2 1/2 foot Biped Project.......Giant Scale Scout

This is a continuation of this thread: lynxmotion.net/viewtopic.php … highlight=

Basically, a giant scale 6DOF scout biped based on the Hitec HS-805BB 1/4 Scale servos. It will be a mechanical skeleton under Vacformed plastic shells based on the Robocop ED-209. I don’t know what it is about the ED-209 but it has always intrigued me. There are some seriously flawed design aspects in it and overly elaborate hydraulic system. But it never was designed to be a real robot, just a tough looking movie prop. I plan to use the ED-209 as an outer shell to a real, walking, talking, tracking Biped.

I’ve almost completed my CAD drawings in Sketchup of my Custom 1/4 Scale brackets and parts. Now I’ve begun fabricating my brackets. I have a couple “different” ideas as far as the geometry of the legs and the foot design. At mid-stance, it stands 26" tall, at full crouch 14", at full stance 32".

I’m still in the learning stages of BasicX programming so hopefully I’ll be more proficient at that by the time I’m ready for the first step. So this will be a learning experience for me.

**I have a couple questions though. What is the maximum current the SSC-32 and the MiniAtom BotBoard can handle? My servos will draw over 20 amps and I need to know if I have to build a Power Board to distribute power to the servos and route the signal wires to the controller or can I run them straight off the controllers?
Here’s some pics:
My servo order just showed up. 12 more HS-805BB servos:


These things are huge!!


They really have to be seen to appreciate the size. Here is a comparison between a standard sized HS-300 servo and some SES brackets.



:open_mouth: Ooh. Shiiiiny. :open_mouth:

I have also tested an HS-805BB to death. :laughing:

Results near stall:
4.8 Volts - 260 oz/in Torque, 1.3 Amp Draw
6.0 Volts - 336 oz/in Torque, 1.8 Amp Draw
7.2 Volts - 405 oz/in Torque, 2.0 Amp Draw (Getting warm)
8.4 Volts - 495 oz/in Torque, 2.4 Amp Draw (Overheating)
9.6 Volts - 510+ oz/in Torque, 2.7+ Amp Draw (Overheating big time)
12 Volts - 540+ oz/in Torque, 2.8+ Amp Draw (She’s toast)

The servo functioned normally and within an acceptable temperature up to 7.2 Volts. At 8.4V, she had some serious power. It broke my spruce test stand and I had to rebuild it with aluminum parts. I tested it to stall at 8.4 then ran it through it’s range of motion for 2 minutes straight with a 5 pound weight at 2" from center then stalled it again. It ran flawlessly and never drew over 1.1 amps. At the end of the 2 minute run and stalls the board and motor was fairly hot. Not burning up yet, but very close. I think the board and motor will take it if they are allowed to cool better. I’m working on a heatsink for the mosfets and motor can. I think this will allow it to run for long periods at 8.4 volts and almost 500 oz/in of torque.

After one stall test at 9.6V she was burning up. That nasty hot electronics smell and the board was almost too hot to touch.

And 12 Volts was just too much for her. I’m surprised the gears lasted this long. The failure could be partly because of the previous abuse testing it but the board fried and the gears exploded at the same time. The box went BANG and the board went POP and shot a little cloud of smoke out the bottom as the chips literally blew apart. After taking it apart, the first spur gear broke into about 6 pieces and the primary spur gear split in two. I’m guessing the primary split and locked the gears with a jolt causing the first spur to shatter.

So, 7.2 Volts at 400 oz/in is possible and 8.4V at 495oz/in may be possible with some cooling modifications. And the gears are good to around 500+ oz/in of torque. If it only had metal gears, it might be worth adding an external H-bridge to power it past 8.4 Volts. Too bad.

I’ll post some pics of the modifications once they are done and tested.

These aren’t done yet and Sketchup Pro is having trouble running the files now that they are so big but here is what I have so far. Once I made blueprints for my brackets I decided to put them together to get a visual of the design.


And here is a side view on top of the Picture of the ED-209.


And here are some pictures of the start of the weapons arms. They will be prototyped using HS-5995TG servos and SES brackets. These pictures really give an idea of how much bigger the HS-805BB servos and brackets are.


:smiley:, looks really good man, i hope that you can hanmdle those amps thats those those absolute tanks called servos draw

I hope I can too. Do you know how much draw the SSC-32 and the MiniAtom Botboard can handle?

