Linear Actuators Home Made

I'm looking at making my own linear actuators for scratch built dozer because I require 150lbs of force at a minimum of 1 second of pushrod travel per cylinder and I need 6 of them. Most companies want at least $400.00 US for each of them. I thoguht maybe I could use a dewalt 1/2 18v 380 watt replacement gearhead for $40 bucks x6 and use a coupling welded to a metal cylinder and a threaded 3/4 inch rod mounted inside the chuck 4 threads per inch to make it go around 1 to 2 seconds load/no load to accomplish this, what you guys think?

UnoDozer:
I'm looking at making my own linear actuators for scratch built dozer because I require 150lbs of force at a minimum of 1 second of pushrod travel per cylinder and I need 6 of them. Most companies want at least $400.00 US for each of them. I thoguht maybe I could use a dewalt 1/2 18v 380 watt replacement gearhead for $40 bucks x6 and use a coupling welded to a metal cylinder and a threaded 3/4 inch rod mounted inside the chuck 4 threads per inch to make it go around 1 to 2 seconds load/no load to accomplish this, what you guys think?

You haven't mentioned the distance of travel required for the actuator.

The first thing you need to do is calculate the power you require.

Power = force x distance (all in appropriate units)

That will tell you if 360 W is enough. Remember to allow a margin to account for friction in the screw.

Russell.

A couple of other things to think about:

  1. Threaded rod is a very high-friction material, and isn't very durable - even with a lot of grease (and you will want to keep it lubed), expect to see more than a bit of wear over time. You may be replacing things often, so design with that in mind.

  2. Threaded rod also doesn't generally have a consistent thread spacing - it is usually just "good 'enuf" - a regular nut will travel fine down the length (only contact 2-3 threads) - while a coupler will bind along the length somewhere. Usually, the ends of the rod are fine (where you would expect to use a coupler) - it's the middle that is problematic.

Thus the reason commercial linear actuators are so expensive - they typically use accurate ACME or ball-thread screws, along with similar travelling nuts, and are also made out of harder, more wear-resistant steel than standard threaded rod.

You may want to - instead of using a steel coupler - use an HDPE travelling nut instead. Such a nut will be self-lubricating, and while it can't be loaded as much, it will cause less wear to the screw. You can make such by taking your HDPE (HDPE can get expensive if you purchase it "virgin" - instead, use lower-cost pre-manufactured cutting boards), splitting the piece to be the nut "down the middle", and then heating the threaded rod and clamping the halves around the rod. The heat will melt and "cast" the threads into the HDPE. It is also possible to cut threads conventionally with a tap, of course.

cr0sh:
You may want to - instead of using a steel coupler - use an HDPE travelling nut instead. Such a nut will be self-lubricating, and while it can't be loaded as much, it will cause less wear to the screw. You can make such by taking your HDPE (HDPE can get expensive if you purchase it "virgin" - instead, use lower-cost pre-manufactured cutting boards), splitting the piece to be the nut "down the middle", and then heating the threaded rod and clamping the halves around the rod. The heat will melt and "cast" the threads into the HDPE. It is also possible to cut threads conventionally with a tap, of course.

Better still use acetal (Delrin) to make the nuts and buy ACME threaded rod, available on Ebay.

Russell.

You can get acme rod and nuts from NcMaster-Carr and MSC.
Don't know how much travel you need, but you might want to look at trailer tongue jacks. Remove the handle,connect your power unit with a lovejoy coupling and you have your actuator.

russellz:
You haven't mentioned the distance of travel required for the actuator.

The first thing you need to do is calculate the power you require.

Power = force x distance (all in appropriate units)

That will tell you if 360 W is enough. Remember to allow a margin to account for friction in the screw.

Russell.

No:

Power = force x velocity

This calculator suggests that a 3/4-6 acme rod will need about 250 oz-in of torque to push 150 lbs.

IMHO the difficult part about dealing with leadscrews is managing the thrust force; you have to make sure that it doesn't push/pull the leadscrew out of its housing or that the thrust doesn't cause so much friction that it becomes harder to turn.

Chagrin:
This calculator suggests that a 3/4-6 acme rod will need about 250 oz-in of torque to push 150 lbs.

