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Macropede studies
05-15-2014, 08:43 AM (This post was last modified: 05-15-2014 08:52 AM by steamboat.)
Post: #1
Macropede studies
Because I am working with a crude RepRap Printer outfitted with a 0.5 mm nozzle I will not be able to print Sho's fine design. Because I like the movement of the 16 legs per side, but can't print so fine, my Micropede will become a Macropede. Maybe after this studies I will be able to shrink everything in size - but at first this is not my goal...

Tonight I went further with the gear design which I explained already in an other thread. It has Module 1.5 gears.

The crank pins of diameter 4 mm will be direct printed on top of the gears.

The gear axis will be build by M3 screws. Yes this is a lot of iron but with 32 gear axis per side I don't want to be frustrated by one not well printed or broken axis.

This is my actual test setup with M3 screws as axis:
[Image: 2014-05-15.002640-k.jpg]


Because this should become a fine and nice running model I also like to have a quite and powerful motor. So I will try to use Sho's fine gear motors. I will power them with a circuit borrowed from a 3$ HobbyKing servo.

From left to right:
12 teeth Module 1 - will not use this fine Module
10 teeth Module 1.5
16 teeth Module 1.5
[Image: 2014-05-15.003037-k.jpg]

Rainer
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05-15-2014, 09:13 AM
Post: #2
RE: Macropede studies
(05-15-2014 08:43 AM)steamboat Wrote:  Because I am working with a crude RepRap Printer outfitted with a 0.5 mm nozzle I will not be able to print Sho's fine design.

HAHA. Its certainly not your printer that is the issue, I don't want people who stumble upon this forum to think that if they had a different printer it would be a possibility. Its not. We all have tried.

I like where your going with it. Not sure about the screws of course, but I get your reasoning totally.

My endeavors have been on hold as I have been working on the rep-walker build...and eyes. I see you have also rotated the motor axis from Sho's like I had. This WILL make the bot wider, but its a lot better then having to design the gearing to change the direction and the inefficiencies involved.
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05-15-2014, 05:09 PM (This post was last modified: 05-15-2014 05:10 PM by steamboat.)
Post: #3
RE: Macropede studies
(05-15-2014 09:13 AM)jmccartney Wrote:  I see you have also rotated the motor axis from Sho's like I had. This WILL make the bot wider, but its a lot better then having to design the gearing to change the direction and the inefficiencies involved.
Additional I will place the motor in the middle of the 16 legs. With this the torque for the last leg will be powered "only" through 12 gears - from the middle to the front and to the back - and not through all 30 gears from the front to the back.

Next will be to design some legs with a nice hip joint...

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05-15-2014, 11:03 PM
Post: #4
RE: Macropede studies
(05-15-2014 05:09 PM)steamboat Wrote:  Additional I will place the motor in the middle of the 16 legs. With this the torque for the last leg will be powered "only" through 12 gears - from the middle to the front and to the back - and not through all 30 gears from the front to the back.
Genius! You obviously have a lot more experience in this than me, while it did occur to me that the last legs would be powered through a long train of gears, it never did that placing the motors in the center would mitigate this.

The other nice thing is moves the center of gravity back. It seems like these small bots are front heavy, but this is a step in the right direction. On thing to keep in mind is it might be nice to run the batteries within the chassis keeping them low.
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05-24-2014, 04:16 PM (This post was last modified: 05-24-2014 04:18 PM by steamboat.)
Post: #5
First run of Macropede leg set
Yesterday I made some progress with the Macropede:

First running pair of legs design for the RepRap printer
[Image: 2014-05-23.175305-k.jpg]


Some hours later 8 legs already:
[Image: 2014-05-23.194147-k.jpg]


This will become definitely the Macropede version (bigger than Micropede) because the leg distance is 15 mm
- with 16 legs this is 225 mm in total.

The original Gakken Centipede has 300 mm max axis distance
while Sho's Micropede copy of the Gakken Centipede has 150 mm for this.

Finaly my Macropede leg unit is as long as the Repawlker RA04 in total including the bumpers - this is quite acceptable for me...

And the ready to use 1/4 unit of 8 legs:
[Image: 2014-05-23.230000-k.jpg]

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05-24-2014, 04:41 PM
Post: #6
RE: Macropede studies
Amazing !

Now I think about torque if you will use this 100:1 HP gearmotor.
If length of leg become twice, the speed become twice, too. But required torque become twice, too.
But even if it can't walk, you can make shorter legs.
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05-24-2014, 11:00 PM
Post: #7
RE: Macropede studies
(05-24-2014 04:41 PM)sho Wrote:  If length of leg become twice, the speed become twice, too.
Would be nice to compare this. Macropedes leg is 40 mm from hip joint to crank and 39 mm from crank to touch point. So this is about a 1:2 ratio. The crank radius is 5.2 mm = 10.4 mm rotating diameter.

Because of the multiple cranks I think we can postulate the legs movement equal to a wheel movement? With the 1:2 ratio this will become a wheel radius of 2x 5.2 mm = 10.4 mm. The circumference of a wheel is 2 * pi * radius = 2 * 3.141 * 10,4 = 65,3 mm total movement with one revolution of all legs. Because we have no total friction and no permanent touch down of the legs (other than with a wheel) we always will have some slip too. - Sho what is your experience about this?

(05-24-2014 04:41 PM)sho Wrote:  But required torque become twice, too.
Hopefully I have not that much loss in my gear like in yours. I will measure the wattage and tell you tonight.

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05-26-2014, 01:05 AM (This post was last modified: 05-26-2014 01:06 AM by steamboat.)
Post: #8
second mutation of the Macropede legs
@ all

I brought the second mutation of the Macropede legs to live.

Two big changes:
- stronger hip segment with optimized geometry
- replacing 32x M3 screws and 64x M3 nuts at the hip
-> by 32x Ø5 mm plastic pin and 32x C-ring
This not only saves nuts and screws but also makes it much easier to assemble it.

I will use M3 screws for the rest of the gear axis because of it's stability and exactness. Additional this gives you the possibility to adjust everything for a good run.

Changed the crank radius from 5.2 to 5 mm and shorten the leg for 1 mm. Small changes only but big steps would take more time to do...

The 8 leg module with Sho's gearmotor takes less than 140 mA at 2,7 Volt = 0,38 Watt. But you can stop it easy by hand (sorry - no current for this).
This is good and bad because nothing can break apart...

Later I will support servos in the Macropede leg module also to keep costs down and make sourcing easy.

[Image: 2014-05-25.162613-k.jpg]

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05-26-2014, 02:33 AM
Post: #9
Current - torque
I repeated the test with 4 rechargeable batteries.
4,5 Volt 150 mA free turning
500 mA with heavy load by finger but still fast turning.
800 mA break current.

I think it is really necessary to have a special current and turning management for robots with legs. To start the legs might need high voltage/current (full voltage / no pulse and allow current of 800 mA for a short time). After the gear becomes loose we have to reduce the voltage to avoid to go to fast. If there is an external blockage (more than 750 mA) Shellmo should stop and shout out loud. Shellmo also could try to recover by going backwards for 1/2 turn - and so on...)

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05-26-2014, 07:10 AM
Post: #10
A dream comes true!
This is the base for all 2x 16 legs - 244 mm long.
All flat bottom, no support - easy to print.
It will be printed (in the moment) in two parts
[Image: 2014-05-25.230400-k.jpg]

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