Updated Charging Circuit

Update 4/21/08: Click here for the latest wiring schematic.

A few weeks ago, I’d posted my simple charging schematic that I’ve implemented in my Artoo. It allows me to switch between normal usage or battery charging. I’m not an electrical engineer by any stretch of the imagination, and my wiring diagram wasn’t very elegant, but the setup worked fine.

Bob Ross pointed out that I really didn’t need to isolate the ground connections in the system while charging. This would save me one relay, and power to run it. He was kind enough to redraw the simplified circuit for me, and also came up with an improved design which allows me to run my droid (low load systems) from an external 12VDC power supply while the batteries charge.

Now that I have my new 60A relays I’m hoping to wire this up over the weekend, but thought I’d share it here first.

[PDF Version]

Thanks again Bob 🙂

Posted by Chris on January 24th, 2008 in Electronics | 3 Comments

Tags: , , ,

Relays for Charging System

I’m using simple 12V SPDT automotive relays in my droid to control switching of power between normal operation and the charging system.

Typically automotive relays are 30A/40A, but I felt I needed something a little bit more substantial. I found these 60/80A relays at SkyCraft for less than $5, which is very reasonable. I’d tried to find something local but came up blank.

The only catch is the terminals are 3/8″, instead of the more normal 1/4″, luckily I found some at Pep Boys for a couple of bucks. I’m hoping to work on getting my electronics re-installed this week and i’ll swap these into my setup at the same time.

Posted by Chris on January 23rd, 2008 in Electronics | 1 Comment

Tags: , , , , ,

R2 Charging Jack/Socket

I feel like I’m on the home stretch getting R2 back together. Tonight I worked on the electronics a bit more.

I plan on re-install the same three 12V 7Ah batteries. However, when the skins go on it’s going to be hard to charge them. So I’ve devised a simple circuit using some automotive relays to allow me to isolate them from the main electronics with a single switch, and charge from an external plug that will run to my Vector Charger.

I wanted to mimic something similar to how Luke charges R2 on Dagobah. The original plug used is some sort of stereo audio jack, but in real life it would almost certainly short when inserted, so I needed to find an alternative.

ESB R2 - Charging Port

After a lot of browsing various electronic and automotive stores I’ve decided to use a 12V car accessory plug and socket for bunch of reasons –

  • They can easily handle the 10-15A the batteries will pull when charging,
  • It’s hard to short the system when inserting it, even if everything is live,
  • If someone was to accidentally plug him into something unexpected – I’d rather it be a 12V device which is almost guaranteed with this type of plug. I couldn’t say the same if I’d gone with some other type of high-voltage plug,
  • Replacement parts are easy to find if I ever need to make up a new charging cable,
  • Theoretically I could plug-in and charge or run other 12V devices off of R2.

I’m going to install the charging port in the same spot as seen in ESB, and I need to make a shelf to hold everything as there’s no frame behind the hole. I cut a curved piece of aluminum that would become the shelf.

I then bent an angle in it to secure it to the new speaker bracket I made a few days ago.

Everything is held in place with just two 8-32 screws

Originally I was going to use a heavy duty DPDT toggle switch to isolate the batteries

But I had problems finding a suitable switch that would work. The one shown above was to really clunky, hard to toggle and not quite heavy duty enough to handle the potential load the drive motors would pull from the battery. So I opted to use a much smaller switch that would toggle the high load through a few standard 30/40A automotive relays. I’ll probably end up replacing these with 60A relays when I get a chance.

To mount the smaller switch I cut a small piece of acrylic and drilled a few holes that would attach it to the 12V socket plug.

I then heated it up for a few seconds to bend it into shape

I also added a status LED so that I’d know for sure when R2 is switch on

Here’s a shot of the back of the automotive relays that will do the switching. I could have probably just used one and just isolated the positive line, but I decided to play it safe and use a second to switch/isolate the ground line as well.

I’ve just bolted them below the support bracket using the same screws that holds the 12V car socket in place.

This is the setup with all the wiring in place.

When the light is green R2 is on, and the charging port is disabled/isolated from the batteries

When the light is off the charging port is live and connected to the batteries. All electronics in R2 are off and I can safely plug in the charging cable which will glow red to show it’s connected to the batteries.

At some point I may also add some red LEDs inside R2 to mimic what’s seen in the movie.

All that remains is the wiring diagram. This is the hand-draw one I worked from, but I’ll try and come back later and clean it up and verify that it matches my final configuration.

Again note – I’m not an electrical engineer so please double check everything if you’re going to try and implement what I’ve done.

