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[[Category:Hardware|Gimbal Build a simple pitch & roll gimbal]] | [[Category:Hardware|Gimbal Build a simple pitch & roll gimbal]] | ||
[[Category:Howto|Gimbal Build a simple pitch & roll gimbal]] | [[Category:Howto|Gimbal Build a simple pitch & roll gimbal]] | ||
<p>Back in May 2009 I had spent some time tossing ideas back and forth with a nice | |||
gent by the name of Jentron on the #flightgear IRC channel (<a href="irc://irc.flightgear.org">irc.flightgear.org</a>). | |||
We were discussing the various methods that could be used to create a very | |||
inexpensive gimbal assembly for pitch & roll control in a home built flight | |||
simulator cockpit.</p> | |||
<p>This is what Jentron developed:</p> | |||
<p> | |||
[[file:jentron_original.jpg]] | |||
<p>As you can see, it's very simple and uses easily obtainable off the shelf | |||
hardware. In fact, this particular example was built entirely from the | |||
resources of his local Ace Hardware.</p> | |||
<p>I've named his original gimbal design the "Mark I" to differentiate it from | |||
the design I'm using - but they're both built from essentially the same | |||
components.</p> | |||
<p>Here is what I call the Jentron Gimbal, Mk II:</p> | |||
<p> | |||
<img alt="Jentron Gimbal, Mark II" src="jentron_mk2-1.jpg" width="640" height="426" /></p> | |||
<p>As you can see, the design elements from the Mk I design are present here | |||
with a couple notable changes.</p> | |||
<ul> | |||
<li>The pitch axis bearings are two separate components.</li> | |||
<li>Simpler interconnect for the pitch axis centering arm - no need for a | |||
hand-fabricated pitch arm.</li> | |||
<li>Reduced part count</li> | |||
</ul> | |||
<p>Jentron's design is perfectly usable in it's configuration, but I needed | |||
to modify it for use with the DIY Cockpit Project.<br>Besides, I'm a geek and | |||
no self respecting geek can resist fiddling with things. :)</p> | |||
<p>Below is instructions on how you can construct this gimbal for use in your | |||
cockpit!</p> | |||
<p> </p> | |||
<hr> | |||
Here's information on how my version of the Jentron Gimbal Mk II was built | |||
and how you can build your own.</p> | |||
<p>One important thing to note - the gimbal is designed to be mounted underneath | |||
the cockpit floor. This is what it looks like from above, in the | |||
"operating" position:</p> | |||
<p> | |||
<img alt="Jentron Gimbal Mk2 - Operating Position" src="jentron_mk2-3.jpg" width="640" height="426" /></p> | |||
<p> </p> | |||
<p>This article will only cover the ins and outs of the gimbal itself. The | |||
reason for this is that your application may be a bit different and you'll need | |||
to adjust other parts of the design to fit your situation.</p> | |||
<p>Two "fancy" tools are going to be required to build this project. </p> | |||
<ul> | |||
<li>1" Step Drill. This is used to enlarge the end holes in the | |||
single-gang extender box.</li> | |||
<li>1/4" Die. This is used for threading the ends of the centering | |||
pushrods</li> | |||
</ul> | |||
<p>A cheap 1" Step Drill can be had for less than $30. In case you're not | |||
sure, a step drill looks like this:</p> | |||
<p> | |||
<img alt="Representative example of a Step Drill" src="step_drill.jpg" width="127" height="95" /></p> | |||
<p>Here's a list of some other common tools you're going to need:</p> | |||
<ul> | |||
<li>Hacksaw -or- a pipe cutter. Pipe cutters work better for cutting | |||
EMT.</li> | |||
<li>Drill </li> | |||
<li>Drill Bits - 1/4" and 13/64"</li> | |||
<li>Pop-Rivet gun</li> | |||
<li>Jig Saw, Band Saw or a Scroll Saw</li> | |||
<li>Two 7/16" open end wrenches</li> | |||
<li>3/8" open end wrench</li> | |||
<li>Philips screwdriver</li> | |||
<li>Vice Grips (2 pair if you can)</li> | |||
<li>Vice or vice-like device</li> | |||
</ul> | |||
<p>Materials needed to build the gimbal box:</p> | |||
<table style="width: 65%"> | |||
<tr> | |||
<td style="width: 202px">1ea single-gang electrical extension box</td> | |||
<td> | |||
<img alt="Single-Gang Extention Box" src="single-gang_box.jpg" width="200" height="133" /></td> | |||
</tr> | |||
<tr> | |||
<td style="width: 202px">2ea 3/4" EMT connectors</td> | |||
<td> | |||
<img alt="3/4" EMT Connector" src="emt_connector.jpg" width="200" height="133" /></td> | |||
</tr> | |||
<tr> | |||
<td style="width: 202px">2ea 3" "T" Brackets</td> | |||
<td> | |||
<img alt="3" T-Bracket" src="t-bracket.jpg" width="200" height="133" /></td> | |||
</tr> | |||
<tr> | |||
<td style="width: 202px"><br /> | |||
