Help with powering 6 DoF Stewart Platform

Robotics and electronics discussion Miscellaneous
1

Hi there,

I’ve recently started work on a 6 degree of freedom platform to simulate various types of motion (waves, a person walking, etc) to test energy gathering devices that could potentially be used to power small scale devices like sensor networks and mobile phones.

I’m using 6 HS-7950th servos (http://www.servocity.com/html/hs-7950th_servo.html) connected to crank shafts to actuate the platform. I’ll be controlling the servos via PC with a micro maestro controller.

My problem is with powering the servos- since they operate at 7.4V and can draw up to 6.2A each (at max torque), whihc means i could be looking at around 30A of peak current (although it’s unlikely that all servos will have to exert max torque at the same time).

I’m connecting the maestro controller to a separate servo power board (http://www.servocity.com/html/servo_power_boards.html) to avoid damaging it with the large currents, but it’s hard to find a regulated 7.4V power supply capable of coping with that kind of current.

I’ve considered using batteries but i’m worried that they’ll drain too quickly with this kind of current being drawn, and the platform may be needed to run through a series of motions continuously so batteries losing charge and decreasing the servo performance could be a problem.

Do you guys know of anything out there that could serve this purpose?
Any advice would really be appreciated.

-Alex

2

Hello.

First off, the Micro Maestro probably has better current distribution than that power board (just based on it not having any traces on the top side). Those traces on the Maestro are only for powering the servos, so even if you blow out a trace, you can just solder some wire back across the pins.

If you can deal with 5V as your supply, you’ll have way more options, including PC power supplies. You’ll probably want to add a bunch of big caps (several hundred to several thousand uF) across the power supply at the servo controller or power board. (Not having space for the caps is another reason I’m underwhelmed by that power board.)

- Jan

3

Hi Jan,

Thanks for the quick response :smiley: . My electronics knowledge is only rudimentary, so I’m not sure what the capacitors would be for. Just to smooth out the voltage supplied to the servos? :confused:

Also, the 7.4V supply is kind of important, because due to the application i need to extract a fair amount of torque and speed from the servos- the platform needs to move up and down at about 6Hz with an amplitude of 25mm, which is pushing the max angular speed of 0.13sec/60 degrees of the servos.
I could possibly drop it down as low as 6V, but I’m worried that any lower than that and the servos won’t have enough power.

I was using the power board more as a sacrifice- i’d be less worried about losing it than losing the maestro…

If there’s no other alternative i guess i could power each servo separately, although that’s going to be pretty expensive :frowning: