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bodhibuilder
09-22-2008, 08:07 PM
Hello everyone!

I am new to the forum and to robotics in general. Nevertheless, I decided to jump right into action; relying on my basic understanding of programming and beginners luck.

I already have a project in mind. To make it work I need to be able to control 6 to 10 motors from my computer. I thought the best, easiest and cheapest way to accomplish that would be to buy the following:

a. Pololu USB 16-Servo Controller
(using this because I want the convenience of USB and the ability to connect many servos)
b. GWS S35 STD Continuous Rotation Servo Motor (6 – 10 of those)
(because its more or less cheap and supposedly it can be controlled by the pololu servo controller, unlike a RC motor that needs also a motor controller attached)

My questions:

1. provided I have a power supply for the servos - would I be able to control these motors through this pololu servo controller without needing anything else? (the usb cable will connect my pc to the controller and the controller will connect to the servos. I will then be able to write some code to control the servo movement back and forward?)

2. what program can I use to write the code for controlling the movement of the servos? I preffer a free and downloadable software, and something easy or similar to C / VB.

3. to power the servo motors, would I be able to connect the following regular battery holder: http://www.robotshop.ca/home/products/robot-parts/power-systems/batteries-chargers/sfe-battery-holder-4xaa.html (http://www.robotshop.ca/home/products/robot-parts/power-systems/batteries-chargers/sfe-battery-holder-4xaa.html)
And load it with 4 regular and rechargeable energizer batteries?

4. is there a simpler / cheaper / better way of accomplishing what i'm trying to do?

This was a long write up, but hopefully my questions are clear and someone can answer them - I would really appreciate it!

Adrenalynn
09-22-2008, 08:52 PM
1. As long as you don't need a lot of torque or speed. Those servos are super wimpy.

2. You can write in any language on any operating system that can open a serial port and force data down it - yes, C and VB are definite candidates!

3. You'll want a 5 cell battery pack if you're using 1.2v batteries. Remember that a battery is only going to deliver its top voltage for a very short period of time before it falls off. At 6v you start at the max servo input and fall from there. At 4.8, you're starting at the bottom and your runtimes will end-up nil.

- WELCOME TO THE TRC! :)

robot maker
09-22-2008, 11:43 PM
i dont know if you know it the current of the servo is .3 amp at full speed no load with very little torque 39 oz,better to go to servocity.com for a better one and using 10 of them can be up to 3 amps no load,so if you are running from a computer also better to use wall transfomer
i think why you might be using it is because it is continuous rotation,but its only a guess
but any servo can be modified for continuous rotation and most servo's at servocity can be bought that way too or have done by a tech at servocity
hs-311 is only $8.99 and has a little better torque 45oz and 180ma no load and easy to modifed

parallax has another that is continuous rotation 45 oz torque for $12.99 8ma idle

bodhibuilder
09-23-2008, 08:54 AM
Thanks for your answers guys!
So at least you guys agree with my choice of controller (pololu) – that’s a start!

Adrenalynn - I chose the servos and the battery packs I mentioned because:
1. I’m looking for a cheaper solution, since I don’t have too much money to spare (too many other expenses), and
2. I live in Canada, so I was looking at what robotshop.ca has to offer. If I order from trossen or servocity then the shipping and the border taxes will increase the cost substantially.
3. I’m new to this, so even after a lot of research and reading there are many things I don’t know/understand/forget to take into account

For the battery, I guess the “Lynxmotion 6v 2800 mAH NiMH Rechargeable Battery BAT-05” do better than my previous choice of 4 AA batteries, but for some reason the robotshop.ca website doesn’t seem to sell a charger for this or most of its battery packs.

Robot_Maker – you are absolutely right – I am looking for a continuos rotation servo, because I am not sure if I would be able to modify a regular one – looking for the easy way out; trying to buy one that’s already set for continuous rotation.

Where can I find instructions on how to modify the Hitec HS-422 Servo Motor for continuous rotation? If I could do that, I would buy it – it seems to have a good amount of torque for the price.

Alex
09-23-2008, 09:40 AM
Hi bodhibuilder, welcome to the TRC!

My one major concern is overlooking just how weak and slow these cont. turn servos are. We have n00b customers call us up all the time with projects in mind using these servos, only to find out about 10min into the support call that the servos are no where near their requirements.

