![emot-4.jpg](https://modelboatblog.tedatum.com/wp-content/gallery/jmotors/emot-4.jpg "The shaft is a rather small 1/8\\" diameter. There are splines to help hold whatever is installed on the shaft.")
Dan Kautz
The XBee Meets the Propeller
I got some time this Labor Day weekend (2011) to get an XBee interfaced with the Propeller processor. The pictures show the tiny interface board required to change the pin spacing from the XBee to fit the spacing on the Prototype Breadboard. This is some more of the micro soldering I have written about before. That’s all this board does is change the pin spacing.
What I can see here is the XBee running in full duplex. That means it can listen and talk at the same time. Just like talking on the telephone. Well, maybe I can’t do that but the telephone does it very well. 🙂 That’s a pretty big deal in the world of communication and has certainly removed some concern from me determining if this system will work fast enough for good control. I think that is not an issue at all now that I can use the Propeller.
Dedicating one of the cogs (processors) in the Propeller to just manage the communications means I can do whatever else necessary with the other cogs and not slow down the two way communications with the shore unit.
HB-25 Motor Controllers
As you can see I have two of the Parallax HB-25 Dc motor controllers now on my workbench. They are rated at 6 to 16 volts (DC) at 25 amps. That should be rugged enough. I figure I only need one for testing but I would like to run twin screws on the demo boat.
The controller is just over 1 ½ inches square and about the same in height. That makes them very small for the power they can handle. What makes them so high capacity is the attached micro cooling fan under the component board. There is a machined heat sink between the fan and the controller chip. The heat sink is drilled with holes like Swiss cheese.
When I first saw these controllers probably a few years ago, my first thought was these were perfect for electric motor control on a model boat; actually large electric motors on a large model boat. Now I get to test my initial premise.
Electrics and water always has me concerned. It is very possible the boat may be operated in times of light rain. So one of my challenges is how to mount and protect these controllers from moisture. If it was easy, anyone could do it. Other than a complete sinking, it’s a matter of splash control.
Then I just need a hull that is unsinkable (Titanic?)
Trials will of course be run in calm waters but who knows what thrills may lay ahead when confidence and reliability allow the operating envelope to be expanded. Maybe build the first model icebreaker with a balsa wood hull. Uh… no, that can wait.
Hot Props
The Texas heat is killing me in the unconditioned shop. It is keeping me away from experimenting with the Xbee and the Parallax Propeller (computer). The inside temperature in the garage shop has been hovering at 100 degrees while the outdoor has been 105 to 107.
This is NOT for a few days mind you. We have been getting this temperature every single day for over two months steady. Yes, every day.
My new shop fan helps a lot at 80 or 90 degrees but near 100 or over it is just like sitting in a blowtorch. No fun. I tough it out in the morning (on weekends) for a few hours but by 10:00 or 11:00 AM, it’s breaking over 100 again.
Actually the little control computers don’t mind this kind of heat. They are very low powered so don’t generate much heat on their own. It depends on how much power you pull from them. I can’t say that about the PC computer that I use to write the application software. I believe it is maxed out with 105 degree ambient air temp trying to cool the processor, hard drive and other PC components. I had one of my CNC computers (another machine) shut down from the heat after running almost four hours. Luckily I had just finished the part I was cutting and was bringing the HB2 back to home position. I don’t do long CNC runs anymore in a hundred degree shop.
I like the newer Propeller processor. With 8 processors or “cogs” it is a “hot” multitasking little controller. That is figuratively hot. Not environmentally hot. I definitely have it earmarked to be the processor on the boat end. I was thinking about it today, and I am going to also use it on the shore terminal.
I don’t think I need its multi cog power on the shore unit but my thinking is to keep the software programming the same “flavor” for the entire project. I can put the BS2 STAMP to other uses.
I have a few ideas how to design the shore transceiver. It will be a small standalone unit. I was originally thinking of using a PC or Net Book as the shore terminal with just an XBee for the communication. The more I thought I decided a control box would be a better interface and not so expensive (to fix) when getting too close to the water, if you catch my drift. A BS2 would be plenty of computer smarts to run things but as I said above, I’m going to opt for another Propeller.
But hey! Who says I can’t play with my options.
With the Propellers at both ends of the communications I can dedicate one or more cogs in each Propeller to just run the XBees at their best transmission rates. Decision made.
If the Texas heat takes a few days off over the holiday weekend, I plan to get a lot more done with testing the com link. Then I can start designing the Propeller proto boards for the real link.
I also discovered there is a new Propeller multicore processor in the works. It will be bigger and hotter that the present Propeller. But hotter will also be the heat it generates. I suspect it will be more useful in applications where enough “shore” power is available and chip temps can be controlled. I think the Parallax Propeller has a great future and will be useful for a long time.
Early Boat Thoughts
Now that I have been working with the proposed control system I realize the subject boat (to be controlled) does not have to be as big as I first envisioned. The first tests will be remote basic control. Just taking control response and range into consideration.
To me that indicates I can run early tests on a smaller and cheaper to build model boat. The smaller size will also mean a smaller single motor will be needed. Less battery size will also be a benefit.
For these reasons, I am considering downsizing my first vision of the model boat required. This change justifies my plan to start with the control system first. I am learning what I need as I go. I am not sure when I will be able to commit to the actual boat selection.
At first I was thinking the bigger the model the better. Still a good plan but a lot more cost than needed for an untested communication system. I was thinking of about a 48+ inch length and a 10-12 inch beam. Now I am considering 24-36 inch length and as wide a beam I can find for stability (and space to work)
If plans go astray, I will have less invested in this experiment. My biggest concern is the reliability of the wireless network. I will spend a lot of time testing that before I have to figure out how to put it in the boat.
The second concern is water proofing. I have built model boats and know I have to seal the electronics from the moisture. I am using an experiment board for now. Next step for installation in the boat will be a prototype board. This will provide permanently soldered components and connections. It will also be larger than a custom designed circuit. I do not know exactly what size the prototype board will be. I have a general idea from the boards I know that are available. So that is why I think I can downsize the model.
The truth I have considered is the first test vessel can be a very simple and crude “pointy box” with a motor and rudder. Ugly yes, but a consideration. I’d rather have a scale model looking test bed for the pictures, but I can be practical if I want or need to be.
When I get to GPS and other enhancements, then I will have to go to a larger test platform. Perhaps then I will include dual motor controls. Fun to think about but first things first.
The Propeller
I can say the Propeller is on the bench. But not the one that spins in the water. This is the Propeller that will serve as the brains of the project. The Parallax Propeller computer chip is actually the larger (.9 x.9 inch) chip near the top of the blue circuit board.
This is a kit for learning how to program and use the Propeller. I am 95% certain it won’t be the same propeller I will use in the actual project. (I’ll buy another, they’re not very costly.) The red and black wires you see on the board, I have just installed. They serve as the “basic wiring” to energize the Propeller on the test board. They are now a permanent requirement for the set-up to power up the processor. You can see the wiring on the box lid.
The USB connection is needed only to program the computer or read text as output in the debug mode. The 9 volt battery powers the Propeller, which incidentally only requires 3.3 volts. There is a regulator included on the Blue board.
I’ll soon have an XBee plugged into the Propeller board.