bigger servos advice

[Flavio C]

hi Gael,

this is my first post and i really want to thank you for the great opportunity, that you are giving to me and to all the people, of taking part to this wonderfull Inmoov project that you created and are developing with all the community, in order to spread robotic knowledge.

I would like to present you the hard work up to now and ask some help.

i am experimenting with the eye colour, you will notice from pictures that my inmoov now has heterochromatic eyes, one eye is green and the other is blue, it remembers David Bowie, and is cute but i will try other combinations just to find the perfect look.

i spent last two month printing parts and reading your instructions and google+ posts, actually i've got a little confused about the "final" servo i am supposed to use for biceps torso and shoulders, i mean the bigger torque ones. i have bought 10 MG996R in order to use for the fingers but i am open to use different servo in one arm to simulate the human right or left-hand habit. so i would like to have on arm stronger.

i need an advice about the 360° servos if they are better than 180° (maybe at same price) i think is easyer to hack them and just invert the rotation to match the other servo when needed.

another question is about the energy line or which are the servos which needs more torque , and how many they are.

i was thinking to buy 

6x pdi6221      360°  20kg

4x pdi-hv5932mg 180°  25/32kg

4x pdi-hv2060mg 180°  48/62kg

this is a list of servos from aliexpress.com and some model is new. i would like to order all the servo in one time cause of the delivery time from cina. 

according to your experience can you tell me which part needs 60kg, which needs 30/40kg and which need 25kg and where i better use the 360°servos? 

Servo  -  Price € -Degrees - Power/Torque -  Dimensions

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>20kg

DS3218       11.5 €   180° [5-6.8v / 18-20kg]  [40x20x40.5mm] 

JX PDI6221MG   7.5€   360° [4.8-6v/ 18-21kg]   [40.5x20.2x38mm]  

JX PDI5521MG 7.7€    180°  [4.8-6v/ 18-20kg]   [40.5x20.2x44.2mm] 

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>30kg

JX PDI-HV5932MG 18.5€ 180° [6-8.4v / 25-32kg]  [40.5x20.5x36mm]   

superHobby CLS 5830HV 30 €  [6-8.4v / 25-32kg] [40.5x20.2x38mm]

JX BLV-HV7132MG  44€ 180° [6-7.4v / 27-32kg][40.5x20.5x36mm]Steel

JX CLS6036HV   21.5€ 180° [6-7.4 v/ 28-35kg]  [40.3x20.2x40.3mm]

RDS3135        13.5€ 180°/270°[6-8.4v / 25-35kg][40.5x20.2x38mm]

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40 to 60kg

CYS-S8218      21€  180°  [6-7.4v/ 38-42kg]  [59.5x29x55.2mm] BIG

JX CLS-HV7346MG 39.4€  ?° [6-7.4v/ 37-47kg]  [40x20x37mm] 

JX PDI-HV2060MG  27/32€ 180°[6-7.4v/ 48-62kg] [65.8x30x57.4mm]BIG

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just wanted to say hello to all the community and the makers that contributed to the inmoov developement.

best regards

FlavioC

[Piero Di Vita]

I'm not satisfied from MG996R.
I'm using it for the jaw, but every time I plug the battery, the servo starts to rotate about 20 degrees.
I've ordered  a JX PDI-6221MG, hoping it will be better.

Piero

[Ray Edgley]

Hello Flavio C,

I have used the CYS-S8218 in my robot as part of the waist assembly created by Bart.

So far no problems.

They do not suffer the turn on jerk that is a problem in the MG996R servos but do require a larger pulse range to achieve the 180 degree rotation.

Internally is is all aluminium body with a neat fit around the motor, this allows for better heat dissipation from the motor.

Just a word of warning:

Gael designed a lot of the joints, gears and gear ratios based on the original Hitec HS805BB which is a 24Kg torque servo and did a wonderful job of it.

While using the higher powered servos will reduce the number of burnouts, you may also find the failures being moved to other parts such as the printed plastic gears.

The servo dimensions are also a bit smaller as well so you will need to print out some adapters.

If you end up using these unit as a replacement for the Hitec HS805BB, please let us all know how you went :-)

Ray

[gael langevin]

Hello Flavio,

On my fourth InMoov I have used only PDI servos and I am very satisfied with the quality and behavior.

I used:

15x pdi-6221     180°  20kg (fingers, wrist, jaw, rollneck)
12x pdi-hv2060mg 180°  48/62kg  (bicep, rotate, omoplate, neck, rothead, top stomach, mid stomach)
 

The printed gears (ABS) for the new shoulders can handle the speed at 7,4V and the force of those servos. The resistance is really related to the material you print with and how you print.

