Introducing the STALKER! (project ended)

[wowy7]

@innerbreed

at th price of the HSR-5990TG (417 oz. in.) Digital Standard Servo i think not… would be nice.

i only plan on using 645’s! would this be enough?

i have been thinking about making the segments shorter ill only know once i have got it working.

I don’t think they’ll be enough. The longer the legs are the more torque you need. I would agree with Tyberius that the HSR-5990TG would have to do, unless you want your robot to puff smoke everywhere .

[tyberius-2]

I can tell you, that based upon having worked with Hitec servos for quite a long time and getting a hands on feel for their torque limitations in many different configurations, the 645s will not be enough. To be honest, I think 5990s will be your only option in this and even then they might get a bit warm. Shortening the leg segments will certainly help though.

Not trying to rain on your parade, just dont want you to make an investment in servos only to find they aren’t sufficient.

[innerbreed]

thank you everyone for your concern with my project.

this information is vital so thanks for the heads up.
Here are some measurements, will this help Zenta.

' [0] ' / // ' /[2]=====[1] 0= Coxa servo Length 70 [mm] ' // ' | // 1= Femur servo Length 130 [mm] ' \// ' \ 2= Tibia servo Length 140 [mm] ' \ '

i think the weight is at about 652.1grams or 23oz. at the moment! with out the top section!!

also you can see here i still have the end tibia piece to go on! and this will require intermal structure made of aluminium + vacuum parts.
http://i531.photobucket.com/albums/dd355/innerbreed/20090103_124052.jpg

[zoomkat]

You may want to get enough servos to complete one leg. Dummies/spacers could be used for the other servos and the bot weighted to its expected operating weight. Then the completed leg could be stress tested doing pushups and such to see how well the servos perform.

[innerbreed]

@zoomkat

You may want to get enough servos to complete one leg. Dummies/spacers could be used for the other servos and the bot weighted to its expected operating weight. Then the completed leg could be stress tested doing pushups and such to see how well the servos perform.

not a bad shout, thanks for that. i may have to try it.

[wowy7]

I don’t think it matters. 645’s wouldn’t be able to handle the leg itself. not to mention the entire robot.

[zoomkat]

not a bad shout, thanks for that. i may have to try it.

Actually you will only be out the cost of one postage and shipping if the servos work as desired and more are ordered. I like doing proof of concept testing of critical components before the big $$$ is spent. Actually it looks like you already have sufficient servos (looks like 4) to complete a leg to do testing. Use dummy spacers for the other servos, appropriately position the other legs for opposite side support, and weight the bot (including the servo spacers) to expected weight.

[innerbreed]

ok this is what we have with the shorter Femur.

http://i531.photobucket.com/albums/dd355/innerbreed/100_0850.jpg
http://i531.photobucket.com/albums/dd355/innerbreed/100_0849.jpg

this design can be done with:
ASB-15B Aluminum Dual Inline Multi-Purpose Servo Bracket. saving the two “L” brackets iv used for photo references.

the only reason i never thought id have a problem with using these servos on this design was that the AH3-R uses them. plus it has 2 extra legs than my quad. gait sequences will work on the bases that i only have one leg up at a time! leaving three (tripod) stance like that of a hex in tripod gait.

with regards to the AH3-R, does the use of 18 hs-645mg’s for 6 legs make it better than the lighter option of 12 hs-645mg’s on only 4 legs.

should i design the leg Measurement more like the AH3-R!?

[tyberius-2]

The AHR-3 has much shorter legs all around, and they are primarily in a 90 degree orientation towards the ground. Having a lateral femur that long is going to cause a lot of strain on both the HipV and Tibia servo. I realize you’re going for a certain aesthetic, but function always seems to get in the way. There were numerous changes I had to implement with my mech design that favored function over aesthetic, unfortunately.

I think shortening the femur as you have will help quite a bit though, depending on how much payload you’re carrying, you might even be able to swing it with 645s. Might go 5645s to play it on the safe side though.

Great design overall btw, hands down one of the coolest looking quads I have seen on the net.

[innerbreed]

@Tyberius

The AHR-3 has much shorter legs all around, and they are primarily in a 90 degree orientation towards the ground. Having a lateral femur that long is going to cause a lot of strain on both the HipV and Tibia servo. I realize you’re going for a certain aesthetic, but function always seems to get in the way. There were numerous changes I had to implement with my mech design that favored function over aesthetic, unfortunately.

I think shortening the femur as you have will help quite a bit though, depending on how much payload you’re carrying, you might even be able to swing it with 645s. Might go 5645s to play it on the safe side though.

yeah i completely understand what you mean! i have already re-designed this robot several times in the past!
yeah the HS-5645MG are more like what i can afford! slowly, and bit by bit.

Great design overall btw, hands down one of the coolest looking quads I have seen on the net.

thanks for that… cheers mate.

