I think it should be fine, the accuracy required isn't massive, the electromagnet should pick up off centre pieces and it doesn't matter that much if they aren't placed exactly at the centre of the square.
This one looks like hobby servos and it's pretty impressive.
http://www.youtube.com/watch?v=zV6EqS9Zrwo

that very nice video...I goto work hard to make my arm work as smoothly as those ones!!! Yes I can! but my mind is following two different thing s at the same time...not too good...

I'll comment the prevoius post very soon...

I am reading that wikipedia link...

thanks!

 

- hobby servo motors = RC servo motors??

- do the 3 motors (joint1,2,3) have to be of the same force (torque)? coz I think the one at joint1 need to support the weight at joint2&3 and the weight of linkage1,2,3,4(+solenoide, + piece) ...

- similarly motor at joint2 must support the components on its left side...and joint3 support weight on its left side too... maybe we should do a rough approximation on the weight...

- also which material to be used for the arm linkage? metal?? and the length of each linkage?

I think for now working with a 12 by 12 inch board is ok (unless the magnet requires a bigger square) as it a matter of saving my ass for now!! no need to impress people...I just want to pass for now...

Another question is which PIC would do a better job? 40 pins of course (16 I/O pins will be used for the board) so I was thinking of using PIC16F877 but it does not have enough program memory (only 8 kb) so I was thinking of using PIC18F46K20 (64Kb program memory & 3936 bytes SRAM) just to be safe...what do you think?

What is really *important* for now...my supervisor want to see a detailed schematics of the arm showing everything...do those motor require a driving circuit/IC? I mean how will the the 3 motors be interconnected and any driving IC??

Also how will the arm be interfaced to the PIC!?

But one thing for sure is that in a week time *serious* programming (24/7) will take place for board & arm.


thanks!

 

Yes, RC servos.
No they don't have to be the same, the one in the middle of the arm would be better if it is a lighter one. The one that rotates the arm doesn't need much torque either.
I think equal length main sections would be OK.
Thin aluminium sheet, or plastic could be OK, light weight is important.
I think 8Kb would be enough, although 18F series have advantages, but you would have to learn new instructions.
Hobby / RC servos have all the circuitry inside, all you need is the regular pulse.

 

Yes, RC servos.
No they don't have to be the same, the one in the middle of the arm would be better if it is a lighter one. The one that rotates the arm doesn't need much torque either.
I think equal length main sections would be OK.
Thin aluminium sheet, or plastic could be OK, light weight is important.
I think 8Kb would be enough, although 18F series have advantages, but you would have to learn new instructions.
Hobby / RC servos have all the circuitry inside, all you need is the regular pulse.

PIC18F instructions are not scary at all...I think they make coding easier...so I think I will go for that unless one gives specific reasons not to use that...

That's correct! they don' need to be of the same torque...
Given that the linkage1 has a vertical position...it doesn't give motor at joint1 too much weight!

but at joint2 needs the higest torque, joint3 should be lighter than joint2 IMO. when you say the one in the middle...guess you referring to joint2 and I think its the one that need to support more weight!

*Equal length main section is a bit vague to me...* don't you think those linkage length should be function of the size of the chessboard and its position relative to the board?

think aluninium sheet...ok I think this would be better over plastic...as plastic might bend...just like in the video you showed ealier!

I think it about time to come up with the 3 motors from digikey and some arm kit (thin aluminin...) that will help mount it...

*sleeping time* I'm dead...but guyz keep posting...

thanks again!

 

Here's what I'm thinking:

If you get it well balanced with counterweights and/or springs, the servos don't have to work as hard.
I think linkages 2 and 3 should be about the same as each other.

 

Ok! this looks ok but this is just a scketch...a real drawing/schematics needs to drawn with measurement...can't present a scketch (of course it my responsability to do that...) I'm just saying that in case someone would come with some measurement!

What about those motor? I mean choices (force/torque) for those 3 joints...digikey's ones would be better as I can get them in no time!

