Powering Multiple Servos From One Battery- What is my circuit missing?


Hey Everyone,

I'm working on a robotics project right now and my limited DIYer knowledge of electrical circuits is failing me. I need to power 7 Rage Standard Metal Gear Servos (RGRS104-16-6vm) and 4 RadioShack Micro Servos using a Tenergy 6V 3300mAh NiMH Battery Pack. I've made a diagram of the circuit I'd like to make, but I feel like there's more to this type of circuit than I've planned for. There are only 9 servo connections because two pairs of Rage Servos will be wired together to share the same battery and signal connection. I'm also open to using a different battery if that's what it takes to make the robot run smoothly (It has to use a rechargeable battery though; It's meant to be portable.)

Would you please point out what I need to add to my circuit to make sure it works properly?

Thanks in advance!

More Info:

Rage Standard Metal Gear Servo RGRS104-16-6vm
Dimensions: 40.8 × 20.1 × 38 mm
Weight: 56 g
Operating Speed: 0.18sec/60degree (4.8V), 0.16sec/60degree (6V)
Stall Torque: 9kg.cm/125.2oz.in(4.8V), 10.2kg.cm/141.9oz.in(6V)
Operating Voltage: 4.8V~6V
Control System: Analog
Direction: CCW
Operating Angle: 180degree
Required Pulse: 500us-2500us
Bearing Type: 2BB
Gear Type: Metal
Motor Type: Carbon
Connector Wire Length: 30 cm.

RadioShack Micro Servo
Voltage: 4.8~6.0V
Torque: 1.5kg/cm at 4.8V; 1.8kg/cm at 6.0V
Speed: 0.12/60ТА at 4.8V; 0.10/60ТА at 6.0V
Size: 23x11.5x24mm
Weight: 8.6 g
Use Angle: <=160ТА

Tenergy 6V 3300mAh NiMH Battery Pack
Chemistry: Ni-MH
Cell Size: Sub-C
Nominal Voltage (V): 6
Capacity (mAh): 3300
Max Continuous Discharge Current: 6A
Battery Charging Current:
Standard: 1A
Weight: 10oz.
Dimensions: 112 x 46 x 23mm (LxWxT)
Connector: Hitech

Link to Diagram: http://imgur.com/BRrWijV

Picture of Powering Multiple Servos From One Battery- What is my circuit missing?
sort by: active | newest | oldest
lukealbertson96 (author) 1 month ago

I'd like to thank @steveastrouk and @iceng for the advice you gave me. I still had issues with the circuit, but in my internet research I stumbled across pre-assembled circuits for RC Hobby use called BECs (Battery Elimination Circuit). With the help of my local RC Hobby shop, I was able to find a BEC that would be able to supply my servos with the right amount of power for $20. I estimate that I spent at least that much on components and shipping to build the original circuits in the first place, so I consider this an adequate solution. Thanks again!

lukealbertson96 (author) 2 months ago

Thanks @iceng and @steveastrouk!

By combining what both of you have suggested, this is what I plan to make:

Diagram.jpg

Make the supply and ground lines as heavy as you possibly can. There's upwards of 9 A of current flow through the connection to the battery !!!

lukealbertson96 (author)  steveastrouk2 months ago

Yeah, I found that out yesterday. I soldered the circuit together on a normal PCB and it shorted and burned a bit when I connected the battery. I'd like to do this on a PCB (it would be a lot harder to do it without one), but I don't know if I can find one with traces strong enough. Any suggestions on what materials/boards to use? How would you assemble this circuit?

Feed the board from the middle, not the ends. Try and put the heaviest servos on opposite sides of the middle.

My simplest preference would be to lay down tinned copper wire to each pin, so you have a much heavier electrical connection, but all your bits and pieces held nicely together by the PCB

lukealbertson96 (author)  steveastrouk2 months ago

Heaviest servos as in the ones with the greatest load? Or just heaviest by weight?

HIghest current load !

lukealbertson96 (author)  steveastrouk2 months ago

I'm ordering more components to try building this board again. Besides reinforcing the solder connections with thicker gauge wire and balancing the servo loads, does this look right?

Servo Power Board Diagram (MOD3).png

YEs, that looks a lot better.

iceng2 months ago

+1 Steve

Also if the battery is more then 3" by wire away, add a big electrolytic in parallel with 0.47 uF film capacitors to this board...

lukealbertson96 (author)  iceng2 months ago

What size of Electrolytic Capacitor?

How many 0.47 uF Film Capacitors, and in what positions?

I do appreciate the help, but I don't do wiring like this on a regular basis, so I appologize for all the questions.

Here you go.

Click the pic to see it all

pcbx.jpg

Big fat electrolytic, 1000uF if you can manage it, in parallel with one 0.47uF - though my preference is usually 100nF/0.1uF.

steveastrouk2 months ago

Connect the ground of the servos to the ground of the Arduino, AT THE BATTERY, not at this board.

lukealbertson96 (author)  steveastrouk2 months ago

I know that the ground of the battery, servos, and Arduino has to be common for the servo positions to be read by the Arduino, but I'm not exactly sure I understand what you're saying. Like this?

Servo Power Board Diagram (MOD1).png

Nearly. Tie the battery to your - point on the drawing, tie the arduino ground with a separate wire to the same - point, don't loop to the arduino ground as you've shown.