4ea 3/16" Pop-Rivets</td> | |||
<td> | |||
<img alt="3/16" Pop-Rivets" src="pop-rivet.jpg" width="200" height="200" /></td> | |||
</tr> | |||
</table> | |||
<p>Now the first thing you're going to need to do is pop out all the knock-outs | |||
in the electrical box and then drill out the ends using the 1" Step Drill. | |||
The hole needs to be large enough to accept the threaded portion of the 3/4" EMT | |||
connector. When you're done, the box should look like this:</p> | |||
<p> | |||
<img alt="Prepped gimbal box" src="prepped_box.jpg" width="400" height="307" /></p> | |||
<p>Next up, you're going to have to use your vice grips (2 pair if you have | |||
them!) to position the 3" "T" bracket on the side of the extension box. | |||
The best way to do this is to measure 1-1/2" in from the end of the "top" of the | |||
T brace and draw a centering line. Measure the electrical box along its | |||
long axis and mark the center of it. The centering lines ensure that | |||
you'll correctly position the "T" bracket on the side of the box.</p> | |||
<p>Position the box and T-Bracket like this:</p> | |||
<p> | |||
<img alt="Illustration showing the correct placement of the T-Bracket" src="t-bracket_position.jpg" width="400" height="307" /></p> | |||
<p>With the vice grip(s) holding the t-bracket in place, put the box in a vice | |||
to hold it down. You're going to use a 1/4" drill bit to drill holes in | |||
the extension box, using the bracket as a guide. Do this for both | |||
brackets. When you've got all four holes drilled, go ahead and pop-rivet | |||
them in place - please be careful to make sure that both brackets are lined up | |||
with one another. The portion of the bracket that sticks out will be the | |||
support for the stick stub. It's got to be as close perfect as you can | |||
make it. In the end, you should have something that looks like this:</p> | |||
<p> | |||
<img alt="Illustration showing both "T" brackets in place" src="both_brackets_mounted.jpg" width="400" height="307" /></p> | |||
<p>You'll notice in my drawing that I'm using screws to hold the brackets in. | |||
This was done because I didn't want to take the time to draw a reasonable | |||
looking pop rivet. :)</p> | |||
<p>The last step is to mount the 3/4" EMT fittings. These hold 3" sections | |||
of 3/4" EMT conduit that act as the pitch bearings for the box. It's | |||
important to get these as tight as you can. They'll take all the force of | |||
the stick moving fore and aft. I recommend using a pair of Channel-Lock | |||
pliers and a vice to make sure those fittings are as tight as you can make them. | |||
If you're paranoid and have a welder, it couldn't hurt it to weld them in place. | |||
With it all assembled, it should look like this:</p> | |||
<p> | |||
<img alt="Completed gimbal box" src="complete_gimbal_box.jpg" width="400" height="307" /></p> | |||
<p>I didn't include the nuts that go to the EMT connectors on purpose. | |||
They MUST be used. :)</p> | |||
<p>Here's an exploded diagram that shows you how it all goes together:</p> | |||
<p> | |||
<img alt="Exploded illustration of the gimbal box" src="gimbal_box_exploded.jpg" width="400" height="307" /></p> | |||
<p>The last part of this assembly is the stick stub. The stick stub is | |||
made from a 7" long piece of 3/4" EMT that has had two holes and a notch cut in | |||
the bottom.</p> | |||
<p>A PDF file of the part drawing is available | |||
<a target="_blank" href="stick_stub.pdf">here</a>. The completed stick | |||
stub should look like this:</p> | |||
<p> | |||
<img alt="Completed stick stub" src="stick_stub.png" width="640" height="491" /></p> | |||
<p>The stick stub is just that - a stub. Your flight grip and lower stick | |||
or "stick box" will attach to this using another 3/4" EMT mating connector. | |||
The stick stub also provides the mechanical interconnect for the roll and pitch | |||
axes.</p> | |||
<p>The next part is the roll axis actuator rod. This is just a fancy name | |||
for a 6.75" long bit of 1/4" steel rod that you've flatted on one end and | |||
threaded on the other. It looks like this:</p> | |||
<p> | |||
<img alt="Roll axis actuator rod" src="roll_axis_acutator_rod.png" width="640" height="491" /></p> | |||
<p><a href="roll_axis_actuator_rod.pdf">Here</a> is a PDF file that shows the | |||
details of making the rod. The hole is sized for a #10 screw. When | |||
installed, it looks like this:</p> | |||
<p> | |||
<img alt="roll axis actuator in the installed position" src="roll_actuator_installed.png" width="640" height="491" /></p> | |||
