Spinningmagnets' RC Friction-Drive Build-log

Got the roller, thanks! I will be flying to Utah on Monday, and I will be driving a U-Haul truck back to Kansas. There are so many good deals on houses here, it shouldn't take long for me to finally have a garage of my own soon.

The drives have been working well for me. The 1.25 inch roller with 24V does 20-MPH on flat land, and the 1.0 inch roller on 36V climbs well.

The soft rubber tire with a round profile (good for cornering) noticeably wore a bit, but the roller had a small contact patch... and to be fair, I was really hammering the drive and breaking traction around 2000W. The flat-tread (wide contact patch) hard-rubber beach cruiser tire is showing no signs of wear.

The 40-grit sand-paper from a cloth-backed wet-dry belt is wearing well, I used the best two-sided carpet tape I could find, and I seal the trailing edge with a smear of JB-Weld epoxy (wrap with tape until dry). I still hope to buy/make some steel rollers in the future.

I added capacitors to the 3 ESCs, and I haven't fried one yet. The CC-ESC data-logged that I was drawing 60A peak on acceleration, and the smallest ESC I have is a 70A-continuous. The 63mm motors are perfect for this application, they only get warm under hard use, and cool off quickly during cruise. I am using the Exceed 295-kV motor the most. It seems to be a well-made unit, but...Its normally listed at around $145, and yet they have occasional sales for $45 (huh? why such a wide spread of price?).http://www.hobbypartz.com/mo1102brmo.html

I'm not satisfied with using a dial on the servo-tester as a throttle. I have one of Matts throttles, but I'm too busy to put it on right now, and I'm certain it will be great when I finally do.

I tried to find the least expensive options that would work well and be reliable under "college-student" duty. The final version has turned out to be more expensive than I hoped for, so...due to price, I doubt many of them will sell. For my summer project I want to use a de-spoked hub as a non-hub to drive a longtail cargo-bike (like John-in-CR).
http://endless-sphere.com/forums/viewtopic.php?f=6&t=26932&start=15#p389622

I may make a frame using methods similar to the Tino Sana wooden bike. I'd make a shape with a big battery triangle and plenty of space just where I need the hub. Only about 14" longer tail than a normal bike.
http://endless-sphere.com/forums/viewtopic.php?f=1&t=10697&start=0#p163929
 
rearengine said:
Kepler! if your out there ... How did your launch ramp work out ? Adien's seems to work fine with out it... Happy Easter to all... Bill

Launch ramp has been great. Works a treat. Originally I needed to set my drives up with a very slight motor to tire contact. It wouldn't cause any drag as such but the slight scrape was annoying. Now the motor gets set 2 or 3mm away from the tire so there is no contact at all. Even a slightly out of round tire or flexing seat post doesn't cause any contact. I think the button throttle suits the launch ramp approach also as its either on or off rather the bouncing between the ramp and tire pickup. I now use it on both the rear mount and the mid mount setup.
mini and midi drive mechanics.JPG

Adrian's setup is different to mine mainly because his is optimised around being a centre mount. He uses a spring to pre load the motor against gravity. My design is optimised for a rear mount and need the spring action get the motor completely off the tire as the movement is no longer aided by gravity. My centre mount doesn't use a spring at all. On this configuration, the launch ramp is even more important to achieving reliable motor pickup. Dampening is all achieved electronically now with the engagement and disengagement silky smooth.
 
spinningmagnets said:
Friction-Drives
Volt / kV-speed chart
For available 63mm motor kV's
1.0" and 1.25" roller diameters


The kV that is listed for a motor, is the RPMs resulting per volt applied. Many factors affect the actual road RPMs in use. The weight of the bike, rider, and cargo is a major factor, and also wind resistance and system friction. In the past, many have found that reducing the kV number by 15% can be a useful (though approximate) way to arrive at a calculated speed which is close to the actual resulting road-speeds.

I have compiled this chart as a rough guide to selecting a motor kV and system voltage. The top number is a 1.0" diameter roller and the bottom number is a 1-1/4" roller. LiPo and LiMn cells have a nominal voltage of 3.7V (and 4.1V when fully charged). Six of them connected in Series (6S) creates a cell-string that will have a nominal voltage of 22.2V; When fully charged, the string will have a voltage that is closer to 24.6V

Edit: I still have the original chart, but it has proven to be off some. I have developed two drive systems that both operate at arount the federal speed limit for unlicensed mopeds, which is 20-MPH (of course, the federal limit does not apply in those states where a higher speed is allowed)

Both are using the Exceed 295-kV motor. For flat land I am using 24V of SLA and the 1.25" roller, and for hill climbing, I am using 37V of LiPo and the 1.0" Roller. For the hill-climber, I am also adding more capacitors and a heat-activated air-cooling fan.

