# Servo Compact Design Problems!!!

Hello,

The Links Of The Image That Descrype The Problem, Please See It To Understand My Problem
http://www50.brinkster.com/dominatorii/

I’m not in FIRST competition, And I’m new in robotics, So please be patient with
me, and use a simple words, cause my English is not so good, Thanks.

The Problem:
I’m building my graduate project it’s a rover robot that move on 6 wheels as
shown on the above figure, this figure is a basic design for my BlackBot,
as you can see, Wheels number 1,2 and 3 are connected together with Track-1,
while Wheels number 4,5 and 6 are connected together with Track-2,

Each wheels from 6 wheels are connected to its servo motors, So we have 6
Servo here,

Now assume that we want to compact the design of this robot, can we
connect the servo number 1,2 and 3 together in parallel connection, Called Con-1
And connect servo number 4,5 and 6 together in parallel connection, Called Con-2

I think its ok, if we connect the first 3 servo together in parallel so the volt
is constant but the current will distributed on each servo,
For example: if we connect the 3 servo in parallel, and apply 5 volt and 300 mA
to this connection, So each servo will take 5 volt and 100 mA, Cause volt is
constant and the current is variable.

The question is:- Is there a way (Circuit) That deliver to each servo a 5 volt and 300 mA.

If you see the above figure I supposed that I have an 2 amplification circuit that will
amplification the power and signal that came from the main board and distribute
it to each servo, so each servo take 5 volt and 300 mA,

Please if you can help me on design, (I mean a PCB) or any other things that help
me, making it, this will be appreciated, also I need confirmation if this method have disadvantage (Such as I will not control the speed), cause the servos in
any ways will take 300 mA, There are something I don’t get it, Can I control the speed of the servo (make it slow down or move fast), and how is this done,
I read many notes about modification of servo and how its work but I’m didn’t
get it, So please if any body, can explain it to me more simply, (The reason my English is not so good), This will be appreciated, and please the confirmation on this design and its disadvantage

You shouldn’t need any fancy circuitry. You should be able to connect all 3 servos in parallel and it should work

The current will divide (if i apply 300 mA) to connection, then every one take, only 100 mA, So How its going to work.

I would like to help you, but I need to know more about what you are working with. Obviously you are using the servos to drive your robot, what are you using as a power supply? Also, in the picture you have a “main board,” what does this main board consist of?

I’m didn’t specify this information cause i’m didn’t set its spicification until now, but i think this is not the problem (assume a convenient motherboard and battry), Is this connection logic, is there drawback(limited speed) or somthing,

I know that must be specification But i’m working in this part right now, So please help me on it, Help me to decide if this optimization is correct and what i need, and also, There is somthing i didn’t get it, (I think all the mainboard are the same, they diff. in its capapilites, # of I/O, I didn’t know if they diff on the volt applyed to the servos? Its Diff?),

The main board will recive a signal from a tranceiver then it will activate a function inside the chip,(According to the signal coming from operator through the transceiver), the power supply used is a battry, (i’m working on this project and i’m new so i’m didn’t decide until now what is the requred volt),

But i asked my question, cause i’m thing that if we assume the ideal power supply and mainboard, What is the drawback of this design, what i need to build it, please try to imagin what i’m need,

Thanks

I think it will work, if you are worried about the current drop can you use a larger power source? If you are getting your servo power source from your motherboard I don’t think you will have a problem, but it depends on the motherboard. I would decide on a power source and motherboard to use, then think about this problem. Have you started building anything?

Here is my robot design,
It’s move on 6 wheels, so we have 6 servo, and 2 another servo to mount camera, and another 2 servo to mount the gun, or the laser-beam, so we have until now 10 or 11 servo,

And we have a camera, mic, GPS, Compass and Transcever,

This is the components, i counted now, so assume if the total current requred to keep the above device work good, is 15 or 20 Am, and the Power supply deliver 25 or 30 Am, So i think there is no problem, But if the the Battry, can deliver more than 14 or 16 Am, So we need to amplificate the current goining to each device, But I’m now talking about these servos (The 6),
I think that The power supply will connected to mother and the mother distribute it,

I’m Didn’t Start yet i’m collecting info. right now, And think…??

Dom-

A solution to this problem could be easy, or could be difficult. We can not be very helpful with out more information from you. I would like to know more about the servos you plan on using to power the wheels. Do you have a website that provides information about them?