<p>The screw is not shown. The attachment will take bit of experimenting | |||
with to get it centered in the stick stub. You want a #10 screw that's | |||
about 1-1/4" long You'll use a "stop-nut" which is basically a regular nut | |||
with a nylon ring pressed into the top. The idea is to allow you to | |||
tighten the screw down enough to take the slop out, but not enough to bind up | |||
the mechanism. Stop-nuts allow this - the nylon ring ensures that they | |||
won't loosen over time.</p> | |||
<p> | |||
<img alt="Roll axis pushrod connection detail" src="roll_axis_pushrod_connection.jpg" width="640" height="426" /></p> | |||
<p>To center the rod in the stick stub, you'll need to get two #10 nylon washers | |||
and a few #10 zinc washers. Place the nylon washers on the "outside" of | |||
the stack. They'll be the washers that will rub on the inside of the stick | |||
stub. The nylon won't produce the noise that a metal washer would when | |||
rubbing against the inside wall of the stick stub. Take the metal washers | |||
and stack them on either side of the rod until you've got the right number on | |||
each side that gives the closest to center fit.</p> | |||
<p>The clevis fork is made by taking a 1/4" extruded aluminum turnbuckle and | |||
cutting off the left-hand threaded end. You then drill a hole that's the | |||
appropriate size for the bolt you're going to use. In my case the holes | |||
were drilled for 1/4" and #10 bolts (not on the same clevis).</p> | |||
<p> | |||
<img alt="Clevis fork made from a turnbuckle" src="clevis_fork.png" width="640" height="426" /></p> | |||
<p>Next up, making the wooden bearing blocks for the gimbal...</p> | |||
<p>First, you're going to need to download the drawing for the bearing parts.</p> | |||
<p><a href="pitch%20axis%20bearing%20drawing.dxf">pitch axis bearing drawing.dxf</a> | |||
- This drawing was saved in AutoCAD 2004 DXF format. You shouldn't have | |||
any problems reading it using any of the freely available CAD programs, you can | |||
download a PDF of the plan | |||
<a target="_blank" href="pitch%20axis%20bearing%20drawing.pdf">here</a>. | |||
The drawing will print full size on a single 11x17 sheet. </p> | |||
<p>The blocks are made from 5/8" Birch plywood. However, any good quality | |||
5/8" (or close) plywood will work.</p> | |||
<p>Please take your time cutting out the bearing blocks. </p> | |||
<p>Here are some recommendations that should help you get a more accurate | |||
result:</p> | |||
<ul> | |||
<li>When drilling the three mounting holes in the bearing base, it would be | |||
a good idea to drill both parts at the same time to ensure that the holes | |||
are placed identically in both parts. The bearings must be square and | |||
aligned to one another or the pitch axis bearing shaft will bind.</li> | |||
<li>When creating the parts with the bearing holes in them, it is far safer | |||
and more accurate to drill all the small holes and the two large holes | |||
<em>before </em>you cut the parts to shape. Trust me, you don't want | |||
to be boring a near 1" diameter hole in a part with nearly no material to | |||
hang on to while the drill does its job. :)</li> | |||
<li>The large bearing holes are specified at .95". The easiest way to | |||
reach that size is to use a 7/8" Forstner or Spade bit. This will get | |||
you to .875" The remainder can be sanded away with a small drum sander | |||
in a drill or a drill press. The idea is to get the size of the holes | |||
to the point where they're just a little bit loose around the 3/4" EMT | |||
conduit that makes up the pitch axis bearing. Make sure that when | |||
you're sanding the parts to shape, you do them in assembled pairs.</li> | |||
<li>If you'd rather not sand the holes to size, you can still get good | |||
results by boring a 1" diameter hole instead of a .95" hole. The fit | |||
will only be a tiny bit looser than what I've specified and it won't affect | |||
how the gimbal operates.</li> | |||
</ul> | |||
<p>Here is an exploded illustration that shows you how the pitch axis bearings | |||
are assembled:</p> | |||
<p> | |||
<img alt="Exploded illustraition of the Pitch Axis Bearing" src="pab_exploded.jpg" width="677" height="486" /></p> | |||
<p>The bearing is assembled using three 1-3/4" #10 pan head screws and three #10 | |||
nylon ringed stop-nuts. It's important that you don't use any washers on | |||
this because the washers will actually rub on the bearing shaft when it's | |||
installed. The base is attached using two 1-1/2" #8 flat head wood screws. | |||
