How to make Lead Screws work

[3543Katie]

I am new to building robots and am making a lift device. I really need help because I don't know how to make lead screws work. I need to know how to power them, and how to attach them onto a arm/ forklift. Also what parts I will need. If you could help me I would love you forever.
-Katie

[TylerS]

Are you dead set on using a lead screw? If you're planning on making a mechanism to lift totes there are many other COTs products that are available specifically tailored to FRC that will be much easier, cheaper, and lighter to use than a lead-screw mechanism.

[Bruceb]

Well we are considering using a lead screw as well and I for one don't think there is a weight penalty. The conundrum I have is trying to figure out much power I need to turn the thing.
The JVN calculator is not usable for this as far as I can tell.
Can someone provide some math for this or a lead screw power calculator?
Thanks

[TylerS]

Originally Posted by Bruceb

Well we are considering using a lead screw as well and I for one don't think there is a weight penalty. The conundrum I have is trying to figure out much power I need to turn the thing.
The JVN calculator is not usable for this as far as I can tell.
Can someone provide some math for this or a lead screw power calculator?
Thanks

You're right they can be made quite light, I spoke too soon.

[pfreivald]

Originally Posted by Bruceb

Well we are considering using a lead screw as well and I for one don't think there is a weight penalty. The conundrum I have is trying to figure out much power I need to turn the thing.
The JVN calculator is not usable for this as far as I can tell.
Can someone provide some math for this or a lead screw power calculator?
Thanks

https://www.youtube.com/watch?v=FUNFcvnKQ-Q

Right at the beginning of this video, you can see our lead screw-controlled claw (something I wouldn't recommend for a variety of reasons--it was far too slow for that application, and complete overkill on torque--but we considered it for a lift this year). The motor and planetary gearbox are attached directly to the non-mobile part of the robot, and the nut is attached to (and able to pivot on) the "elbow". As the screw turns, the nut rides up and down on the screw, forcing the distance to change and thus pivoting the claw.

For a forklift, you'd have a simpler setup: The motor would mount in line with the carriage motion, at one end. The carriage would contain the nut, and as you turned the screw you'd lift the carriage up and down.

Calculating the torque/speed at any given power requires treating the lead screw like an inclined plane to calculate the mechanical advantage. (So if a single rotation of the screw has a circumference of 1 inch, but the nut moves .5", you have a 2:1 reduction.)

Efficiency really matters, though--they tend to be resistant to backdrive, but slower than you expect them to be, especially under load or if the screw bends.

[Dad1279]

Originally Posted by Bruceb

.......
The JVN calculator is not usable for this as far as I can tell.......

For an approximation** I use the Linear Mechanism tab, and adjust pulley diameter and gear ratio for the turns per inch of the leadscrew.

For pulley diameter I use 1/pi (.318) (forces the spreadsheet to 1 unit of revolution to 1 inch of travel)

Then in addition to whatever gear/sprocket/belt ratios you are using to drive the shaft, add a gear ratio (Drivingriven) of 1:[tpi of screw] (1:5 for a 5 tpi acme screw)

**This does not take into consideration friction/loss of the leadscrew, which could be very high (steel screw/nut needing lubrication) or low (ballscrews, etc) so design conservatively.

[jman4747]

Originally Posted by Bruceb

Well we are considering using a lead screw as well and I for one don't think there is a weight penalty. The conundrum I have is trying to figure out much power I need to turn the thing.
The JVN calculator is not usable for this as far as I can tell.
Can someone provide some math for this or a lead screw power calculator?
Thanks

Manufacturers often have papers like this to help with using the products.
http://pic-designcatalog.com/images/.../section_3.pdf

http://www.sdp-si.com/D810/PDFS/Ball...l%20Inf o.pdf

[mentorDon]

Originally Posted by jman4747

Manufacturers often have papers like this to help with using the products.
http://pic-designcatalog.com/images/.../section_3.pdf

http://www.sdp-si.com/D810/PDFS/Ball...l%20Inf o.pdf

There is some excellent information in the PIC design catalog pdf. I would also suggest to make your design using the screw in 'tension' instead of 'compression'. If your design forces are compressing the screw, use the MAXIMUM COMPRESSION LOAD vs. LEAD SCREW LENGTH graph on page 3 to determine buckling limits. As an example, using a 3/8 dia screw with a force of 100 pounds, the maximum screw length using the 'A' method (fixed - free), is about 12 inches.

[InFlight]

A lead screw will easily work, but you will need a lathe do some machining on the screw ends for bearing supports. I’d suggest driving it with a ~ 40:1 gearing and an HTD pulley or chain sprocket drive.


IGUS has hardware and design guides.

http://www.igus.com/wpck/3556/drylin...zgewindemutter

[tr6scott]

I had contacted igus for recommendations, and help calculating, but seems the team is going a different direction. I'm electrical mentor, so don't ask any questions of me, just posting as it may help others.
I was hoping for a solution that would not backdrive, but to get the speed we wanted 2 seconds up, 2 seconds down, that was not going to work, so if you use this solution you will need to power motors 100% of time or add some brake mechanism to hold the load.

===================

- How far apart will the 2 lead screws be located?
Distance between the two lead screws will be between 18" and 22"

- Where will the center of gravity be in relation to the nuts?
The cg of the totes will be 2" off the center of the nuts.

- Will you be using a liner guide as well?
Yes, we plan on using some Alum extrusions (Acme, 80-20 with their slides componets)


Please confirm?
- 60 lb load
- 2 foot stroke
- 1 foot/second

Due to the speed a high helix nut will be needed. Unfortunately the high helix are not available in the anti-back lash version. Please advise and I will get the report over to you.

[snoman]

http://firstchoicebyandymark.com/fc15-037

they are out of stock now. but you can look up the specs

[asid61]

You could go with ballscrews if you have the cash. Low backlash (almost none, like 0.003" at the worst) and higher lead, and hugher max speed.

[Dan Richardson]

We have a calculator on our site to help determine speeds and forces: http://dartactuators.com/calculations-actuators/

You can also download our step files to see some of our design considerations in using a lead screw.

[JamesCH95]

In 2013 we machined the end of a lead screw into a 1/2in hex and mounted it in a typical FRC hex bearing and drove it with a VexPro gear with a 1/2in hex. Everything was sandwiched together with a 10-32 cap screw in a hole tapped into the lead screw. It was drive by 2 CIM motors and a 775+cim-u-lator with a single gear reduction, around 16:72. 72t gear being mounted on the lead screw.

It worked well, we had no issues all season with it.