New rack for the truck - light mounting, motorized fold-over antenna
I am taking a class this quarter called "Custom Production". Basically the class is to come up with an idea and go through the design process and production process on an individual, non-manufacturing basis. Boy, what a great class to take advantage of! If you read my blog enough you'll notice a few other projects I have done or am working on (or have worked on that are on hold - IE: the amplifier). This is one type of class project I really take to. This quarter is no different.
Intro to the idea and original problem:
I sort of had an idea early on, in fact before the end of last quarter. When I was on my snowboarding adventure (out in the big blizzard) I had my strobe light running (amber caution light) for better visibility . I realized the light I have isn't all that powerful. It is a North American Signal Company DFS350MX-A - the smallest one they make.
I am trained by and registered with the National Weather Service for storm spotting (as part of my public service in Ham radio, it's a lot of fun - but I will say that I am not a storm chaser, although I do that for fun too). So, I use the strobe when I am out and about watching the weather as well. The big blizzard just made me realize how tiny it really was - not good if I stop on the side of the road in heavy rain, I wouldn't be visible until someone got real close.
That said, I don't have a place to mount a good light on the truck. Magnet mount lights are great, but they are for temporary use. My 350 is a magnet mount, but I still hard-wired it to a switch on the dashboard. It is not a well-mounted setup.
For my next light I am considering getting a bolt-on of some kind, probably a 650 tall series (again, NA Sig Co - they do make some well-built lights). The problem here is I don't want to bolt anything to the truck. I don't like making holes in the body anywhere that is visible. I only make holes for what I need to make a hole for - such as running wire through the firewall or out the back of the cab to the rear for power or coax for an antenna.
The idea I came up with is to make a rack that goes behind the window of the cab to serve as a mounting point. I guess they are called both "back racks" and "headache racks". I don't know what to call it, so I'll just call it a "rack".
Further advancing of the idea, more uses:
In my thinking I came up with the idea to mount my Diamond SG-7900A dual band antenna to the rack as well. It is currently on a magnet mount and the truck doesn't move without it hehehe.
I have had a couple situations where the antenna has come off - I hit a fallen branch after a storm. It would be best to permanently mount the antenna to something solid, something that wont break or let loose.
The rack is absolutely perfect for this! In fact, I can make it work for me even better. One thing I hate to do is get out of the truck and monkey around getting to the antenna to fold it back when I go in to parking garages. I have avoided parking garages as much as I possibly can because of this. The truck is a pain in the butt to move around inside a garage to begin with, but having things that you need to take down just to park in one in the first place adds to the inconvenience.
The solution - make a motorized fold-over base! Think about it - have a circuit set up so I can push a button in the cab to raise and lower the antenna. That would be awesome!
I like to off-road. When I get the chance I always enjoy a little 4-wheelin'. What's an off-road truck without off road lights? Again, the rack to the rescue! It is a perfect place to mount over-head lighting.
So, this is what the project is: a rack that sits behind the window and a little higher than the cab so I can mount a light and put a motorized antenna mount on.
Rack theory and design:
When I was looking in to the design of these racks they all mount to the top of the bed rails. This is all well and good, but in my case I have a cap on there. I don't have access to the bed rails to make that kind of setup work in the same way.
So, I looked at the truck and was thinking about different ways to mount the rack. I looked at bolting it to the back of the cab (the body itself) or the front of the bed (again, the body itself ). This would require gaining access to either side - the easiest way to do that is to take the bed off. I had to do that when I put my body lift on and I would rather avoid that process - it takes a while to do it right.
I noticed there are holes on the frame - right between the bed and the cab. So, I am going to try and make these holes work for my rack. This means the main attaching point will be all the way down on the frame. The issue with that is the height of the mount is too tall and the distance between the bed and cab restricts the size of material for the mount such that it would be too flexible. With the antenna on there the rack would probably move so much it would hit the cab and bed, not to mention how much it would vibrate going down the road.
I'll need to add in some support above the frame - preferably to the front bed rail. Since the cap is on there I'll have to make a bracket/clamp that is thin enough to slip under the rubber seal. This shouldn't be a problem.
I decided to make a cardboard mock-up of the rack so I had a full-size model to work with in conjunction with the truck to test the fit and finish.
Here you can see the beginnings of my mock-up. The pencil lines are a little faint on there. I measured the cab and it is around 70" wide at the bottom of the window and tapers to 55" wide at the roof. The rack should fit the contour of the taper as well as rest high enough off the cap so it won't restrict the cap's movement when I open it as well as provide an unobstructed view of the bed lights and tail light on the roof. That means the bottom of the top bar will lie at least even with the roof. I will have to play around with some other dimensions to see what they would be like before I settle on a width, though - I want to make sure the rack "fits" right.
