Why not friction drive?

[etard]

I live in Southern California where it rains maybe 30 days a year. I know that a friction drive sux in the rain, but is it really that bad considering efficiency? I heard that it only requires about 5 pounds pressure against the tire and if you use a 1 inch wheel, you are getting a 26:1 gear ratio. It seems with all the talk about RC motors that everybody is hung up on the drive. Is friction drive noisy, inefficient, or otherwise micky mouse? Can somebody please tell me why I shouldn't go this route?
I have been thinking about simplicity and weight. I want to cut and attach a gates timing belt drive to a rim, mount a motor with a belt sprocket to the rear triangle with a cable actuated engage to rim. To keep my bike light and stealth, I want to use an rc controller and just carry the battery in a backpack. Would there be a major loss of efficiency on account of the friction from a straight line drive (motor plane) to a circular (rim) driven? What are the limitations of this in watts, anybody?

[swade]

Good question. I'd like to hear others weigh in on this as well!

[TylerDurden]

They suck in wet weather.

[AussieJester]

Never really grabbed me, seems rather 'ghetto' and as mentioned they arent great in the wet and wouldnt be good for off road use...That said your in a situation where neither effect you, i have always been one to give it a go and see how it works rather than ponder over whether it will... best of luck

[fechter]

The Zap DX and EV Warrior friction drives have a pretty long track record. If properly implemented, the efficiency is not too bad. It is certainly one of the simplest ways to get the required reduction from a high rpm motor to a bike wheel.

Roller material is quite important. There are several types. From what I've heard, the later Zap drives used something that resembles a grinding wheel that's made of sintered sand or the like. These did better in wet weather, but still suck in the rain. Other rollers are typically some kind of knurled steel or metal with a sandpaper-like coating. Roller wear can be significant.

The motor mount linkage can also be designed so that roller pressure increases with torque and decreases when the load is light. This optimizes efficiency and reduces the chances of slippage.

Roller slippage, even for a second, can ruin a tire. This means you will be limited in how much power you can apply during acceleration. If the controller current limit is set correctly and the motor mount is well designed, it should be impossible to slip during normal operation.

[etard]

Thanks Fechter, always spot on and informative. I wonder if it would be possible to match up a roller with the repetitive pattern of the tread on a mountain bike tire, and in essence you cog directly to the tire.

If I could get the whole package (batt., controller, motor, etc...) down to under 10 pounds, I might be able to market this as something of an emergency kit. Maybe a click and play dewalt setup, you take the battery/s you need Or better yet, a way for freeriders to get up the hill, so they can go down

I would like to have a click in bracket that I can attach somewhere around the rear triangle, and take off and put in a backpack for the ride down. I think if people can preserve the essence of their mt. bike then you could get them to spend some coin on an accessory that enhances your mt. bike experience . I like my bike the way it is, i dont want to lug a mt bike with wires and 30 extra pounds around the outback, I would rather put 10 or 12 pounds on my back, and preserve the handling of my ride.

Does anybody feel me !

[Drunkskunk]

the idea sounds great, but a friction roller wouldn't have the power to pull you up much more of a hill that a wheelchair ramp without slipping. and a motor and battery combo under 10 pounds wouldn't be able to do much distance as a hill climber at any speed.


keying the roller to the bike's tread sounds great, except for the way a tire works. roll over a stick, and the tread compresses under the bike, but the rest of the tire expands proportianly to the area compressed. that makes the area between the tread blocks expand, and takes the roller out of alignment, which would then very likely tear up the tread.

