BrickBear

Somethings going down at Kurt Drive Yards:

Update on this, I’ve been working on the spring compression method to make it easier for the leg to straighten. I’ve made a diagram of what should happen and what shouldn’t happen. i think i need to take a look at my first design, i’ve been developing something that seems good but i think my first one where the spring was compressed by the pressure on the foot might be the smartest idea.

Progress update. I think i’ve found the final design for the spring bent leg, i’m going to attach all four and see if I can get it walking. (Probably not today though) edit: on further inspection the chances of this being successful may be slimmer than anticipated

I haven’t made much progress in the last weeks. Just fiddling when in passing. Must get back to it next weekend and that Facebook reaction certainly sounds good and suggests the current iteration maybe is worth pursuing.

So I decided to investigate some other solutions to the wobble and i’ve come up with actually quite a neat system. Basically I move the linkage that was originally connected to the cam to it’s own separate gear. That means I have one worm gear moving two gears, the first gear makes the hips move up and down, the second moves the leg forward and back. This makes the leg have a connection above the hip joint as opposed to below it and has significantly mended leg wobble. The caveat however is a new knee bending mechanism needed to be introduced. I tried a few things and managed to come up with a system whereby knee bend is initiated by a spring and when the foot is on the floor, the kneebend is counteracted by the weight of the walker pressing down on the foot. This means I need to order 4 more softer springs or figure a way to modify it so the spare rubber pieces can be used. The yellow axle would be connected to the ankle joint.

Progress update, I modified the feet further, now the feet lie flat and the rubber pieces extend out to the side, still providing friction, but with much more stability. secondly I have come up with a head mechanism, but it needs work. I intend to have the head act as a counterbalance and it seems to work well if it’s positioned just right however I think I want to shift the body weight left and right when walking as in a real animal too just so balance is not solely reliant on a complex head mechanism. I estimate that once fully panelled it will be around 40cm tall. note the second picture looks funny because I very badly clipped put the background and the head seems much larger than the feet cos of the angle. The right rear leg is raised off the ground by about 1cm. The head is currently acting as the counterbalance, you can probably see the mechanism by the neck, it’s a sort of seesaw that gets pushed up by the shoulders which turns a gear and that gear connects to a cam which moves the neck. I did power the legs a little and it showed some promise of being able to move. Lets hope for further progress.

No cheese wedges are the little plastic 1x1 triangles i’ve placed both of them angled face opposite one another on two plates on the 4x4 round piece that goes on top of the AT-AT foot underneath the liftarm that connects the “ankle” joint to the lower leg. I just call the rubber pieces “rubber pieces”

Yes, i’ve redesigned the feet so that they have grips underneath them now. This prevents feet slippage. And i’ve reduced leg wobble by placement of two plates topped by two cheese wedges facing each other under the part of the liftarm that joins to the foot.

That is useful to know. Alas I cannot test your theory this weekend due to being ill but I shall stare longingly at my model from my bed.

Yes, basically the (soft) spring(s) would be half a pin hole longer than the current pivot point for the foot when fully extended. This would give the illusion that the foot has touched the ground when the next foot lifts. As the leg moves the spring could then contract to the position that you currently have the feet in (adding a stopper to prevent it contracting more) and that may well solve the problem of the foot not quite touching the ground upon its step forward, being the soft kind of spring as well it should not place too much pressure on the ground if any to affect the balance as the weight of the walker would compensate.

I reckon you could fix the cadence problem (i.e only one foot off the ground) not by tweaking the gearing and mechanism but by adding a spring or two to each foot. With the spring pushing the previous foot forward a little it should in theory touch the ground as the next foot lifts, giving the illusion all is in sync. As for my AT-AT’s balance it’s more the issue is that is has the potential to fall forward left or forward right if the weight isn’t on the feet on the ground but i’m hopefully going to remedy this with the seesaw mechanism.

Brilliant. Looks very exciting.

