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Gimbal Project

17,652 bytes added, 16:05, 17 January 2012
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[[Category:Hardware|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>).&nbsp;
We were discussing the various methods that could be used to create a very
inexpensive gimbal assembly for pitch &amp; roll control in a home built flight
simulator cockpit.</p>
<p>This is what Jentron developed:</p>
<p>As you can see, it&#39;s very simple and uses easily obtainable off the shelf
hardware.&nbsp; In fact, this particular example was built entirely from the
resources of his local Ace Hardware.</p>
<p>I&#39;ve named his original gimbal design the &quot;Mark I&quot; to differentiate it from
the design I&#39;m using - but they&#39;re both built from essentially the same
<p>Here is what I call the Jentron Gimbal, Mk II:</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>
<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>
<p>Jentron&#39;s design is perfectly usable in it&#39;s configuration, but I needed
to modify it for use with the DIY Cockpit Project.<br>Besides, I&#39;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
Here&#39;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.&nbsp; This is what it looks like from above, in the
&quot;operating&quot; position:</p>
<img alt="Jentron Gimbal Mk2 - Operating Position" src="jentron_mk2-3.jpg" width="640" height="426" /></p>
<p>This article will only cover the ins and outs of the gimbal itself.&nbsp; The
reason for this is that your application may be a bit different and you&#39;ll need
to adjust other parts of the design to fit your situation.</p>
<p>Two &quot;fancy&quot; tools are going to be required to build this project.&nbsp; </p>
<li>1&quot; Step Drill.&nbsp; This is used to enlarge the end holes in the
single-gang extender box.</li>
<li>1/4&quot; Die.&nbsp; This is used for threading the ends of the centering
<p>A cheap 1&quot; Step Drill can be had for less than $30.&nbsp; In case you&#39;re not
sure, a step drill looks like this:</p>
<img alt="Representative example of a Step Drill" src="step_drill.jpg" width="127" height="95" /></p>
<p>Here&#39;s a list of some other common tools you&#39;re going to need:</p>
<li>Hacksaw -or- a pipe cutter.&nbsp; Pipe cutters work better for cutting
<li>Drill </li>
<li>Drill Bits - 1/4&quot; and 13/64&quot;</li>
<li>Pop-Rivet gun</li>
<li>Jig Saw, Band Saw or a Scroll Saw</li>
<li>Two 7/16&quot; open end wrenches</li>
<li>3/8&quot; open end wrench</li>
<li>Philips screwdriver</li>
<li>Vice Grips (2 pair if you can)</li>
<li>Vice or vice-like device</li>
<p>Materials needed to build the gimbal box:</p>
<table style="width: 65%">
<td style="width: 202px">1ea single-gang electrical extension box</td>
<img alt="Single-Gang Extention Box" src="single-gang_box.jpg" width="200" height="133" /></td>
<td style="width: 202px">2ea 3/4&quot; EMT connectors</td>
<img alt="3/4&quot; EMT Connector" src="emt_connector.jpg" width="200" height="133" /></td>
<td style="width: 202px">2ea 3&quot; &quot;T&quot; Brackets</td>
<img alt="3&quot; T-Bracket" src="t-bracket.jpg" width="200" height="133" /></td>
<td style="width: 202px"><br />
4ea 3/16&quot; Pop-Rivets</td>
<img alt="3/16&quot; Pop-Rivets" src="pop-rivet.jpg" width="200" height="200" /></td>
<p>Now the first thing you&#39;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&quot; Step Drill.&nbsp;
The hole needs to be large enough to accept the threaded portion of the 3/4&quot; EMT
connector.&nbsp; When you&#39;re done, the box should look like this:</p>
<img alt="Prepped gimbal box" src="prepped_box.jpg" width="400" height="307" /></p>
<p>Next up, you&#39;re going to have to use your vice grips (2 pair if you have
them!) to position the 3&quot; &quot;T&quot; bracket on the side of the extension box.&nbsp;
The best way to do this is to measure 1-1/2&quot; in from the end of the &quot;top&quot; of the
T brace and draw a centering line.&nbsp; Measure the electrical box along its
long axis and mark the center of it.&nbsp; The centering lines ensure that
you&#39;ll correctly position the &quot;T&quot; bracket on the side of the box.</p>
<p>Position the box and T-Bracket like this:</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.&nbsp; You&#39;re going to use a 1/4&quot; drill bit to drill holes in
