Author Topic: Roller Project  (Read 612 times)

Offline smthrll

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Roller Project
« on: April 27, 2017, 10:30:28 PM »
I was hoping to get some input from some folks on a project I'd like to tackle.  I'm still new to machining and I roughed out a sketch that I hope will help explain.  I'd like to create:
- although shown as 2 separate rollers, the inertia roller will be placed inside the outer roller
- the inertia roller will have bearings pressed into the ends (shown in blue), and it will spin on a fixed shaft.
- the stub on the inertia roller will protrude beyond the outer roller, so it can be driven by a belt

My question:
- can I press a bearing in the outer roller and have it ride on the inertia roller's stub
- I'm guessing there will be a problem with the bearing rubbing on the face of the inertia roller - I'm not sure of the proper way to create a gap between the bearing and the face of the internal roller.  The inertia roller will be running about 3x faster than the outer roller.   I thought maybe leaving a bit of a raised surface on the stub shaft to ride against the inner ring of the bearing. 

My apologies to all the engineers and machinists that are doing a face palm right now....

Rollie

Offline awemawson

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Re: Roller Project
« Reply #1 on: April 28, 2017, 02:58:08 AM »
It probably me being slow on the uptake, but I'm having a problem visulising what you are trying to achieve.

It seems to me you are trying to construct three elements, all mutually co-axial and separated by bearing races, is this the case?

Perhaps were you to reveal your application it would be clearer as I've no idea what an inertia roller is!
Andrew Mawson
East Sussex

Offline mattinker

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Re: Roller Project
« Reply #2 on: April 28, 2017, 04:45:37 AM »
Like Andrew I don't know what an inertia roller is!
To prevent the face of the outer bearing touching the "inertia roller, you can either space it away with a washer or leave a small step on the end of the said "inertia" roller.
Maybe I'm completely off the track!!

Regards, Matthew

Offline smthrll

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Re: Roller Project
« Reply #3 on: April 28, 2017, 10:04:03 AM »
Thanks for the replies.  You are on the right track completely and have described the question better than I.

-project is for the back roller for a set of bicycle rollers.  It is a trainer that allows the rider to bike as if he was outdoors.  I've attached a picture of Trutrainer's product.  It has an internal flywheel in the last roller - this allows the rider to coast, as the inertia keeps driving the outer drum on the middle roller even when stopped pedaling.

So yes, all 3 elements are mutually coaxial and separated by bearing races.  Maybe a washer or a small step is all I need for separation?  I was worried about wearing out the bearing race of the outer roller rubbing on the end face of the inertia roller. 

I can understand the roller rotating on a fixed shaft, but I wasn't sure if there's problems with the outer roller rotating on another spinning shaft.  Tried reading the SKF bearing catalogue - bearings are actually pretty complex.  Once everything is assembled, there is really no way to provide lubrication. 

Rollie


Offline awemawson

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Re: Roller Project
« Reply #4 on: April 28, 2017, 10:52:49 AM »
Probably just a collar or thick washer is all you need.  :scratch:
Andrew Mawson
East Sussex

Offline JHovel

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Re: Roller Project
« Reply #5 on: April 29, 2017, 08:00:11 AM »
That looks clever. So the front and middle roller drive the internal (heavy) flywheel roller at something like 2 or 3 times the speed of the outer roller. So when pedalling stops, the middle and front rollers are driven by the internal flywheel roller for a little while by the drive belt, while the outer rear roller is only ever driven by the bike tyre.
Do I understand this correctly?
Cheers,
Joe

Offline smthrll

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Re: Roller Project
« Reply #6 on: April 29, 2017, 10:43:47 AM »
That's it exactly.  Some trainers have an external flywheel that try to accomplish the same thing (kreitler rollers for example), but this is a nice compact way of doing it.   I've obtained some 2.5" steel tube,  I.d. being 1".  It weighs 17 lbs so I think it'll make a nice flywheel.   Writeups I've seen on the Trutrainer product say a 13lb flywheel spinning at 12000rpm if the rider can do about 50km/h.  They use a 4:1 reduction ratio  (3.5" diameter roller / 0.75" stub shaft)

I'll probably use the suggestions given here,  space the outer roller's bearing with a thick washer.   Maybe use a c-clip on the outside of the bearing to hold everything in the proper place on the stub shaft.

I'm certainly open to ideas though.

Rollie

Offline philf

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Re: Roller Project
« Reply #7 on: April 29, 2017, 01:44:24 PM »
Hi Rollie,

The TrueTrainer literature quotes:

"Additionally, viscous drag forces between the flywheel and roller simulate wind and rolling resistance."

The gap between the flywheel and roller may be critical.

I'd rather be riding on the road! 30 minutes on a turbo trainer and I'm drowning in a pool of sweat. :(

Phil.

Phil Fern
Location: Marple, Cheshire

Offline smthrll

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Re: Roller Project
« Reply #8 on: April 29, 2017, 02:32:37 PM »
I agree 100%, but it's almost May and I used my snow blower last week!   I just kind've figured that if I start this project now,  maybe I'll have it done  for when the snow comes in September again.  Maybe that drag will allow 200 watts resistance.

I also was thinking that if I can't get it quite right,  maybe I'll just pull the flywheel out and position it as a fourth roller,  kind've like the kreitlers except it would span the full width from rail to rail.