There may be a simple misunderstanding. A servo to me is a small device, containing an electric motor, gear reduction, and some electronics that allows it to move the motor to a position and maintain that position. They are used in making remote controlled model airplanes and cars. Usually they can only rotate a fixed amount, maybe 300 degrees. It sounds like your servos can rotate continually. This makes me think that your servo is different then what I consider a servo. You may mean an electric motor.

Does your servo look like this? http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXVW07&P=ML

This is important because making a simple electric motor move and making a servo move are very different.

Also, you’re English is very good. It is not an easy language, and you manage to communicate your self better then some English speakers do! Keep up!

-Andy A.

I sound a problem here, Do you mean that the servo can’t be used to move a rover to any distance I want,

If the servo isn’t the correct choice, then what is best motor that I may used to deliver to me fast and strong rover, also I hared that the servo can be modified to move continually, so how you said that its maximum degree is 300,
Please if I’m wrong correct my info,

Thanks, I know that servo is small electronic device, BUT the thing that I don’t got it, is the time frame that I apply to servo to work!!!

I sawed a lot of robotics project (rovers) that use servo, so how they make it continually,

I Think That There Are Something Called Servo Modification That Allow Servo TO Operate Continually (Did you here about it), Or The Servo After Modification Operate 300 Degree,

you make me feel that there are problem using servo, So Please Tell me if I’m wrong or what is the problem

Here is a link that tells you how to modify a servo for continuous rotation.
(i have never tried it myself)

http://www.acroname.com/robotics/info/ideas/continuous/continuous.html

Sorry I don’t have time to be of more assistance but these links may help you out.

Modifying servos to rotate continuously:
http://www.seattlerobotics.org/guide/servohack.html

Lots of (bigger) robot parts:
www.robotmarketplace.com

Good place to buy servos (smaller ones and bigger ones too):

Lots of good small robotics parts and kits:
http://www.parallax.com

Thanks,

But i already know how to modify the servo, i have 5 or 8 tutorial on servo modification, My question, Is the servo are correct choice in my project?

If true then (What is the drawback of the above design? and how can i build it?)
Else (What is choice here? (The Motor that will work.))

Thanks,

I think the servo will work for you. I can’t say if it is the best choice because I don’t know the specifications of the servo you are using and the size of your robot. Instead of using the modified servos you could use DC motors, which I think for your purposes will be pretty much the same thing.

The drawback to your design is that turning will be difficult, but if your motors are powerful enough it should not be too big of a problem. There may be an issue depending on your power supply, if you have enough for the motors. Other than that, I’m fairly sure you will be able to accomplish what you have in mind using your current setup.

John,
What many of the people here are familiar with are the servoes used in Radio Controlled cars and airplanes. They are not designed for continuous use as a drive system. A servo takes a power supply voltage and a control signal and makes the output shaft turn to a particular angle. This is useful for steering and wing control.
When you spoke of a servo motor in an earlier post, you may have been referring to a stepping motor. This device is similar to a servo in that it can have very precise control of the motor shaft but it can rotate a full circle and is meant for continuous duty. The motor in a video cassette recorder(the one that drives the tape) is a stepping motor. Unfortunately a stepping motor requires very sophisticated electronics to drive it. So again it is the wrong motor to use.
You also did not specify the weight of the rover you are building. If it is in the 50 to 100 pound range, then any of the kit motors we use will be OK. You can get a lot of power from a little Fisher Price motor and you can buy the motor and transmission from many sources.
If you are building something that is only a few pounds, then small motors of the type in toy cars would work just fine. I don’t know if Radio Shack has any stores in your country but they carry everything you need for a small project.

Thanks a lot guys, I’m really appreciate your help, In this message I will tell you about my robot, Here is the details

I will never describe my project as best as you will see now,

My project is a something that I hope that our army look for it, its a thing popular, you even know it, its a scout and carry on a gun.

Did you here about SWARD (http://www.foster-miller.com/) and (http://www.foster-miller.com/lemming.htm) These guys provide a complete mobile platform that will replace the soldier in the battlefields,

My Project is the same the above, But with little modification, If you the manual sheet provided in above link, then you will know my specification, But the diff between my rover and SWARD, that my one is simpler than the SWARD and will use transceiver,

Now after you know the rover I need to build and the Spic. I needed can you advice me what is the best choice in the motors and what is the convenient transceiver (range between 300 meter and 600 meter), And any advice you find that it will help me,

I’m really thanks for your help guys,

For turning it will not a big deal, cause the left 3 motor are separated from the right 3 motor, So I may send a signal to move the left group to forward and a diff. signal to the right group to move backward, so the rover will turn right, That’s it, Of course if there are no another problem you may see, Tell me if you see a problem,