You mention that you are wanting to use 6 - 10 of them, but no mention of what your project actually is and what you are trying to accomplish. The more details you provide all of us, the more able we are to give you the best possible answer:)

robot maker
09-23-2008, 11:25 AM
i going to make tutorial on making you own servos to have a higher torque with less current and how to modify them ,but it will be awhile since i have many projects to finish,but
to modify hs-311 is fairly easy ,just a matter of removing a pin or nub on the main gear and remove the area in plastic gear where it attaches to the pot or remove the pot
seattlerobotics has a tutorial on modifying one http://www.seattlerobotics.org/guide/servohack.html
might also try ebay.ca for servos at a cheap price



Thanks for your answers guys!
So at least you guys agree with my choice of controller (pololu) – that’s a start!

Adrenalynn - I chose the servos and the battery packs I mentioned because:
1. I’m looking for a cheaper solution, since I don’t have too much money to spare (too many other expenses), and
2. I live in Canada, so I was looking at what robotshop.ca has to offer. If I order from trossen or servocity then the shipping and the border taxes will increase the cost substantially.
3. I’m new to this, so even after a lot of research and reading there are many things I don’t know/understand/forget to take into account

For the battery, I guess the “Lynxmotion 6v 2800 mAH NiMH Rechargeable Battery BAT-05” do better than my previous choice of 4 AA batteries, but for some reason the robotshop.ca website doesn’t seem to sell a charger for this or most of its battery packs.

Robot_Maker – you are absolutely right – I am looking for a continuos rotation servo, because I am not sure if I would be able to modify a regular one – looking for the easy way out; trying to buy one that’s already set for continuous rotation.

Where can I find instructions on how to modify the Hitec HS-422 Servo Motor for continuous rotation? If I could do that, I would buy it – it seems to have a good amount of torque for the price.

bodhibuilder
09-23-2008, 12:01 PM
Alex – that’s a good point, I should tell you more about my project, I just didn’t want to make my post too lenghty.
My project: I want to build something like a Vexplorer: a wheeled rover with a robotic arm on top of it. But I want the arm to have more joints and more control. Initially I just want to have all the electronics and mechanics work and be controlled being attached to my computer – that’s my first goal. When I ‘master’ that, I will add more complexity.
I think this is an appropriate first project, both in complexity and in resources required.
I always thought that if the motor was weak I can just add some gears, of course it will decrease the speed, but I’m not racing anywhere.
Robot_Maker - I looked at the link you post on how to modify the motor. The use a different motor there than the HS-422 – would it be the same procedure modifying the HS-422? In any case, I think this will complicate things too much in terms of a noob’s project. Maybe the easier way is to just buy an already modified servo. At the same time – maybe I don’t need a continuous rotation motor for at least half of my project – the robotic arm, but that’s another topic.

Adrenalynn
09-23-2008, 12:17 PM
The arm is where you need the torque. If you're wanting to pick up more than a feather, you'll either need a LOT of gearing (ie. very slow) or better servos. MUCH better servos.

Those servos unmodified wouldn't lift the weight of an arm more than a couple inches log, let alone the weight of the servos out on the end of the arm. Adding more degrees of freedom means more servos means more overhung weight. Even a single HS645 won't lift the weight of four more servos out 10" from the center line of the first. There's, unfortunately, a reason arms are expensive. You can go the vex big gear route, but the more weight you add the more gearing it takes the slower it goes - at some point you'll get old and die waiting for the arm to lift a pingpong ball. ;)

Sorry - not trying to be discouraging, just trying to help you consider where and how you'll spend your [limited] budget.

robot maker
09-23-2008, 12:48 PM
look at the parallax link they have one already modify for $12.99
adding gears is a good way to have more torque,look at the pan and tilt designs for ideas and how much speed changers on adding a gear ratio,you always make a cheaper design,since i made many
only problem with adding a gears is that you need to remove the pot from the servo and put it on the main gear for feedback
i would buy like 1 or 2 just to see if modifying them is easy then buy the rest ,and at the same time see if you have enougth torque for your project


Alex – that’s a good point, I should tell you more about my project, I just didn’t want to make my post too lenghty.
My project: I want to build something like a Vexplorer: a wheeled rover with a robotic arm on top of it. But I want the arm to have more joints and more control. Initially I just want to have all the electronics and mechanics work and be controlled being attached to my computer – that’s my first goal. When I ‘master’ that, I will add more complexity.
I think this is an appropriate first project, both in complexity and in resources required.
I always thought that if the motor was weak I can just add some gears, of course it will decrease the speed, but I’m not racing anywhere.
Robot_Maker - I looked at the link you post on how to modify the motor. The use a different motor there than the HS-422 – would it be the same procedure modifying the HS-422? In any case, I think this will complicate things too much in terms of a noob’s project. Maybe the easier way is to just buy an already modified servo. At the same time – maybe I don’t need a continuous rotation motor for at least half of my project – the robotic arm, but that’s another topic.