So I actually came up with and implemented a much simpler solution for weight distribution on the front feet this morning. (The back feet lift fine already because the head leans the weight away from them) It’s basically all about the heads attachment system. So above the front two legs “shoulders” are a sort of see saw mechanism. When one front leg lifts up it causes the seesaw to rise on the side of the raised leg. The head which is connected to an axle on the seesaw then rotates toward the front leg that is not raised because of weight and gravity. Because the see saw is moved directly by the legs, the weight on the seesaw created by the head is transferred to the leg that is not raised and so stability is achieved. It’s so simple and such a relief to have achieved this. Also @Nelson you might find this solution interesting.

And then I said but back leg first, the camels is reversed, I acknowledged that.

Ooh that is clever. I’ve watched the first an unhealthy amount of times. It’s interesting how the camel lifts at the shoulder at its front like Nelsons. It’s definitely the same gait (albiet back leg first then front leg)

Looks like a brilliant start, I have to admit I’m somewhat jelly of the stability of yours.

A new year, perhaps a time for new solutions. Here’s to achieving our AT-AT ambitions in 2025

Thats just where the steering pivot point is, a turntable is a stronger pivot piece than an axle or pin.

Whose a good boy? I realised I couldn’t make it walk without the head being added as that’s the heaviest part. (Note the head seems bigger here, it’s just perspective) Lifting the feet with head acting as a counterweight. What i’ve noticed is that the feet do still slip a little on the ground with the head added. But the springs are really good at holding the weight. I also have new batteries which really upped the power of the xl motor. My main problem now is the head function, I need to have the head rotate based on the movement of the legs so it remains an effective counterbalance. Still, the model has never been so stable!

Ok so I also introduced stoppers to the front. This has significantly improved balance as the legs are nwo limited to the movement they should have been. Also strengthened the central pivot for steering. Everything has been reinforced basically. Need to see if it walks now.

@Nelson First of all may the best man win. You raise a good point about the leg raising I could try adjusting the positions of the cams by disengaging the middle. And yeah i’ve checked out Philo’s home been using it since I was a kid. Regarding the weight of your model, do you think it might be worth sacrificing certain levels of detail for functionality? Like maybe you could get some prints or stickers for detail on larger plates?

Some good news, i’ve begun adding the legs and implemented various features to counteract some problems I was having. One problem I was facing was when placed the legs would slide (as if doing the splits). I had this same issue on the previous one which is why I remade the chassis in the first place, I thought it was a suspension issue but To fix this I merely needed another 2x1 beam to be inserted onto the existing cam shaft to act as a stopper which could have been done on the old chassis. But nevermind, this chassis is stronger so it’s progress either way. Referring to @Nelson suggestion to take the weight off of the back leg diagonally opposite to the current leg lifted up off of the ground I have found that now without the “splits” motion occuring for my model that this is a natural byproduct of my mechanism design anyway. As a result upon adding the other legs it stood perfectly even with one leg raised. I just hope the torque of the xl motor is enough to move everything once the bodywork is placed. I’ve defrictioned joints, modified the suspension all to reduce resistance on the motor. I believe the XL motor can take up to 14nm according to wikipedia 9.8nm is roughly enough for a 1kg weight to be lifted a metre. I’d be interested to know how much resistance towards the motor the hard suspension provides in terms of weight. (I guess that would be how much weight the spring can hold at full length under load?)

New version moving, lossy gif. No legs yet.

Ok so I’ve nearly finished modifying the frame. I’ve added the gearbox mechanism to adjust the front and back cams independently of each other, i’ve added an L-Motor and repositioned the grey technic frames one hole over as stated last time. one problem i’ve run into is the l motor isn’t really powerful enough with the resistance of the springs having increased. So i’m going to upgrade to the xl motor. Otherwise, the mechanism is now stronger and more polished than before and the positions of everything should be enough to support a battery box, steering motor and ir reciever as well as bodywork. That is very impressive. I’m guessing you’ll have to upgrade to a thicker gear if possible?

The real reason is much simpler, I have many black pins and fewer grey ones in my main technic boxes so I like to use them for things where it’s absolutely necessary for the frictionless stuff.