosilica,

looks like your frame has plenty of room to accommodate the drive unit. I didn't mean to confuse with my first comment, what I built is a friction drive.
It looks like your frame has a cable for the front derailleur running down behind the seat tube. This would be in the way of the mounting bracket, unless you build your bracket to open in the rear.
Motor choice: the housing of the motor you linked is only 28mm, your tire is 38mm (nominally). A wider tire usually has less pressure, so the drive will push down into the tire quite a bit, and then the tire might get wider than the spinning part of the motor. The motor I linked is not much more expensive, but has almost double the width of the housing.

My bracket has two parts: a seat tube mount built from HDPE (wouldn't use it again, too soft, use Delrin instead), and a 1/4 inch aluminum plate.
The plate is pivoting around a 8mm axle that goes through the bracket. Distance from the axle to the axle of the motor is 50mm.
The plate also has a pin pressed in that engages in a hole in the bracket with two small screws as stops to prevent the motor from hitting the frame and engaging to far into the tire. This is critical to the functioning and the efficiency of the drive. You can control the maximum engagement and angle by sliding the mounting bracket higher or lower on the seat tube. This part takes some trial and error. I can post another picture which shows the motor at its running position.

Make sure you have some form of glue or strong sticky tape under the inner tube otherwise it will slip off the motor.

Good luck,
kolby

 

[kosilica]

OK, I will follow your advice for the motor. But will it run properly because it is designed for at least 30V and I intend to use battery rated at 22V?
Any pictures of bracket (disassembled also) would be great. I am still looking at the ideas on how to design it. In the end I will have to wait for the components to arrive before making anything.

 

[kolby]

Kosilica,

sorry I haven't had much time lately to update here. I will try and get some sketches of my bracket up tomorrow. Meanwhile, I tried my other motor on my bike, the G110 EasyMatch at 219 kV (pretty similar to the motor you first mentioned). It runs fine, but it makes a lot more noise at comparable speeds to the 160 (the bigger wider motor). My G160 is rated at 245kV and I would actually go with a higher KV rating for the slightly smaller motor. Once I get a little more time, I want to try a 50-54mm motor, I'm just not using the power numbers that the bugger motor provides. With the watt meter, I'm seeing around 1100-1200W peak, and I'm curious to see if the smaller motors can handle it. I'm sure those will be even noisier.

- kolby

 

[kosilica]

Hey kolby,
No problem, thanks for helping, no matter how often you are here
I will order the parts in a few days. So, I can use that 160 motor on a 6s battery?