Alex
09-23-2008, 01:12 PM
Also, if you're looking for positioning control, which I'm assuming you are with the robotic arm, you won't have this capability with continuous turn servos. When a servo is modified to continuously turn, you loose positioning control.

bodhibuilder
09-23-2008, 02:27 PM
Wow! All very good and informative inputs - I really appreciate it guys! Now I see this is going to be a little more difficult than I thought. Better find out now than later though! So I guess the conclusion of this servo dilemma is that I will need stronger (more expensive) servos as well as some gears. I’ll think and research some more the servos I want to buy and I’ll let you know when I decide.

How about the power supply? For about 7 or 8 servos: what would be the best product to buy to power their movement? I was thinking of buying the “Lynxmotion 6v 2800 mAH NiMH Rechargeable Battery” and a charger for it, as I mentioned before. Would that be a good enough choice to power all of these servos, or is there something else I should be aware of?

robot maker
09-23-2008, 02:49 PM
depends on 3 factors,how many servo's,current at full torque and run time each one is on,plus any other electronics that need power
good idea to start and learning coding is to buy 1 servo,doesnt matter any type cheapest would be better,then servo controller that you are looking to buy and a wall transfomer
then latter work out the servo's need for the job you are trying to do
a good page to start is http://www.societyofrobots.com/robot_arm_tutorial.shtml
a very good page on what is needed and calculator for getting the needed torque for your arm



Wow! All very good and informative inputs - I really appreciate it guys! Now I see this is going to be a little more difficult than I thought. Better find out now than later though! So I guess the conclusion of this servo dilemma is that I will need stronger (more expensive) servos as well as some gears. I’ll think and research some more the servos I want to buy and I’ll let you know when I decide.

How about the power supply? For about 7 or 8 servos: what would be the best product to buy to power their movement? I was thinking of buying the “Lynxmotion 6v 2800 mAH NiMH Rechargeable Battery” and a charger for it, as I mentioned before. Would that be a good enough choice to power all of these servos, or is there something else I should be aware of?

bodhibuilder
09-24-2008, 09:56 AM
That’s a good resource – I will definitely use it in my plans.

I have another question, however. I found this servo motor:

The GWS Standard SO3T STD Servo Motor
http://www.robotshop.ca/home/products/robot-parts/motors/servo-motors/gws-servo-en/gws-standard-s03t-std-servo-motor.html (http://www.robotshop.ca/home/products/robot-parts/motors/servo-motors/gws-servo-en/gws-standard-s03t-std-servo-motor.html)

it looks like it has a really good amount of torque (Apparently 100 oz) and its not expensive at all, would that be a good choice then (in compare to the other ones that have half the torque)?
Does anyone know what its degrees of rotation are? And if I could fairly easily modify it for continuous rotation later on?

Adrenalynn
09-24-2008, 10:51 AM
Just by way of comparison:

The crustcrawler SG5 arm has 343oz-in at the shoulder, and 133oz-in at the elbow. (805BB and 645MG)

The standard on the SES arm is 2 x 133 = 266oz-in at the shoulder, 133oz-in at the elbow. (3 x 645MG)

What are you looking to lift, and how long do you envision the arm being, and how many servos itself is it going to have to lift?

bodhibuilder
09-24-2008, 11:43 AM
I understand I will have to add some gears, but would you say my choice of motor is better than the earlier suggested 39 – 49 oz of torque motors?

I am not sure how much I am planning to lift. I guess the arms you mentioned seem like a good aim/idea to strive for, in terms of weight, lenght, amount of servos, etc.

i am still wondering where i could find about the degrees of rotation for this motor i chose, and if I could fairly easily modify it for continuous rotation later on.

Adrenalynn
09-24-2008, 01:09 PM
It'll be the same range as their other [unmodified] servos - all they've done is modify it by adding a larger intermediate stage. That being the case, don't try to rotate it with your fingers! You'll break/strip the cheap plastic gears...

~120deg would be expected. Some will do a little less, some a little more. With any servo, you need to CAREFULLY test their limits.