If you have printed the older shoulder version, be carefull when the robot is at full speed, specially if you make him lift an object (Bottle of water for exemple)

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

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[Flavio C]

You have got the point of my question about torque and position. thank you 

so you confirm that the better fit is with all the same kind of servos and don't get benefit in scaling the torque depending on the ammount of connected parts?

just one explanation about your answer: 

i have tryied to adapt the MG996R in the Biceps lower piston for test purpose, and it worked  slowly.. ok.   (i did not make any hacking) but the issue was that 

 it stopped after 180° and the biceps raised only about 20-30°.

do you think that if use the PDI 360° 20kg  there and in  homoplate piston, i could avoid hacking gears, and control it with and external pot leaving the servo with his pot inside? 

considering that there is no more a fixed zero point, it could work.

i am going to order the nervo board and wanted to ask if i can receive it with  also the ribon cable and all the parts needed with the nervo-boards ,adding the extra cost to my order?

i hope you can do it, because i am new to this electronics components, and i don't want to check all the web and maybe get the wrong things.

thank you

best regards

Flavio

[gael langevin]

Hello Flavio,
Having the potentiometer outside the servo case extends the potential of degree movement for the Bicep, this is the reason the poor(you are lucky it didn't burn instantly) MG996R can only operate the bicep 20- 30°.

I think the PDI 360° are continuous servo, without potentiometer position feedback.
I would avoid that because someone in a recent post talked about the issue with those servo.

A 300° PDI servo(they have a pot for feedback) would NOT have enough turns to fully operate the Omoplate or the Bicep and certainly not the Rotate or Shoulder.

You will need to hack the servo, sorry about that. I know it's a bit scary the first time, but you will learn about it and have more experience understanding a servo motor.

A simple math rule I practice for torque=result: get the highest torque servo you can as long as the speed doesn't decrease for torque value.
A 20kg for omoplate is ok but the servo will get tired and hot and will die sooner.

I do not sale the ribon cable because I do not have a good provider. I only sale what is online in the InMoov shop.

I really wish I could provide that for you, but unfortunately not yet.

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov

[Ray Edgley]

I did see Gael beat me to this, but, you are not going to be able to avoid hacking the servos.

Gael has done an incredible job of designing gear boxes and pistons that take multiple rotations to create a linear output.

Please not that a gearbox as designed here will reduce the output speed and give an increase is the output torque at the same time.

This reduction in speed also reduces the output angle, so if your servo turn 180 degree, then your output will be reduced to a point much less than that.

This means to get the amount of rotation we need the servo is going to have to turn multiple times.

Even with the use of the gearbox to give much greater torque, some of the joints still need a lot of torque, such as the shoulder.  While some people have used the smaller servos here, don't expect the arm to lift anything more than its own arm.

The output from the Arduino is a pulse of a set width where the width represents the position the servo is to be in, the servo uses the pot inside the servo to determine what the current position is and drives the motor forward or backwards to reach that position. A pot as used in all positioning servos, has a limited range, typically 270 degree, however there has recently been one that goes as much as 300 degrees.

The continuous type or 360 degree servos, don't have an installed pot, instead they have a resistor bridge with 2 match resistors to form a center point and the PID loop internally is a little altered as well.

If you were to use a 360 servo, then you will have to modify the servo, removing the two resistors, if you can find them and replace them with the wires to your new pot.

It is easier to modify the normal positioning servos, as you just follow the wire from the pot, you are just extending these wires as you are better off using the pot that come with the servo.

Gael has done a great job of showing how to do this on his web site.

I would avoid using the MG996R servo, they are a low powered motor with poorly designed electronics. 

How you didn't get smoke out has me beat. 

They are a cheap servo, but after you have replaced them a few time, you will find that it would have been cheaper to have just used a servo at 2 or 4 times the cost.

I like the JX PDI6221MG servos, they are stronger, do not suffer the power up jerk the MG996R do and so far I haven't burnt any out.

Building the Inmoov robot will make you learn new skills, learning is not a bad thing.

By the time you are finished, you will have played with 3D printing, electronics, wiring, and programming.

Have a good read over the whole of the Inmoov.fr site, particularly the build yours section even down to the comments.

Gael has put a lot of very good well explained information there.

Regards,

Ray

[gael langevin]

Thanks Ray for your output.

Your explanations are very clear and detailed, this is very usefull for others to learn.

Gael Langevin

Creator of InMoov

InMoov Robot

@inmoov