1800 W 80 V PSU for servos

I've put together a simple unregulated power-supply for use with the DC servos that are going on the cnc-mill in the near future. The design is as simple as it gets: 230 VAC input, fuse, 2-pole switch, inrush-current limiter, 1.8 kVA toroidal transformer with twin 30 V secondaries in series, diode bridge, and finally four 10 000 uF electrolytes.

I did a load-test by hooking up various random devices I could find. It didn't exactly go as planned, since most stuff I could find is designed for 230 VAC. I had a resistor rated at 2000 W, a 500 W halogen lamp, a small oven etc. so you would think I could have gotten up to full load? But no, the stuff rated at 230 VAC doesn't dissipate nearly as much energy at 70 VDC 🙁

I was surprised at the largish voltage drop measured, but it's totally unregulated so something like this was to be expected. At about 7 A load I measured a voltage ripple of 1.4 V - which seems OK. A fit to the latter points show an effective series resistance of about 1.9 Ohms for the transformer. I've extrapolated my measurements with dashed lines up to around 1000 W which I estimate is the maximum we will ever use. Hopefully the voltage drop will not be problematic, since overall the system is under closed-loop control.

A new, faster RMG

Rob Guyatt, designer and builder of RMG winches has answered to the challenge from the super-quick arm-winch camp by sourcing a new motor for the RMG280D (the most popular model for an IOM). The motor is about 15% faster than the previous model, while torque is about the same or slightly less.

Couple the new faster winch with a bigger diameter drum, which trades torque (force on the sheeting line) for speed, and Rob has been measuring sheeting times, using a typical 310mm travel, which are very similar to what is achieved with an arm-winch. Above the RMG 280D with standard 26 mm drum in the middle, 32mm drum on the left, and 42mm drum on the right.

Here's the latest from Rob's drawing board (well, CAD program...). A spring loaded drum ! If I understand correctly one spool of the drum is fixed (and could be a spiral spool), and the sheeting line is connected to this spool. The other spool is spring loaded and will take out any slack in the return line of an 'endless loop' type sheeting system. Especially useful if the sheeting spool is of the spiral type, since the amount of sheeting line travel per revolution is then variable, and the spring loaded spool absorbs this variability.

Here the new RMG is sitting in the Noux RC-tray. There's just about room for the largest 42mm drum (flange outer diameter is about 50 mm). There's a thumb-screw on the drum, but it's a bit too high - the lid won't go on like this, so perhaps I'll grind down the thumb screw to about half its height. I've also taped on some supports for the battery, and a 6-cell AA battery fits comfortably. The idea for the rudder servo is that it will hang in an L-shaped bracket from the vertical wall of the RC-tray, final design and wether it will be stiff enough is still to be confirmed.

Update 2007Feb14: Rob has now finalized the design of the spring-loaded drum design and is offering it for sale at www.rmgsw.com 

X-peak 3 plus

I've sold my Cockatoo (some setup notes and pics still to come I hope...), and along went most of my other gear, batteries, charger, Tx, two RMG's etc. So I'm slowly replacing everything during the long and dark Finnish winter - hopefully to see an operational new Noux sailing in April '07 or so...

Here's the new charging system - very similar to the one I used previously. The charger is the new updated 'Plus' version of the Jamara X-peak 3. This charger is also sold under numerous other names (swallow, etc.). The plus version has slightly increased maximum charging and discharging current specifications compared to the old one, otherwise it's mostly the same. A backlight has been added to the lcd screen - useful in dark and dim places. It runs off 11-15 VDC so at home I use a switched mode powersupply (black, right) to transform mains electricity to 12 VDC at max 2.5 A. I chose the 30 W PSU for it's convenient size, it fits in the toolbox whenever I go sailing, but it does mean I'm limited to max 2.5 A charging current. The switched-mode circuitry will accept any AC voltage between 100 and 240 V, so abroad I can simply use an adapter (white plugs, bottom). At a sailing place without mains electricity, an adapter for the cigarette-lighter connector in a car (left) can be used.

The new batteries are AA Sanyo cells with a capacity of 2700 mAh. I got the spot-welded from beatcom, much better than risking damage to the cells when soldering by hand. I've fitted a transparent heat-shrink myself - I'm hoping it will allow me to spot any leaking cells or corrosion on the contacts. I got a pack for the Tx also, which with the DX6 voltage regulator mod should last for more than a whole sailing day.

Since a few years now I'm using the Deans Micro 2R plugs. It's a nice system where the plugs are identical, you just switch polarity between battery and charger (in my system the battery + pole is connected to the pin). I like the fact that these have no moving parts, are gold plated, and can be assembled without any special tools (just a soldering iron). They're also small (I understand these are popular with indoor flyers) and are rated for a high current.

A new Shuffle


Based just on images on the web, I immediately decided to pre-order the ultra-cool new Apple Ipod Shuffle.

I got free shipping when pre-ordering, and the good news is that applestore actually held their pormised shipping date - it arrived by courier today !

After just 10 minutes with the unit I'm almost certain it's a 'keeper'. It's tiny, very light, has a built-in belt-clip, and stores up to 1 Gb. One feature I missed on my previous mp3 player was a FF/REV within one song, but that doesn't seem implemented... a keypad-lock similar to cell-phones is a nice touch though.

The manual suggests first installing iTunes, and then plugging in the unit. Without iTunes, I tried just downloading songs onto the shuffle but that won't work, why Apple ? why ? 🙁 . I don't need or want iTunes, so I'm thankful to people like Martin Fiedler who take the time to create workarounds. Martin's shuffle-db worked like a charm !

More 2.4 GHz radios and modules

Predictably, more and more RC-manufacturers are introducing "crystal-less" 2.4 GHz remote control systems.

Spektrum has come out with a new 7-channel system called the DX7. It's not on their website yet, but Horizon hobby has it for sale. This one is supposed to be a radio for 'real' models, not only meant for park-flyers like the DX6. I wonder if there will be a problem with 'CE' approval with regards to the output power - A rumor I heard was that the 'CE' marked version of the DX6 has a reduced output power compared to the US model ??

There's also a new player on the market, Xtreme Power Systems, which will introduce their new xtremelink module+rx combo shortly. They too promise increased range and reliability. In contrast to Spektrum, who talk about either 40 or 80 simultaneous working modules, Xtremelink claims up to 390 000 simultaneous active modules ! Also, up to 1 mile ground based range. Pricing and deliverytime still open.

The Futaba modules I noticed back in January were on display at Model Expo in the spring but the local agent said it would take some time before they come to market. I've detected no activity in the Futaba camp so far...

For the new boat, I've bought myself a DX6. Naturally I'm going to mod it a bit before use ;). I've ordered a switched-mode regulator which supposedly will reduce the current drain of the Tx a lot. Also, I've gotten very used to the 'no antenna' look and feel of the Futaba 3VCS with a Spektrum module (especially usefull when it rains, the whole radio goes inside the Tx-cover, no leaking hole for antenna needed). But the stock DX6 has an antenna that sticks out :(. Cell-phones have had internal antennas for years and nobody buys phones with external antennas anymore - so the DX6 antenna needs to go inside the case too ! I'll report later how that goes...

Temp controller for curing box

Curing epoxy mouldings typically requires elevated temperatures (+ 40 to 70 C) for 4-12 h. Previously we have done this in a cardboard box with a car-heater continuously blowing hot air into the box. By adjusting the number and size of holes in the box the temperature can be crudely varied.

Here's an attempt to create a better heater with temperature control.

Temperature controller with display and input buttons on the left. White temperature sensor in the middle. 200 W heater-blower box on the right.
Continue reading Temp controller for curing box

Futaba strikes back !

One of the most exciting things for a while now in the R/C world has been the 'no crystall' radios operating on 2.4 GHz from both Nomadio and Spektrum

Now it appears that the big players are entering the game. These pics of an upcoming Futaba product were just posted to the IOMICA forum:

The Rx on the right supposedly has two internal antennas (no wire antenna exiting the Rx) and weighs only 14g !

These images were found at
http://data.robbe-online.net/robbe_pic/P1001/P1001_1-F1901.jpg and
http://data.robbe-online.net/robbe_pic/P1001/P1001_1-F0901.jpg
but otherwise there seems to be very little information available...

If anyone knows more about this system please post a comment below !