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The Motion System
After a lot of trial and error to find the right way of making the motion
system both responsive enough but cheap enough we finally chose this solution.
After the raw fabrication is finished paint it not only for looks, but to
prevent rust and corrosion. We found a nice epoxy paint at the good old Home
Depot (maybe I don't go there enough but I don't have much to make fun of).
Epoxy paint can take a long time to dry to make sure its totally cured before
you work with it. Also one benefit of the epoxy paint is if you weld this
yourself, and its your first welding project, you can hide your welding
'talent' under a good layer of paint.
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The drive system's heart
After trying four other completely different motion systems we chose to modify
a standard automotive winch from harborfreight.com (get the extended warranty,
and keep the parts). This motor is very high torque, and we only need a max of
15 Degrees of off set in either direction for this project. At about $50 it was
way below the next option in price, and with some basic modifications it fit
our needs perfectly.
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Bearings and pulleys...
For the actual transfer of power from the modified winch motor to the platform
we will be using some garage door pulleys. These are really built strongly and
are very inexpensive at 10.00 each. We will weld on of the bearings so it wont
spin any more and mount it to the winch. A trip to AutoZone, Pep Boys or Home
Depot and a 10.00 belt and we are in business.
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Next up is modifying the winch. Basically
we don't want any of the mounting bracket, cable, hook, or reel. There are 2
hex bolts on the bottom that will need to be removed to realize it when it is
taken apart a small shaft will come out with the reel, save this and set aside.
Also there is a lot of heavy grease. Usually there lithium grease in this type
of unit so be cautious with it.
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| With the mounting bracket removed we can
see the winch motor and gear house are self contained. There are a set of
spider gears inside the motor that interact with a gear on the end of the cable
reel. This can be removed with a simple screwdriver and bolted to the new
pulley on our project. Now just a heads up here, the housing to this is cast,
not machined. So if you drop it or hit it too hard in this process its possible
to crack or break the housing. This would be bad as cast metals are extremely
difficult to weld. |
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Looking at the bottom of the winch motor
we can see the 2 bracket mounting points the old reel and mounting plate were
mounted to. We will be using these to mount the motor to the base of the force
feedback platform.
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| With the new pulley attached, use a
standard 1/2 inch bolt about 1 3/4 inches long to mount the pulley to the
motor. I recommend using an impact wrench to secure it as the motor spins a bit
making it hard to get it real secure. Additionally I took and welded the pulley
to the barring and the barring to the bolt to make sure things wouldn't come
undone after assembly was complete.
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Next up, mount the assembled motor to the
frame in the space under the supporting brace. Use some good high quality bolts
if you have access to them to make sure it stays good and secured to the frame.
One thing as a hint here is use some washers as shims between the frame and the
motor so that you can make sure you get a good proper fit on the belt to the
other pulley.
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| To complete the main part of the motion
system we will be building out the upper bearing assembly. This is really easy
and straightforward. Just weld a 2 foot piece of the 1X1 that we have been
using to the top half of the bearing. This cross piece is what the upper
platform will be resting on. Secure the upper platform to this piece with 2
bolts. Attach the bearing (spinning freely) to the upper portion of the base.
One in front and one in back with a good long bolt, taking care not to
overtighten it.
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With everything attached add the belt and
check for snugness in the belt. If you can grab hold of the mounting arm up top
and force it to slide you need to get a smaller belt or remove some shims. You
should be able to put a fair amount of weight on this with out it budging. Like
one's body weight. The last thing you would want is the belt slipping in use. I
know this is a crappy pic, but the belt is there if you look hard enough.
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| Mount an upper platform bearing system in
the front of the simulator as well. Alternatively, up front you could use a
flanged bearing and a bolt as an axel to make it lower profile and sleeker
looking.
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Place the platform onto the support arm
on the base and attach with a couple bolts. The belt will be on the inside of
the platform so if you want to make a guard for this you may. Or not, if you
are into the whole school of hard knocks thing. |
| Attach the power cables from the winch
controller to the motor and secure firmly. The only real caution here is clean
cable management and arcing. Don't get sloppy when it comes to power, kinetic
or not. Clean cable management means no cables to get stuck in pulleys and
gears. And securely attaching the power leads helps prevent arcing and fire
hazard.
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Next up is gutting the main controller to
the winch. We will basically be cutting the cables at the controller its self.
Or you can get creative and use it as an override control to the simulator. The
main thing we want is cable that can handle the current we are using and good
solid connections.
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| Next up is attaching the cables to the
relays. There are 2 relays here. See the electrical diagram on this for any
clarification. The key here is good heavy duty relays that have very fast
switching. if you wanted there are other commercially available speed
controllers that are often used in robotic combat that could be used as well
and will offer a more accurate and responsive result. But as those are about
300-400 each and we are doing this on the cheep we would rather invest $5.00
relays and the rest in our rims.
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The main power supply to this is really
straight forward. Just meet the requirements of the winch. We are using a 30
amp 12V power supply that is also fused and variable. The benefit to using a
variable power supply is huge when it comes to adjusting the sensitivity of the
platform with out affecting the steering wheels performance. We were able to
find ours on eBay. As a safety precaution we chose to remove the cover to allow
better airflow so that it can be run for extended amounts of time.
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| The main data hub to this contraption is
the USB hub we mounted apposing the motor. The data for the steering wheel will
plug into this to help in cable length as well as keeping the computer thats
running it at a safe distance. Also to consider is a USB 5.1 sound card. There
are several on the market from SoundBlaster to generic. But the benefit is that
you will need only a single USB connection to the simulator to get the effect
you wanted.
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So there you have it. The platform is
mounted and the motion system built and connected. I strongly recommend
checking your wiring once over to make sure that you don't have any wires
crossed. But other than that it's not too hard to do and really gets the job
done. |
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