View Full Version : [Project] Hi all some suggestions on my servos

05-03-2012, 02:02 PM
Hi all guys
Its a long time I read this forum and I really like it.
I'm Luca from Italy and I've a looooong lasting project for a biped (maybe for a mech if I success).
I'm writing this post to ask your opinion on what I've built in this long time.
this is my first experiment


its a hitec 805Mg based servo

I worked a lot on it and I hope I obtain something utilizable


torque seem to be good, the motor itself can push really harder than this but geartrain can't support it, I first try with a bigger 50Kg balance?? and a 1 inch horn but the servo broke it so I think to put a longer arm (10cm) and use a little digital balance??


I know this test is ....useless... but I do it just for fun

So What you think ? Do you think this will work in a biped? does I miss something?
thank you a lot bye

05-10-2012, 12:24 AM

I hate to be the bearer of bad news but I don't see things really working out for you using that servo, especially for a biped in mech warfare. It is just the wrong tool for the job in my opinion. The servos while strong 33% stronger than an AX-12, are heavy 4* as heavy. Yes you could build a humanoid using what you got, but I wouldn't recommend it. Not sure if you can get them in Italy but seriously check out the Dynamixel Servo line or the bioloid kit. Heck, wait a while and check out the Hovis Lite. The point is building a humanoid from scratch is a bear of a problem. Getting it to walk is even harder without feedback. I have been using smart servos for the past three years and I will never look back.

I ran down the hobby servo road a few years back...it wasn't worth it. I had to write my own servo controller software and even then getting things to walk properly never really happened for me. With smart servos you can get so much more information from the bot, it makes tweaking things really easy.

I hope this helps more than it hurts.


05-10-2012, 03:41 PM
uhm 33%?
but ax12 torque isnt it 15kg*cm?

05-10-2012, 11:46 PM
HS-805MG (http://www.hitecrcd.com/products/analog/giant-scale/hs-805mg.html): 19.8[kg-cm] at 4.8[V], 24.7[kg-cm] at 6.0[V]. 197.03[g].
AX-12A (http://support.robotis.com/en/techsupport_eng.htm#product/dynamixel/ax_series/dxl_ax_actuator.htm): 15.5[kg-cm] at 12[V]. 53.5[g].

So, ~28% more torque at 4.8[V] or ~59% more torque at 6.0[V]. Still ~3.7 times heavier.

05-11-2012, 11:49 AM
sorry probably my english is so bad that I can't explain myself properly, but like you see in the video the servo are not anymore 805 they do 19-20kg on 10cm arm more if I succed on strenghten the geartrain (the maxon motors is a re-max 29mm 22 watts , nearly double the normal ex-106 mounted 24 mm 12 watts)
the servo give over 200 kg*cm and weight with the case made on alluminium the new gear etcetc 320g nearly double of the ex-106 but the gain is the dimension it is near the dimension of a ex-106
the pololu board give me PID , can be drived directly by usb and chained with other board other other than PWm signal or analog signal
I drive it at 28V and it requires 1.4A at 20 kg*10cm

I cant do the test with shorter arms cause it broke my 50kg scale the first time I try to test it so I decide to do the test with longer arm and lower digital scale.

sorry for my english and thanks for your reply


Here we have robotis to but they cost really big money an ex 106 cost nearly 500 €

05-11-2012, 07:53 PM
Ah. Sorry. I read:

its a hitec 805Mg based servo and kinda skipped the rest since hobby servos are not my thing.

Instead it is an actual homebrewed servo even further up on the scary (strong) scale than the Invenscience Torxis servos (800 oz-in (http://www.pololu.com/catalog/product/1391) and 1600 oz-in (http://www.pololu.com/catalog/product/1390)). That is impressive. I've been wanting to do something similar based on a brushless DC motor, but there are too many projects pulling my mind into too many pieces in different directions to get much of anything done.

05-12-2012, 11:44 AM
so? do you think it gonna work if I build a robot with that?
thanks for the reply

05-12-2012, 02:10 PM
If you can home-brew sixteen servos like that, and they are mechanically and electrically robust, I believe you can build a robot with those.

05-12-2012, 07:26 PM
Should work, but I've got one small question, how will you power your robot? Depending on the size of the robot the power the servos will draw might be quite substantial, so what kind of battery life are you after? Or will it have a cable to a benchtop power supply or something?

05-13-2012, 04:25 AM
I'm gonna power it with li-po the battery AH will depend on how much weight the finished robot can carry
I'will start with 4 (two parallel and 2 serial) 2000 mAh 4S lipo distributed like two on the legs on two on the back of the robot
its like 1kg battery