The motor there is what I was originally going to use for the fold-over antenna mount. It has about a 150:1 reduction on it, lots of torque but not much speed. I will explain my troubles with the antenna mount design in a bit.
The antenna pictured there is the actual one that will be mounted on the rack.
Here the mock-up is resting up on the truck to show where it is going and the relative size. The view from the front of the truck shows the height best, although it will actually be a bit higher - the bottom won't be level with the top of the cap.
Antenna mount theory and design:
The antenna mount is the most challenging aspect of this whole project. There aren't any antenna mounts on the market that I have ever come across in my 7 years of being a Ham radio nut . The closest thing out there is the Diamond K9000 series motorized mounts. They aren't the greatest products made, several people have had problems with their durability. However, the bigger issue for me is the max antenna size rating is 45" - my SG-7900A is 62.5" - WAY over the limit.
So, I am stuck with needing to make my own. That isn't a bad thing at all - it adds to my creativity with the project and sense of accomplishment once it is done. The theory behind my idea is to have a motor with enough torque to drive a worm gear or a lead screw that would be strong enough to support the wind loading of an antenna 60 some inches tall going down the road at highway speeds.
I would say I am over-engineering this one just a bit, but I am working with materials I have easily accessible. The motor that I was originally going to use, as shown in a previous picture, has a 150:1 gear reduction. For driving a low reduction worm gear this would be fine. I could also mount the motor 90 degrees to the axis of rotation for the antenna since the worm gear would have to change the direction of rotation 90 degrees from the rotation of the motor output shaft. Because the motor has a flat pancake shape that would work nicely. The box to house the mechanism would be fairly large, but it would not be overly tall.
The problem I came across with this setup is I don't have a worm gear set to use for the project. I looked around online real quick and came to the conclusion that I was going to need to spend a lot of money on the gears to get ones that would be adequate for my application. I don't have a whole lot of money to spend, so I decided to change my approach.
My next idea was to use a lead screw. If you don't know what that is, basically a long bolt acts as the driving device against a nut. Either the nut or the screw can be driven, the one not driven is anchored so it wont rotate. The advantage of this setup is you get a tremendous amount of push/pull power.
Another advantage of this is I can make or purchase relatively easily (a trip to the hardware store and a couple bucks) I can have a suitable screw/nut. However, a disadvantage I ran in to is the screw would have to mount in-line with the motor shaft. That flat pancake motor/gearbox would soon get pretty tall.
The even bigger disadvantage, though, is the time it would take to move. The 150:1 reduction on the motor left me with 26RPM's. If you do the math, on a 3/8"x16 screw and 2" of movable distance the time it would take to go through one cycle (up or down) would be about 22 seconds. That means it would take 22 seconds for the antenna to go up or to lay it back. I don't know about you, but I don't feel like hanging around for 22 seconds for an antenna to go up and down!
Since the motor's RPM's are set, the only way to cheaply change the time is to change the pitch of the lead screw. Even still, the time isn't going to change too dramatically - we're only talking a difference of about 10-12 rotations over the length of that screw.
Luckily I got another motor to use instead. This one has a gearbox on it and runs at 88RPM's at 12 volts. This is a large improvement over the 26RPM's of the other one.
At the same 3/8"x16 screw the time with the new motor is about 15 seconds. This is a big improvement over the 22 seconds before, but still... I don't want to wait around for 15 seconds for my antenna to go up and down.
I went to the tool room and scrounged around looking for a tap and die set. I got one and found tap for a 3/4"x9 thread, the lowest pitch I could find in there. A 3/4" screw is pretty big, though. Considering the room the motor will take up to begin with I think the screw size is a negligible dimension. I am making this all from scratch anyway, so I can make it work.
With the 9 pitch screw I knocked the cycle time down to just under 12.5 seconds. This is still a decently long time, but it's the best I can do. I think I can live with it!
The differences between the worm gear approach and the lead screw approach is that the worm gear transfers the plane of rotation 90 degrees from the plane of the output shaft on the motor. In my case with the antenna mount, the motor would lie 90 degrees from the direction the antenna rotates - in line with the truck, front to back. The lead screw approach uses a motion parallel to the motor output shaft. Basically, what you are driving (in my case a threaded insert on a lever that the antenna mount is attached to) is being driven linearly - in a straight line, not rotary - a set radius about an axis. The threaded insert on the lever will move exactly in the same line as the output shaft on the gearbox. It is still possible to drive a rotational device in a linear fashion, however you loose the linear force and speed.