So am correct to say that those 3 motors would be independent of each other? I am talking about hardware interfacing here...I mean they will not be connected to each other...ie each motor will be given a different signal to get a specific position, correct?

so how each motor is interfaced to the mcu? ...will do some google about it asap...

I will try working on the measurements for each linkage...but i'm also correct to say that the size of the board will be needed in determining the measurement, correct?

I also believe programing needs to get started...check my 'brilliant idea thread...' for that as it will also be needed for programming the motors


thanks!

 

<oops> Just recalculated, because the chess piece is at the end of the arm and got +1000 g cm and -1000 g cm for joint 2 on the counterweighted whole arm. Joint 3 remains at 500 / -500 g cm.
These are just static forces so moving the arm requires more </oops>

Digikey servo is a bit weak, but it might be enough if you use counterweights.
Digikey servo is 43 oz in torque which is about 3000 g cm
The one I linked to earlier is 133 oz in / 9500 g cm
I did a few calculations to see how much difference it would make, with numbers plucked from the air (I just realised that I forgot the weight of the servo at joint 3, but the calculations would have to be redone with real values and the weight of the arm anyway).

The top half of the calculations are for joint 3 and linkage 3, with and without counterweight.
The bottom half is for joint 2 and the whole arm, with and without counterweights. With the counterweights the centre of gravity of linkage 3, the solenoid and counterweight is pretty close to joint 3 so that is why I'm using 20cm as the pivot length.

 

Thanks so much Mark for your time and help!

I had a quich look at your drawing and mesurements...I will read it again a couple of time...but seems to make sense...but whats the length of linkage1? (from base to joint2) did you consider the board size?

OK! assuming we using the board size I discussed in earlier post...it a 12 by 12 inch (~30.5 cm by 30.5 cm) board (playing area) and it's 5 cm high (NOT talking about its thickness)...I think this '5cm should be taken into account for linkage1. the outer square is ~ 36 cm by 36 cm (so there's a 3cm distance in each side between inner and outer square).

So I think the distance between 'linkage1 and 1st row' + the distance from '1st row and 8th row' should be included in determining the length of linkage 2 and 3.

Will be back in 3-4 hours as I'm studying for an exam...BUT I think the arm should look exactly like you've drawn it...

OK Will buy the motors from anywhere as long as they powerful enough for this purpose!

I think we should also have some *weight* at the base to keep it in balance or else it will always fall towards the end of arm direction...

Like I said I will have a good look at your attachment again...coz I might have said somethng you already solved/taken into consideration.

[edited]

This is the chessboard ia buy tomorrow: http://www.ebay.com/itm/Chess-Set-3...312&pid=100033&prg=1011&rk=3&sd=221130143873& but from local store...unfortunately there's no measurement from the link!

it a 12 by 12 inch (playing area) and from quick mesurement I made from the store, I found the following:

- each square size is: 3cm by 3cm;
- it's on a stand of 5cm high (take a look at link);
- border size (outer square): 36cm by 36cm;
- inner square: 29cm by 29cm;

when I buy the board tomorrow I will confirm these values as I will re-measure them.

- relative position of center of rotating servo: to be determined by ourselves;
- weight of servos (unknown as it has not been chosen yet)
- weight of solenoid is known: 100g (if i'm correct)
- chess piece: will measure tomorrow...will consider the heaviest one
- weight of magnet to place under each piece: 0.63g
- weight of thumb metal tacks: not sure...can approximate ...must be less than 0.63g
- weight of linkage (actuator): I'm sure it varies with length so we can determine that! we can use thin sheet metal...

we can make some approximations...taking the worst case scenario!


Thanks a million!

 

The values I used were just nice round numbers to make the calculations easier, so the results are only approximate compared to the real board. It would have to be done again, with servo, arm, electromagnent and chess piece weights and the real distances to work out the best counterweight weights.

 

I believe arm design (scketch) in post #87 is perfect...just need to work it out with actual values...I think the first think is to identify the *torque and weight* of each individual motor! as I need to order them asap!

will think about it...thanks!