I’m waiting on a backorder for a Lynx scout, ssc32, botboard/atom pro, and 12 HS-475’s from Robotshop. I’m going to modify the scout to resemble the geometry of my biped and use it to test some gaits on a smaller scale.

I can’t wait to get the scout. It’s alot less work than fabricating your own parts. lol Thanks Jim. :slight_smile:

My other BotBoard/Atom pro, SSC-32 and POD camera system just arived yesterday. These will be for the Giant Biped. I’ve got some pics of the start of the brackets. I’ll post them later.

P.S. Did you get your battery packs yet Chunga? My motors from you finally got through customs according to the tracking. I haven’t checked your tracking yet though. I’m tritling my thumbs with my work robot until I get the other 4 motors so it gives me time to work on the Giant Biped.

no, sorry, i dont know how much draw they can handle

P.S. no, they haven’t came yet, i think there is going to be the long process of the customs that my package to you went through it said it will arrive the 5th of january, after like…4-5 days in customs cause thats what mine went through…actually, it was 9 days…but whose counting? :laughing:

The SSC-32 can pass 15amps per side for a total of 30 amps. If you are going to need more than that you may want to consider powering the most demanding servos off board.

Glad to help! :slight_smile: You may be dissapointed with the performance of the robot with 475’s though. If they were 5475’s then it would work ok with minimal payload. I’ve never tried it with analog 475’s. Let us know how it works out.

The 3D renderings of the robot look fantastic. If I were doing it I would scale it back a bit though. I’d reduce it down about 30%. I think the tibia is a bit long even for these servos. I hope I’m wrong. :smiley: Good luck with it.

Yep I knew the smoke level was 12vdc. :wink:

It would still benefit from the FET’s low on resistance. The analog servo uses bipolar transistors and they drop some of the voltage. This adds to the heat in the output stage.

Thanks for the advice Jim.

I would have gone with other servos but I didn’t want to spend alot on it when I was only using it for familiarizing myself with some gaits and the controllers. I’ll be running an SSC-32 and 7.4V lipos. The 475’s are around 70ish oz/in at 6.0V so I’m hoping at 7.4V, they will be able to perform simple gaits. I’ll let you know once it shows up.

If the SSC-32 can only handle 15 amps per side, I’ll make a Power board to parallel the servo + and - to a lipo and run the signal lines to the SSC-32.

I thought the tibia looked a bit out of proportion as well. I’ll probably shorten it to match the femur. I wanted to follow the dimensions of the ED-209 as much as possible but I also wanted the hip joint to end up directly above the ankle joint for obvious geometric and center of gravity reasons when crouching.

I made up a servo mount and C bracket for the ankle. I’m using 1 1/2 " X 1/8" 6061 Aluminum Bar Stock. I greatly underestimated it’s ability to resist being bent straight. lol I was bending 1" wide bar stock with no problems but with the added width, this stuff is tougher. It works well when heated but I don’t have a jig large enough for 1 1/2 wide stock that will permit heating. So instead I annealed (Heat very hot,500 F, then quench quickly in cold water) the lines where they were to be bent then bent them after they cooled. This worked well but didn’t give me enough accuracy in the size of the bend. I ordered a Bar stock bender so I can heat them and bend them accurately more easily. I’ll build more brackets once it gets here.

Here are some pics of the start of the ankle joint still in the rough, no grinding, sanding or rounding yet. And no mounting holes. It’s sitting next to an assembled SES C bracket, Servo mount and HS-300 standard servo for size reference. The brackets are amazingly strong. I could have used thinner aluminum but the weight difference was minimal and the 1/8" stock is very difficult to bend or flex, even by hand.




:open_mouth:, those things are some bigguns

i hope those servos can hold up that aluminum, its pretty damn big

I have a feeling you’re right. I’m trying to keep in mind that bigger is not necessarily stronger. The servos and bracket are so huge compared to standard servos and brackets that it really peaks the imagination. At this scale, it really teeters on the line between hobby robotic components and industrial/commercial robotic components.