John,
You have not mentioned any specs for size, weight or budget. I can recommend the chassis, transmission, CIM motor combination as being able to move anything up to about 150 lb. In sand, you will need some extra protection to keep the grit out of moving parts. You can’t beat the Innovation First control system but I don’t think it will give you the range you think you need. It is good for a couple of hundred feet, maybe as much as 400 feet in line of sight.
As far as budget, the above parts will cost several thousand dollars (US) If you are looking to go smaller, say about 50 to 75 pounds, then the Fisher Price motors and transmissions should do a good job. They are designed for children’s cars and work pretty well for being plastic. Those can be had much cheaper and are available through surplus houses like American Scientific.
Let us know if there is any information you can give us for specifications.

Hallow,

After my last post, I asked the biggest mall in robotics in Egypt, I asked them about my requirement, and the surprise that a lot of components are not available there (Just is not like I saw in the net, But they have a collection of things that I think it will help, Its included below), But the good news that, there are another technique they tolled me to use.

Here is the technique I will use in my project, And here a good specs about my robot, to help you to help me,

Specs of my Robot:-

[li] The Robot Specs…[/li]*******************
1- The size of my robot is 60 cm height, 30 cm width,

2- It will use 4 DC Motors, these Dc Motors are connected to 2 tracks (such as tank), each track will include three wheels (These wheels are free, I mean not connected to any motors it’s just used to pull up the track) (Its just like the tank).

[li] -> Details for stage (2)[/li]----------------------------
-The DC #1 & #2 Will be in the right side and DC #3 & DC #4 Will be in the left side,
-The DC #1 Will be in the front of the rover that will take the front of track,
-The DC #2 Will be in the rear of the rover that will take the rear of track,
-In between the DC #1 And #2 (Front of Track And Rear) There are 3 Wheels.
###################

3- These 4 DC motors will derived from a DC Driver board that will take its power from a Motorcycle Battery (or similar)-(12 Volt and 20 A)->(Maybe I don’t know yet), The battery will be recharged through 3 or 4 dynamo->(Maybe), So there is no need to unplug the battery to recharge it, and will provide long live mission,

4- The Driver board will connect a Main Board that will manage the direction of each motor, through the driver.

5- The Main Board of the robot (I don’t have any information about it yet, but its on the shelve in the malls) assume it will connected to PC that will be inside the robot chassis, (Not complete PC, Just Mother, HDD, VIGA, Sound Card And Wireless Network Card (That will act as Transceiver (That will deliver and send info, to operator))).

6- The sensors (GPS, Temperature, Compass, Camera And Mic), will connected directly to the pc through its ports,

[li] -> Details for stage (6)[/li]----------------------------
I have an interface board called K8000 from velleman.com that have an parallel interface to pc, this board have an 4 input analog & 16 in/out digital & 9 Output Analog, It will be use for temperature sensor and the switches that will used for interrupt the pc (Example if I push a witch, then this will interrupt the pc and my SW so it will activate a voice recognition program, or activate the autonomies mode, and so on), The rest of sensors I will ask for there interface port.
I think that the camera & Mic & Temperature sensor are not the problem, (cause its interface is known and easy),
The problem will be interfacing the compass and GPS (I think it will be the problem cause I don’t know what is the output of these sensors), I have question here, can I attached them to my interface card or to any port on my mobile PC??
###################

7- The robot maybe include 2 or 3 Motorcycle Battery that will automatically recharged from dynamos.

8- The Robot Mobile PC will take its power from battery #1, And motors take its power from Battery #2 And Sensors and other components may take its power from battery #3 (And all these Battery will be recharged automatically)

9-the load of the rover will be 35 or 40 KG or More, so I will buy a stronger DC, that will achieve these constraints (I think that there are such these motors for this load??!!)

10-Indeed the DC will contain a gearbox (Its the hardest problem, Cause there is no body here have these gearbox and its hard to build it, and its hardest to get it from outside the country.)

11- Please If any Important Specs. are not mentioned Please PM me,

(*)The Operator Specs…
1-Its a personal computer that attached to it a wireless network card, Just it,
2-There will be access point between the Robot PC and The Operator PC,
3-The range of this wireless network is 300 Meters line of sight, If the access point in the middle between the Robot PC and Operator PC, and the range will be 150 Meters if the access point is beside the operator,

(*)The SW Specs…
1-Its normal network program using Winsock.ocx that will retrieve the real time video and sound and sensors reading from Robot PC to Operator PC and Send instruction From Operator PC To Robot PC That will execute it,