No idea how modification would be, honestly. I've never torn one of those apart. Since they're just a slower/geared-down version of their other servos, it _should_ be identical.

4mem8
09-24-2008, 01:35 PM
Most servos are pretty much the same inside [ model aircraft type] even the HSR5990, 330oz @6v and 440oz @ 7.2v digital are very much the same as most servos, It's just gearing, type of material used [Titanium gears] HSR 5990, Metal, Karbonite and plastic, All these servos have their strengths and weakness, and you have to choose the right servo for the job in hand as Adrenalynn has stated, If not you will end up striping the gears if your choice is wrong and you lift to much weight that is designed for that servo. Just bear in mind bodhibuilder that on an arm the strongest servo will be the base servo as it has to lift eveything, the weight plus ALL the other servos, As you go up the arm joints the servos can be of a lower torque untill you reach the outer grippers which do not have to be high end servos unless you want to crush the object you are picking up.

robot maker
09-24-2008, 03:12 PM
any servo can be easy modified,i have done so many of them and very easy,main gear that has a spine has a nub or pin on it to only move 180 deg,so all you need is to remove it,second part is the pot,it has -180 then 0 and 180+ to make is 360 deg,just remove it or cut the wires or remove the inside of gear that is attached to it,easy way without removing the circuit board and unsolder the motor is to remove the gear assembly cover,remove the gear that has the pin that needs to be removed,and the gear that is on the other side connected to the pot and remove the inside of the gear with a dremel tool or drill bit till the gear moves and the pot doesnt,other way is to remove the bottom plate under solder the motor and very carefully remove the circuit board,some have a pot with wires some has a pot solder to the board,is mostly takes a hour or less to modified a servo

bodhibuilder
09-26-2008, 08:33 AM
Alright, so I have taken all of your excellent advice regarding servos and torque, and I came up with the following selections: (I look at the robotshop.ca website, because I live in Canada, and shipping from the US is just too costly).

Please let me know if you think these servos are sufficient enough to power the robot arm I want to make.

For my robot arm (in order from shoulder to hand):

1. Hitec HS-805BB Giant Scale Servo Motor (343 oz torque)
http://www.robotshop.ca/home/products/robot-parts/motors/servo-motors/hitec-servo-en/hitec-hs805BB-servo-motor.html (http://www.robotshop.ca/home/products/robot-parts/motors/servo-motors/hitec-servo-en/hitec-hs805BB-servo-motor.html)

2. Hitec HS-755HB Giant Scale Servo Motor (183 oz torque)
http://www.robotshop.ca/home/products/robot-parts/motors/servo-motors/hitec-servo-en/hitec-hs755hb-servo.html (http://www.robotshop.ca/home/products/robot-parts/motors/servo-motors/hitec-servo-en/hitec-hs755hb-servo.html)

3. Hitec HS-475HB Servo Motor (76 oz torque)
http://www.robotshop.ca/home/products/robot-parts/motors/servo-motors/hitec-servo-en/hitec-hs475hb-servo-motor.html (http://www.robotshop.ca/home/products/robot-parts/motors/servo-motors/hitec-servo-en/hitec-hs475hb-servo-motor.html)

4. Hitec HS-422 Servo Motor (57 oz torque)
http://www.robotshop.ca/home/products/robot-parts/motors/servo-motors/hitec-servo-en/hitec-hs422-servo-motor.html (http://www.robotshop.ca/home/products/robot-parts/motors/servo-motors/hitec-servo-en/hitec-hs422-servo-motor.html)

Alex
09-26-2008, 10:45 AM
It depends:



Is the 755 for the elbow?
What kind of weight are you planning on moving? I know you mentioned before that you're not sure, but this is critical to know if you want to figure out what servos are best suited for your needs. Exact amount isn't necessary, a close range would do for now (ie. 1 1/2lb - 2lbs, 1/2lb - 1lb, etc.).
How long is each section between servos (eg. humerus and ulna)? Section length is just as critical as weight in determining what servos you need.
Are you building your own brackets? I'm probably stating the obvious with this one, but the Giant scale servos require a special bracket because of their size.

There's a calculation you can do once you figure out the weight you'll be moving along with the sections, but I'm not quite sure what it is. Hopefully someone else here can chime in on this (link?).

bodhibuilder
09-26-2008, 11:14 AM
Hey Alex – I’m not sure about the length or the weights, but I guess I would be ok with lifting half a pound with an arm that’s the size of ¾ of a human arm when extended.