Posted by Chris on December 27th, 2007 in Electronics | 2 Comments

Tags: , , , , , ,

Dome Drive – Possible 24V Solution

It does look like I may end up trying running the Pittman Dome Motor at 24 volts as a test going forward. I can’t see adding a gear at this point in time.

This leads me to my next problem, my battery sub-system is all 12 volts. I’ve had no need for 24 volts in the body as my main drive motors the NPC-2212’s can only run at 12 volts, and everything else is stepped down from 12 volts using Dan’s distribution board.

I know how easy it is to create 24 volts from two 12 volt batteries, which I have and can do with what I have on hand, but configuring in series and then tapping off for 12 volts adds a level of complexity for charging the batteries w/o removing or rewiring each time. There’s also the problem of one battery draining faster.

For those unfamiliar with creating 24 volt from 12 volt batteries, this is a really good site explaining how and some of the problems.

One of the problems he talks about is charging unbalanced batteries in parallel and something called a “Battery Equalizers / Balancers” which can fix this problem. The unbalance comes from the 12 volt tap on a 24 volt system, and the two batteries discharging at different rates.

I’m hoping someone has tried an equalizer in their droid before. I’ve found a lot of information on equalizers, mostly large clunky boxes for RV’s and buses, but there are smaller version out the like this one.

What I’m hoping is to use the 3 12 volt 7amp batteries I’m using right now in parallel, and then combine two of these in series for 24 volts. For charging have a switch/circuit to disconnect/isolate them from anything in the droid and reconfigure just in the parallel state to charge all 3 batteries together.

Tall order I know without causing a short circuit or fire 🙂

Posted by Chris on December 5th, 2007 in Electronics | No Comments

Tags: , , , , , , , ,

Back from C4 – R2 Lives!

I’m back from C4 and R2 performed really well.

I was able to finish the basic structure, the dome, the electronics and he was fully RC’d and running around most all of the days at the con. As you can see I also fixed the dome and got most of the blue painting done. Battery life was excellent and the Roboteq AX3500 speed controller / NPC-2212 combo worked out great. I was in both races and the little guy far exceeded my expectations of what I thought I’d be able to do at C4.

This is me driving back to the hotel on the last evening ready for transport back to the Bay Area – Yes I drove him home 1/2 mile to the hotel without incident.

Chris and R2 - C4

I still need to sort through my photos and upload them and post a full write-up, but wanted to post something other than having my dented dome as the top post in the blog 🙂

I also intend on going back and catch up with blog posts on all the building I did before I left.

Posted by Chris on June 1st, 2007 in Events, General | No Comments

Tags: , , , , ,

Thinking about dome electronics placement

With all the dome work yesterday I had time to think about it’s electronics and how I’m going to lay things out.

I’ve seen some people bond the dome ring to the dome, but I don’t think it’s such a good idea for me. For one I’m using the dome base plate that supports the periscope, and I’m thinking I’ll attach other things to it as well. The base plate is also bigger than the ring and it restricts access from the underside, so there would be no way to get in and fix a lot of things.

So the dome will split in two and I know have the dilemma that I’ll need decide where to put some things, either in the base or up in the dome, and then worry about running wires. For example, only the lift mech needs to attach to the dome plate, and it makes sense to put the weighty batteries down there too.

Initially the dome will contain the following this that are powered

  • Power Distribution Board – 12v in, 9v, 6v, 12v out
  • Front Logic -9v
  • Rear Logic – 24v
  • PSI’s- 9v x 2
  • Holo Projector Lights – 12v x 3
  • Vex Controller for Periscope Lift Mech – 6v
  • Batteries – 2 x 12v
  • Lift Mech Speed Controller – 12v

Later on I’ll be adding a few servos attached to the panels.

I think I’m going mount most everything on the dome base plate and run 3 power lines up into the dome with quick release.

Here’s a rough idea on layout

R2 Dome Electronics Rough Layout Idea

Posted by Chris on May 7th, 2007 in Dome, Electronics | 6 Comments

Tags: , , ,

Real Battery Harness

A few nights ago I finished the last few parts of my frame structure and also constructed a real battery harness that will sit above the center leg mounting plate.

It will hold 3 standard 12v 7amp batteries in the droid a nice low center of gravity. I’m hoping the design will allow easy access for charging and removal.

Real Battery Harness

The bottom plate is the center foot mount and attaches to frame ring #4.

It’s based on a photo I saw on this site and thought it was a good design to hold the batteries.

Posted by Chris on May 5th, 2007 in Body, Electronics | No Comments


Newer Entries »