Because we are going to be on the road for such a long time, I wanted a decent size TV to watch movies on. I decided on the Samsung 49" 8000 series due to its very shallow depth of 1.7", thin bezel and high quality picture. There is no room anywhere in the Airstream a TV of this size can be permanently mounted without blocking a window so I decided to conceal the TV in a cabinet at the foot of the bed. I would then use a TV lift to raise the TV up in front of the curb-side window for veiwing.
When I came up with this idea in my brain, I never thought it would be so much work to execute. Perservience paid off and I ended up with the perfect solution.
I first bought a TV lift from Firgelli Automations, but when I received their 30" Pop-up Lift ($760.00 CDN), I found it to be very heavy and bulky. It would be a great TV lift for a cabinet in a house where size and weight are less of a concern. I could not fit it into the space between the queen size bed and wall. I then bought a 30" Linear Actuator ($149.99 CDN) from Firgelli thinking I could make it work, however, the motor and gears are mounted below the lead screw, making the retracted length of 37.88" is too long for this application. I only have 64" from the floor to the bottom of the overhead storage, the top of the bed is 34" tall, and the TV is 24.5" tall so I need it to travel the full 30" for the TV to reach its optimal viewing position.
Instead of using a prebuilt solution, I decided to use CNC (3D Printer) parts to make a custom lift. The plans are available below. The total depth of the TV lift including the 1.7" TV is only 4".
Original Parts List:
- 2, 8mm lead screws at least 34” long, 900mm would give me a bit extra to custom cut down
- 2, lead nuts that match the lead screws
- 3, timing pulleys - one for the bottom of the motor and two for the bottom of the lead screws
- 1, timing belt
- 4, pillow blocks
- 1, 12 VDC motor
- 1 pair of drawer slides
The original plans called for two lead screws, but it was too hard to get them in sync. All the lead screws had bends in them, some suppliers were better than others. Even the most minor of bend in the lead screw resulted in binding when using two in tandem. My second prototype used one lead screw and I found this to be the best solution.
Now that I was only using one lead screw I wanted to use a larger diameter, but this proved very hard to find. A T10 (10mm) or T12 (12mm) diameter lead screws would have been best, but I was not able to find either diameter with a 4mm lead at a reasonable price.
Pitch is the distance between screw grooves and is commonly used with inch sized products and specified as threads per inch.
Lead is the linear travel the nut makes per one screw revolution and is how ball screws are typically specified. The pitch and lead are equal with single start screws. For multiple start screws the lead is the pitch divided by the number of starts.
There may be more than one thread strand on a single lead screw. These are called starts. Multiple start lead screws are usually more stable and efficient at power transmission.
You can identify the number of starts of a lead screw by viewing the end of the lead screw. The figure above represents the most common types, single, double, and four start lead screws.
The length of the "lead" determines how far the lead nut will travel with each revolution. A lead of 4mm means the lead nut will travel 4mm along the lead screw with each revolution of the lead screw. An 8mm lead gives you 8mm of linear travel and a 2mm lead will result in 2mm of linear travel with each revolution.
8mm diameter leads screws are commonly found with a 2mm and 8mm leads, but after experimenting I found the ideal lead was 4mm. I wanted the TV to raise into position in no more than 30 seconds, a lead of 2mm required the RPMs to be too high. Higher RPMs accentuated any bends in the lead screws resulting in noise and binding. The 8mm lead was so steep the weight of the TV allowed the lead screw to spin down freely. This meant when the TV was in the raised position, there would be too much presure on the timing belt system to keep the TV up in place. A 4mm lead allows the TV to raise 30" in 18.7 seconds with the lead screw spinning at 612 RPMs.
The math: 30" = 0.762m ÷ 4mm travel per revolutio = 190.5 revolutions required to travel 30".
The reason I used 612 RPMs is because I bought this motor from ServoCity.com:
Heavy Duty Premium Planetary Gear Motor - 612 RPM
This motor is great for this application. To mount the motor I bought the 32mm Bore Bottom Tapped Clamping Mount, it was the perfect choice to mount the motor.
My first set of lead screws (8mm diameter, 8mm lead) came from Spool3D.ca. They arrived bent, but Derek worked quickly to replace them. The second set that arrived were close to perfect. As noted above, the 8mm lead is just too steep for this application.
My second attempt at buying lead screws was from Banggood.com, I found the 10mm diameter T10 Lead Screw 36" Lead Screw with Brass Nut, but the 2mm lead proved to be too shallow. Banggood.com reshipped the order two times before I received resonably straight lead screws.
My thrid lead screw purchase was from ServoCity.com. I ordered their 8mm Lead Screw ($29.99) from them so I could see the quality, it was the best quality lead screw and lead nut by far. Sadly, I already knew it would not work for my application as their only option was the 2mm lead. The ServoCity.com 8mm Lead Screw Nut, 0.770" Pattern ($7.99) was my absolute favourite out of all the ones I ordered die to the extra flange on the top. It allowed for the easiest and most precise installation to the aluminum bracket I fabricated. Here are the specs:
8mm Lead Screw Specs:
Material: Stainless Steel
Number of Starts: 4
Outside Diameter: 8mm
The number of starts
My fourth and final lead screw purchase was the T8 Lead Screw Dia 8MM Pitch 2mm Lead 4mm Length 1000mm with Copper Nut THSL-1000-8D from Amazon.ca for $36.71 CDN. It is only 8mm in diameter and the lead nut doesn't have the extra flange I liked so much on the Servo City one, but it has the 4mm lead that I needed.
I found the 3GT (GT2-3M) 9mm Timing Belt - 210mm Closed Loop at MakerParts.ca where I also bought the GT3 Aluminum Timing 9mm Pulley with 8mm Clamp Bore - 20 Tooth. I did not need a gear reduction so went with a 20 tooth pulley on both the lead screw and motor shaft.
Here is a parts list of everything used in the final build:
1, T8 Lead Screw Dia 8MM Pitch 2mm Lead 4mm Length 1000mm with Copper Nut THSL-1000-8D from Amazon.ca - $36.71 CDN
- 1, GT3 Aluminum Timing 9mm Pulley with 8mm Clamp Bore - 20 Tooth, for lead screw- $12.89 CDN
- 1, GT3 Aluminum Timing 9mm Pulley with 1/4" Bore - 20 Tooth, for motor - $9.72 CDN
- 1, 3GT (GT2-3M) 9mm Timing Belt - 210mm Closed Loop - $12.89 CDN
- 2, KFL08 Pillow Block Rhombic Bearing - $6.00 CDN
- 1, Heavy Duty Premium Planetary Gear Motor - 612 RPM - $39.99 USD
- 1, 32mm Bore Bottom Tapped Clamping Mount - $5.99 USD
- 1, External Limit-Switch Kit for Actuators - $18.00 CDN
- 1, Rocker Switch - Sustaining - $9.00 CDN
- 1 pair , 30" - 200 lbs Drawer Slides - $49.00 CDN
Parts cost $167.10 CDN plus $45.98 USD for a total of $224.56 CDN or $179.68 USD (exchange rates will vary over time - published 2017-01-18)
I also bought some aluminum angle and plate as well as some screws to put it all together. All in all it was about 1/3 the cost of the prebuilt TV lift from Firgelli and fits into a very slim cabinet.
I will be producing a detailed video of the prototyping process and final build. Check back later.
If you would like more details, email me:
Version 4 - working TV lift
Bent lead screws