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Yet another cheap and easy to build motion platform!
Hello everyone,
I'm new here (I just joined last week). When I introduced myself to the forum I mentioned that I've built a motion platform. AndyT reply to my post immediately and requested that I post pictures, diagrams, etc. Well here it is. I don't pretend to know all the answer far from it. Actually, it's my first time doing this and I'm sure some of you guys are much better at this than me. Just before I begin I want to say that I took many great ideas from Jim at http://www.jimspage.co.nz/intro.htm and from Roland van Roy at http://www.simprojects.nl/. I'm sure you have visited these sites already. They are simply superb sites that give lots of information about building motion platforms.
Ok the specs are: (refer to the pictures)
- 2 axis platform.
- The top of the platform is 4 feet on the roll axis by 6 feet on the pitch axis. I figure I will have enough space for 2 passengers (One can dream no ?). The bottom part of the platform is 5 feet on the pitch axis by 3 feet on the roll axis.
- I needed a platform that could move around about 500 pounds.
- I use 2 Ford Crown Victoria 1997/1998 wiper motors. One for each axis. They cost about 50 Canadian dollars each if you buy them used.
- I used a pulley system. The more pulleys you use the less torque it creates on the motor shaft. The drawback of this is of course a slower movement.
- I use a high quality ansi standard #25 (1/4 inch between the links) chain and 2 sprockets (one for each motor) of 23 teeth. I needed about 25 feet of chain. The cost was about 100 dollars for the 2 sprockets and the chain.
- I use a modified car driving shaft in the middle of the platform (Thanks Jim for this one!) as a support. The universal joint moves about 35 degrees on both axis so that's more than enough. The driving shaft was cut and welded between 2 steel plates of 1 foot by 1 foot. I did not do this myself. I went to a welding shop and they charge me 50 dollars.
- The platform is made of wood.
- The power supplies for the motors are: One 24 volts 10 Amps and one 500 watts ATX computer power supply for supplying 12 volts. More on this below.
- It had to be cheap and easy to build (It cost me about 350 Canadian dollars and it was really easy to build. Trust me, if I can do this anybody can.
Some notes about the platform (again, refer to the pictures):
- I made sure that the chain for the pitch axis is exactly in the middle, perpendicular to the roll axis. The same goes for the roll chain. This is important because when you roll and pitch at the same time you want to keep the chain on the sprocket and in the pulleys! Since the driving shaft was right in the middle, thus blocking the passage of the chain, I had 2 choices. Make a hole in the middle of the shaft to pass the chains through or raise the driving shaft and pass the chains under it. I chose to raise the shaft.
- The pulleys are wide enough for the chain and they have a nice ridge so the chain does not come off. The pulleys and motors are held in position by metal corners (buy strong ones especially for the ones holding the motor as it generate a lot of torque). The pulleys are able to rotate on their own axis thus minimizing the friction of the chain against the pulleys. You can buy all this at any hardware store.
- The motors have 2 speeds (slow and fast) and they are usually ran at 12 volts (voltage of a battery in a car). I choose to run the motors at 24 Volts for fast speed and 12 volts for the slower speed. I need the slow speed for the wash out algorithm. Why 24 volts ? Well, they have a lot more torque and they turn faster. I know I'm probably running them over spec but I can't seem to kill these guys. They are just very tough. I've been doing a lot of stress tests and they are still in great shape. Besides, they are not that expensive anyway if I need to replace one.
- During my load tests I would put some weight say in the front until the motor could not lift the platform anymore. It's normal and I suggest you don't fight this unless you have a lot of money to spend on more powerful motors or you want to get into hydraulics). The key is to use the physics to your advantage. When I'll build my enclosure and I'll put panels and screens, etc. I will take great care at making sure that the weight of the front is equal (well as much as I can) to the weight in the back taking passengers into consideration. The same applies for left and right. If you balance everything properly, it will take very little effort to lift the platform. That being said, I will obviously not construct the enclosure with 2x4! I will keep the weight to a minimum.
- The platform can move about 15 degrees on both axis. It's more than enough as I'm building this for an airliner not a F-16! A note on this. When I started this project, I was tempted to build the platform so it could move say 30 degrees on both axis. I realized quickly that it's much more complex to build and when I finally hooked that platform to MS flight sim I noticed that 8 degrees is of movement is plenty. You will be tempted to do the same but please resist. You simply don't need that amount of movement. What we are interested in is the "start" of motion in a direction not the total amount of degrees the platform can move.
- One last thing. Be patient. I've built and rebuilt and rebuilt.... many times before I got it right. It's just the nature of this hobby. When I thought I got it right, I would perform some load tests (I would put lots of weight on the platform) and I'd realized that a pulley was misplaced or something else was wrong. Whatever it was, I would take it apart and fix it. It took me about 80 hours to build this. One very last thing. Don't be a hero. If you cannot do something than pay somebody to do it. You will save a lot of time. In my case I did not know how to weld and I did not want to know either! So I paid 50 dollars to a guy to cut and weld the driving shaft to the steel plates.
I hope that this example will help you with your project.
cheers
Louis