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Worm gear discussion
04-29-2014, 09:30 AM (This post was last modified: 04-29-2014 09:32 AM by steamboat.)
Post: #11
worm gear alternative
I am still looking for an alternative of the worm gears. I have still the above mentioned belt idea in mind but agree that it would be better to have as many parts printable as possible. While my RepWalker parts were printing I designed a small gear-wheel and printed it 5 times while I assembled the RepWalker. Have a look here:
[Image: 2014-04-29.011053-k.jpg]


The 3 wheels at the bottom will drive the legs. The black points are marking the crank pins for the leg movement. With 16 teeth we have to place the crank pin 2 teeth ahead for every leg. So we get the 8 different leg positions.

The purpose of the gear wheels at the top are to distribute the force and rotation in that way that every crank pin will rotate in the same direction.

Tomorrow I want to print out some more gear-wheels and learn more about the precision needed and the necessary forces to move 16 wheels/legs with such a gear.

Rainer
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04-30-2014, 01:06 AM
Post: #12
RE: Worm gear discussion
I am getting to the point with the cranks where I am not sure they are practical to print. They are too weak. I am leaning towards working something like this out instead and incorporating better cranks. Also these would be way way easier to print and interchange.
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04-30-2014, 01:09 AM
Post: #13
RE: Worm gear discussion
Rainer when you get some time can you sketch out on paper like you did for the "bearing cover" how these would integrate with the chassis. Also how do we easily transfer the direction of the motor? Just so I can get a better visualization of the system you propose.
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04-30-2014, 02:10 AM
Post: #14
RE: Worm gear discussion
(04-30-2014 01:09 AM)jmccartney Wrote:  ...how these would integrate with the chassis...
In the moment it is not my goal to integrate something. I am totally focused on designing and printing a working solution to move 16 cranks in the right manner. I even don't think about the size of the complete gear.

(04-30-2014 01:09 AM)jmccartney Wrote:  Also how do we easily transfer the direction of the motor?
For me this is step x of 100...

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04-30-2014, 04:54 AM (This post was last modified: 04-30-2014 05:09 AM by steamboat.)
Post: #15
Ra-Gear-2014-04-29
Hello James,

I made this to give us an imagination of what is possible. In the moment everything is a little to big. Crank pin Ø 5 mm. Gear axis Ø 8 mm. Gear Module 1.2.
[Image: 2014-04-29.202332-k.jpg]

Everything is turning easily and free even with the way to small axis and no axial guidance for the spur gear.




The 4 crank axis have a distance of 65 mm. with 16 axis this would be 260 mm. The actual Shellmo design is build with an distance from axis to axis of 10 mm equal 150 mm total length. So my design needs a reduction for about 0.6. I will have a look if it is better to shrink the gears or to halve the amount of teeth to 8. But gears with so feew teeth are not good in some geometrical reasons - bud this is theory for efficient cars etc...

Rainer
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04-30-2014, 05:42 AM (This post was last modified: 04-30-2014 05:42 AM by sho.)
Post: #16
RE: Worm gear discussion
Sorry to be late,
I can imagine what you try to make. Beautiful !
You can make it with 8 teeth gear, too.

I want to think about this more !
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04-30-2014, 06:30 AM (This post was last modified: 05-01-2014 07:35 AM by steamboat.)
Post: #17
RE: Worm gear discussion
(04-30-2014 05:42 AM)sho Wrote:  Sorry to be late
You are not late - you are the early bird - must be in the morning in Japan?!

I finished the axis caps. In the moment they are glued to the axis. Not the best solution if you have to repair the gear by exchangign such a crank gear. Clip? Screw?
[Image: 2014-04-29.221328-k.jpg]



If I design something like that, I do not need an outer frame and also the crank with it's pin can be designed and printed more easy - my opinion...

The disadvantage is that the crank radius can not be bigger than the gear radius. So the legs can not stand so close together than with an ordinary crank. The crank circles in opposite can interfere with each other and enable the legs to stand closer to each other with a bigger stroke - but maybe that is not the issue here.

This picture shows what I am talking about. Have a look at the crank pins and how close the legs stand by each other. This is impossible with my gear arrangement...
[Image: 2014-04-30.232900.jpg]


I will follow this tomorrow and show you all results.

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04-30-2014, 09:07 PM (This post was last modified: 04-30-2014 09:08 PM by steamboat.)
Post: #18
RE: Worm gear discussion
If you want to integrate this idea into the existing micropede design, you could change the existing gears to this spur-gear design and place a row of distributing spur gears on top. For better imagination I show here a picture of Sho's original design:
[Image: 2014-04-30.125100.jpg]

I will try out a new design for the complete chassis because of my not so fine home printer resolution.

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05-01-2014, 04:01 AM (This post was last modified: 05-01-2014 04:45 AM by steamboat.)
Post: #19
s=15 mm gear generation
I did a 8 teeth gear design. It is build with module 1.5. This gives a theoretical axis distance of 12.75 mm. With an axis distance of 15 mm the crank gears don't interfer. So with this the leg base would be 15 times 15 mm = 225 mm still bigger than todays Shellmo - but with my printing abilities I think I am at my edge. Still everything has to be done precise. I also have not designed an axel ficture to keep the gears from falling off the axis.
[Image: 2014-04-30.194510-k.jpg]


Nozzel 0.45 mm - layer height 0.5 mm - width 0.6 mm (hopefully)
[Image: 2014-04-30.194502-k.jpg]


I did some measurements of my spur gear. It should have an outer diameter of 14.6 mm. I printed 12 pieces. The outer diameter varies from 13.8 to 14.0 mm. So this is why I had to reduce the axis distance as mentioned above.

I will recalibrate my printer and see if I can change something. But especially with only 8 teeth there is a need to be accurate in this.

If someone want to print this crank gear please feel free to download it here:
Zahnradkurbel 8 mm

Rainer
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05-01-2014, 07:46 AM
Post: #20
RE: Worm gear discussion
23:36
I did a new calibration. Now the gears have an outer diameter between 14.0 and 14.2 - still about 0.5 in diameter missing. Maybe this is also because of the small radius at the gear tips.

In my KISSlicer I can set an "Inset Surface" to correct something like this. Will try out tomorrow if I can bring it to the correct outer diameter.

This is important to keep a good contact of all teeth between all gears and to prevent the legs from de-phasing. OK, I could trim everything to my printer deviation - but what would other people do?

Would be nice if someone could print out my gear and tell me the outer diameter.

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