[64ragtop]

Have ya ever seen a "Whizzer" gas powered bike? I can't find on their website http://www.whizzermotorbike.com/ whether they use a toothed belt, or just friction. What they DO do, though is drive an intermediate size pulley attached to the rear spokes. What they DO NOT do is drive the rear tire with a drive wheel that will inevitably wear the tire in some fashion to some degree. From their pictures, it looks as if proper sizing of the motor and driven pulleys and/or the use of a toothed belt (or not), and adequate motor/controller/battery power would address the problems with friction drive and could easily cost less than hubmotors ot chain drive lashups. It also looks like a good way to use R/C motors and controllers. would probably want to have bearings at the outer end of the motor shaft, but a simple machined casting should accomplish that! If there's a downside, I don't see it. I can hardly believe it's not been done before - or has it, and new technology makes it practical now (or not)....

ATB

BC

[AussieJester]

I should of mentioned in my initial post that there are quite a few friction drive setups over on http://motorbicycling.com forum i am also a member on. They also have
a dedicated "Whizzer" thread if you want to look at the rides up close of individual members they can be forund here I also spotted a thread What's the best drive roller? Haven't read the entire thread but the first few posts mention BMX bike pegs, i have a couple sets here myself from curbside collected bikes, in case your not familiar with them i took a snap of the ones i have here-->



Welcome to them if you think you could use them and are happy to put a few $$$ towards postage? Alternatively...ChopperUS sell them reasonably cheap and Alan getz things dispatched immediately payment has cleared from past experiences, he is VERY efficient. One fella i noticed in the thread was applying JB weld and sand to the knurlings of the pegs apparently it improved traction

Something else i thought of are die grinder bits, the large stone variety i wasn't able to find a single pic of one heres a link to a kit http://www.sjdiscounttools.com/ir301k.html The pink stone is the one i was thinking of, you can buy similar for drills, also sanding drums for drills (bigger version of the variety as per used on dremels. I found this Site (check the Centerless and Cylindrical Grinding Wheels link)

Few ideas for you anywayz...

[michaelplogue]

http://www.davesmotors.com/store/spindles.html

.

[MitchJi]

Hi,

Another option would be using one of these belt drives (should be quiet):
http://www.bikeengines.com/index.htm

The first and only geared belt drive bicycle assist engine on the market.

The Drive Ring is made of nylon, reinforced gear material, for long life and durability. Fits 24", 26" or 700c wheels with 32 or 36 spokes. Rotate the ring over your wheel until the spoke slots align with wheel's spokes, using our 4n1 Ring/Spoke/Gear Key; the spokes easily click into the slots. Securely fits most spoke sizes from 15 gauge to 12 gauge. **Click here for 'How to' use our 4n1 Key**

With our patented design, the drive ring is self centering, there is no adjustment - one piece to install and it doesn't come off easily. The Drive Ring requires 1 1/4 inch between the rear fork and the spokes for proper clearance. **Click here for How to measure**

The geared Drive Belt is Kevlar reinforced for long life and durability. Although most of our customers find the belt will last for more than a year, riding style dictates belt life. Breaking strength of 1280 lbs. Extend the life of your belt, reduce stress and pedal a stroke or two as you take off or accelerate.

[EVTodd]

The problems with friction drive are blown WAY out of proportion by people that haven't tried it.

I'm personally a big fan. If you look at my other posts you'll see my Kollmorgen friction drive setup (although the pictures of the bike are old, still the same basic idea). I'm running 36 volts at the moment and it's good for around 22 mph. Today I got 15 miles out of my sla batteries (three 7ah).

It's true. Friction drive sucks in the rain. I don't see any way around that. But in the dry it's great. My bike is also a great hill climber and I live in an area with some good size hills (I'm also not a small guy). I don't know the grades but they are a lot steeper than a wheelchair ramp. I also ride some easy dirt trails in my area without a problem. The big issue for me is the weight of the batteries. But with all the money I saved on my 'ghetto' setup (heck, I even call it that) I can spring for some pings soon.