My intention with this is to push hobby robotics to the edge in scale. And keep the price reasonable. Everything I build, whether it’s planes or helicopters, I do big. I don’t know why but I love big planes and big helis. I just appreciate the work involved in creating something on a larger scale than normal. I also hate building things that are common. I like to build something and afterwards someone says, That’s awesome, or That’s the biggest _____ I’ve ever seen. I like to be unique. I could build a regular sized scout but I don’t have the programming proficiency to make it unique in abilities like others do. So I’m making it mechanically unique instead by doing it big

This project would be very possible with industrial servos or gear motor and gearbox joints. But the custom work and price alone would make it very difficult for most hobbyists and enthusiasts to built one. HS-805BB’s are very inexpensive. I found the 12 I just ordered for $20 US each. A steal!! They can normally be had for $30 to 60 US each. If it is possible to build a 2 1/2 Foot biped with $30 servos and some modifications, I think that is awesome. I want to push the 805 to it’s limits and then build the biggest robot possible around them. From there, we will know how big of a robot the servos can really support when they are pushed. One can always make a slightly smaller one to perform better.

This project will no doubt have some trial and error involved becasue of the scale and the components involved. I also expect to encounter some negativity and doubt from others during the building. That’s ok. Critisism is helpful.

I’m sure everyone here will help me out as the project progresses. I, for one, am excited to see if it can be done. If not, I’ll build an 18" biped with moster servos and crazy power for it’s size. Eitherway, byt he time I’m done, we will all have some experiences and real testing to base future designs on.

Hey Jim, I was wandering aimlessly around the assembly section of your site and found a picture of this:

A Lynx 209 Scout. I’m assuming it’s called a 209 because of it’s resemblance to the ED-209 Droid. I didn’t even know you sold a biped chassis like that. It looks awesome. I had no idea.

Also, was curious if the Biped Scout kit that you sell is still made with the lexan parts or does the kit come with the SES brackets like the picture of the scout on your website? I’m not sure what version I’ll be getting from Robotshop but hopefully the SES version.

Oh yes I built an Ed-209 style Biped. :smiley: There is video of it walking somewhere… Looking… Well I will see if I can dig it up at work. It was submitted by Pete Miles.

We converted the Scout to aluminum legs quite some time ago. When we do a major overhaul like that we normally take it out of stock for a month or longer. This gives us time to work, and allows for the current version to filter through.

On the brackets I would definetly go to .09". You say the weight differench is minimal, but I submit to you it is significant. Like 30% less. When you are making biped robots you do everything you can to shave off an ounce here and there. If the .125" brackets weigh a total of 48oz. Thats only 4oz. per servo btw. :wink: the the same brackets in .09 would be 34oz. a weight savings of 14 oz. almost a full pound lighter.

It reminds me of a documentry on bridge building I saw once. They said anyone can build a bridge that can hold 500 tons, but not anyone can build a bridge that can just cary 500 tons. The trick is to build the robot to just be rigid enough to hold itself together. Unfortunately any overkill will add enough weight to seriously jepordize functionality. Just my conservative nature. :wink:

hmmmmm 14 oz is alot. I just had a scrap piece of thinner aluminum bar and I assumed it was also 6061 but maybe not. It could be alower grade with differentalloys causing an increase in weight. I’ll have to pick up some thinner stock while I’m waiting for my Bar forming tool to show up.

I can understand shaving weight. Flying foamies and small indoor planes, shaving every gram can mean better performance. Same with giant scale electrics. The lighter, the better. I may have underestimated the importance of this in robots. My work project I’m doing has a finished weight of over 55 pounds and in this case, the heavier, the better. So weight isn’t something I was watching. I shouldn’t have let this habit translate into my other robotic projects. I’ll try to think more like an airplane builder wile I’m designing it.

So you would think that the kit I get from Robotshop should be aluminum? They must just still be using the original photo of the lexan version on the website. That is what I was hoping.

As always, thanks for your insight Jim. After all, you did design and do produce the worlds most popular amateur robotic kits and parts. I would guess you must know a bit about robot design. :wink:

nice design!

and their uge those servos lol

man i have to admit that is the coooollist biped i have ever seen
looks like somthing from starwars don’t you think?
but the only thing i don’t realy like about it
is that its so tall but yet so skinny
is it possible to make the legs wider?

I think the legs are already far apart. I think if their is metal over it like in hte last picture it’ll look realy nice. it’s true it looks like hte starwars!! it’s awsoeme! now just to make it walk like them 8)

Thanks guys. I like how it looks too. Making the legs wider will increase weight dramatically, and unnecessarily. Don’t forget that this is just the skeleton of the robot. I’m molding a vac-formed “shell” or skin to mount onto the components so it looks more like the ED-209. So it will be alot thicker but not until the skin is on. That will come after a working gait is established and the robot is fully functioning.

I’m dying in anticipation waiting for my form bender to show up. Thanks again for the motivation.