[edited]
BTW, as joint4 has been removed...what to replace it with to always allow the linkage4 to always stay in a vertical position? (90 degree to the horizontal)?

 

BTW, as joint4 has been removed...what to replace it with to always allow the linkage4 to always stay in a vertical position? (90 degree to the horizontal)?

The joint stays, you just dont need a servo, because the weight of the solenoid will be enough.

 

post #88 has been updated with some measurements...and 12 by 12 board will be bought tomorrow! ok!?

As for the motor , this will do right? http://www.ebay.co.uk/itm/Hitec-Ult...-Universal-HRC32645S-/360371294216#vi-content

I can order them on monday if I get confirmation from member here!
but the above one is 133.3 oz torque...this would be for which joint? which torque required for the other joints? I need to order them by next monday as it will take some time to get to me! while we still doing the design...


thanks!

 

That would be good for joint 2, for the others something a little smaller should be fine like this from the same seller:
http://www.ebay.co.uk/itm/Hitec-Pro...Control_Parts_Accessories&hash=item25757b3bdc

 

I believe arm design (scketch) in post #87 is perfect...just need to work it out with actual values...I think the first think is to identify the *torque and weight* of each individual motor! as I need to order them asap!

Thanks
I should be able to work out the dimensions if you know:
The size of the individual squares, size of border, relative position of centre of the rotating servo to the board. I'll have a look tomorrow.
To work out the counterbalances and torques, I'd need weights of everything, including servos, solenoid, chess pieces, etc. Also thickness and material of the arm itself.
This is a pretty nice design, just sheet metal:
http://www.cnczone.com/forums/rc_rob..._software.html

 

OK! I am placing an order for those 3 motors now...

one: 106.9 - 133.3oz
two: 45.8 - 56.9 oz

 

It would be good if possible to have a ball bearing for joint 1 only as the loads on it are not just rotational, you could build your own easily enough or get one of these:
http://www.servocity.com/html/standard_hitec_servoblocks.html
I think it fits your servo but best to check.
It's probably not vital, but will make life easier for the servo and protect it from knocks to the arm.

 

I haven't paid yet as I asked the seller if it has a fast shipping method and still waiting for his response but will definitely pay before end of day whether or not he respond!

I'm trying to check if the same seller has that ball bearing too...actually I was also thinking about joint1...as the arm should Not fall forward due to UNbalance (if I may say)...so will that ball bearing help for that or it purpose is to only...?

To check if it fits I think we need to know the number of teeth of the motor and ball bearing...will check if that info is given...

Also the stand on which the arm will be attached should have a certain weight to balance it out...I mean so the arm does not lean/fall forward! and that stand should be ~ 5 cm high ...same height of board

 

Can you find that ball bearing on ebay...as I already have an account there it would be much easier to buy it...

 

I'm trying to check if the same seller has that ball bearing too...actually I was also thinking about joint1...as the arm should Not fall forward due to UNbalance (if I may say)...so will that ball bearing help for that or it purpose is to only...?

With the counterweights the arm has a tendency to lean back if no chess piece is lifted, but lean forward when lifting one, so a weight or simply bolting it to the board or the piece under the board is required.
The main reasons for the bearing are that leaning and also the approximately 1kg weight of the arm pressing down. I'm not sure what loads the bearings in the servo are designed for, but it's better if they only have a rotational load.

To check if it fits I think we need to know the number of teeth of the motor and ball bearing...will check if that info is given...

Also the dimensions of the servo and mounting holes. I think it says it is for standard Hi-tec servos, but best to have a quick check.

 

Ouff....sounds like lots of work this arm...


yep standard hi-teck servo...it should fit and if it doesn't I'll have one made here...
so if I get you well its purpose is to have the weight of arm Not crushing the motor, huh? sorry if ima bit slow understanding...I'm actually studying for my exam on monday and take a look here now and then...

Ima try to order that too...hope i still have some cash... LOL....

But I'm a bit scared...hope I'll have everything on time...

Thanks!