the extension box, using the bracket as a guide.&nbsp; Do this for both
brackets.&nbsp; When you&#39;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.&nbsp; The portion of the bracket that sticks out will be the
support for the stick stub.&nbsp; It&#39;s got to be as close perfect as you can
make it.&nbsp; In the end, you should have something that looks like this:</p>
<img alt="Illustration showing both &quot;T&quot; brackets in place" src="both_brackets_mounted.jpg" width="400" height="307" /></p>
<p>You&#39;ll notice in my drawing that I&#39;m using screws to hold the brackets in.&nbsp;
This was done because I didn&#39;t want to take the time to draw a reasonable
looking pop rivet. :)</p>
<p>The last step is to mount the 3/4&quot; EMT fittings.&nbsp; These hold 3&quot; sections
of 3/4&quot; EMT conduit that act as the pitch bearings for the box.&nbsp; It&#39;s
important to get these as tight as you can.&nbsp; They&#39;ll take all the force of
the stick moving fore and aft.&nbsp; 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.&nbsp;
If you&#39;re paranoid and have a welder, it couldn&#39;t hurt it to weld them in place.&nbsp;
With it all assembled, it should look like this:</p>
<img alt="Completed gimbal box" src="complete_gimbal_box.jpg" width="400" height="307" /></p>
<p>I didn&#39;t include the nuts that go to the EMT connectors on purpose.&nbsp;
They MUST be used. :)</p>
<p>Here&#39;s an exploded diagram that shows you how it all goes together:</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.&nbsp; The stick stub is
made from a 7&quot; long piece of 3/4&quot; 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>.&nbsp; The completed stick
stub should look like this:</p>
<img alt="Completed stick stub" src="stick_stub.png" width="640" height="491" /></p>
<p>The stick stub is just that - a stub.&nbsp; Your flight grip and lower stick
or &quot;stick box&quot; will attach to this using another 3/4&quot; EMT mating connector.&nbsp;
The stick stub also provides the mechanical interconnect for the roll and pitch
<p>The next part is the roll axis actuator rod.&nbsp; This is just a fancy name
for a 6.75&quot; long bit of 1/4&quot; steel rod that you&#39;ve flatted on one end and
threaded on the other.&nbsp; It looks like this:</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.&nbsp; The hole is sized for a #10 screw.&nbsp; When
installed, it looks like this:</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.&nbsp; The attachment will take bit of experimenting
with to get it centered in the stick stub.&nbsp; You want a #10 screw that&#39;s
about 1-1/4&quot; long&nbsp; You&#39;ll use a &quot;stop-nut&quot; which is basically a regular nut
with a nylon ring pressed into the top.&nbsp; 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.&nbsp; Stop-nuts allow this - the nylon ring ensures that they
won&#39;t loosen over time.</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&#39;ll need to get two #10 nylon washers
and a few #10 zinc washers.&nbsp; Place the nylon washers on the &quot;outside&quot; of
the stack.&nbsp; They&#39;ll be the washers that will rub on the inside of the stick
stub.&nbsp; The nylon won&#39;t produce the noise that a metal washer would when
rubbing against the inside wall of the stick stub.&nbsp; Take the metal washers
and stack them on either side of the rod until you&#39;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&quot; extruded aluminum turnbuckle and
cutting off the left-hand threaded end.&nbsp; You then drill a hole that&#39;s the
appropriate size for the bolt you&#39;re going to use.&nbsp; In my case the holes
were drilled for 1/4&quot; and #10 bolts (not on the same clevis).</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&#39;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.&nbsp; You shouldn&#39;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>.&nbsp;
The drawing will print full size on a single 11x17 sheet.&nbsp; </p>
<p>The blocks are made from 5/8&quot; Birch plywood.&nbsp; However, any good quality
5/8&quot; (or close) plywood will work.</p>
<p>Please take your time cutting out the bearing blocks.&nbsp; </p>
<p>Here are some recommendations that should help you get a more accurate
<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.&nbsp; 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&nbsp;
<em>before </em>you cut the parts to shape.&nbsp; Trust me, you don&#39;t want
