A friction drive folding bike

[ferias77]

Hi,

After the light electric stand up scooter, with a friend I will try a folding bike with a friction drive.
The bike will be this : http://www.decathlon.fr/b-fold-20-pouces-id_8186827.html
I will put the friction drive here :

I used a part of photograph of the commuter booster website, I hope it is not a problem, Adrian.

- Motor : the same than the scooter : 6374 170kv http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=7870
- Controler : the same than the scooter : Turnigy Brushless ESC 85A w/ 5A SBEC http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idproduct=10331
- Batteries : the same than my scooter and my e-bike (18.5V 20 Ah)

Next soon !

Eric

 

[adrian_sm]

:lol: Looks good mate.

FYI. If you plan on something like my friction drive, it adjusts by sliding it up and down the seat tube.
This bike looks like it has limitted opportunity for this.

But apart from that looks great.

- Adrian

I really need to get my throttle interface released. Because it makes controlling the friction drives so easy. Would be perfect for your scooter too.

 

[ferias77]

Thanks for your reply Adrian ! If you want a beta tester for your throttle interface, i'm here
I plan something like your commuter booster, and I didn't know it was necessary to adjust by sliding it up and down the seat tube.
I will draw it and see if it is possible. Could you give me an idea about the value of x (angle between the commuter booster axis and the tangent to the tire when the moteor comes in contact with the tire)?


Eric

 

[adrian_sm]

Throttle interface is getting closer now. Just trying to decide on the different variants I will offer. I can put together a minimal version that doesn't have a display and offer that now, but I am still resolving how I mount/enclose the display before I offer that variant. But after some coding work today, it looks like I will be able to have the same code running behind the scenes for both, which means it will be possible to upgrade to a display version easily at a later date.

As for the angle, the one you have drawn is actually not the one you are interested in. It is the angle between the swing arm pivot centre, the contact point between motor and tire, and the centre of the rear wheel. The critical angle between these is dictated by the coefficient of friction between the tire and the motor. This can vary depending on if you have grip tape or not. But a rough number would be 150-degrees, (or 30 degrees if you extend the wheel centre to contact point line past the contact point)

The advantage you will have is that you can easily modify the swing arm length to help make this angle correct, where as I had to make mine more universal. So you can probably avoid the need to slide the drive up and down the seat post.

Hope this helps

- Adrian

P.S. If you want to measure the coefficient of friction, a simple method is to rest the motor on the tire with the brakes on. Keep resting if further and further down the tire, and note when it starts to slide across the tire, rather than roll. Then then angle between vertical and this point, tells you what the coefficient of friction is.

 

[ferias77]

Throttle interface is getting closer now. Just trying to decide on the different variants I will offer. I can put together a minimal version that doesn't have a display and offer that now, but I am still resolving how I mount/enclose the display before I offer that variant. But after some coding work today, it looks like I will be able to have the same code running behind the scenes for both, which means it will be possible to upgrade to a display version easily at a later date.

I would be interested by the minimal variant ! For me, it would be enough.

As for the angle, the one you have drawn is actually not the one you are interested in. It is the angle between the swing arm pivot centre, the contact point between motor and tire, and the centre of the rear wheel. The critical angle between these is dictated by the coefficient of friction between the tire and the motor. This can vary depending on if you have grip tape or not. But a rough number would be 150-degrees, (or 30 degrees if you extend the wheel centre to contact point line past the contact point)
The advantage you will have is that you can easily modify the swing arm length to help make this angle correct, where as I had to make mine more universal. So you can probably avoid the need to slide the drive up and down the seat post.

Ok, so for a first test, it is that, ok?

P.S. If you want to measure the coefficient of friction, a simple method is to rest the motor on the tire with the brakes on. Keep resting if further and further down the tire, and note when it starts to slide across the tire, rather than roll. Then then angle between vertical and this point, tells you what the coefficient of friction is.

Here, I am not sure to understand ? How do I hol the motor? With the hand? With the complete friction drive or only with the motor?
Thanks, you are my rescuer :wink:

 

[adrian_sm]

I would be interested by the minimal variant ! For me, it would be enough.

Great. It will still probably be a couple of weeks away.

Ok, so for a first test, it is that, ok?

Yes. That is more like it, thanks for the image that is much clearer than my words.

