Oh well, here’s another android. I shall still be working on number 6, but I’ve had so many thoughts about doing it differently again that I’m making another prototype.
This android is kind of a cross between 3 and 6. It has quite similar legs to 3 but will use wiper motors in the body pulling cables to the leg joints so it can be more spindly than 6. This is why it’s called ‘Mr Stick Legs’.
I am trying to reduce the motor count from five to three for walking and also build in the ability to rotate the legs so it can walk around corners and turn on the spot. Because the legs don’t have any motors mounted in them they are also able to bend further and so it should be able to go up steps/stairs. The body will also hinge at the waist so it can shift its centre of gravity forwards and backwards.
The legs are quite similar construction to android 3, only they are longer and the hinges are made of steel. All the joints will be metal on metal instead of just holes in the wood:
Already the mechanism feels much smoother and tighter, here are the legs assembled into their familar twin parallel pieces:
Pulleys will pull cords down the legs to operate each joint, each leg will have its own motor which will pull different length cords as it rotates further, and also different cords to operate different joints when it turns in reverse. Along with springs and gravity this will allow a number of functions in each leg from one motor.
Pictured below are the motor mounts for each leg, a pulley on one of the leg joints, and the pieces that make up the pulleys laid out – they are made from a round MDF ‘washer’ and two large steel M8 washers:
So, I have to make the ankles and hips next, also the knee-cap arrangement that will stop the legs bending the wrong way…
Just a minor update; I have built the ankles and started the feet:
Everything is taking a little longer as steel is a bit harder to engineer than wood.
I have now built the ankles / feet and started the hip assembly. The hip joints that let the android shift its weight from side to side will be close together like a human pelvis – the previous androids had the hip joints directly above each leg. The leg rotating meachanism will also be here so all the hip joints are as close together as possible. This will also mean that as the android leans sideways one leg will be lifted off the ground automatically without bending. Here are the two legs propped together for now:
The wiper motors will fit to each bracket at the top:
I still have to make the ‘pelvis’ assembly to hold the legs together, also the knee-caps which is quite important to make the legs bend in the right places with only one motor.
I have now made the knee caps which stop the leg bending in the wrong direction. These are crucial to make each leg work with only one motor:
They are made form two parallel wooden sections – at each end are skateboard wheel bearings that run on the legs like wheels. Here they are attached to the knees along with some bungees that pull the legs straight:
I’ve also attached the wiper motors to each leg now that they can support their own weight. Still no hips though so the legs are again propped together:
I have to make the pulley for the motors so I can test each leg bending etc but they appear to bend and spring back ok when I just ‘squash’ them manually.
I have built the rest of what makes up the hips from some right-angle brackets that I got from B&Q:
I had to cut them about a bit to make them fit around the leg motors, four of them make two brackets like this:
Each bracket has a piece of M12 rod attached to it which will in turn ‘plug into’ the body allowing the legs to rotate, they hip brackets also allow the android to lean sideways:
The next major part to make is the ‘pelvis’ that the legs attach to, this assembly will have a third wiper motor in it that pulls the android side to side. It will also have hinge points for the rest of the body to attach to allowing the android to bend at the waist.
I have started to make the pelvis assembly which also holds the motor to make the android lean from side to side:
Here it is mounted on the legs:
The shaft in the middle is attached to the motor and will have a pulley on it with a string attached to the inside of each leg. The legs will be sprung outwards with bungees attached between the first ‘cross bar’ on the outside of the legs and the top of the ‘T bar’ on the hip assembly.
There will be a front and a back to the assembly to hold another pulley on lower down between the legs – the front section will also brace the motor drive shaft on a bearing. Somewhere on the sides of the assembly will be pivot points for the torso and associated lever from it’s motor. For now it looks like this:
Next are the other parts of the ‘box’ that make up the rest of the pelvis…
I started to add brackets to the pelvis for the front panel but then I decided to see how well it would stand up with some more bungees added. I’ve got it to statically stand on one leg, the bungees are in approximately the right places but will be moved a little to they don’t interfere with the motor pulleys and cables when they are in place. The right leg is cable-tied where the motor would pull a string as the pulley etc doesn’t yet exist:
I just have to sort out the leaning side-to-side motor which needs to have the pelvis extended downwards so another pulley is held lower down in between the legs, this will allow it to pull one leg closer to the middle and let the other spring outwards causing it to lean to one side:
A few modifications:
The ankles are now sprung inwards to help get the android back to the center once it has leaned to one side, they also have end stops in both directions to stop it leaning to far over and stop the foot springing down too far:
The cable has been added to the centre motor that makes it lean sideways, for now the ends of the cable are attached to the thighs from the inside so the legs get pulled inwards against the springs on the outsides. The front panel holds puleys lower down between the legs:
I have also sort of started the body. I found this piece of pipe assembly in my local DIY store:
This will form the main part of the body, a plastic plate fits the front perfectly:
So it will look something like this:
There will be a kind of L-shaped bracket which runs down the back and under the bottom of the pipe part. This will allow mounting the hinge for the body to pivot front to back and also a place for a small back-pack to be attached. The back-pack will mainly hold the ‘body motor’ but also a mains Power supply I think so the whole thing will run from a single mains cord (or potentially batteries).