IMHO the difficult part about dealing with leadscrews is managing the thrust force; you have to make sure that it doesn't push/pull the leadscrew out of its housing or that the thrust doesn't cause so much friction that it becomes harder to turn.

Yes that's the challenge, 12 threads per inch took 14 seconds to go 8 inches with a 0-600 rpm dewalt ac drill I was testing. I need a minimum of less than 1 second with load to move the rod up down. Larger diameter rods seem to give coarser threading, I can go up to 1 inch diameter before it starts to look odd for the size of machine. I don't know if this will work but I'm thinking using the arduino to program "switch limitiers" into the drill to set start and stop points so I won't run out of threads. I'm looking ot make 2 8 inch pushrod travel 2 6 inch and 2 four inch not including the amount of material to hold onto.
Here is one rod I found......
http://www.ebay.com/itm/304035-3-1-2-10-x-36-inch-3-foot-5-start-RH-Acme-threaded-rod-for-lead-screw-CNC-/131629230945
and another ........
http://www.ebay.com/itm/304070-3-1-5-x-36-inch-3-foot-1-start-Acme-threaded-rod-for-lead-screw-CNC-/141809752011
The first one has a much more aggressive threading pattern, thinking it will give me a faster pushrod travel assuming the drill will handle the loads, perhaps that one is not meant to take a nut at all and I need to consider the second one instead but in a much coarser thread.

An Acme thread requires an Acme nut. It should not be hard to find a nut that fits the thread but often you will see "half nuts" which are split lengthwise to allow the nut to be disengaged from the thread.

Have you considered a rack and pinion drive.

MarkT:
No:

Power = force x velocity

Doh :blush:

Of course. Work = force x distance.

Russell.

Also note that if you have a "5-start" thread pattern, you'll need a 5-start nut to fit.

The term "start" is how many threads spiral around the rod - think of it like the number of teeth on a gear. Normal threaded rods (and bolts and screws) have "1-start" threading - meaning a single spiral around the rod.

The more "starts" you add, coupled with the angle of the thread to travel, tolerances of the nut (and any anti-backlash measures) determine how much force needed, how much force can be transmitted, and the speed the nut will travel along the rod.

More starts also mean a generally higher cost (for both the rod and the nut used).

Finally - ACME thread taps and dies (for cutting your own threads and such) - are not cheap - no where near cheap - just keep that in mind if you need to make custom threads.

Because of their rapid 'lead', multi-start threads (especially those with more than 2-start) are better suited to applications where linear movement of the 'nut' causes rotational movement of the 'screw' rather than rotational movement of the 'nut' causing linear movement of the 'screw'

it might be more interesting to make a replica of a bulldozer that uses the old cable control for the blade instead of hydraulics. An alternative might be to use boat trim tab setups.

https://www.google.com/search?q=bulldozer+cable+control&num=100&lr=&as_qdr=all&tbm=isch&tbo=u&source=univ&sa=X&ved=0CB4QsARqFQoTCPjtvtSD7cgCFQGGJgodbiwDLA&biw=1062&bih=541

Good point Jackrae. If it is required for the actuator to stay put with the 150 lb load and the motor powered off you really need a single start thread and choose the drive speed accordingly.

Russell.

Having been around and driven various bulldozers all my life, I was interested in your post and all the replies. One reason for using hydraulic cylinders to operate the various components of the bulldozer is to apply equal force to the cylinders being actuated. Cylinders to lift and lower the blade must operate simultaneously and supply equal force to each side.

How do you intend to coordinate force and movement using screws?

Paul

How do you coordinate both force and movement? If the blade is unevenly loaded I would think that it needs more force on one side than the other for coordinated movement. I may be completely wrong but would like to know more.

To coordinate movement, irrespective of force, with a screw actuator you can use a servo with position feedback or you can use stepper motors.

Russell.

If the actuators are operated as servos, the blade will go to where told to go or the actuator will stall/break.

zoomkat:
If the actuators are operated as servos, the blade will go to where told to go or the actuator will stall/break.

It's easy enough to control the maximum torque by monitoring the motor current to avoid overload damage.

Russell.

russellz:
It's easy enough to control the maximum torque by monitoring the motor current to avoid overload damage.

Russell.

If the blade is made strong enough, as it should be, one motor will be doing all the work. The other will just be following.

Paul