I’m almost done with prepping the aluminum skirt.

With the olive paint and screws this pieces would looks more at home attached to the Nautilus or some Steampunk project don’t you think?

I’d bolted on the strips a few weeks ago and had given it a coat of primer, but I still needed to go back and file down down the  strips a bit.

I’ve also filled some of the seams with Bondo. All that’s left is to give it another shot of primer then it’ll be ready for the white top coat.

I’ve been busy the last few days and not had much time for building. I did get to work on the ankles and legs a little bit more and I think I’m pretty much done, minus one small piece that I need to buy something for to fix.

I’ve mentioned this before, but now that the ankles are back attached the to the feet it was hard to slip the battery boxes over the motors.

The right box went on no problem but I had to make a small adjustment to the left one one and open up the hole a tad. I also had to shave a little bit more off the top of one of the motors, to get the box to sit flush with the foot.

The boxes are really springy with the hoses attached and and there is no way the two screws that are supposed to push fit into the slots will hold the boxes flush to the feet. At least I couldn’t get it to work satisfactorily.

I think I’m going to have to come up with another method of securing the boxes, and will probably use some super strong magnets. That way I don’t need to fiddle with setting screws in tight spaces.

I ended the evening with attaching the legs to the ankles. I used pan head bolts, lock washers and fender washers instead of the countersink Phillips. This will hopefully give them more substance and grip on the legs. The 10-24 Phillips work their way loose way to easy even with thread lock glue, and I’ve had a few wiggle loose during a single outing and sheer off. If this fix doesn’t work I’ll knock out the 10-24 threaded inserts in the legs and use 1/4-20’s bolts instead.

I’m going to try and paint the bolts and washers white to hopefully hide them a bit.

That just leave the battery harnesses and back foot strips to silicon in place, and of course the magnets to hold the boxes.

I’m trying to resolve a lot of issues before I get to fully re-assembling my droid. It’s a real pain to pull him apart and I want to fix a bunch of things that have been bugging me like the slow dome. Another thing on my to-do list is the speaker.

I chose to use a 15W Horn Speaker on the recommendation of someone, and it does reproduce R2’s tinnie/metallic/middy sounds great. The price was right at the time too, but I think I can do better. It’s not as loud as some R2’s I’ve heard using in similar setups – which is my main motivation to find something different. The horn also takes a lot of space and I’m hoping to re-appropriate that for some electronics.

I’ve spend some time learning all about Ohms, Watts, Dbs and how they related to speakers and amplifiers. We’ve all heard the terms when we go out and buy the latest home theater surround system, but I never really understood what that meant in reality, e.g. you have 4 x 4 ohm 30Watts speakers and how that turns into how loud the speaker system is in Dbs.

Part of the problem deciding which new speaker(s) I should use is that the specs on the CF3 sound system I’m using from ACS are rather vague. They say the built in amplifier can deliver 20 Watts, but they don’t say if that’s across both channels, or if it’s per channel. And they don’t state how many Ohms the speaker should have.

With some digging I found that the sound board uses an AD 1994 chip, and here’s a summary of the specs

• 105 dB dynamic range
• 2 x 25 W output power (6 Ω)
• 1 x 50 W output power (3 Ω)

As you can see it’s rated at 50W for one channel or 25W on two. A lot more than the 20W than that ASC rates the CF3 system at. Also notice the 3 and 6 ohm for the speakers. Most speakers you find are either 4 or 8 ohm, maybe 16. Even if the amplifier can only do 20W, my current horn speaker falls short of taking advantage of that.

Tomorrow I’m going to call them up and ask some questions and report back.

Useful links –

• CF3 Manual and Data Sheet
• AD 1994 Chip Spec
• All about Ohms, Watts, Amps and Speakers

I’ve continued to do research and testing on my dome drive system, and it does look like I need to change the motor out for something with a bit more humph.

It seem that a few people are happy with driving the recommended GM9413 Pittman motor at 24V instead of 12V with good results, but I really want to avoid introducing the complexity of 24V into my system just for one motor. It will complicate charging the batteries at best and the shorten the system run time between charges, and at worse reduce the overall battery life unnecessarily.

In the last day or so I’ve got a lot of great advice from fellow builders, including a lot of links that helped me decide which new motor to go with. I wanted to stay with a Pittman if I could to hopefully avoid redesigning the dome drive system, and it looks like one of the variations of the Pittman GM9236 would work. It comes in a few different gearings and voltage ratings.