Here, I am not sure to understand ? How do I hol the motor? With the hand? With the complete friction drive or only with the motor?
Thanks, you are my rescuer :wink:

Just hold it in your hand, rest it on the tire, and see if it wants to slide or roll. It is pretty crude, but gives you a feel.
It is a good way to see/feel the difference between motor can on tire, and adding the grip tape.

A more accurate method (and how I recommend adjsuting the Commuter Boosters on the bike) is to actually have the motor mounted on the swing arm. Rear brakes on. Lightly rotate the swing arm so the motor touches the tire. Then try rotating the motor, it should slip in the non-drive direction, and climb the tire in the drive direction. Then adjust the contact angle and repeat. But this method requires that you have already manufactured the swing arm, and can change the geometry easily by slide the drive on the seat tube or something. But if you can quickly mock something up close to the geometry you want, this is the best method, but I would recommend mocking it up in a way that you can adjust the geometry relatively easily since your bike will be restricted in how much you can slide it up/down the seat tube. So you may need to try different pivot arm lengths, by having different motor mount holes, or pivot axle holes.

- Adrian

 

[ferias77]

Just hold it in your hand, rest it on the tire, and see if it wants to slide or roll. It is pretty crude, but gives you a feel.
It is a good way to see/feel the difference between motor can on tire, and adding the grip tape.

A more accurate method (and how I recommend adjsuting the Commuter Boosters on the bike) is to actually have the motor mounted on the swing arm. Rear brakes on. Lightly rotate the swing arm so the motor touches the tire. Then try rotating the motor, it should slip in the non-drive direction, and climb the tire in the drive direction. Then adjust the contact angle and repeat. But this method requires that you have already manufactured the swing arm, and can change the geometry easily by slide the drive on the seat tube or something. But if you can quickly mock something up close to the geometry you want, this is the best method, but I would recommend mocking it up in a way that you can adjust the geometry relatively easily since your bike will be restricted in how much you can slide it up/down the seat tube. So you may need to try different pivot arm lengths, by having different motor mount holes, or pivot axle holes.

- Adrian

Thanks for the explication Adrian, it is clearer like that !

With my friend, we bought the bike yesterday. For the price, the quality is very good, and the folding is simple. I am measuring and designing the bike with Catia to see how to integrate the friction drive.
I have my 6374 170kv motor, but my friend has no motor. I thought ordering the 6354 200 kv which will be easier to integrate to the bike : http://www.leaderhobby.com/product.asp?ID=9394001100056
Do you think it is ok ?

Eric

 

[adrian_sm]

Don't know. But if it was me I would give it a go.

 

[ferias77]

Don't know. But if it was me I would give it a go.

Sorry Adrian, I don't understand what you mean when you say "I would give it a go". You think it would be ok?
The design is almost finished, images soon.

Eric

 

[adrian_sm]

It should work. But with less thermal mass, may overheat faster than the larger motors.

I would be confident of it being fine if you restricted the power. I have run smaller motors than this on my bike with a 500-1000w limit by my brain box.

- Adrian

 

[ferias77]

It should work. But with less thermal mass, may overheat faster than the larger motors.

I would be confident of it being fine if you restricted the power. I have run smaller motors than this on my bike with a 500-1000w limit by my brain box.

- Adrian

Ok, perfect. I designed the bike and the friction drive, respecting the 150° :





Now I have to put the spring and the stops. I would like they are external, in order to be easier to adjust. Reading the forum a few weeks ago, I saw a friction drive with external stops, but impossible to find it now. Somebody has an idea where it was?

Eric

 

[Quent]

After the light electric stand up scooter, with a friend I will try a folding bike with a friction drive.

Hi all,

I am the friend and for my first post I present my friction drive concept for the B'fold bike. I'm currently working on the bike fixation prototype. I will post pics later.
I have no doubt to find help and advice here

Below the 1st concept:

 

[adrian_sm]

Oooo. Cool. Looking good.

Couple of comments.
1) The spring where you have modelled it will need to be a tension spring to help lift the motor, not a compression spring
2) Is that slot above the main pivot and behind the spring is the means of limiting the rotation of the swing arm?
If so I can't see how you are going to be able to adjust the end points of the travel. This is quite important when setting up the drive
3) What are the two screw heads on the other side of the main pivot/clamp block?
4) consider using countersunk screws for attaching the motor to the swing arm. It helps firmly locate the motor on the swing arm.
5) How is the swing arm attached to the pivot shaft? This needs to be very secure.

- Adrian

 

[Quent]

Quick responce !
Thanks for the advices

1) The spring where you have modelled it will need to be a tension spring to help lift the motor, not a compression spring

It's clear for me, if i don't find how attach the tension spring into holes, i'll put a compression spring below the pivot point.

2) Is that slot above the main pivot and behind the spring is the means of limiting the rotation of the swing arm?
If so I can't see how you are going to be able to adjust the end points of the travel. This is quite important when setting up the drive

Yes it's to limit the movement.
I agree for the adjsutement, before finding the good angles i will limit from another adjustable point.

3) What are the two screw heads on the other side of the main pivot/clamp block?

there are 4 screws used to fix the two parts of the fixation element (each side of the tube)

4) consider using countersunk screws for attaching the motor to the swing arm. It helps firmly locate the motor on the swing arm.

I totaly agree with you on this point

5) How is the swing arm attached to the pivot shaft? This needs to be very secure.

there are two big stainless stell plates each side of the swing arm (in order to maximise the contact), and the translation is block by a screw. i will leave the minimal space to allow moving. if this don't work i'll think to an alternative solution (I hope to bypass the bearings ).

thanks, I am aware of other advice

 

[bose]

2) Is that slot above the main pivot and behind the spring is the means of limiting the rotation of the swing arm?
If so I can't see how you are going to be able to adjust the end points of the travel. This is quite important when setting up the drive

Yes it's to limit the movement.
I agree for the adjsutement, before finding the good angles i will limit from another adjustable point.

You could put a set screw on each side of the slot to limit movement, but you will need to move the slot down a bit.

Nice rendering by the way!

 

[ferias77]

Hi,

Yesterday, I modified the servo tester to plug the hall throttle. With a servo, it works, even if the travel is not totally linear : the beginning of the travel is linear, then the middle is slower and the end is linear.
When I replace the servo by the ESC, the ESC doesn't initialize... At 0% throttle, there is maybe a little throttle and the ESC doesn't initialize? Do you have seen this problem? How to solve it?
I hope the bike will be finished soon, but I have many other projects at the moment...

Eric

 

[adrian_sm]

It sounds like you need to update the ESC throttle range. This us usually done by holding full throttle, turning on the ESC, waiting for some beeps, then adjusting to minimum throttle, more beeps, then it is done.

- Adrian

 

[ferias77]

It sounds like you need to update the ESC throttle range. This us usually done by holding full throttle, turning on the ESC, waiting for some beeps, then adjusting to minimum throttle, more beeps, then it is done.

- Adrian

Thanks Adrian !

I didn't see on the turnigy manual that it was possble to calibrate the throttle range. I will try it this evening !

Eric

 

[ferias77]

I made the throttle calibration yesterday, and it works perfectly ! Now I have to mount the friction drive on the bike. Photographs soon...

Eric

 

[Quent]

Hi,

I have done some pics of the prototype, everything goes well, excepted one thing... the throttle calibration... I have the two first BIPs for high gaz, but not the others after low position... we will see this tomorrow !

Wait & see...

Schematic tube fixation :



Bike :

 

[Kepler]

This is shaping up to be a nice variation on the concept. Good work.

I really like the way you have locked the pivot axle to the swing arm.

I can see mechanically there are two more areas for you to attack, adjustable swing arm travel adjust and some way of neutralising the weight of the motor.

What do you have in mind here?

 

[ferias77]

Hi,

That's ok, I made the first ride with my friction drive folding bike yesterday ! No stops for the swing arm at the moment, I have to put them... And everything is fixed with tape... I was too hurried to test it. :wink: For the spring, I used a sandow for the prototype. I will see after how I do for the final version.
Weight with 2 5S 4900 mAh batteries : 15.9 kg (13.8 kg for the naked bike)
Top speed : 33 km/h, I think there is sliding between the motor and the tire... I have to had grip and to adjust the geometry.
No load power = 33W : That's a good surprise, I expected more.

Photographs :





Today we will try to unerstand why it doesn't work for Quentin...

Eric

 

[adrian_sm]

What motor is that? I thought you were going with the AerodriveXp SK Series 63-74 170Kv

 

[ferias77]

What motor is that? I thought you were going with the AerodriveXp SK Series 63-74 170Kv

No, I let the 6374 170 kv on the stand up scooter. We ordered this :
http://www.leaderhobby.com/product.asp?ID=9394001220364

 

[Quent]

Calibration issue resolved, we have tested the Eric's servo tester on my bike, throttle calibration is done correctly.