If you chose to use 44V-48V, the available kVs of the 63mm motors would provide you with a very wide range of top-speeds, with the 295-kV providing an estimated 27-MPH.
thank you" finally someone who knows what their talking about & right to the T.
 
Great thread. Thanks SM.

After 3 years, what is the update on this design? The whole FD topic sort of went dead as I scoured ES for newer news, designs, reports, etc.

Once starting from the head of the thread, I understand why all the extra bolts. Looking at the picture at the link it was less intuitive of what was going on. And the one-way drive shaft is certainly not identifiable just from the picture.

What are the limits on this design? Has anyone posted 25, 30, 35+ mph? How much slippage?

What about durability?

I'm hoping EVTodd weighs in as he has a lot of time with this too.

Thanks
 
If you try to use a round-profile tread on the tire (good for cornering), it will slip a lot, especially with the slightest bit of moisture picked up from the road (because of the small contact patch). Todd suggested that I switch to a fairly flat (square?) profile tread, often found in a selection of beach cruiser tires. Found a cheap one at a local WalMart, and the rubber composition turned out to be fairly hard, which I also preferred. It worked as Todd described, MUCH better traction (no slippage unless very wet)

The power limit is dependent on the traction of the roller against the tire tread. My Castle ESC logged 1,000W peaks with no slippage. On flat land I got 20-MPH with 22V using a 1.25-inch roller, and in hilly terrain it actually climbed quite well when using 37V on a one-inch roller, also providing approximately 20-MPH.

I calculated the components to provide 20-MPH because that is the legal limit, and I hoped to sell a handful to some of the local college students. Every one was too nervous about LiPo to buy, and cell-man at em3ev.com had not yet started selling high-current non-lipo cells.

I rode my friction drive to and from work for a single summer/fall when the weather was nice...winter came and I put it in storage. I am happy with its performance, but I like riding faster E-bikes now, so it is just collecting dust next to my workbench as a work of art. It was a fun project and I really enjoyed every minute of it.

I never tried any voltage above 10S LiPo (37V?) or any speed over 20-MPH.
 
Hi SM,
The 40-grit sand-paper from a cloth-backed wet-dry belt is wearing well, I used the best two-sided carpet tape I could find, and I seal the trailing edge with a smear of JB-Weld epoxy (wrap with tape until dry). I still hope to buy/make some steel rollers in the future.
Did you upgrade from the sandpaper or did it hold up well and provide sufficient friction? Would be great if it held and avoid having to upgrade it.

Did the drive shaft lift off the tire while coasting or did the clutch bearing reduce drag sufficiently that contact was not an issue?

Could you venture an estimate on the maximum movement of the drive shaft into the tire?

Thanks
 
Did the drive shaft lift off the tire while coasting, or did the clutch bearing reduce drag sufficiently that contact was not an issue?

There are two features of this style of friction drive that reduces drag when you are pedaling with no power on. First, the drive slides up and down, so...when the power is on...the roller pulls itself deeper into the tread. As the roller is pulling itself into the tread, the entire drives slides towards the tire with the roller. When the power is off, the wheel spinning forward pushes the drive forward until it's barely touching.

The second thing that reduces drag is that the roller has one-way clutch bearings inside it. They "grab" when the motor is on, but when the motor is off...the roller freewheels along with the tire (the roller shell spins along with the tire, but the shaft and the motor do not spin).

The roller must have a small portion of the roller touching the tread at all times (so that when power is applied, the roller can be pulling itself into the tread). Gravity and the weight of the drive is what makes it rest against the tire. Anyone who is skeptical about how much drag is felt would be very surprised that you cannot tell when it is touching or not (it wouldn't be touching if the angle of the drive's mount is adjusted wrong).
 
Thanks. It seemed from the ETodd video the drive shaft was constantly spinning but wanted to confirm. This also seems to resolve the problem some have with the power not engaging immediately while the wheel is turning.

Did the sandpaper hold up and get solid traction or did you upgrade?
 
The 40-grit wet-dry sandpaper worked very well, but I haven't ridden the friction drive since I put it aside last winter, so many other projects to play with...
 