I have a theory on efficiency when it comes to friction drive too. I think it's better than many other methods. Think about it. If you try to accelerate too fast with a hub motor you just dump amps from your battery and don't move. If you do the same with friction drive it will slip and you know to back off thus saving battery power. I've also read some theories that all of your power is wasted through the 'friction' between the roller and the tire. Bull I say! You don't need to have the roller THAT tight on the tire. In fact, I keep mine fairly loose. I also haven't had any problems with tire wear in well over 1000 miles (and I've slipped the roller plenty). I suppose if you had a TON of power going through a VERY abrasive roller you could put a wear spot on a tire but with any reasonable motor (for a bike anyway) it shouldn't be an issue. I also don't see a need to have the ability to adjust the tension while riding. If you have a clutch bearing inside the roller there's no need to remove it from the tire. It feels like a normal bike when the motor is off. Btw, it's also very quiet.

I'm using a knurled 6061-t6 aluminum roller and I've found it wears more than the tire. I think what is does after a while is push the knurls over a bit (I'm using a smaller knurling tool). I just put it back in my lathe and re-knurl it. The diameter of it, however, hasn't changed since it was made.

I started out thinking friction drive would be a fun thing to play with until I moved up to a hub motor but now I just don't see a reason to switch.

My next project will be an rc motor mounted to some u-channel aluminum with, you guessed it, friction drive. I'm hoping to make a very light setup for short trips. Heck, Recumpence even said he has a friend with an rc motor friction setup that will go 48 mph .

I know most people here like exotic setups and the latest stuff (I do too) but for me (and my uses) it's the easiest low cost way to get a stealthy e-bike.

[64ragtop]

I have to confess passing on criticism of friction drive that I've read "somewhere". Coming from the swamps of Southeast Texas, I've always believed that roller slippage would make friction drive impractical in wet regions. But having spent some time with several e-bike and scooter projects, I see advantages that I had overlooked before. I'm concerned about stresses to bike spokes from hubmotors, and chain drive rigs as well. The acceleration stress bypasses the spokes with friction drive. In the same way, rim brakes pass the deceleration forces directly to the bike frame. Seems like this could help with spoke life and keeping wheels true.

Something that might help with wet slippage, too might be machining the drive roller to an arch closely matching the tire's cross sectional radius rather than the straight rollers I've seen. That would provide more contact area between the drive roller and the tire. Anyway, it's certainly an interesting alternative to what I had seen (and bought) that might only need some more development.

ATB

BC

[paultrafalgar]

A while back I came across this French system of friction drive:
http://www.cybien.fr/
it drives the rims each side of the wheel rather than the tyre.
I even emailed them to see if they would sell just the motors rather than the whole bike: they won't!
However, I see no reason that two RC motors couldn't be used in this fashion driving in opposite rotations of course
(is that possible with RC motors) and suspended by something like a large brake caliper, such that the two motors can be pulled simultaneously from driving the rim with a control from the handlebars. Rubber drive rollers clamped with sufficient force to the rim shouldn't slip, even in the wet.
See also
viewtopic.php?f=14&t=5175&p=79887&hilit=cybien#p79887
and
viewtopic.php?f=2&t=5162&p=78042&hilit=cybien#p78042
What do you think?

[EVTodd]

I found that french system interesting too. The only different thing about it is that it appears to have some kind of rubber rim under the normal rim that the rollers spin on. I'm not sure I would want to use the actual wheel sidewall but maybe with the right kind of rubber it would work.

As for dual rc motors, that's one thing I'm thinking about playing with this time. Either have two rollers or run them both on opposite sides of a roller (like the old ev warrior). In my mind it seems you could use a couple of lower cost outrunners and esc's that way and not put as much stress on them, maybe I'm way off there but it would be fun to try.

I have thought about all kinds of different rollers too. I also thought about making one that cogged with a tire but I just don't know if it's worth the effort since I'm pretty happy with a basic knurled roller. And with my luck I would buy a 4th axis for my cnc mill, make a program, get the roller made and you would never be able to find that brand of tire again. lol. I think it would make more noise too.

