RoboSavvy Forum

Robobuilder metal joints

2009-11-20T12:31:21+01:00

Hi Ketchup

I don't really know where those may be available in EU.
We've had them for sale for a short time on Robosavvy but the interest was very dim (nearly null) and we dropped it.

Instead we stock the Metal Brackets Kit which includes the Leg Brackets Kit (with the addition of the circular Metal Joints) + The Arm Brackets (which include extra brackets for a 3rd DOF in the arm) + Chest.

Regards
Pedro.

Statistics: Posted by PedroR — Fri Nov 20, 2009 12:31 pm

Robobuilder metal joints

2009-11-19T19:06:16+01:00

Thanks for the details, Pedro.
Do you know where we can get the "Leg Brackets Kit"?

Thanks!

Statistics: Posted by Ketchup — Thu Nov 19, 2009 7:06 pm

Robobuilder metal joints

2009-11-18T14:23:51+01:00

Hi guys

I have just received the official announcement today about the availability of the metal joints for Robobuilder.

They are sold as Metal Joint sets and consist of
- 6x Mtl Joint #2
- 4x Mtl Joint #6
(enough to build a 16 DOF humanoid)

The price for each Set is ~31.50GBP + VAT (total of 36.23 GBP inc VAT).

I don't know when we will have those in stock though. We have just ordered with Robobuilder and we ordered a lot of stock so I'm not really sure when we'll be getting these in stock.

FYI the robot shown in the picture above, seems to consist of:
- Standard 5720T
- Leg Brackets Kit (we don't stock those but their main purpose is to add weight to the lower part of the robot to lower the center of gravity and also improve reliability on the legs).
Not sure if here they are using the round metal joints on the metal brackets; they are usually plastic. Only the Full Mtl Brackets kits we stock come with the circular metal joints standard.
- Custom Chest Part. Not sure if they sell it standard in that colour.
- Metal Joints Set

It looks like a typical configuration for their Korean audience. When I attended KRGF there were 5720T with Leg Metal Brackets (but Plastic Joints) all over the place in Amateur League.
That configuration is quite popular there.

I leave the space open for your discussion about the metal joints.

In any case, I think you need to be careful when using those because in old days, any severe hit would break a plastic joint; with the new metal joints the energy of any impact will be passed on to the internal gears.
In my opinion I would do 2 things:
1- Use all metal gears
2- Set up the compliance / PID to allow some elasticity on the joints. This way you can protect the internal gears as the elasticity effect would absorb much of the external force. (this one I learned from Rob Farrel in KRGF )

Regards
Pedro.

Statistics: Posted by PedroR — Wed Nov 18, 2009 2:23 pm

Robobuilder metal joints

2009-11-18T00:38:46+01:00

I've now snapped two Joint No 2 (and have no spares). I think there's a design flaw - on the joint the point where the neck narrows is very thin. At the knees the entire upper body weight goes through that point.

So I've created a 3D print piece http://www.shapeways.com/model/64074/joint2.html which you could print in stainless steel (but it will cost $12 each) and I haven't tried it myself yet. (So caveat emptor!)

cheers

Statistics: Posted by l3v3rz — Wed Nov 18, 2009 12:38 am

Robobuilder metal joints

2009-11-18T00:29:38+01:00

Oooooh. I want those metal leg parts! My plastic ones have stress cracks where the screws go through.

I like the chest cover, too. Looks better than the stock one.

Anyone know where I can get those metal leg parts?

Statistics: Posted by Ketchup — Wed Nov 18, 2009 12:29 am

Robobuilder metal joints

2009-11-17T14:48:12+01:00

Saw this picture on Robobuilder web site

Looks pretty cool - but notice it seems to have metal joints (at knees)

The head eyes are a hack - which there is picture showing how to do again on the web site. (two led wired directly to power bus - very simple). I actually find very useful a similar hack I've done, as you can see if the robot is on from the front.

Also on the web site there is a new firmware download that has added "free motion" wck programming - not sure what that means - it says to refer to user guide for more details - but its not mentioned in any version I have.

l3v3rz

Statistics: Posted by l3v3rz — Tue Nov 17, 2009 1:49 pm

Robobuilder metal joints

2009-10-29T12:12:17+01:00

Hi Mark

Thank you for your compliment.

In fact Robobuilder began shipping the metal joints with the metal brackets by the time we started stocking them.
That's actually why there was a price increase in the Metal Brackets Kit after the initial batch.
Nevertheless I think it's worth the cost because if you're going for the metal brackets it means you'll probably be looking for improved strength and reliability and therefore using metal joints makes all sense.

Regards
Pedro

Statistics: Posted by PedroR — Thu Oct 29, 2009 12:12 pm

Thanks

2009-10-29T03:18:09+01:00

Hi Pedro,

Thanks for the as always most informative and courteous response. You are the voice of reason and you are right it is truly best to have a weak link in the joints to protect the servos which are the single most costly element in the robot. I guess my hobby fanatical ways wanted to see an all alloy robot for fun and I will keep my eyes peeled if that last element is release in alloy just to say I have it as part of my kit.

On a slight tangent note I bought the metal brackets (leg only) a while back and for some reason they did not come with the round metal joints, wasnt from you guys directly, it's been a while so I wont try to get it corrected as my case is so old.

Last but not least budget permitting I will most probably order the metal kit from you all to get those round joints.

Keep up the great work and I look forward to seeing the new kits released from all the manufacturers for Christmas.

Cheers

Mark

Statistics: Posted by Raymond — Thu Oct 29, 2009 3:18 am

Robobuilder metal joints

2009-10-28T12:48:58+01:00

Hi Raymond

Indeed Robobuilder has spoken about the intention of supplying those joints in metal sometime in the future although that's not confirmed.

However, to be honest, I don't think there's much point to it.

The idea behind the whole plastic joint system is to make the robot easy to assemble and keep the price down.

If you want to go up to more robust solutions, then you have the Metal Brackets Kit, which includes not only all metal joints (the round ones) but also the metal brackets which will offer much more stability in operation because the whole metal structure makes the robot and joints more resistant to torsion.

I think that the robot will always break by the weakest link.
This is my personal opinion but but I would prefer that it breaks by the joints because they are cheap and easy to replace.

Otherwise if they are metal (and we don't have something like the metal brackets to offer improved stability), whenever there's high torsion or side forces, they will be passed inside the servo/gears and most likely will cause damage to the servo.

In any case, if metal joints are to be released we will let you know and make a few available.
However, as, I said above, I don't have confirmation that these will be available.

Regards
Pedro.

Statistics: Posted by PedroR — Wed Oct 28, 2009 12:48 pm

Clarification

2009-10-27T23:19:51+01:00

Hi Pedro,

Sorry the joints I'm speaking of are the ones that connect to the gear#4 (the gear and shaft) to connect one servo to another.

Cheers

Mark

Statistics: Posted by Raymond — Tue Oct 27, 2009 11:19 pm

Robobuilder metal joints

2009-10-27T14:16:56+01:00

I have just checked the product page and indeed the picture of the robot uses the circular joints in plastic.

That is NOT the case anymore. The metal brackets kits come with the small round joints in metal.

Please refer to the PDF here
http://robosavvy.com/RoboSavvyPages/Rob ... _20DOF.pdf
to check the complete part list.

If I misunderstood your question please let me know.

Statistics: Posted by PedroR — Tue Oct 27, 2009 2:16 pm

Robobuilder metal joints

2009-10-27T14:14:15+01:00

Hi Raymond

I'm not sure I fully understood your post, but the fact is that the Metal Brackets Kit come with METAL JOINTS.

That's actually the reason why the price went up compared to the initial price.

You get the Metal Brackets + The small circular joints in metal.

The plastic joints may be maintained (I think mainly for aesthetics and some stabilization) but they hold almost none of the weight. All the weight is supported by the metal brackets which in turn are attached to the Small Circular joints.

Statistics: Posted by PedroR — Tue Oct 27, 2009 2:14 pm

Actual joints

2009-10-27T00:11:44+01:00

Hi Again,

I was thinking to be financially feasible for most users I would like to suggest that the joints most used for the humanoid be offered initially and in bags of 5 pieces so it offers flexibility in purchasing and won't sit on the shelf for all but those with 'Trust Funds'. If nto entertained perhaps I can have some custom made just to try out but that's another story. Hope my siggestion is well received and embraced by Robobuilder.

On another totally different note I am looking forward to hearing more specifics on the new Robotis Robot coming out soon.

Cheers

Mark

Statistics: Posted by Raymond — Tue Oct 27, 2009 12:11 am

Robobuilder metal joints

2009-10-26T14:51:26+01:00

Hi All,

Looking at all the metal brackets it is clearly apparent after upgrading there is the weak point of the joints. That is the weak link. Most apart from the gears is astehtics. Any plans of Robobuilder to complete the robustness design by releasing aluminioum joints?

Thanks

Mark

Statistics: Posted by Raymond — Mon Oct 26, 2009 2:51 pm