PDA

View Full Version : Lynxmotion Hexapod for a Mech base...



Robot Dude
08-06-2009, 02:17 PM
I was asked to post here concerning our hexapods used as a base for a mech. The goal for me is to hopefully answer common questions that may arise.

The Phoenix is a very popular hexapod. The design (credit to Zenta) is somewhat stylish and very functional.

Here is a video of Phoenix carrying around a 2.5kg payload. Now make no mistake, this is robot abuse. As the manufacturer of the Phoenix I'm a little more conservative in the payload, thinking maybe around 1kg.

YouTube - Payload test 2,5kg

The Phoenix is fast. With longer femurs it's able to move faster than the SES based hexapods. It's not significant though.

Will it make a good mech? The room inside the bot is pretty much all used up just in batteries and microcontrollers. Any additional weapons, cameras, and the like would need to go on top. So it might not look quite as elegant when competition ready. We are talking tight fit here...

Also the servo horn bears the entire load on the legs. This looks awesome, but is simply not as strong as the SES based hexapods.

The BH3, AH3-R, BH3-R, CH3-R are much more reasonable platforms for this competition. I don't have exact payload specifics for these bots. It's a very difficult thing to quantify, but servo torque goes down as the femur length goes up, so these bots are much stronger than the Phoenix. The femur on the Phoenix is 3" compared to 2.25" on the SES based bots. With comparable servos the CH3-R is 30% stronger than Phoenix. The math doesn't lie. Plus the SES based hexapods have support on both sides of the servo for added stability. The tibia length varies on these bots and does not contribute to the payload to the extent the femur does. So payload is a win. The speed is a little slower though. All of these bots have a place to mount the turret. They all have ample room inside and on top if needed.

The control aspect. These bots use the Bot Board with Atom Pro 28 with the SSC-32. For an idea of what the Atom Pro/SSC-32 combination can do check out the infamous A-Pod video on youtube.

The code is very complex utilizing inverse kinematics for elegant hexapod robot control. The front end can be changed from PS2 control to serial control or some other type of control scheme, but the hard part is done already. Adding a pan and tilt for the turret is already in the program. Adding the code to shoot the guns should not be too difficult. Writing it from scratch would be, um, difficult.

I'm not addressing other platforms as this thread is about Lynxmotion hexapods. I'm not going to bash them, and would not expect this thread to turn into one of those...

BH3

http://www.lynxmotion.com/images/jpg/bh304.jpg
AH3-R

http://www.lynxmotion.com/images/jpg/ah3r02.jpg
BH3-R
http://www.lynxmotion.com/images/jpg/bh3r01.jpg
CH3-R
http://www.lynxmotion.com/images/jpg/ch3r01.jpg
Phoenix
http://www.lynxmotion.com/images/Products/Full/phoenblk.jpg

Adrenalynn
08-06-2009, 02:36 PM
RobotDude Wrote:>> I'm not addressing other platforms as this thread is about Lynxmotion hexapods. I'm not going to bash them, and would not expect this thread to turn into one of those...

I, for one, will aggressively moderate any bashing or thread-jacking in this thread. I appreciate your taking the time to address the appropriate LM Hex products here, Jim! Thanks!

MSK Mech Commander
08-06-2009, 02:45 PM
Do you know how much slower the CH3-R is than the Phoenix? If the CH3-R isn't that much slower than the Phoenix then it seems like the CH3-R would be a better choice.

jes1510
08-06-2009, 02:55 PM
One thing to note is the "road" size in the arena. Do you have any information on the turning radius of these platforms?

Thanks a lot for taking the time to post this stuff here. It should be a great help to those wanting to enter the hex League.

Robot Dude
08-06-2009, 02:56 PM
@ Adrenalyn

Thanks!

@ MSK Mech Commander

The only reason the Phoenix is faster is due to the longer femur. It's not easy (at least for me) to quantify the speed increase. The Phoenix femur is about 30% longer than the SES based legs, but I seriously doubt it converts directly to a 30% increase in speed. It might be that simple, not sure. Of course that assumes identical servos in both bots. The CH3-R can work great with 475 servos which are faster than 645s so ymmv... :P

MSK Mech Commander
08-06-2009, 03:03 PM
Thanks a lot for taking the time to post this stuff here. It should be a great help to those wanting to enter the hex League.