I know there’s a calculator that helps determine required torque provided you specify length, weight of motors and the arm, but I’m not sure about the details yet myself. I was just wondering if the motors I specified are decent enough to move around a beginner’s (me) robotic arm and at the same time lift a tennis ball or maybe a can of coke.

I hope to build my own chassis – when you say brackets do you mean the things on which I will mount the motor? In that case, yes, I hope to build it myself.

bodhibuilder
09-26-2008, 11:21 AM
(oh, I forgot to answer: the 755 is the elbow, yes, and the 805 is the shoulder)

Another question I have (getting back to servo controllers) is which controller should I use to power these motors? I was contemplating between the following 2:

1. the Pololu USB 16-Servo Controller

2. Phidgets Advanced Servo 8-Motor

I want a USB, which both have. And the price is very close. The pololu can control more servos, but for some reason i have the impression that the phidgets advanced will be much easier to control (both in terms of supported languages and documentation), is this true? In that case I will probably go with the phidgets advanced. anything else i forgot to take into account?

Adrenalynn
09-26-2008, 12:31 PM
Neither are capable of "powering the servos" - they're only capable of controlling the servos. Power for monster servos needs to come directly from a power source, not the controller.

"human arm" is kinda loose in definition.
My arm is about 21" from shoulder to wrist (I'm pretty tall at almost 5'10")
The Crustcrawler SG5/6 is about 15" from shoulder to wrist

That's, roughly, around 70% of my arm length.

It uses an 805BB at the shoulder, a 645MG at the elbow. It's not going to be lifting any full soda cans unless it has a LOT of spring tension to counter the weight. Tennis ball = no problem. An arm that can lift both a ping-pong ball and a full soda can with any precision is very very tough to design due to balance issues.

I know we seem like a broken record here, but you *must* define the task before you define the arm/servos/power/controller/anything else.

Another thing to consider in your design is how you're going to counter-balance the arm... Have you studied the other ~15" arms out there, like the SES (using dual 645's at the shoulder) or the Crustcrawler SG5 (using a single 805BB at the shoulder) ? You would probably be well advised to do so...

bodhibuilder
09-26-2008, 01:09 PM
Thanks of the input Adrenalynn. I understand what you are saying – I have to define what I want to do in order to successfully do it. I cant achieve a ‘goal’ if I don’t know what it is….

I guess I already explained that I’m doing this to begin and learn, and it doesn’t matter that much what it lifts, but for the sake of purpose, I will define my goal:

I want to build a similar arm to the one you just mentioned; the crustcrawler SG5-6!
It seems like a decent project, and since I am already planning to use the same motor for my arm’s shoulder, it works out great!

As for the counter, I was thinking exactly that; a spring tension to couter the weight.

I have studied a few similar robotic arms, but I only noticed the crustcrawler now. I even found a good manual on how to assemble it, which I might use for design ideas when creating my own.
http://www.crustcrawler.com/downloads/manuals/SG5-6Manual_V3.4.pdf (http://www.crustcrawler.com/downloads/manuals/SG5-6Manual_V3.4.pdf)

and OOPS I didn’t mean to say the servo controller will power the servo, my bad! I know it needs another power source for the actual powering.

But could you give me some input for my dilemma between the 2 servo controllers I mentioned? It would greatly help me advance in my journey in the world of robotics!!!

robot maker
09-28-2008, 01:01 AM
in this thread i put a calculator link for finding how much is needed
http://www.societyofrobots.com/robot_arm_tutorial.shtml
http://www.societyofrobots.com/robot_arm_calculator.shtml
tells you everythinhg you need to know about building a hand


Hey Alex – I’m not sure about the length or the weights, but I guess I would be ok with lifting half a pound with an arm that’s the size of ¾ of a human arm when extended.

I know there’s a calculator that helps determine required torque provided you specify length, weight of motors and the arm, but I’m not sure about the details yet myself. I was just wondering if the motors I specified are decent enough to move around a beginner’s (me) robotic arm and at the same time lift a tennis ball or maybe a can of coke.

I hope to build my own chassis – when you say brackets do you mean the things on which I will mount the motor? In that case, yes, I hope to build it myself.

Alex
09-29-2008, 11:07 AM
awesome robot maker! thanks for the links:)

Could you add them to our Links Directory?

http://forums.trossenrobotics.com/links