Did I loose you yet? Basically, driving the antenna to rotate up and down with a lead screw means the speed of rotation is non-linear - the speed accelerates and decelerates as the angle of rotation increases/decreases. Since my antenna is just going up and down I don't think this is a problem. As long as the antenna goes up and down and does so in a reasonable amount of time I don't care.
Next issue. Because the speed is not constant I wanted to balance it so at least it is symmetrical. This lead me to place the axis of rotation of the lever that the antenna mount is attached to half way between the high and low points of the screw. Then, maintain a 45deg angle between the driven side of the lever and the screw on both the high and low points. If you add that up (45deg at both ends) you get 90deg, a perfect right angle.
Because of the layout of the motor and gearbox I have I was perplexed by where to place the screw drive mechanism in relation to the motor. The lever has to rotate in line with the shaft, so there were only a couple ways that it could be mounted to achieve that relationship. After a lunch break I figured out how to do it in a way that makes the most sense - lay the motor/gearbox on it's side and mount the lever 90deg to the screw in a vertical configuration.
Finalizing the designs:
The next process is to finalize the design - work out a few bugs. The ideas and design concepts are there, now I need to tie them together and make them work with the processes and tools I have available.
We don't have a good way to bend tubing. Because of this I am going to cut and weld the tubes for the rack instead of bend them. This will add to the care I need to take in laying out the parts and welding the parts, but it is the easiest way to make it work.
The box to fit the fold-over mechanism needs to be created. Once I get the dimensions of everything with the device I can work on the box. One more design issue I have is to seal the box from the elements. This means there will have to be a round plate that rotates with the antenna, or a rubber sheet. I like the plate idea best - it will be the most durable.
The box will lie in the center of the top tube of the rack. There will be two top tubes welded to the fold-over box instead of one going all the way through. Another benefit of this approach is that the length of good tubing I need for the top tube is cut in half. I can have two good short pieces rather than trying to find one good long one.
Continuing the project:
I am still working on the bugs with this. I need to have plans and a timeline of when this is to be completed. That will be the task in the next couple days. I hope to have the plans and most of the timeline done by the end of the weekend so I can go in Monday and start the fabrication process.
I will post more pictures and drawings as I get to that point. I have a couple pages of ideas sketching, Ill scan those here and post them later.
Intro to the idea and original problem:
I sort of had an idea early on, in fact before the end of last quarter. When I was on my snowboarding adventure (out in the big blizzard) I had my strobe light running (amber caution light) for better visibility . I realized the light I have isn't all that powerful. It is a North American Signal Company DFS350MX-A - the smallest one they make.
I am trained by and registered with the National Weather Service for storm spotting (as part of my public service in Ham radio, it's a lot of fun - but I will say that I am not a storm chaser, although I do that for fun too). So, I use the strobe when I am out and about watching the weather as well. The big blizzard just made me realize how tiny it really was - not good if I stop on the side of the road in heavy rain, I wouldn't be visible until someone got real close.
That said, I don't have a place to mount a good light on the truck. Magnet mount lights are great, but they are for temporary use. My 350 is a magnet mount, but I still hard-wired it to a switch on the dashboard. It is not a well-mounted setup.
For my next light I am considering getting a bolt-on of some kind, probably a 650 tall series (again, NA Sig Co - they do make some well-built lights). The problem here is I don't want to bolt anything to the truck. I don't like making holes in the body anywhere that is visible. I only make holes for what I need to make a hole for - such as running wire through the firewall or out the back of the cab to the rear for power or coax for an antenna.
The idea I came up with is to make a rack that goes behind the window of the cab to serve as a mounting point. I guess they are called both "back racks" and "headache racks". I don't know what to call it, so I'll just call it a "rack".
Further advancing of the idea, more uses:
In my thinking I came up with the idea to mount my Diamond SG-7900A dual band antenna to the rack as well. It is currently on a magnet mount and the truck doesn't move without it hehehe.
I have had a couple situations where the antenna has come off - I hit a fallen branch after a storm. It would be best to permanently mount the antenna to something solid, something that wont break or let loose.
The rack is absolutely perfect for this! In fact, I can make it work for me even better. One thing I hate to do is get out of the truck and monkey around getting to the antenna to fold it back when I go in to parking garages. I have avoided parking garages as much as I possibly can because of this. The truck is a pain in the butt to move around inside a garage to begin with, but having things that you need to take down just to park in one in the first place adds to the inconvenience.