I second that! This thread is essential!:)



@ MSK Mech Commander

The only reason the Phoenix is faster is due to the longer femur. It's not easy (at least for me) to quantify the speed increase. The Phoenix femur is about 30% longer than the SES based legs, but I seriously doubt it converts directly to a 30% increase in speed. It might be that simple, not sure. Of course that assumes identical servos in both bots. The CH3-R can work great with 475 servos which are faster than 645s so ymmv... :P

So if I used 645s on the CH3-R, would it be a LOT slower, or just barely noticeable?

Robot Dude
08-06-2009, 03:04 PM
One thing to note is the "road" size in the arena. Do you have any information on the turning radius of these platforms?

Thanks a lot for taking the time to post this stuff here. It should be a great help to those wanting to enter the hex League.

These bots have a zero turning radius. So that should not be an issue.

For those who may not be keen to the 3DOF hexapod. There are two controls for driving these bots. think of it as a joystick and a half. lol The full joystick controls translation. Put a plate down on a table and place your hand on the plate. Move it around but keep your fingers pointing away from you. That's translation. Rotation is just that, rotating in place, the cool tihing about these bots are you can do both at the same time. What is the "road" size? these hexapods need about 18" wide roads.

Robot Dude
08-06-2009, 03:12 PM
I second that! This thread is essential!:)



So if I used 645s on the CH3-R, would it be a LOT slower, or just barely noticeable?

I'm in the just noticable camp. It's probably 10-15% slower. I'm thinking aiming and good vision are as important as speed in this competition.

MSK Mech Commander
08-06-2009, 03:24 PM
So which do you think will be a better mech overall?
From my perspective it's a trade-off. If I want speed, then I get the Phoenix. If I want payload, then I get the CH3-R. Right?

darkback2
08-06-2009, 03:25 PM
First of all, thank you for posting this thread, I think the information will be invaluable for people wanting to join the hex league.

Maybe people who have any of these hexes, might do a quantified speed test. Say inches per second straight forward with no payload? Also if people could post videos demonstrating the mobility of each of these platforms...

Also, if Hex owners could start threads on mounting turrets and such...maybe even reliable control methods. I think it would be helpful to anyone trying to get involved.

DB

Adrenalynn
08-06-2009, 03:36 PM
>> but I seriously doubt it converts directly to a 30% increase in speed.

As I see it in my mind, and I'm only creating a hypothesis - it's an oblique triangle, right? So the angle of the two leg parts is going to dictate the length of the step. It would be a 30% increase if it were square. Otherwise, the step distance is the adjacent side of a triangle, right? Hmm. Maybe I should draw a picture before publicly guessing. ;)

[edit] @ DB - it'd be difficult to make that test unless you standardized on a gait. The gait is going to dictate the speed and, largely, the payload capacity. Two identical 'bots could have substantially different velocity-made-good and payload.

Robot Dude
08-06-2009, 03:42 PM
So which do you think will be a better mech overall?
From my perspective it's a trade-off. If I want speed, then I get the Phoenix. If I want payload, then I get the CH3-R. Right?

The criteria are payload, speed, and available real estate. I don't know if there is an answer to which is the best overall.

darkback2
08-06-2009, 03:47 PM
@ Adren,

I guess I was thinking as a generalization. Point taken though...

I remember last year/earlier this year getting ready for robogames, a bunch of us tried running our mechs next to/over a ruler to see how fast they were and to try to make improvements in speed...So...mine being the slowest, and issy the fastest...I'm thinking for the people who are on the fence having more information however general might help...I believe there are several standard gates that either come preprogrammed, or have been published for each of these configurations...so lets suggest a trigate?

DB

Zenta
08-06-2009, 04:23 PM
Hi,

I just want to shoot in some arguments about payload capacity and speed.

Payload capacity isn't directly in realtive to the length of the femur, but the maximum horisontal distance between the tars (feet of tibia) and the center of femur axis. The major advantage of the SES based legs with support on both side is that it is much more stable and save the femur servo horn for all the stress. In theory the Phoenix can handle even more than 2,5 kg extra load if you decrease the horisontal distance I mentioned to the half of the total length of the femur (not recommended though). But that will also affect the maximum speed. In Xan's BAP code you define the "home" or Init positions of each leg. If you move the leg closer to the coxa center the payload capasity increases but decreases the total travel-length (and speed).

The speed are determined by the maximum total travel-length of a leg. Also the coxa design and how close the legs are placed affect the speed. I guess a relative large inline body would give a very fast speed in forward and backward direction. And combined with a coxa with a relative large horisontal distance between the coxa servo and femur servo you will get a strong and fast hexapod.

So by increasing the maximum extension of a leg you get a faster hexapod but also reduced payload.

Edit: Of course, the gait method also affect the speed and max payload.

-Zenta

Adrenalynn
08-06-2009, 04:28 PM
Cool - so my theory/visualization was correct! Pythagoras remains my hero. :)

Zenta
08-06-2009, 04:37 PM
Cool - so my theory/visualization was correct! Pythagoras remains my hero. :)

Oh, I didn't see your previous post. (I had to help my wife with something while writing the post). A visualisation of your thoughts would make it more clear.;) But I believe you are into something there..

mannyr7
08-06-2009, 05:34 PM
Regarding the Phoenix and payload capacity: Has anyone ever used a PSH-04 Injection Molded Servo Hinge w/ BB http://www.lynxmotion.com/Product.aspx?productID=399&CategoryID=75 (http://http://www.lynxmotion.com/Product.aspx?productID=399&CategoryID=75) to double up on those femur pieces and connect the pair with a standoff?

FlowbotX
08-07-2009, 10:15 AM
Manny, I am hoping to do the same thing...double up the femurs using the injection moulded bracket. (I also want to add springs...but that is another story)

The closest thing to it that I have seen is Xan's "hybrid" which uses two "C" brackets...here: http://www.lynxmotion.net/viewtopic.php?t=5348

Zenta
08-08-2009, 10:09 AM
Regarding the Phoenix and payload capacity: Has anyone ever used a PSH-04 Injection Molded Servo Hinge w/ BB http://www.lynxmotion.com/Product.aspx?productID=399&CategoryID=75 (http://http://www.lynxmotion.com/Product.aspx?productID=399&CategoryID=75) to double up on those femur pieces and connect the pair with a standoff?


It should be possible to do but the extra femur would make some restrictions to the total travellength of the legs since they might crash into each other. But its a relative easy fix to reduce the maximum travellength.

I did use those Molded servo hinges on my A-Pod. Worked very fine and the legs got much more stable.

-Zenta

MSK Mech Commander
08-13-2009, 07:20 PM
If I'm going to use a Phoenix for a mech, will I absolutely NEED metal servo horns?

darkback2
08-13-2009, 07:32 PM
Hey Msk,

The short answer to your question is yes...(more a qualified answer.)

The phoenix's femer...or thigh bone connects directly to the servo horn...which is taking the entire load...so at any given time it will be carrying 1/6 - 1/3 of your robots total mass. A plastic servo horn will probably not be able to take the wait without bending/distorting resulting in poor performance, or in the least will greatly limit your robots payload. Over time the plastic horns will probably strip out and fail.

Similarly the screws that pass through the femer into the horn will probably rip out over time.

Now...that said you are more than welcome to give it a shot. If I remember correctly you have a sponsor. You can always cut a couple phoenix parts out yourself if that helps, or even scratch build a phoenix like bot...

Hope this helps.

DB

MSK Mech Commander
08-13-2009, 07:45 PM
Yes, that does help a lot, thanks.:)


...If I remember correctly you have a sponsor...
I wish...:(

Spartan001
08-15-2009, 04:03 PM
A Ch3-r modified with a johnny 5 top and airsoft guns mounted "droideika style" would be a perfect mechwars hexapod entry.

Adrenalynn
08-15-2009, 04:50 PM
What purpose is there to a "J5 top" in MW other than to add weight and strain servos without function?

Robot Dude
08-17-2009, 03:27 PM
What purpose is there to a "J5 top" in MW other than to add weight and strain servos without function?

Just a guess here... To increase the coolness factor! lol :D

Having actually built and controlled a CH3-R with J-5 torso, it's a big project! If you threw 5990's in the legs it is possible, but wow it'd be a chore to make it into a mech.

Here's an image just for grins...
http://www.lynxmotion.com/images/misc/j601.jpg

DresnerRobotics
08-17-2009, 03:41 PM
Given that you would in fact need 5990s for the legs... you're correct, it really would just be for aesthetics given that you need little more than a pan/tilt to hold the weapons and camera. A humanoid upper torso on a biped makes sense because it allows you to get up if you fall, etc.

Your J5-Hex is pretty cool though Jim ;)

Adrenalynn
08-17-2009, 04:02 PM
And "cool" does serve a purpose. And "cool" it would be.

Heck, I'm running a custom-written curses/text-based IRC client under Google Android operating system on an original C3 with 16MB of RAM and no HD. Because it's "cool".

So I'm not one to judge. But I would differ with "would be a perfect mechwars hexapod entry" If we drop the word "perfect" or substitute "cool" for the word "perfect" - then I'd totally be on the same page. ;)

darkback2
08-17-2009, 05:05 PM
I was thinking it would be really cool if you replaced the arm with guns, removed the head, and mounted a wifi camera on the chest. You could mount one sensor panel in front of the camera, the other on the back, the side ones could me mounted on the sides of the guns.

Depending on how many DOF you could afford to retain in the arms, you could probably still use them to get up if you fell...On that note...Hexapods falling? Really! I thought squidword falling was a shame, and he had a leg fall off! :P OOOH you could use the guns as mellee wepons if you managed to get close enough...You could sort of swing them around and hit the other robot's target plates.
DB

tom_chang79
08-21-2009, 03:35 AM
Jim, I think by far, the best platform to use to carry a load would be your *H3-R series with a base-rotate on top...

That was my goal with a hexapod at first, to have the base rotate and mount an arm on it (like your arm kit) and have the CH3-R go up and be able to grab things...

But darn it, you came out with the Phoenix chassis and I jumped on that right away! Your Phoenix chassis is just too darn sexy to resist!!!

LM has too many great hexapods, and I just don't have enough $*Time (money dot time)

Hehehe...

----

Jim, the Johnny five + CH3-R reminds me of the series by Square Soft (video game company), Front Mission

tom_chang79
08-21-2009, 03:40 AM
I thought squidword falling was a shame, and he had a leg fall off! :P OOOH you could use the guns as mellee wepons if you managed to get close enough...You could sort of swing them around and hit the other robot's target plates.
DB

How did his hexy's leg fall off? Is anyone here using Loctites or Permatex Thread Locks?

I personally use Permatex's Thread Lock (Blue) which works great for all metal-to-metal thread contacts...

Adrenalynn
08-21-2009, 03:44 AM
I know Fergs was using liberal doses of Loctite. I came home with a life time supply of 242/Blue that he didn't want to transport via the airlines. :)

darkback2
08-21-2009, 07:33 AM
How did his hexy's leg fall off?

Hey Tom,

If your talking about squidword, (he is a quad)...

I originally built squidword using HS 645s I had laying around. As he got heavier and heavier (about 10 pounds in the end), I slowly 1 or 2 at a time started upgrading the lift servos to hs 5990s.

I replaced the rear hip swing servos at robogames. Not a problem, except I had already loaned my loctite to XX2747...In my haste I didn't bother to loctite the screws...and then sort of forgot about it.

So...mid match one of the screws holding the leg bracket came off as the leg was in mid step..The leg was therefor not under the robot, and that is how a quad falls down.

Good thing it was all caught on video.

DB

lnxfergy
08-21-2009, 10:29 AM
I know Fergs was using liberal doses of Loctite. I came home with a life time supply of 242/Blue that he didn't want to transport via the airlines. :)

Yeah, on the Bioloid, most of the screws stay in nicely (the black composite they are molded from almost works like a lock washer). However, the larger M3 screws used for the bearing end (opposite the horn) are a pain. By the time you tighten them enough that they won't fall out the joint feels really stiff (at least to me). I preferred to loctite liberally and go with the screws not entirely tightened down. I also had some SES components for Issy's legs, and those had to be loctited down.

-Fergs

tom_chang79
08-25-2009, 06:00 AM
darkback2, 5990s? That's sweet... I've always dreamed about building a quad/hexy with 5990s. Imagine a quad made of that, it wouldn't be a liittle dog, it'd be a little horse!!!

Regarding the hinge screws for the Bioloid servos, has anyone ever replace those plastic bushings for some real bearings? I've been taking some measurements and I*think* you can fit some flanged bearings that comes with LM's C-brackets for those. You might have to get some washer to make them snug against the hinge part of the AX-12s...

Not sure, I've been meaning to give that a whirl... Do busy with the Phoenix at the moment. I"m also restoring my CH3-R at the moment. Was planning to sell the CH3-R chassis, but CH3-Rs are just too darn neat...
---

I wonder how many LM hexes we'll see at Robogames 2010? There's going to be a new hexapod class right? I'm predicting that the *H3-Rs will be the staple at that event, with the Phoenix and MSR-H01s here and there.

Ok, I better get cracking on the software...

MSK Mech Commander
08-31-2009, 09:54 PM
It's mentioned in another thread that some of the quads can get a little imbalanced and top-heavy from the turret needing to clear the legs. Will any of the Lynxmotion hexapods present the same problem?

darkback2
08-31-2009, 10:27 PM
Yes?

For me it wasn't so much a matter of needing to clear the legs as it was that I designed my robot to be top heavy.(i thought more about aesthetics than function.) Charlie was just heavy heavy (not bottom or top.)

As for hexapods, I'm not sure it will be as much of an issue because you can have three legs on the ground at any given time, which is one of the advantages of building a hexapod.

DB

Robot Dude
09-01-2009, 09:08 AM
Nah, the hexapod design doesn't have any problems with being top heavy. When standing (with femur level) the legs are just even with the top of the chassis. Even with the body lowered the legs are only 2.5" above the top of the chassis. If the guns are mounted on our base rotate kit which is about 2.0" tall the guns could easily clear the legs. We will be working on illustrating how to add guns to a CH3-R soon. It's not going to be difficult. 8)

Zenta
09-07-2009, 01:03 AM
Hi,

I just came over this Phoenix hexapod with a gun on top. I don't know who made this (called Jojobest on Youtube). And I believe he is running his own IK engine on an Atmega 162.


http://www.youtube.com/watch?v=CeiwkwgF1gA

-Zenta

Robot Dude
09-14-2009, 05:12 PM
It's mentioned in another thread that some of the quads can get a little imbalanced and top-heavy from the turret needing to clear the legs. Will any of the Lynxmotion hexapods present the same problem?

Here is an image of an AH3-R hexapod with a "pan and tilt" I threw together last weekend. The P/T is using some new parts I recently added to the SES. They are 1/4" and 1" hub spacers. The guns mounted in much the same way as they did on the BRAT Mech. This is the first time I connected anything to both sides of the "C" bracket. It worked out perfectly! The spacing on the gun barrels worked out perfectly. You can move all around the legs, but they will not touch. Here are some images. It's a work in progress for now.

http://www.lynxmotion.com/images/temp/hexmec1s.jpg

http://www.lynxmotion.com/images/temp/hexmec2s.jpg

http://www.lynxmotion.com/images/temp/hexmec3s.jpg

Adrenalynn
09-14-2009, 05:16 PM
That looks pretty frightening! :) Cool though!

mannyr7
09-14-2009, 05:40 PM
This is the same P/T setup I use on Clyde. If you orient the 'C' bracket forward, you can attach an SES electronics carrier here, which has the same hole pattern as the two bottom screws of the Trendnet camera. Some 1/4" and 1/2" nylon spacers and 1 1/4" 4-40 screws and nuts (2 each) from ACE hardware is all it takes.

http://forums.trossenrobotics.com/gallery/files/2/8/4/0/cimg4237.jpg

praelian
09-14-2009, 07:58 PM
Here is an image of an AH3-R hexapod with a "pan and tilt" I threw together last weekend. The P/T is using some new parts I recently added to the SES. They are 1/4" and 1" hub spacers. The guns mounted in much the same way as they did on the BRAT Mech. This is the first time I connected anything to both sides of the "C" bracket. It worked out perfectly! The spacing on the gun barrels worked out perfectly. You can move all around the legs, but they will not touch. Here are some images. It's a work in progress for now.







That is exactly what I'm trying to build lol; I've already got an order out for the base, may have to pick up the P/T portion for the weapons. By chance, do you have the specific part numbers so I can throw more mech-money your way!

I was looking at attaching two stripped (heavily modded) defenders but already have the tank guns for back up.

Are the standard kit servos (645MGs) holding up or have you upgraded to 5990s?

Very awesome!

MSK Mech Commander
09-15-2009, 09:25 AM
Here is an image of an AH3-R hexapod with a "pan and tilt" I threw together last weekend. The P/T is using some new parts I recently added to the SES. They are 1/4" and 1" hub spacers. The guns mounted in much the same way as they did on the BRAT Mech. This is the first time I connected anything to both sides of the "C" bracket. It worked out perfectly! The spacing on the gun barrels worked out perfectly. You can move all around the legs, but they will not touch. Here are some images. It's a work in progress for now.

http://www.lynxmotion.com/images/temp/hexmec1s.jpg




DUDE. THAT. IS. AWESOME.
Looks great! I was planning on doing the same thing for my Phoenix but I probably would have screwed it up and gotten stuck if you hadn't done it first. Thanks!:D

...Oh, um, by the way, what do you mean, "...in progress"? Hoppers and a camera?

Robot Dude
09-15-2009, 11:52 AM
That is exactly what I'm trying to build lol; I've already got an order out for the base, may have to pick up the P/T portion for the weapons. By chance, do you have the specific part numbers so I can throw more mech-money your way!

I was looking at attaching two stripped (heavily modded) defenders but already have the tank guns for back up.

Are the standard kit servos (645MGs) holding up or have you upgraded to 5990s?

Very awesome!

I've added a new image. This illustrates the part numbers used.


http://www.lynxmotion.com/images/temp/hexmec3i.jpg

I've not used the 5990 much. Don't think it's necessary for this. The 645's do a great job for hexapods and there is easily a couple popunds payload using them.

Robot Dude
09-15-2009, 11:58 AM
YOU. STOLE. MY. IDEA. JUST. KIDDING.
Yes! I know how to put the turret together now, but I'll have to customize my Phoenix somehow to make it unique.:D Nice job!

...Oh, um, by the way, what do you mean, "...in progress"? Hoppers and a camera?

Thanks! Yes we will be adding the camera and ammo hoppers in our free time. lol This is really an easy build. There is little to do mechanically that is not off the shelf. Some programming needs to be done to accomodate the two extra servos, etc...

DresnerRobotics
09-15-2009, 12:34 PM
:O

Wow, just wow. That thing is awesome!

Two mechs in less than 2 months, I think Jim is making the rest of the competitors look like slackers!

MSK Mech Commander
09-15-2009, 08:29 PM
:O

Wow, just wow. That thing is awesome!

Two mechs in less than 2 months, I think Jim is making the rest of the competitors look like slackers!

Count that seconded.;)

sam
09-15-2009, 08:32 PM
:O

Wow, just wow. That thing is awesome!

Two mechs in less than 2 months, I think Jim is making the rest of the competitors look like slackers!

I haven't even started designing mine!

No fair! ;)

Robot Dude
01-13-2010, 11:58 AM
I have been working with Zenta on making his T-Hex a product for all. I'm still working on tweaks, but it's getting very close. Here is an image of the prototype. This is using 2DOF legs. For fun I will attach an image of the beast with the 4DOF legs. 8)

1687

1688

darkback2
01-13-2010, 12:11 PM
Great...something else I can't afford but really really really really really want!

DresnerRobotics
01-13-2010, 01:07 PM
I have been working with Zenta on making his T-Hex a product for all. I'm still working on tweaks, but it's getting very close. Here is an image of the prototype. This is using 2DOF legs. For fun I will attach an image of the beast with the 4DOF legs. 8)

1687

1688

Holy crap. AWESOME!