Coming back to this design and found myself asking the same question but did not see any reply. Does the slider style keep contact all the time. From the EVTodd video it shows the spindle turning until wheel is stopped and continuing to spin while coasting at speed. Obvious question is how much drag there might be while coasting? If the spindle pressure is very slight then the only drag would be from the motor. Any guess at percentage of efficiency lost?
 
windtrader said:
Coming back to this design and found myself asking the same question but did not see any reply. Does the slider style keep contact all the time. From the EVTodd video it shows the spindle turning until wheel is stopped and continuing to spin while coasting at speed. Obvious question is how much drag there might be while coasting? If the spindle pressure is very slight then the only drag would be from the motor. Any guess at percentage of efficiency lost?

I use rollers that have a one way clutch bearing inside. When coasting the roller simply freewheels and adds no drag.
 
Yes. I forgot that part. One complaint I've read is the motor protrudes sideways. Why has there been no variation that stacks the motor above the spindle then uses a small belt/pulley to connect them. it seems like a rather simple mod with out adding much resistance and really cleans up the mounted unit. Additionally one could fine tune the RPM with different pulleys.
 
windtrader said:
Yes. I forgot that part. One complaint I've read is the motor protrudes sideways. Why has there been no variation that stacks the motor above the spindle then uses a small belt/pulley to connect them. it seems like a rather simple mod with out adding much resistance and really cleans up the mounted unit. Additionally one could fine tune the RPM with different pulleys.

I don't have any problems with the motor sitting off to the side where I have mine mounted. I've never even come close to hitting my foot on it while pedaling but I suppose that could change with frame size or monster feet? I had considered adding a pulley arrangement similar to what you mentioned at one point but it adds complexity which, to me, defeats the purpose of using friction drive. It's much easier just to pick a motor that matches it's rpms to your battery.
 
I have to agree with Todd on this. There is nothing stopping anyone from making a similar drive that has the motor above the roller, and using a belt to connect them. However...the motor on the side has been very unobtrusive, and the knife-in-fork connection of the two in-line shafts (like an older cars distributor) has proven to be utterly reliable, without adding any belt noise.

The good news for you is...these are so easy to make with just a drill, vice, and a hacksaw...you can have one of the style you like anytime you set your mind to it.
 
It was a fleeting thought when considering the stacked configuration: adding complexity to a clean and simple design. It just seemed like the motor sticking out would look like a wart hanging out there as well as some commented about it catching on stuff. As you say these are so simple and cheap to build, no harm in trying one or both out.

It still leaves me dumbfounded why interest in FD is so low. For anyone looking at a legal 250w electric boost, this just seems the obvious choice. Oh well
 
windtrader said:
It still leaves me dumbfounded why interest in FD is so low. For anyone looking at a legal 250w electric boost, this just seems the obvious choice. Oh well


Friction drive gets a bad rap because there have been some crap commercial products out there over the years. It would be like if Yugo all of the sudden made a really good car. Who in the hell is going to buy a Yugo with that reputation? People also don't want to believe that a drive so simple and cheap can do the same thing as their super expensive drives. I've noticed that when people here on the forum build a FD they either try to make a drive that's too simple in design or go over the top with it. Either way seems to create a less than stellar experience.

I now have a hub powered ebike, a bafang powered bike and my friction drive. The friction drive is the one I go to first because it still feels like a bike. It also easily outperforms the other two (all three run at 36 volts using the same battery pack that I swap from bike to bike).

If you're going to post on here about FD you better learn to ignore every person that says it wears out tires in 3 miles, can't be used on gravel or a dirty road, etc... Have fun with it!
 
The performance and length of life for the wearing components had an exponential boost as soon as I took Todds suggestion and found a beach cruiser tire with a hard rubber compound, and also a squared-off tread profile.

When I was using my first tire that was already on the bike, it had a round profile with a soft compound that performed well in curves when leaning the bike in a turn (which isn't really my style, I am a low-speed cruiser guy). The roller only grabbed a thin strip down the center of the tread, and the softer compound was worn away quickly...also, it slipped easily with the slightest amount of moisture due to the small contact patch between the roller and the tread.

The flat/squared-off tread provided the roller with full contact across the entire width of the tire, and the harder compound would obviously wear better (which it did). As a side note, the hard beach cruiser tire was one of the cheapest ones I've ever bought (for those who fear the cost of frequent tire replacements).

