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Thorbear.H
02-02-2014, 07:04 AM
i am cutting a new chassis for my phantomx, doing some changes for easier battery acces, mounting of aditional boards and cameras and so on. but, how much will increasing the span of the body reduce payload capability? i am looking to widen the body 48mm between the middle legs. will this have a dramatic effect on payload capability?

jwatte
02-02-2014, 10:56 AM
The width of the body doesn't matter much when in static rest, although if dynamics make the body be a lever arm, then the change in payload is proportional. So, if the width was 100 mm, and now it's 150mm, you'd lose 33% of payload capability.

To understand why the body width doesn't matter in static situations, consider children's wooden blocks. You can build two pillars with a long block across them. The torque between the pillars and the top-block will be effectively zero (a "perfect hinge.") Now, consider building an "M" shape with a hinge in the middle -- the torque needed at the center will need to be enough to counteract the weight of the top block, times half the width of that block.

Here's an illustration:

http://watte.net/walker-torque-explanation.png

Thorbear.H
02-02-2014, 12:56 PM
thank you for the response. the body was 200mm, i plan to make it 248. so if i follow your above calculation, that turns out to be ca. 20% lost capability.
but, in your experiment, the overall length of the unit is constant, i plan to only strech the body itself, and add a 4th servo to the leg, which effectively move the point of contact invard to the body. this will make the contact point of the middle legs only 40mm wider. i am hoping this will even out things, altoutgh very little.
seems like i will realy strech the limits, with six extra servos for 4th DOF, i add 330g + extra brackets and camera.

KevinO
02-02-2014, 01:16 PM
Just a note. When I made the phantomX 4dof I did notice a quicker battery drain due to more weight and more servos. Though I'm sure you are already aware. I was getting 10-15 min on the 2,200 mah battery. I ended upgrading to 6,600 mah to compensate.

Thorbear.H
02-02-2014, 01:53 PM
as i am new to robotics, so i will probably have my hex connected to the computer for quick troubleshooting, and use an external powersupply. i have read your thread about your 4 DOF walker, it will be usefull for me.

KevinO
02-02-2014, 06:34 PM
use an external powersupply

Make sure you use one with sufficient amps! :)

Thorbear.H
02-15-2014, 04:52 AM
kevin: i have ordered a powerfull external supply now. but, as i placed my order late when there were 10% discount, i placed the order quicly, not reading that the bulk pack with ax 12's don't come with the brackets :(

so the 4th DOF will have to wait, until i can get more brackets printed.

anyway, i made a prototype chassis in some thin aluminium i had lying around, and used a bowl for mounting the electronics in several layers. the middle legs are now 49 mm further away, and the length of the body is a bit shorter. i tried to simulate the electronics i will be using by putting a weigth of 540g and walk, and it does so without dificulties. with the bowl and camera, it now looks adorable :p