Gallery, Projects and General > How do I??
Roller Project
JHovel:
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?
smthrll:
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
philf:
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.
smthrll:
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.
smthrll:
I've been making some progress on my project - usually by doing things at least 4 times til I almost get it right. I have the inner flywheel with the stub shaft complete. I ended up welding a steel plate onto the ends of my .75" walled cylinder. I then bored some bearing pockets and pressed them in. I then turned the cylinder between centers (no stub shaft at this point), and took a finishing cut. It seemed to work well, I can spin it up to 2000 rpm with no vibration and almost no run-out. Not sure if it's proper form to use deadcenters on bearings, but it worked good.
Trouble started when I attached the stub shaft (originally used 82 Degree countersunk machine screws). Everything was running true, I cut the shoulder for the bearing to sit against, cut the micro-grooves for the belt, the snap ring, and everything was good. However, I didn't realize how important those countersunk pockets were. These were cut on the drill press, and I don't think my accuracy was as good as it should've been. When I removed the shaft from the cylinder, and then re-attached it again - good luck! Out by .006"! I closed up the countersunk holes, ruining my pretty bright finish, and used hexbolts. Now I can adjust the bit of wiggle room and everything runs true again.
I attached a picture of my outer aluminum drum as well. I'm really struggling here - it's about 20 inches long, and my lathe only has about 16" of travel. I had a really nice finish on the aluminum, but then had to swap the drum end for end in the steady rest. The result is a fine line trying to match up the finishing cut on one half, with the finishing cut on the other. I promptly ruined the finish with some fine sandpaper, trying to get rid of that line. I'd ask for solutions, but I suspect the answer is going to be "buy a bigger lathe" if you want to do bigger work.
This forum is great, thanks for all the ideas and problem solving tips I've found in other posts.
Rollie
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