What knocked me out when I saw Todds drive was that it was clearly capable of lifting the seat/seat-post/drive/cargo-rack+battery...with no tools...and easily bring them indoors for charging and anti-theft. Not a concern for most riders (I stored and charged it in my garage), but...some college students aren't allowed (or don't have room) to bring the bike indoors.

I was living in a third-story apartment at the time I built mine. If anyone wants to build a similar drive, I have some of the parts and components, and would sell them at cost + shipping for those who want to experiment. I thought I would build a couple more drives, but the bits are just collecting dust.

ignore every person that says it wears out tires in 3 miles, can't be used on gravel or a dirty road, etc

These are concerns commonly expressed by someone who hasn't ridden one like Todds design. I regularly data-logged 1,000W at 37V of LiPo, and it climbed steep hills very well (without overheating) using a one-inch roller and a 63mm RC outrunner with a 149-Kv doing roughly 20-MPH

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windtrader said:
It was a fleeting thought when considering the stacked configuration: adding complexity to a clean and simple design. It just seemed like the motor sticking out would look like a wart hanging out there as well as some commented about it catching on stuff. As you say these are so simple and cheap to build, no harm in trying one or both out.

It still leaves me dumbfounded why interest in FD is so low. For anyone looking at a legal 250w electric boost, this just seems the obvious choice. Oh well

Some people go from friction drive to middrive through the chain. I've pretty much had my fill of the latter because I built my first one of that type about 20 years ago. Now as i get older and weaker, I'm seeking to minimize weight. Once i crossed the 50 point, my body just seemed to spiral downward. I was doing my usual chores in the yard and did a move that wasn't completely unusual in those circumstances and I felt the ligaments in my knee joint stretch with some pain. An eighth inch more stretch and my knee could have blown out. I really need stem cell therapy or some other type of DNA renewal.
 
That picture is great as it shows the simple and compact and portable nature of the entire drive system. Adding a compact battery/controller pack and throttle would make this complete. To make this even more portable one could use a wireless throttle using bluetooth or wifi in a smartphone. thus eliminating any throttle wiring.

One benefit of this sort of system which is not touted much is the ability to use the drive on different bikes. The ease of removing the drive is generally touted as a anti theft benefit but this could so easily be put on different bikes in a few seconds.

I understand the horrible impression given off when mentioning FD but we should peel this back one layer to see just who is reacting so negatively. My bet is the folks with the negativity are motorized bike communities such as ES, whizzers, gasser bikes, etc. The general bike riding community and that subset open to motorizing are likely much less aware of FD at all much less the unearned bad image and reputation.

One other observation is the tendency at least in some corners here is the holy grail of going 50 mph+ on a bike. So much of what is needed is to add weight and more weight. Weight for motorcycle rims and wheels to not blow up. More weight for batteries to drive the heavy motors, etc.

The FD is so light it can be put on nearly any super light bike and the added efficiency of not having an extra 50 pounds and high tire resistance alone makes for much less needed power.

Oh well - I'm sure this thread has biased viewers but it just seems like the FD approach should be far more popular for the low and mid end folks who just want a nice boost and not want to get sweaty or just don't feel like pedalling that day.
 
Uh oh! I smell another commercial friction drive being thought about! :D

I don't know. I've said this for years and taken heat for it here but I think it would be very hard to convince even the general public about friction drive. Even if they're not in the know about ebikes they tend to think it's too simple. A lot of people want an electric bike to give the appearance of being more high tech than than.

On a side note, I personally think it would be a nightmare to sell drives like this. There are just too many different kinds of bikes with different geometry these days.
 
EVTodd said:
I think it would be very hard to convince even the general public about friction drive. Even if they're not in the know about ebikes they tend to think it's too simple.

Maybe. Maybe not.

Try searching "Solex Moped" on google images to see the many and varied uses of friction drive bikes. Maybe because it's French?

Simonism
 
Simonism said:
EVTodd said:
I think it would be very hard to convince even the general public about friction drive. Even if they're not in the know about ebikes they tend to think it's too simple.

Maybe. Maybe not.

Try searching "Solex Moped" on google images to see the many and varied uses of friction drive bikes. Maybe because it's French?

Simonism

Yup! Even better, look up "Solex Prototype Racing". Cool as... But I still personally don't think there's a huge market for friction drive. It sucks that there's such a negative perception about it but there just is.
 
That hook dancing around on that cable near the spokes was exhilerating :shock: ...
 
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