[innerbreed]

@zenta

Hi,

Are you able to estimate the complete weight of the robot and how long is the longest segment (femur part)? With that in mind it should be easy to calculate if the 645MG have enough torque.

how can i calculate the torque needed?

(Stalker quadruped)
weight = 1.4lb
Femur Length 130mm
Tibia Length 140mm

of legs 4

(AH3-R hexapod)
weight = 4.6lb
Femur Length 70mm
Tibia Length 108mm

of legs 6

(Phoenix hexapod)
weight = 4.9lb
Femur Length 76mm
Tibia Length 106mm

of legs 6

[xan]

Hi Innerbreed,

Nice pic with all the legs connected. Good to see that everything is coming together! I hope you solve the leg / torque problem.

Xan

[zoomkat]

Just looking at the angled servos, they will add an extra layer of programming to account for the way the leg will swing in a non horozontal arc when the servo moves the leg. I think it is very important to make a single working leg to study how it will move and how the angle of the rest of the leg will be affected.

[innerbreed]

i will be trying to account for this by having the femur and tibia move with this arc. not sure how just yet. yeah it may be a good idea to study one leg example and see how to do it.

thanks

[robotdude]

Don’t forget the little known servo helper… The extension spring.

Just connect it so it pulls the opposite direction as gravity pulls on the chassis. The main place it would help is on the bottom of the vertical hip servo. It has a pro and con effect. The pro is it helps hold up the chassis when the legs are down. The con is it makes it take more energy to lift the leg off the ground. Something to consider…

[innerbreed]

GOT IT COVERED!
in the earleir parts of this thead iv used springs too.
http://i531.photobucket.com/albums/dd355/innerbreed/100_0855.jpg
http://img208.imageshack.us/img208/5912/20080311204604ye7.jpg

[zenta]

@innerbreed

@zenta

Hi,

Are you able to estimate the complete weight of the robot and how long is the longest segment (femur part)? With that in mind it should be easy to calculate if the 645MG have enough torque.

how can i calculate the torque needed?

(Stalker quadruped)
weight = 1.4lb
Femur Length 130mm
Tibia Length 140mm

of legs 4

(AH3-R hexapod)
weight = 4.6lb
Femur Length 70mm
Tibia Length 108mm

of legs 6

(Phoenix hexapod)
weight = 4.9lb
Femur Length 76mm
Tibia Length 106mm

of legs 6

Hi,
I’m guessing that 1,4 lb is not the estimated weight of your stalker since all 12 645 servo will have a weight of total 1,8 lb alone. My LM Phoenix have a weight of about 2,1 kg = 5,6 lb (I’m not very familiar with lb, so I’m using a web based converter to find the correct lb value. Lets assume your Stalker will have a total weight of (5,6/6)x4 = 3,7 lb (rounded) .

For a tripod (3 legs) thats 1,25 lb = 0,46 kg per leg. When standing with a perpendicular tiba and the femur in horisontal position that would require about (0,46 x 1,3) 6 kg/cm holding torque for the femur servo. The 45 deg mounting position of the coxa are not considered here.

[innerbreed]

yes his does not inclued the weight for the servos in the legs, as i dont have them yet!

so from what you are saying there will be enough torque with the 645’?

When standing with a perpendicular tiba and the femur in horisontal position that would require about (0,46 x 1,3) 6 kg/cm holding torque for the femur servo.

Stall Torque (6.0V): 133.31 oz/in. (9.6kg.cm)

[zenta]

@innerbreed

so from what you are saying there will be enough torque with the 645’?

Hi,
I didn’t finished my post completely since I had to put my kids to bed…

It all depends on how far you’ll need the foot to travel and extend, as long as you keep the leg in a posture that doesn’t require much further extension (than 130 mm) you should be safe with the 645. Using some spring might be a good idea too. (In theory the 645 should manage extension up to around 17 cm (about 8 kg/cm) max horisontal distance between tars and femur joint.)

[innerbreed]

@zenta

@innerbreed

so from what you are saying there will be enough torque with the 645’?

Hi,
I didn’t finished my post completely since I had to put my kids to bed…

that was a long bed time story!
i know what you mean, i got a boy of three, and wife is pregnant with second boy… building my army slowly!!

It all depends on how far you’ll need the foot to travel and extend, as long as you keep the leg in a posture that doesn’t require much further extension (than 130 mm) you should be safe with the 645. Using some spring might be a good idea too. (In theory the 645 should manage extension up to around 17 cm (about 8 kg/cm) max horisontal distance between tars and femur joint.)

Anyway… this is great news, of course’ if i stick to the rules and dont extend more than that. thanks for helping me with this. i think i may shorten the leg anyway. just so im not tipping on the edge of destruction, and doing that will also make the performance better.

i spent time and [size=67]“money”[/size] (the wife might be listening) getting some new bracket designs made up and now if i change things i cant use them!

just heard that with regard to the contest, Any robot that has shells or armor covering SES components need to be stripped off. its going to be naked!

thanks again.