An Advanced Friction Drive System

Hello everybody, what a great construction! Is it true that if the pressure of the motor to tire is higher, the friction drive has better efficency? So when motor(roller) is hardly pressed to the tire, everything works better?

Greetings form Poland, Robert!
 
Beejaxon, there are certain benefits in tiny motors to having them spin at very high RPM's.

With a conventional style of motor, it has a fixed outer can connected with the copper wire coils, and the shaft with permanent magnets spins. That is an "in-runner". At some time in the past, RC enthusiasts experienced problems with very high RPMs (10,000-rpms+) so the "out-runner" was invented.

The copper wire coils that make up the stator are fixed to the end cap, and the permanent magnets are mounted inside the cannister walls. The outer can and the magnets spin. They still must be balanced to work well at high RPMs, but bits of stuff coming loose and causing a catastrophic out-of-balance condition became much less of a problem.

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Thanks for the kind words guys, its much appriciated.

Beejaxon,

Welcome to the forum. I am using a standard RC outrunner motor in this design. The motor is sandwitched between two plates. One plate has the motor body attached to it and the other plate supports the other side of the motor by holding an output shaft attached to the outrunner casing. This output shaft would usually have an aircraft propeller bolted to it.

Power for the motor comes from the speed controller which is built into drive. The speed controller is very compact and uses the aluminium side plates as heat sinks. The battery isnt showing in the last picture but it uses a small pack that can easily be mounted in a varity of places

These two pictures should explain it better.
 

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robert.smu said:
Hello everybody, what a great construction! Is it true that if the pressure of the motor to tire is higher, the friction drive has better efficency? So when motor(roller) is hardly pressed to the tire, everything works better?

Greetings form Poland, Robert!
Click to expand...

Hi Robert. Welcome also.

For best efficiency you need to keep the pressure against the tire as low as possible but high enough so that the drive roller doesnt slip. As you add power you need more pressure on the tire and as such will loose some efficiency here. However, this is design pushes harder on the tire as you put more power on and completely decouples when you are coasting. Low power efficiency is improved greatly and when switched off, except for a little added weight, the drive has no impact on the bike at all.
 
Thanks so much, Kepler and Spinning Magnets. Those pics helped a lot, especially the shots of the opened motor. So the leads to the battery are attached to the bearing on one end of the motor, which is bolted to the brackets, right?

What an awesome, intuitive setup Kepler. I'm researching options to power my trike under construction, and I want to keep it lightweight, and cheap. This seems to be one of the best options I've found so far. Do you mind sharing your cost in the motor, controller, and batteries?

Thanks again guys, Keep spinnin!
 
Beejaxon, you should create a build thread for the trike. :)

Takes some extra time to do, but it does two things:

--people can chime in when they see something potentially problematic (something already tried and found wanting)

--others can learn from what you do, and new things you come up with
 
beejaxon said:
Thanks so much, Kepler and Spinning Magnets. Those pics helped a lot, especially the shots of the opened motor. So the leads to the battery are attached to the bearing on one end of the motor, which is bolted to the brackets, right?

What an awesome, intuitive setup Kepler. I'm researching options to power my trike under construction, and I want to keep it lightweight, and cheap. This seems to be one of the best options I've found so far. Do you mind sharing your cost in the motor, controller, and batteries?

Thanks again guys, Keep spinnin!
Click to expand...

The motor I use is a Hyperion 4045 320kv motor and was selected because it has a one of the smallest can diameters for a motor this size. There are some options out there though. Criteria is a motor less then 50mm in diam, 200 to 300 kv range, 2000 to 3000 Watt power range. Both Hyperion and Scorpion make suitable motors.Budget on around $170 US. Speed controler needs to to be a high quality unit with Castle Creations being the best for the application I have found so far. the 100A ICE ESC is a good choice for this setup budget on $150 US . In relation to batteries, I use a small 5S 5ah pack from Hobby City which is around $50 US. Keep in mind this is for a hill assist application and is way too small if you want to be passenger most of the time. You would need 4 of these for any reasonable distance as a passanger.
 
Kepler,
I just droped in to say. TOP JOB on this design & exicution.
I have a buddy interested in getting his bike electrified, after playing around on my lil' bmx.
He has opted for us to build a cyclone type unit & utilize the bikes drive train.

I really tried to sell him on the benifits of this set up, especialy as his bike has an aluminum frame.
I am inspired on the minimalist nature of this design.
Between EVtodd & yourself I have added friction drive as a a legit drive option for bikes.
again good show. T
 
This is so awesomely cool and kickass. I think the fact that your a mechanical engineer helps.
 
Bee,

The most significant difference between an "outrunner" and an "inrunner" is that the airgap is at a greater percentage radius in an outrunner, due to the magnets taking up less space than the stator. So, for a given case diameter, the turning moment, and therefore the torque, is greater in an outrunner than an inrunner. This is the advantage of outrunners - the disadvantages are slightly poorer efficiency and a worse heat path from the coil to the outside (they need to be vented).
 
Just a heads up - HobbyKing finally got restock on Turnigy AeroDrive XP motors from 160kv to 270kv, large but perhaps useful for this application - I got a 170kv unit for testing last week.

Hope it helps!
-Mike
 
I saw that. I just placed an order for one for testing on the Mk3 version of the drive (under constuction).

MK3 enhancements.
Universal mounting system to suit 90% of bikes
Intergated 4ah battery pack with external booster pack connections
Intergated overcurrent protection
Up spec motor for increased run duty

Stay tuned :mrgreen:
 
Cool, get that motor to work will ya... then we both have the same working block and perhaps we can integrate the slightly larger (but much cheaper) infineon 6fet PCB in place of the HV110?
I'll show ya how to do halls on this motor, when I figure them out (should be this coming weekend as I am solo and have time for bench work).

Can't wait to see MKIII - this is for CNC fabrication goal?

Integrated battery? Going to rename this iZip "friction"?

-Mike
 
Shouldnt be too difficult to test the cheaper motor.
Halls and the 6fet will be the ideal arrangment so looking forward to seeing what you come up with.

And yes, the aim of MK3 is to make it repeatable.
 
so did i just read that you are a mech engineer? if so, ill assume you did the calculation as to the resistance loss.

off the top of my head i would think that the resistance would be huge, either you would get slipping or the motor would use a lot of energy to overcome the friction onto the tyre, what did you do to overcome this, or isnt it as big as i think it is?

sweet project though, i love a nice clean build, compact is a bonus :D
 
bandaro said:
so did i just read that you are a mech engineer? if so, ill assume you did the calculation as to the resistance loss.

off the top of my head i would think that the resistance would be huge, either you would get slipping or the motor would use a lot of energy to overcome the friction onto the tyre, what did you do to overcome this, or isnt it as big as i think it is?

sweet project though, i love a nice clean build, compact is a bonus :D
Click to expand...


You should probably read the whole thread to see how his drive works. These moving friction drive systems only apply full pressure when needed. At partial (or even full) throttle on flat ground for example, it starts to move back way from the tire until it's barely touching. At full throttle from a stop or when you need more torque (for climbing a hill, etc) the mount moves the roller back into the tire. The great thing is this all happens automatically.

As for big losses from the friction of the roller to the tire... It doesn't take as much pressure to avoid slipping as you might think. You also save on not using another means of transferring the power. You have losses with a chain or belt drive too. I personally find my friction drive setup to be very efficient. I think the word "friction" makes people think of heat, energy loss, popped tires, etc... It's just not the case with a well done system.
 
oh ok, thanks todd, i didnt realise the pressure was variable onto the tyre, i thought it was an on/off sort of thing. i just thought that with a smooth rotor onto the wheel it would slip far more easily, but apparently not.

sorry for any noob questions, im trying to learn about the systems :D i must say im quite impressed.
 
I really dont like the term "friction drive". As Todd has pointed out, it really gives the wrong impression on how the power is delivered. In reality, a common run of the mill vee belt setup uses the same priciples to obtrain drive. A vee belt drive is kept under constant tension to maintain drive and the actual contact area on the drive pulley is smaller then most would realize. Also this is steel to rubber contact, just like our bike drives. Fact of the matter is that efficiency between a Vee belt drive and our frictions drives would be quite close.

I have never bothered to carry out the calculations and would need to go back to the books to fugure it out but real world testing has shown that my hub motor setup and friction drive setup use very similar power outputs for a given speed.

I really think its about time this type of drive was re named "Roller Drive" rather then "Friction Drive" :)
 
How about pressure drive? Or even static/dynamic drive
I agree that "friction" sounds derogatory or atleast doesn't bring to mind the refinement you and Kepler have acheived...
Perhaps dynamic pressure drive?
-Mike
 
"Contact Roller" drive is probably as good a term as any. You could technobabble it with "Variable-Geometry Dynamically-Controlled-Pressure Synthetic Malleable-Surface Roller to Tire Tread Surface" drive. "Variable-Geometry" always makes things sound nifty. :)
 
APR sounds like a Toyota Event = )_ (or terms)
Sadly I have nothing better to offer, except... maybe get away from what it is and go for what it does..
LitePower would seem appropriate as would liteassist or... you get me, then there are always initials as the MS eDrive..
-Mike
 
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