Your word “pinned” this time gave me an idea that might work. If you can design things so that each raised leg comes to a resting position very close alongside the body, then a section of springy piano wire (stiff in short lengths) could be extended through a hole in the body to support the leg. (It would be good if the wire could extend at an upward angle so the leg would be trapped in a Vee between the wire and the body.) Retracting the wire would allow the leg to be lowered again. You would need one of these wires for each leg, but they could all be extended and retracted by a single bellcrank. The bellcrank could be driven by a single solenoid that is activated only long enough to change position but does not cause continuous drain on your battery. The bellcrank can be sprung to maintain fully open or fully closed positions. You could probably adapt a fairly cheap O gauge or HO (UK OO) gauge model railroad switch machine to do the job for you as that is what they are intended for anyway. If you have room to lay the wires out in a nearly circular curved path from the bell crank to the exit points from the body, you should not need to build any kind of complicated and weighty intermediate linkages. Unlike rope, you can push reasonable lengths of piano wire. If absolutely necessary, you could run the wires inside flexible plastic aquarium tubing to give more control - something like choke cables.
Thanks for the idea RoboTed, it provided me with some inspiration for my next design. :mrgreen:
Now from what I understand, the main objective is to have the feet secured when horizontal so that no strain is placed on the leg servo during flight. What if some kind of holding dock for the feet was created?
Something the feet brackets were moved into and then clamped in place so that the leg servo could be turned off because once clamped, the foot bracket couldn’t move until released which is when the leg servo would power up again and movement would continue as usual.
I’ve updated the idea slightly since producing these CAD models so I shall upload the newer ones once I draw them up. :mrgreen:
So moving on …
This idea involves the stepper motor being moved towards the bottom of the foot bracket with an elongated top which will have a unique “key” design that will be what feeds into the centre of the docking system (which will have the mating half) - I quickly drew up some kind of triple point trident fail . Also, in the updated idea, there’ll be a hole close to the key section in the top half - the reason will be explained further on.
The docking system will have 3 layers - the central and base layers will be fixed whilst the top layer will be allowed to move up and down to release/lock the foot bracket. The image below shows the docking system with the base missing - you can see how the foot fits into the mating half of the central layer.
Next up is a picture of the whole docking system. The top half will have pillars that extend down to the base layer - this links in with the hole in the foot bracket. I was planning on using something similar to a hole punch system where the following would occur:
Top layer raised.
The foot bracket would be fed into the central mating half of the dock system.
The top half (with the pillars) would be lowered and the pillars would pass through the holes on the foot bracket.
Everything is tightly clamped in place.
I would now not only have the key locking in place but the pillars stopping it from moving as well.
The docking system will be mounted onto the body (which will have to be square or circle based for the purpose of symmetry of quadcopter) and because of the clamping, there should now be a fixed rotor-to-rotor distance too.
The system will have to be elevated to the right height so that the foot brackets feed in nicely but apart from that, to my inexperienced eyes, it looks like it might work … Your opinions guys?
AKdaBAOUS
P.S. Ignore the grey pillars, they were there for the original idea because I was going for a fixed distance between layers which definitely wouldn’t work so I have no idea why I put them in.
I did some reading on propellers and pitches, etc. and one page I read said that if you happen to be upgrading from a 2 blade to a 3 blade propeller, then you can shorten the diameter by an inch but keep the pitch the same.
I’m not sure if that applies here as well but if it does, am I right in assuming that if I add more blades, I can shorten the diameter each time? Or there a certain limit to how much I can shorten it?
Hypothetically speaking, if the propeller happened to have, say, 6 blades, would it be possible to then have the diameter set to about 8 inches?
I’ve done some pretty rough estimation for the mass of the robot (excluding the battery pack) and comparing NEXUS’ mass into this as well (as a reference point), I think the mass of the robot (excluding the battery and brackets) is leaning towards 0.8-0.9kg and hoping that the larger sections (i.e. foot-rotor brackets and main body and perhaps the docking) will be 3D printed, with the rest being carbon fiber or something along those lines.
I’m guessing total mass including a battery will be around … 1.75-2 kg?
Um, yes. I also have a question about the stepper motors - the idea is to choose one which is high power, low RPM so we get more torque out of it?
I don’t really mind paying the extra if I get better performance and lifetime out of it. :mrgreen:
Plus, I’m using some servos from older robots so I should be saving some money there.
Hi, AK,
One possible consideration here - you will have to confirm or deny this with people who know these servos much better than I.
I recall reading that most of these hobby servos do not feed their current position back to their controllers. Therefore the controllers do not know where they are when power is applied. So the controllers send them almost violently fast to some “initial” position before proceeding in a gentler more “controlled” fashion. If you build them so the holding dock keeps the feet very near the “initial” position, then the motion should not be too violent when the leg servos are powered up again. However, building them this way would also mean that the extended standing position could not be near the “initial” position. So powering up in a standing position would cause an immediate violent move to the near retracted position.
There may be servos out there which do tell the controllers where they are, but I expect they are among the most expensive.
Yes, you’ve got a point there RoboTed …
I was hoping to have the legs in the holding dock as their “0” position and then they would move into their secondary “0” position for walking by rotating 90 degrees to the right (or left depending on what side you’re on) and then when the robot was “finished for the day”, the legs would go back into the dock and the robot would power off so that when it turned on again, since the servos were already in their “0” position, there wouldn’t be any jerking movements.
Since the hexapod was going to be a basic 2 D.O.F with a fancy leg bracket design, I’m hoping that along with the extension from the foot bracket, when the robot moves into it’s “0” standing position via the smoother, controlled motion, it should have a decent amount of height above the ground to not worry about anything else.
I’ll be posting an image of the new leg design along with some CAD “sketches” of the updated docking system later on today. ^___^
. Also, in the updated idea, there’ll be a hole close to the key section in the top half - the reason will be explained further on. 
