Let's Make Robots!

Getting ready for the service droid :)

So I've ordered the Dagu service droid :) http://letsmakerobots.com/node/38776

I'm getting the service droid with a Rover 5 (4 motors/encoders), 4 channel motor controller and Dagu Red Back Spider.

I already have a Rover 5 with 4 motors on which I use the 4 channel motor controller and Red Back Spider. I'm powering everything from a 2S Lipo (3000mAh). You can see it here: http://letsmakerobots.com/node/31410 or on my blog: http://www.bajdi.com/category/rover-5/

On my current Rover 5 the 2S Lipo feeds 3 devices:

  • Motor controller
  • Red Back Spider
  • UBEC (powers the 4 servos of my gripper)

I also needed a separate 5V regulator to power the logic of the motor controller. You could use the 5V from the Red Back Spider but I prefer a separate regulator. If you power the motor controller and detach the 5V logic voltage you risk the chance of blowing it up. I destroyed one controller that way. I recommend you use the screw terminals to connect the logic voltage (and not the pins).

Another thing I needed was a 3V3 regulator for my wireless nRF24L01 modules (the Red back spider does not have a 3V3 vreg).

To accomplish the above things I soldered some terminals and 2 voltage regulators to a piece of perfboard. I later added a voltage divider to read the battery voltage, then I needed some transistors (for my "headlights") and so on... The board became a real mess after a while. I then started playing with Eagle and designed a small PCB for my Rover.

I started thinking about the service droid and what I would need to connect everything. The service droid comes with 8 servos. I think that's a bit to much for the 3A regulator on the Red back spider. I'm planning to add a Raspberry Pi + Camera (already have both), that also needs about 1A @ 5V (RPi+wifi+camera). I would prefer to power the RPi from the 5V on the Red Back Spider.

I've now come up with the following PCB to power and connect all the various devices on my service droid:

High resolution PCB: http://www.bajdi.com/wp-content/uploads/2013/11/Service-droid-PCB.png

High resolution schematic: http://www.bajdi.com/wp-content/uploads/2013/11/Service-droid-schematic.png

The board has 2 regulators. An LM1084 5A 5V low dropout linear regulator and a small low dropout LP2950 3V3 regulator. It has all the necessary pins and terminals to connect all the electronics. I chose those regulators because I have them in stock :) The servos will be powered with a 5 or 8A UBEC, since I have a bunch of spares from my hexapod projects :p

I would like to know what you guys think about it, any things I should add? And how you would power/connect all the electronics on a service droid / Rover 5.





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Bajdi- Thanks for all the good info on your site. I'm following some steps behind you with much less experience. Ive built the SD kit but now I'm studying the manuals and existing examples of people using the Rover 5/Spider/4 Channel Controller configuration to learn how to wire it together and program it. Baby Steps you might say. Once I get over the learning curve I'd like to create a basic wiring diagram for the SD that shows this combination and how to set it up, unless someone beats me too it. ;) That will help those that follow to get up and running faster.

Ah nice to know the 2 shoulder servos can be powered from a 2S Lipo. I'll make some changes to the PCB :)

The Spider is designed to take a shield made from prototype PCB so you could just use Prototype PCB instead of the custom PCB. Alternatively change the design of your PCB so it just plugs into the Spider as a shield. That would be a neater, more compact option.

Admittedly this is the only problem I see with the kit. The shoulder servos really need to be powered directly from a 7.2V NiMh or 7.4V LiPo to be at full strength.

The other servos are better working from 4.8V - 6V because otherwise they get a bit twitchy (too much power causes them to over compensate when trying to maintain position).

I must remember to update the manual with this info.

You mentioned that you thought 8 servos might be a bit too much for the Spider controller. I don't think this is really a problem.

4 of the servos (wrist and gripper) are little black duck servos. These are 2Kg.cm miniature servos and are unlike to draw much more than 500mA each when stalled.

2 of the servos are 3Kg.cm, standard sized servos for the pan/tilt assembly. Unless you head is going to be massive then these are unlikely to draw much current when moving and should draw almost nothing when the head is not moving.

The 2 shoulder servos are your only power hungry servos. These are 12Kg.cm metal geared servos which can easily draw over 1A each under heavy load. To ensure the arms are at maximum strength these servos should be powered directly from your 2S LiPo.


Note: The kits will start being packed on the 21st November 2013. They Should be shipped this weekend.