There was one specific 12V version I was shopping around for, the GM2936S018, which delivers about 3 times the torque, and about twice the RPMs of my current motor, but it was around $130, and I’d rather find something a little cheaper if I could. Then Bob pointed me at another GM9236 model that was very similar, but only $23 at a surplus store. They’re used/surplus but probably worth the risk so I ordered one to try. It has very similar specs delivering a lot more torque and hopefully went it’s installed, spin the dome a little faster 🙂

So here’s the links I used for my research and where to find motors

• Pittman website – not very good if want to look up older models, and you need to register to download specs.
• Skycraft Surplus – carries a lot of surplus motors, and right now has the GM9236 in stock.
• Skycraft’s Pittman Motor Guide
• Click Automation’s Pittman Spec and Price List– good overview and side by side comparison of a lot of the Pittman’s out there.

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 🙂

Okay, I promise this will be the last KHF post for a while. I bought a bunch of plugs from Ace and tried them out tonight and I think I’ve found a keeper.

It’s a small nylon plug that normally leafs out when a nail is pushed through, but I removed the nail and tapped the hole for a bolt.

I’m pretty sure it’ll hold for now, but would pull out if I gave it a really good tug. The good thing about this plug is that the expansion happens at the top in side the aluminum KHF holding it snug.

I also tried a small metal wall plug, but it didn’t work so well and deformed when expanded in such a tight space in the tube. I’d probably have to replace it every time I took the hoses off, it also didn’t grip the hose so well as the nylon one.

Tonight I’ve started to work on some dome stuff, including the dome drive system which has been bugging me for months.

I’m using Darren’s dome drive kit (based on Atomic Pickle’s) and it uses the Pittman GM9413-2 geared motor. Spec’d at 12v, 19.7:1, 142RPM.

To me it seems sluggish and rotates slowly compared to a lot of other droids I’ve seen, especially when I change direction. It could be the weight of the dome, which is around 17lb with all the accessories. Including all alu parts, like HP’s, surrounds, radar eye, dome ring, and periscope, plus the batteries, smoke/fire-extinguisher etc. etc. But I’m sure I’m not the only one with a heavy dome.

I’m wondering if others are experiences sluggish domes who are using this Pittman either from Darren’s kit or from AP’s? Especially if your dome is heavy?

According to the GM9413-2 data sheet on the AP site, the motor is rated at 12v, which is what I’ve been running it at, but on the motor itself the label says 12/24v.

I’d rather not run it as 24v if I can help it – but if it would help I could re-configure some of my batteries as a last resort.

The only other thing I can think of is the slight sagging in the mounting, but the motor is making full contact with the rockler bearing. Maybe it’s not doing a great job of holding on or maybe pushing too hard against the rockler bearing?

I know many Sennaites are using the Saturn motors at 24v for the dome, but I’d rather not switch class of motors right now. I’ve posted to the Yahoo! Group to see if anyone has some suggestions specific to the Pittman motors.

Edited to add some videos. Here’s the Pittman running at 12v directly off a battery, no speed controller so startup is instant and it looks okay right now which I don’t understand. I’m wondering if it’s a speed controller issue, or maybe even a problem when he’s angled in 3 legged mode. mmm.

And here it is running at 24v – super fast I know, but I’d rather the top speed be fast and I can slow it down with the transmitter/speed controller commands.

Now to troubleshoot why the 12v spin seems okay.

I did some further testing tonight, and held the body at an angle while the dome spun. Man, is there a lot of force whipping around while it turns, even at the slower 12v. I can feel it struggle on the up swing as the two heavier side of the dome comes around. 24v helped a lot but I need to go back and put the speed controller back in the loop to confirm my test and see how snappy it is looking left and right.

More re-assembling tonight after painting last week. I did a mix of things from the feet to working on some skin panels.

I got the feet and ankles back together, and using the hex bolts worked out great. It was a breeze installing the ankle details.

With everything R2, there’s always a few steps back with a dozen forward. Today it was the braided hoses. I’d planned on using these expanding rubber plugs to hold the cables in place, but they didn’t quite work as I’d hoped. For some reason rather than bunching up and expanding the nut inside just moved/ripped up the rubber with minimum expansion as shown. The ‘bulge’ at the top being the maximum width.

Back to the drawing board and Ace Hardware tomorrow to look for an alternative. I was tempted to try Douglas Olson’s KHF System again, but space is very tight and they’ll not work for me with the JAG feet and drive system.

The other problem I had was once I tried to install the battery boxes they wouldn’t fit over the NPC motors. All the test fittings I did while filing down the tops of the motors was done without the ankle on the foot, so now I have less room to bend the box over and down onto the motors. An easy fix, but I was hoping to get the feet, ankles and legs back together tonight and now I can’t.

I also worked a little bit more on the frame and got the front vents installed and attached to the frame at last. Not sure how I’m going to fix in the blue surround at this point. Maybe silicon, but I want to be able to remove it easily with the skins. The fit is tight and I can see when removing the skins that it may get pulled off with little effort.