Linear Actuator with JE PLG motor - Pneumatic alternative

I’ve been working on a linear actuator design that utilizes the Johnson Electric PLG motor. FYR, I work there so that’s why I have focused on that motor. The motors native application is to drive a lead screw to open a power liftgate so this is falling in line with the motors native application.

The target for this design has been to use as a pneumatic alternative for those times you don’t want to commit to pneumatics. It is also useful when you might want precise location which are very difficult with pneumatics. Speed and resilience was the main focus so the lead screw I chose (IGUS 50mm/rot) is fast and can be back driven with little effort. Most parts are 3D printed with others easily obtained without much effort. I’ve gone through many iterations and have found a good compromise of simplicity and robustness although not yet FRC competition season battle tested. There is very minimal machining involved and you don’t need a high degree of precision for the machining required. Here’s a BOM and a 3D step model.

I have tested two designs and below is a graph of the output. Y axis is inches/sec:

  1. 1:1 motor to lead screw gearing & 25mm linear actuation per lead screw rotation (blue line below)
  2. 1.5:1 gearing & 50mm linear actuation per rotation (red and yellow line below)

    Note: this graph was obtained by adding weights to the mechanism shown in the video below. It could go beyond where the lines stop but I just chose to stop taking data at those points as you really don’t want to operate beyond that too much.

This video shows condition 2 which seems the best for the objective mentioned. It reaches 15 inches/s at low load condition which one may see when actuating a mechanism not working against gravity (ie horizontal low friction configuration).

It does back drive at about 5lbs (motor locked) which helps for the resilience part. If you provide hard stops you can avoid the typical and dreaded jamming issues so common with these types of linear actuators. Adding some sensors that give feedback on limits are useful to back off or cut power so you’re not holding at stall for long periods. This motor does have a thermal switch that will cut power before the motor makes magic smoke but you’d only want that as a last resort. Still working on some options for limit switches.

I would be curious what others think and would appreciate any feedback. I’m sure there’s room to improve and build on it. Over the years I have found this to be a design that could have really come in handy which is why I’ve invested time in it and am sharing. Also, hoping to provide teams another use for the JE PLG motor. Putting my affiliation aside it is a nice little motor.

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This is super cool! I like the PLG motor, and this just took it up another notch in usefulness. Thanks!

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Love the looks of this, and may end up building one for testing myself. A couple of questions:

  • What are the M5 bolts for? A quick glance at the CAD and I’m not seeing where they go. The BOM describes them as fasteners for “Main Tube Attachment” and “Tube Adapter to 3/4 tube”.
  • Are you utilizing the JE-PLG-410, or the JE-PLG-149? I ask because the 149 model appears to be discontinued now, with it’s replacement (the 410 model) being slightly less powerful.
  • Is there any reason you’re aware of that the Aluminum version of the AndyMark hex shaft for these wouldn’t work (with the square connector instead of the spline)? AndyMark only appears to have the aluminum one in stock.

The biggest “concern” I see here is the cost of the lead screw and associated nut. At $65 USD for a 300mm lead screw, and $30 USD for the nut, a roughly 12in stroke would cost just under $100 USD, not including the costs of the motor and other odds/ends.

Again, love the concept and think it has the potential to be very useful, but the price has me a little leery (perhaps I’m also completely undervaluing what a device like this should cost in FRC).

Thanks for the feedback Brian! Would love to get more feedback if you decide to build.

I do have some cleanup with the BOM as there is probably a few more tweaks. The M5 bolts not shown in the CAD is for attaching the end cap and the main tube to the mount base. You’ll see holes on those parts for these bolts. I am using the JE-PLG-410 although you can use the 149 as well. Unfortunately I have no control as my company decided to replace that motor. The aluminum adapter would work just fine it’s just a tad on the large size so fit of the bearings and pulley is very tight. It’s just a pain to deal with which was the main driver for the steel adapter as that stock tends to run smaller than Aluminum hex stock. The steel adapter will be offered in FirstChoice round 2 and is the preferred option for the reasons mentioned.

I agree that cost is a bit steep but it’s a nice lead screw. Maybe I’ll look for some alternatives a bit less draining on the pocketbook. I did notice a lead screw in FirstChoice (Powered by AndyMark) which is 25mm/rot but a different adapter. I have made a design that works with that but don’t have access to the part. It would work although slower and appears not to be as efficient as the IGUS which has a low friction material. maybe we can all push on IGUS to offer lead screws instead of the standard options they provide each year which my team has many unused from all the years they’ve been donating the same parts.

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Thanks for the insight! I definitely agree the igus screw you’re using is nice.

The one in FIRSTChoice is rather nice from a cost perspective of veteran teams (at the cost of performance as you pointed out). Having received those in the KOP for many years, we (and im sure many other teams) have plenty of those kicking around that would otherwise continue to go unused.

I’ll have to see if we can spare some credits to maybe pickup some parts for this in the next round of FIRSTChoice.

If not for a lead screw application it sure makes for a nice (yet expensive) fidget toy. Everyone that handles it can’t put it down :slight_smile: :smiley: Glides like it’s on air. I hear that IGUS is pretty good about providing maybe a free sample if a team asks. Would be nice if IGUS would provide credits so teams can choose what they want. They have really nice products but should work towards a model that reduces the amount of parts over the years that go to waste.

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