You should countersink the holes for them as shown in the model above.</p> | |||
<p>Now that you've got the bearing blocks made, you're going to need to lay out | |||
the position of them on the base plate. This spacing will vary, but | |||
generally a distance of about 6-1/4" should be sufficient. When you do | |||
your bearing block layout, you'll also want to mark out the space needed to | |||
allow the gimbal box to protrude up through the cockpit floor. In my | |||
version I'm using a hole that's 5-1/2" wide and 5-1/4" high.</p> | |||
<p>You'll now want to make the pitch axis bearings. They consist of two | |||
short lengths of 3/4" EMT conduit cut to a length that will allow them to fully | |||
seat in the EMT mating connectors on the gimbal box and extend at least two | |||
inches on the pitch actuator side and about 1/2" on the roll axis actuator side. | |||
Below are examples that show you roughly how it should look.</p> | |||
<p>Pitch axis connection end:</p> | |||
<p><img src="pitch_axis_bearing_detail.jpg" width="640" height="426" /></p> | |||
<p>You'll note here how the centering rod for the pitch axis is mounted to the | |||
bearing. I'm using a #8 eye bolt that has a locknut on both sides to hold | |||
it in place. I chose a #8 because the eye is perfectly sized for a 1/4" | |||
bolt. You can also just barely see the Du-Bro ball-link that I'm using to | |||
connect the pitch axis to the potentiometer that connects to the computer. | |||
The ball-links are very inexpensive and very handy to use. The ones I | |||
chose are threaded and have a long enough reach for them to be able to pass | |||
through the side of the clevis fork. You can see the nut for the ball on | |||
the inside.</p> | |||
<p>Roll axis connection end:</p> | |||
<p> | |||
<img src="roll_axis_pushrod_and_center_interconnect.jpg" width="640" height="426" /></p> | |||
<p>Here you can see why the roll axis side of the pitch axis bearing needs to be | |||
so short. When you move the stick to the far left, the back end of the | |||
clevis fork can't come in contact with the bearing tube.</p> | |||
<p>You can also see the roll axis potentiometer connection. Just like on | |||
the pitch axis, I'm using a Du-Bro ball-link on the clevis end, and a Du-Bro E/Z | |||
Connector on the potentiometer end. This is a very simple and very | |||
reliable way to connect your axis pots to your stick gimbal.</p> | |||
<p>The last component I'm going to cover is the centering mechanism.</p> | |||
<p>The centering mech is very simple. It consists of a 1/4" steel rod | |||
that's been threaded on one end, a clevis fork made from a turnbuckle, a pair of | |||
springs and some locking collars.</p> | |||
<p>In my design the steel rod is 10" long. Your application may and | |||
probably will vary. Here's a picture of the assembly:</p> | |||
<p> | |||
<img alt="Roll axis centering mechanism and pot connection" src="roll_axis_centering_and_pot.jpg" width="640" height="426" /></p> | |||
<p>As you can see, the whole thing is very simple. A 1x1 L bracket is | |||
bolted in place and has a 5/16" hole to allow the rod to pass through it. | |||
A collar on either end holds the spring in place. The springs are | |||
compressed against the center bracket just slightly. This provides good | |||
centering force for the gimbal. </p> | |||
<p>One option you may want to consider is using two spring pairs. If you | |||
stack a lighter spring atop a heavier spring, your gimbal will have light force | |||
around the center and it will increase as you move the controls. This | |||
happens because small movements around the center only compress the light | |||
spring, while movements toward the travel ranges compresses both the light and | |||
heavy springs.</p> | |||
<p>That's really all there is to it! Below you'll find various pictures of | |||
the assembly that will help out in building your own. If you've got | |||
questions please feel free to join the | |||
<a href="http://www.simpits.org/mailman/listinfo/simpits-tech">simpits-tech</a> | |||
mailing list!</p> | |||
<p> | |||
<img alt="Misc. Pictures" src="roll_axis_pushrod_and_center_interconnect-2.jpg"></p> | |||
<p><img src="pitch_axis_pushrod_and_pot.jpg"></p> | |||
<p><img src="pitch_axis_pushrod_and_pot-2.jpg"></p> | |||
<p><img src="pitch_axis_bearing_detail.jpg"></p> | |||
<p><img src="pitch_axis_bearing_detail-2.jpg"></p> | |||
<p><img src="gimbal_box_detail.jpg"></p> | |||
<p><img src="roll_axis_pushrod_connection-2.jpg"></p> | |||
<p> </p> |
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