to be boring a near 1&quot; 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&quot;.&nbsp; The easiest way to
reach that size is to use a 7/8&quot; Forstner or Spade bit.&nbsp; This will get
you to .875&quot;&nbsp; The remainder can be sanded away with a small drum sander
in a drill or a drill press.&nbsp; The idea is to get the size of the holes
to the point where they&#39;re just a little bit loose around the 3/4&quot; EMT
conduit that makes up the pitch axis bearing.&nbsp; Make sure that when
you&#39;re sanding the parts to shape, you do them in assembled pairs.</li>
<li>If you&#39;d rather not sand the holes to size, you can still get good
results by boring a 1&quot; diameter hole instead of a .95&quot; hole.&nbsp; The fit
will only be a tiny bit looser than what I&#39;ve specified and it won&#39;t affect
how the gimbal operates.</li>
<p>Here is an exploded illustration that shows you how the pitch axis bearings
are assembled:</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&quot; #10 pan head screws and three #10
nylon ringed stop-nuts.&nbsp; It&#39;s important that you don&#39;t use any washers on
this because the washers will actually rub on the bearing shaft when it&#39;s
installed.&nbsp; The base is attached using two 1-1/2&quot; #8 flat head wood screws.&nbsp;
You should countersink the holes for them as shown in the model above.</p>
<p>Now that you&#39;ve got the bearing blocks made, you&#39;re going to need to lay out
the position of them on the base plate.&nbsp; This spacing will vary, but
generally a distance of about 6-1/4&quot; should be sufficient.&nbsp; When you do
your bearing block layout, you&#39;ll also want to mark out the space needed to
allow the gimbal box to protrude up through the cockpit floor.&nbsp; In my
version I&#39;m using a hole that&#39;s 5-1/2&quot; wide and 5-1/4&quot; high.</p>
<p>You&#39;ll now want to make the pitch axis bearings.&nbsp; They consist of two
short lengths of 3/4&quot; 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&quot; on the roll axis actuator side.&nbsp;
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&#39;ll note here how the centering rod for the pitch axis is mounted to the
bearing.&nbsp; I&#39;m using a #8 eye bolt that has a locknut on both sides to hold
it in place.&nbsp; I chose a #8 because the eye is perfectly sized for a 1/4&quot;
bolt.&nbsp; You can also just barely see the Du-Bro ball-link that I&#39;m using to
connect the pitch axis to the potentiometer that connects to the computer.&nbsp;
The ball-links are very inexpensive and very handy to use.&nbsp; 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.&nbsp; You can see the nut for the ball on
the inside.</p>
<p>Roll axis connection end:</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.&nbsp; When you move the stick to the far left, the back end of the
clevis fork can&#39;t come in contact with the bearing tube.</p>
<p>You can also see the roll axis potentiometer connection.&nbsp; Just like on
the pitch axis, I&#39;m using a Du-Bro ball-link on the clevis end, and a Du-Bro E/Z
Connector on the potentiometer end.&nbsp; This is a very simple and very
reliable way to connect your axis pots to your stick gimbal.</p>
<p>The last component I&#39;m going to cover is the centering mechanism.</p>
<p>The centering mech is very simple.&nbsp; It consists of a 1/4&quot; steel rod
that&#39;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&quot; long.&nbsp; Your application may and
probably will vary.&nbsp; Here&#39;s a picture of the assembly:</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.&nbsp; A 1x1 L bracket is
bolted in place and has a 5/16&quot; hole to allow the rod to pass through it.&nbsp;
A collar on either end holds the spring in place.&nbsp; The springs are
compressed against the center bracket just slightly.&nbsp; This provides good
centering force for the gimbal. </p>
<p>One option you may want to consider is using two spring pairs.&nbsp; 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.&nbsp; 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&#39;s really all there is to it!&nbsp; Below you&#39;ll find various pictures of
the assembly that will help out in building your own.&nbsp; If you&#39;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>
<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>

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