[Drunkskunk]

Don't get me wrong, I'm not knocking all friction rollers. Just the application of this one. Friction rollers are fine for use when its flat and dry, and reasonably clean road conditions. For wet, dirty conditions, and hill climbing, friction rollers are the wrong tool for the job.

you wouldn't take a Porche 911 turbo to go rock cralling in Moab, and you wouldn't take a lifted rock crawler Jeep to race in La Mons.

[EVTodd]

Don't get me wrong, I'm not knocking all friction rollers. Just the application of this one. Friction rollers are fine for use when its flat and dry, and reasonably clean road conditions. For wet, dirty conditions, and hill climbing, friction rollers are the wrong tool for the job.

you wouldn't take a Porche 911 turbo to go rock cralling in Moab, and you wouldn't take a lifted rock crawler Jeep to race in La Mons.

Like I said, I ride some pretty big hills around here and it works great. I also don't see why you would think you need clean road conditions. I ride on dirt, gravel, pretty much all conditions except wet (It really, really does suck in wet). I will say though, if I intended it to be a true off road bike I would choose a different drive system just because of the wet issue.

I just wish I could get some people on here to try my bike. I think they would be surprised. A local guy with a WE kit that tried it and was shocked. He now wants me to help him build a second bike. Some of you guys with super high power wouldn't be impressed but I only have around $125 in my motor, batteries, and controller. And for me, cheap is kind of the point of having an electric bike.

And actually, Porsche made some pretty good rallye cars. http://www.autoblog.com/media/2006/07/porsche-959-rally-dakar-dusty-resized.jpg

The issue in the past has been with really cheesy friction systems. It's a low cost way to make an e-bike so companies that made them used crap motors and cheap parts. From what I've seen on the internet, people that make their own friction system tend to go the cheesy route too. It' usually a non-freewheeling roller just hanging off a junk motor.

And don't get me wrong either. I'm just enjoying the conversation, I don't want to get in a big debate over it. I do totally understand why people don't think it would work. It just seems too easy and 'ghetto'. That's ok though, I like being different and most important, cheap. lol

[etard]

Great discussion guys! Now, Fechter mentioned a setup that increased the pressure of the roller as torque permitted, that seems like it would solve tire slippage on steep inclines. Does anybody have a pic or patent link that I could see to understand how this works?
Drunkskunk, can you explain further the problem with a matching tread to roller design? I cant wrap my mind around the physics of going over a log or rock, and that shifting the tire to the roller.
That Whizzer setup is out of the question. Is there a place I can go to see the different roller setups already in use? EVtodd do you have a picture of your setup, and how would you do it different if you had chance with more money ($500 without battery)?

[EVTodd]

This thread shows a picture of my little setup:

http://endless-sphere.com/forums/viewtopic.php?f=2&t=6822

I'll try to get an updated picture of my bike today. I basically mount that motor setup to a rear seatpost rack. I also have supports that go to the frame that stop it from moving side to side. One of my fears has always been hitting a big bump and having the whole assembly shift to the side resulting in the motor getting stuffed into the wheel.

As far as improving it with more money. I guess the only thing I would change at this point is using an rc motor and controller. I'd rather save the rest of the money for batteries. I'm not sure I could even think of a way to spend $500 on the friction drive part of it. But I also have a couple of small cnc machines in my garage that save me $$$ instead having someone else making the parts.

[recumpence]

My buddy with the RC motor friction drive setup has his motor carriage setup in a leading link fasion. With his arrangement, the more torque you pull, the harder the wheel presses into the tire. That increases his efficiency.

Now, think of this, with an RC setup, all you need to do is mount a high torque servo in parrallel with the ESC input and you have a way for the roller to be pushed onto the tire when the throttle is on and it will retract as the throttle is reduced. Heck, it will also increase roller pressure by amount of throttle.

I think friction drive is a good idea, especially for those who do not have a ton of time for fabrication (or machines to do it).

My buddie's friction drive setup runs 48 mph (big RC motor on 48 volts) and was all made with had tools and Ace Hardware materials.

