Introducing a new Johnson Electric PLG motor for 2020

Johnson Electric is introducing a new brushed motor to FRC through FIRST choice round 2 and I thought I would do a little write up to give some detail so teams can make an informed choice if they want to consider. I will be supporting questions and feedback on this motor and I know FRC very well as I’ve been a mentor for almost 20 years. It was announced in an earlier FIRST blog but I’m sure largely overshadowed by the brush-less options being introduced. I too am excited to to see brush-less making its way into FRC although brushed motors still have a place in the medium to low power requirements and possibly for teams who don’t have large pocket books.

This motor is typically used in automotive applications to drive a lead screw for operating the tailgate in SUV’s. PLG stands for power lift Gate. Here are a few details to summarize…

  • 2 stage planetary motor ~ 1.15" in diameter and 4" in length and ~1/2 lb.
  • Gear reduction is 22.2:1
  • Free speed is ~ 410RPM and stall torque is ~4.5Nm.
  • 2 hall sensors are integrated in order to get output on motor direction, speed, and distance. There are 6 wires of which you really only need 2 (red and black) to operate. The 4 extra are for optional hall feedback.

Some initial thoughts for where this motor could be used…

  • moving and indexing power cells inside the robot. Speed seems good for that.
  • Since it’s light weight it’s a good motor to put on an end effector.
  • Driving a lead screw for precise positioning of a mechanism (ie shooter positioning).

A link to the screen steps document can be found here. Trying to provide as much useful information as possible for mounting and interfacing. I’ll also include some videos to see actual speed and some application suggestions.

An adapter is being offered to covert the motor output to an FRC standard 1/2" hex. The adapter includes an 8mm hole if teams want to add a lead screw which is a typical size for many 3D printers and is readily available on Amazon. Suggest to drill and tap a set screw and grind a flat area to keep it locked.

I hope teams will consider this motor this year for their FirstChoice round 2 selections. I will do everything I can to make sure there is support if there are any issues and will monitor this forum often.

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I’m not sure if this will wind up on our robot in 2020 (still lots to discuss), but I appreciate the heck out of suppliers that make the effort to make their donated items easy for teams to integrate. (stares in throttle motor)

Thank you to Johnson Electric for making them available!

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Your Welcome Billfred. I’m only speaking on behalf of Johnson electric as an engineer and not an official spokesperson but everyone here is excited to be a part of FIRST. As some older folks may remember JE was the motor on the old Fisher Price gearboxes of many years past.

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Looks very interesting. Will these be available for purchase through AndyMark or through another source?

It should be available for sale through AndyMark but still some details to work out.

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Are model files available for the 3D-printable mounting components shown in the screen steps documentation? My apologies if the links are there, but I didn’t see them in the screen steps or on the FIRST Choice product page. The CAD file has only the motor and the adapter, not the mounting components.

Yes I will be posting that. Just wanted to work out a few minor bugs as some of the pockets are a bit tight.

If I can’t buy spares, I will not push for it to go on our robot. Hoping the details with AM get ironed out soon.

I completely understand and have planned for that. I have a good stock of extra parts on hand for just that reason. Somehow it will be make available for teams to purchase as extras and replacements.

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Being able to purchase would be a big criteria in me deciding to use this motor, and ideally that information would be available prior to the closing of FIRST Choice round 2 priority lists on Thursday.

Thank you for this thread. It helps us a lot. As we are a python team with limited resources, for us, when new gear comes out (especially during build season), we look at a few things.

  1. How easy will it be to incorporate the programming into our robot (we would love to help develop code for new hardware in the python forum, but our skills are just not there yet, but we are improving fast). This motor seems to fit that bill well.

  2. How easy will it be to put on our robot. We have finally realized that standardized (ish) mounting plates make our lives much better. As such, if these were available to teams, we would definitely consider this motor, however, for us, since it looks like we would have to fabricate some mounting pieces in order to incorporate this motor into our designs, it may not work for us this season. To echo sentiments above, if others are available after FC closes, or mounting plates like the AM-4166 come out, we will definitely consider it. Until then, we stick mostly to the rs, cim, and PG lines for continuity’s sake.

Still, this looks to be an incredible motor. Thank you for sharing.

~ Mr. R^2

You’re welcome Mr. R^2. It should be very easy to incorporate code to read the hall pulses. I’m currently getting some support from AndyMark on reading hall pulses with the RoboRio which is the more difficult item and I’ll make sure to add programming details as well once that is sorted out. The voltage threshold on the pulse is right for the Rio but the motor requires a 1Kohm pull-up and I’m not sure if the integrated Rio pullup will work or if additional steps are needed in-between.

As I create the content and think of solutions…my thoughts are completely with your kind of teams in mind. As an introduction year for this motor feedback is very critical so it’s very important that teams give it a shot and we hear what works, what doesn’t and if teams find this motor useful. If useful then we will take the steps to provide a ready to go mounting solution. One of the solutions proposed uses U brackets which can be found at many hardware stores and it targeted to teams with minimum machining capability. I know that format well as my current team used to be that kind of team. A small amount of precision is needed to match the bolts to the pockets to keep the motor from rotating but aside from that it is very easy to implement and works very well. It is pretty easy to make that proposed solution work with the 1x1 predrilled square tube provided by AM and Vex if that’s your format. Also, there are plenty of companies that will 3D print parts for you if you don’t have access to a printer. I plan to provide the models for the proposed 3D printed solution.

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Kevin swooping in again with more motors.

Is this motor designed for the thrust load of a leadscrew?

Think so. Native application is to drive a 12 start lead screw. I’ve been experimenting with a 4 start lead screw but have not pushed the limits to the max.

In the native application is there another bearing or bushing taking the thrust load?

There is a bearing and a pretty aggressive spring. It’s pushing up a tailgate so needs that assist. I’ll post some pictures of the part I disassembled and will add some suggested methods for FRC design.

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Hypothetically, is there an automotive application that uses one of these FRC motors to power a lift gate that I might find at the wrecker? Say like a Ford Explorer or Kia or something? :slight_smile:

The motor is so well integrated in any of those parts you would find in a junk yard and it’s so hard to disassemble (also dangerous because of the large spring) so I don’t recommend that. Also, the motor interface is not completely standardized. It’s not too hard to replicate if you don’t include the large spring for assist. I noticed that AM has a thrust bearing if you need.

I was just thinking about a readily available linear actuator that isn’t a DART. The large-spring could pose a problem from the ‘stored energy’ aspect though.

There doesn’t seem to be too many options does there?? One of the big disadvantages (as with the Dart)… if you don’t have limits or they fail it’s very easy to jam and that isn’t always so easy to fix.

For something like positioning a shooter where it doesn’t see a whole lot of impacts it’s really not too hard to fabricate using available parts and a little 3D printing (or precision machining). I’ll try and add some ideas to the screen steps.