The solution - make a motorized fold-over base! Think about it - have a circuit set up so I can push a button in the cab to raise and lower the antenna. That would be awesome!
I like to off-road. When I get the chance I always enjoy a little 4-wheelin'. What's an off-road truck without off road lights? Again, the rack to the rescue! It is a perfect place to mount over-head lighting.
So, this is what the project is: a rack that sits behind the window and a little higher than the cab so I can mount a light and put a motorized antenna mount on.
Rack theory and design:
When I was looking in to the design of these racks they all mount to the top of the bed rails. This is all well and good, but in my case I have a cap on there. I don't have access to the bed rails to make that kind of setup work in the same way.
So, I looked at the truck and was thinking about different ways to mount the rack. I looked at bolting it to the back of the cab (the body itself) or the front of the bed (again, the body itself ). This would require gaining access to either side - the easiest way to do that is to take the bed off. I had to do that when I put my body lift on and I would rather avoid that process - it takes a while to do it right.
I noticed there are holes on the frame - right between the bed and the cab. So, I am going to try and make these holes work for my rack. This means the main attaching point will be all the way down on the frame. The issue with that is the height of the mount is too tall and the distance between the bed and cab restricts the size of material for the mount such that it would be too flexible. With the antenna on there the rack would probably move so much it would hit the cab and bed, not to mention how much it would vibrate going down the road.
I'll need to add in some support above the frame - preferably to the front bed rail. Since the cap is on there I'll have to make a bracket/clamp that is thin enough to slip under the rubber seal. This shouldn't be a problem.
I decided to make a cardboard mock-up of the rack so I had a full-size model to work with in conjunction with the truck to test the fit and finish.
Here you can see the beginnings of my mock-up. The pencil lines are a little faint on there. I measured the cab and it is around 70" wide at the bottom of the window and tapers to 55" wide at the roof. The rack should fit the contour of the taper as well as rest high enough off the cap so it won't restrict the cap's movement when I open it as well as provide an unobstructed view of the bed lights and tail light on the roof. That means the bottom of the top bar will lie at least even with the roof. I will have to play around with some other dimensions to see what they would be like before I settle on a width, though - I want to make sure the rack "fits" right.
The motor there is what I was originally going to use for the fold-over antenna mount. It has about a 150:1 reduction on it, lots of torque but not much speed. I will explain my troubles with the antenna mount design in a bit.
The antenna pictured there is the actual one that will be mounted on the rack.
Here the mock-up is resting up on the truck to show where it is going and the relative size. The view from the front of the truck shows the height best, although it will actually be a bit higher - the bottom won't be level with the top of the cap.
Antenna mount theory and design:
The antenna mount is the most challenging aspect of this whole project. There aren't any antenna mounts on the market that I have ever come across in my 7 years of being a Ham radio nut . The closest thing out there is the Diamond K9000 series motorized mounts. They aren't the greatest products made, several people have had problems with their durability. However, the bigger issue for me is the max antenna size rating is 45" - my SG-7900A is 62.5" - WAY over the limit.
So, I am stuck with needing to make my own. That isn't a bad thing at all - it adds to my creativity with the project and sense of accomplishment once it is done. The theory behind my idea is to have a motor with enough torque to drive a worm gear or a lead screw that would be strong enough to support the wind loading of an antenna 60 some inches tall going down the road at highway speeds.
I would say I am over-engineering this one just a bit, but I am working with materials I have easily accessible. The motor that I was originally going to use, as shown in a previous picture, has a 150:1 gear reduction. For driving a low reduction worm gear this would be fine. I could also mount the motor 90 degrees to the axis of rotation for the antenna since the worm gear would have to change the direction of rotation 90 degrees from the rotation of the motor output shaft. Because the motor has a flat pancake shape that would work nicely. The box to house the mechanism would be fairly large, but it would not be overly tall.
The problem I came across with this setup is I don't have a worm gear set to use for the project. I looked around online real quick and came to the conclusion that I was going to need to spend a lot of money on the gears to get ones that would be adequate for my application. I don't have a whole lot of money to spend, so I decided to change my approach.
My next idea was to use a lead screw. If you don't know what that is, basically a long bolt acts as the driving device against a nut. Either the nut or the screw can be driven, the one not driven is anchored so it wont rotate. The advantage of this setup is you get a tremendous amount of push/pull power.