The head obvously mounts on top and the arms will have seperate brackets and big curved ‘shoulder pads’ so they hang underneath each obvious arm place on the body. As the plastic plate is semi-translucent coloured lights can show through from the back in different places.
As the legs seem to be able to lean themselves onto each foot so far I have to make the majority of the rest (body etc) to get an idea of final weight before messing with the balance anymore. So, the android should appear to be complete quite quickly…
I have now made the body mounting ‘brackett’ / back-pack assembly:
It fits on the back of the upper body and also underneath so there is quite a lot of space behind for electronics etc:
The body is held with one universal joint at the front and two linear actuators at the back taken from the previous androids. This makes the whole assembly like a tripod where two of the legs can get longer or shorter:
This allows the body to tip forwards:
and side to side:
Next I have to make the arm and head brackets/platforms and start to think about the control electronics. There is a little work to do on the legs but this can wait until all the weight is on top.
I’ve added a few things to the android today. The bases/brackets for the head and arms have been added, the shoulder hinges are just below where the pipes point upwards now, this puts the proportions of the body and legs back how they should be:
The back also has an extra body panel at the back of the legs, this has two pegs poking through the bottom that attach to each rotating hip so I can later actuate them to turn the legs:
Now it looks like this:
Next will be shoulder joints and the pan/tilt head assumbly which will only really hold it’s eyes and other sensors. I’ll probably take the electonics from the previous android for the majority of the motors so it may be doing stuff quite soon…
I have now built some arms for the android, they don’t have motors on yet but will operate along the principle of being sprung against gravity and having cordless screw driver motors pulling them down and back to front, the green ties are there to stop them popping up. The head is just a mask stuck on a spray can for now:
The linear actuators that supported the upper body have gone for now as the whole thing fell over during testing and some bits snapped. For now the upper body is held up with two strips of steel. The mains power supply is fitted to the back so everything can run from one mains cable:
The original electronics built for the previous androids have been folded in half and now they fit in the body, it will operate with the control system I built here for the previous androids:
Here’s a full length shot:
The android can lean from side to side now, driven by commands from the serial port on my PC (Rs232). So, the next steps are to get the leg motors working too and attempt walking. I’ll also work on the arms, at least to get the motors fitted so I can remove the ties.
I have added a video of the androd walking around, it is on the videos page here.
He’s a bit wobbly when he’s on one leg, but this is because all that holds the leg straight is a bungee cord on each side. The plan is to make the legs a bit more rigid for sideways movement, although this has proven a vauable test to see how much I could reduce the motor count and mecahical linkages to simple flexible cords and springs – a bit like a human. (Mr Stick Legs has only three motors for walking).
I have now replaced the stings that pulled the inside of the legs with rigid rods from the wiper motor assemblies. The gait is now a bit more stable and reliable, I’ll post another video as soon as I make one.
I’ve also removed the body as that pipe section and wooden arms were quite heavy, I’ll probably re-use that on another android (thinking about resurrecting the legs from android 4). I’ve aslo made sure that I can fit the head on that I am building here, so now the android looks like this:
As the original pipe-section body was round it didn’t leave much space for anything inside. Now I have space for the control electronics and also a mini-itx motherboard so I can get a whole computer in there with Wi-Fi etc on.
Taking off the body made it walk much better, although I still have a bit of work to do on the legs to ‘tune them up’. However, I have to watch the weight and centre of gravity so I plan to make any body panels out of foam sheet or cardboard and the arms out of balsa wood using the smallest motors I can (probably hobby R/C servos for the elbows down.
I’ve now fitted the following items into the head of Mr Stick Legs:
–PICAXE 40X development board.
-RS232 12 channel R/C servo controller
-Belkin USB to Serial adapter.
The PICAXE is controlling the legs as before with the rest of the associated electronics in the android’s chest. The servo controller is for the camera pan/tilt mechanism and the forearms/grippers which I am yet to build:
Here’s a close-up of the items at the back of the head:
The portable PC is now in the android’s stomach, here you can see the ports at the side which will be under his left arm:
So now it looks like this:
The only hardware construction left is:
-The arms, for which the brackets and pulleys are already mounted.
-The actuator to rotate the legs so it can turn on the spot.
-Maybe some tweaking of the legs once all the weight is on board.
I have now fitted an addional mains power supply to the android to power the camera and video sender so that any nasty electrical spikes from the motors don’t affect the picture. This is fitted inside another aluminium box on it’s back along with some switches to turn the various things on and off:
I have also started to build the arms in an attempt to get all the weight on board so I can sort out the gait again. The shoulder will rotate with some big motors that you can see ‘facing down’ at the moment, the forearm/elbow will use two R/C hobby servos as well as the hands: