"Squish" and "Brontus"



Oops, my mistake -- I just found them via a Google search:
http://www.servocity.com/html/servo_mount_gears.html
I don't know why I couldn't find them before.
So this does offer a potential solution -- if your frame had all the joint hinges built into it, with a gear on each joint shaft, then you could use these to drive the joint from a servo, without the servo experiencing any lateral force at all.
Thanks, - Joe
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I have what they call a "threaded stud," which sounds like the makings for a good joke, but it's actually a useful hardware item. It's molded plastic with a flat flange on one end, and a threaded post off the other. It uses a very high contact adhesive (3M VBH) on the flange, and once placed on the bottom of the servo and allowed to set, is extremely difficult to remove. You then use a nylon or steel nut to secure the threads through whatever support you're mounting to on the other end.
The biggest problem is that the dimensions of the flange are larger than the base area of the typical servo, so you have to cut it down a little. Not hard, but it makes for an amateur-looking setup.
Let me know if this sounds like something you'd like to try, and as a Budget Robotics customer I'll send you out a sample.
-- Gordon
Joe Strout wrote:

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Joe Strout wrote:

I have also milled new bottom plates out of Delrin (a very durable plastic), adding the missing stud an allowing for the idler. It is alos easy to add a channel and cutout for the wires, so they come out at the other end.
This works great, but it is a lot of work and an new (or modified) CAD file needs to be created for every servo type. For my particular machine, I also need to do four manual tool changes, so at 20 bottom plates, I am busty for two hours and I mill away 80% of the Delrin which then becomes toxic waste.
The obvious way would be to mill a negative instead and have these plates injection molded, but again, that would be different for every servos type. Something I would highly recomend to a servo manufacturer.
Finally, there is a project on the web, OpenServo, that gives instructions, pcb layout and the firmaware to build drop-in servo electronics that are controlled via i2c (a high speed two wire serial bus, making the controller obsolete) and knows everything and anything about the servo (power consumption, own ID, position to 12 bit resolution, temperature inside the servo, etc., etc.).
To sum this up, I would generally be willing to organize injection molding and pcb production and soldering, but we would need to agree on a single servo type, and we would need to be able to organize the sale of 1000 or more servos.
Matthias
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Matthias Melcher wrote:

Looks like you're gonna have a lot of binding and/or foot skidding in the feet, as the knee servos rotate to lift and lower the frame, and also as the hip servos rotate the flegs front-back. You should be able to see this if you put the bot up on blocks and exercise all the servos.
If you rotate the knee servos by 90-degrees, the linear distance between the front feet will change by about 8-cm. And as you rotate the hip servos +/- 45-degrees, the distance from the feet to the side of the frame will change by about 9-cm.
.

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dan michaels wrote:

Yes, that is correct. Thanks for even estimating the amounts. The goal was to make it as simple as possible and use only eight servos. Skidding is allowed by using pegs under the feet. If the terrain is flat, I don't have to lift the feet too much and I can do short steps to avoid most of the slip.
The next iteration will be a 3DOF per leg quadruped from wood, basically the continuation of this guy from 1999 (before CNC).
http://matthiasm.com/hwRoQ1.html http://matthiasm.com/hwRoQ1leg.html
Matthias
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That's very cool; I hadn't seen that before. I really like your approach of cutting 2D parts and assembling them into 3D structures. It lends itself very well to laser cutting, available on the net from services like Pololu.
I also like the way you released the drawings and assembly instructions. These days, rather than JPEGs for pasting to wood, I might suggest vector art of the sort that can be sent directly to someplace like Pololu. Then, anybody could use your drawings, as-is or modified, to replicate what you've done -- and hopefully feed back some improvements to the community. A true open-source model, applied to hardware gizmos.
This is something I've been struggling with myself: should I spend my limited budget on Lynxmotion "servo erector set" parts, or instead learn to cut and assemble my own parts, as you've done? Ultimately I'll probably do some of both. Lynxmotion's prices are really very good; I suspect that one of these brackets, if cut commercially from (say) lexan, would end up costing more than the Lynxmotion equivalent. On the other hand, you can make custom parts shaped almost any way you need, whereas with the SES you may end up cobbling together a shape that is suboptimal.
Best, - Joe
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Joe Strout wrote:

Thanks. Yes, it was an inner fight, but in the end, I decided to put image files up. That's how I built tha quad myself: I glued printouts on with Elmer glue, cut it with a small saw, and later peeled the paper off again. I had no CAD experience back then either.
I am involved in a few OpenSource software projects, and feedback has been very mixed. I would not expect too many valuable additions from the outside (never mind if the *do* come, of course). I have seen many commercial copy and past jobs of my stuff though... .

I will probably do that with Squish as soon as I find a way to take contributions, so I can easily add sensor rigs, camera towers, etc. to the web page.

The Lynxmotion stuff seems pretty cool. It's probaly the rigght to not limit yourself, but buy whatever was already invented and fits your budget, and add those parts that are too expensive or too custom. I myself would say that I am some silly purist, having to build everything myself, but that's just me ;-)
Matthias
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