Another advantage of this is I can make or purchase relatively easily (a trip to the hardware store and a couple bucks) I can have a suitable screw/nut. However, a disadvantage I ran in to is the screw would have to mount in-line with the motor shaft. That flat pancake motor/gearbox would soon get pretty tall.
The even bigger disadvantage, though, is the time it would take to move. The 150:1 reduction on the motor left me with 26RPM's. If you do the math, on a 3/8"x16 screw and 2" of movable distance the time it would take to go through one cycle (up or down) would be about 22 seconds. That means it would take 22 seconds for the antenna to go up or to lay it back. I don't know about you, but I don't feel like hanging around for 22 seconds for an antenna to go up and down!
Since the motor's RPM's are set, the only way to cheaply change the time is to change the pitch of the lead screw. Even still, the time isn't going to change too dramatically - we're only talking a difference of about 10-12 rotations over the length of that screw.
Luckily I got another motor to use instead. This one has a gearbox on it and runs at 88RPM's at 12 volts. This is a large improvement over the 26RPM's of the other one.
At the same 3/8"x16 screw the time with the new motor is about 15 seconds. This is a big improvement over the 22 seconds before, but still... I don't want to wait around for 15 seconds for my antenna to go up and down.
I went to the tool room and scrounged around looking for a tap and die set. I got one and found tap for a 3/4"x9 thread, the lowest pitch I could find in there. A 3/4" screw is pretty big, though. Considering the room the motor will take up to begin with I think the screw size is a negligible dimension. I am making this all from scratch anyway, so I can make it work.
With the 9 pitch screw I knocked the cycle time down to just under 12.5 seconds. This is still a decently long time, but it's the best I can do. I think I can live with it!
The differences between the worm gear approach and the lead screw approach is that the worm gear transfers the plane of rotation 90 degrees from the plane of the output shaft on the motor. In my case with the antenna mount, the motor would lie 90 degrees from the direction the antenna rotates - in line with the truck, front to back. The lead screw approach uses a motion parallel to the motor output shaft. Basically, what you are driving (in my case a threaded insert on a lever that the antenna mount is attached to) is being driven linearly - in a straight line, not rotary - a set radius about an axis. The threaded insert on the lever will move exactly in the same line as the output shaft on the gearbox. It is still possible to drive a rotational device in a linear fashion, however you loose the linear force and speed.
Did I loose you yet? Basically, driving the antenna to rotate up and down with a lead screw means the speed of rotation is non-linear - the speed accelerates and decelerates as the angle of rotation increases/decreases. Since my antenna is just going up and down I don't think this is a problem. As long as the antenna goes up and down and does so in a reasonable amount of time I don't care.
Next issue. Because the speed is not constant I wanted to balance it so at least it is symmetrical. This lead me to place the axis of rotation of the lever that the antenna mount is attached to half way between the high and low points of the screw. Then, maintain a 45deg angle between the driven side of the lever and the screw on both the high and low points. If you add that up (45deg at both ends) you get 90deg, a perfect right angle.
Because of the layout of the motor and gearbox I have I was perplexed by where to place the screw drive mechanism in relation to the motor. The lever has to rotate in line with the shaft, so there were only a couple ways that it could be mounted to achieve that relationship. After a lunch break I figured out how to do it in a way that makes the most sense - lay the motor/gearbox on it's side and mount the lever 90deg to the screw in a vertical configuration.
Finalizing the designs:
The next process is to finalize the design - work out a few bugs. The ideas and design concepts are there, now I need to tie them together and make them work with the processes and tools I have available.
We don't have a good way to bend tubing. Because of this I am going to cut and weld the tubes for the rack instead of bend them. This will add to the care I need to take in laying out the parts and welding the parts, but it is the easiest way to make it work.
The box to fit the fold-over mechanism needs to be created. Once I get the dimensions of everything with the device I can work on the box. One more design issue I have is to seal the box from the elements. This means there will have to be a round plate that rotates with the antenna, or a rubber sheet. I like the plate idea best - it will be the most durable.
The box will lie in the center of the top tube of the rack. There will be two top tubes welded to the fold-over box instead of one going all the way through. Another benefit of this approach is that the length of good tubing I need for the top tube is cut in half. I can have two good short pieces rather than trying to find one good long one.
Continuing the project:
I am still working on the bugs with this. I need to have plans and a timeline of when this is to be completed. That will be the task in the next couple days. I hope to have the plans and most of the timeline done by the end of the weekend so I can go in Monday and start the fabrication process.
I will post more pictures and drawings as I get to that point. I have a couple pages of ideas sketching, Ill scan those here and post them later.
posted by Steve at
9:43 PM
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