Oh, he did fight with tire wear untill he "Discovered" simple knurled aluminum as a drive wheel. Problem solved.

Matt

[EVTodd]

Matt,

What are your thoughts on running 2 smaller outrunner motors? I'm thinking about making a dual roller setup just for kicks and giggles. You can get some of the 80 amp or so motors/controllers on ebay dirt cheap. My theory is that with 2 motors it would take a lot of the strain off of the cheap esc's.

I'm wondering if I could get around the same power as my single kollmorgen setup with something like this. Maybe run 2 small rc type batteries to power the motors. Would be a cool, lightweight short range bike (5 or so miles) for running errands close to the house and my short trip to work (yes, I know, I could just pedal that far, but that's no fun). Maybe use a motorcycle throttle running to two slide potentiometers wired to 2 servo testers.

I know you've been warning me about the cheap esc's but it's tempting to try it. I also found a thread on an rc forum about the mystery controllers lasting a lot longer if you pop the heat sinks off and reinstall them making sure they touch all the fets. I guess they don't contact all of them stock.

[recumpence]

I would say use two motors into one roller (one motor on the left and one on the right).

It should work fine. I like the logic on easing the controller load!

Matt

[etard]

Those Frenchmen are using some huge motors ! I think that a clip in mount on my rear triangle(full suspension), with a servo like Recumpence says that will squeeze the motors' rollers together when more throttle is applied would work perfect. Now, if you could just incorporate an anti-slip circuit similar to the ABS system used on even cheap chinese scooters (my 150cc claimed to have abs) you could do away with all the haters .

The dual motor setup could have several advantages:
1. You could have two different motors that phase in or out, one with high torque, and the other hi rpm efficiency.
2. If one goes out you still have one to get home
3. You could run two smaller battery packs

I am about to take the plunge, but I want to take advantage of the 30% off live.com is doing on ebay. I know castle creations are the best controllers, but what about the Rc Smart combo on ebay Would two of these work?
http://cgi.ebay.com/RC-Model-560-KV-Outrunner-Brushless-Motor-80A-ESC_W0QQitemZ300265958408QQihZ020QQcategoryZ34055QQtcZphotoQQcmdZViewItemQQ_trksidZp1742.m153.l1262

Or one of these
http://cgi.ebay.com/RC-Model-833-KV-Outrunner-Brushless-Motor-80A-ESC_W0QQitemZ270286448116QQihZ017QQcategoryZ34055QQtcZphotoQQcmdZViewItemQQ_trksidZp1742.m153.l1262

Or one of each?
Also, The input voltage is only for 30 volts, what if I tried to put 36, or 48 volts into one of these? the milwaukee 28 volts might work though, huh.

[EVTodd]

I still say you don't really need the adjustable friction pressure but if you can figure out an easy way to do it it would be cool to have. Traction control on the roller would be fun though. Actually, that might not be that hard to do with a simple encoder setup.

I think I'm going to go ahead and take the plunge too. It's getting cold here and I need a new project anyway. I'll probably use 2 of the same motor as I'm not sure how you would time two different types to work together.

And I'm still going for cheap cheap cheap. I can always upgrade to a castle creations esc later.

[etard]

Would you recommend the lower rpm/v motor like the 560 or would you go a little higher? I did some visual measurements, and it seems that I will want a motor with minimal length if I go 2 motors on 1 roller cuz a wide setup will interfere with my heel on the upward stroke while pedalling. Unless, I put the roller underneath the bottom bracket, then I might need to add an extra roller for the chain to go around the right side motor.
I wonder if you gain or lose efficiency with 2 motor, 1 roller as opposed to 2 roller, 2 motor.
Is there any way to amplify the throttle signal and just split it to the 2 controllers. Or can you program the controllers to except different input parameters? I just got my magura throttle, and I love the build quality. Maybe I could use another servo (controlled by the throttle) to two pots. By the time I'm done this thing will have a trigger and a steering wheel, maybe some joysticks, HAHA!!