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Yet another PF speed control mod
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The PF Speed Control (8879) can be exasperating, but some MOCs demand it. This mechanical mod makes some of its quirks a little easier to live with.
About this creation
Please feel free to look over the images and skip the verbiage.

Over the years, I've developed an intense dislike for the Power Functions IR Speed Control handset (8879, hereafter "SCH").



The bare SCH with the mod presented here behind it.

Problem is, some MOCs demand the SCH. My motorized prop-carts (e.g., MPC3 below), outboard powerboats (e.g., Earline below), and Round Up amusement ride are cases in point: Without some way to limit motor power, these otherwise well-behaved MOCs would either be effectively unsteerable or way too fast.





Apart from the fact that it's IR-based (don't get me started), I have 2 main beefs with the SCH: (i) Lack of positive control over absolute power level. (ii) Small angular separation of power levels.

I'm sure LEGOŽ had their reasons for the SCH's design (cost and durability in young hands come to mind), but it still seems out of keeping with the well thought-out products I've come to expect.

The simpler and much more user-friendly 3-state (full forward, off, full reverse) Power Functions IR Remote Control (8885) is basically a dead man's switch with a brief delay. It commands the IR receiver on the same channel to cut the power after a delay of ~1 second if IR contact is lost.

The SCH, on the other hand, tells the IR receiver to keep putting out the juice if contact is lost. I've had some very close calls with MOCs headed for disaster after losing IR contact with the SCH. (Of course, the SCH's kill buttons are useless in such situations.)

Like most of the SCH mods found on MOCpages and elsewhere, this MOC is a mechanical band-aid intended to take some of the sting out of these shortcomings and improve the ergonomics for AFOL hands in the process.

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Design notes

It might well be possible to add hard stops to the SCH dials, but the only way to gain more positive control over the 13 power levels in between is to enlarge the angular separation between them, and that's what I've done below.



Each click-stop on one of the SCH's orange dials changes the power level by ±1 (e.g., from 3/7 to 4/7) until the ±7/7 power levels are reached. Continued turning of the dial in the same direction has no effect thereafter. At 21 click-stops per revolution, the power levels are just 17° apart on the dials.

The 26° separation afforded by the 36:24 dial gearing makes speed selection much more reliable, and the 36-tooth double-bevel gears turn out to make excellent thumbwheels with a very comfortable feel.

Better yet, the gearing happens to amplify the auditory and tactile click-stop feedback built into the speed dials.

The ergonomic changes discussed below are big wins 99% of the time.

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More photos

Of the many SCH mods I've tried, the one presented here is my favorite by a wide margin. It shares some features with other mods I've seen, but the total package is my own design.





The large 36-tooth gears serving as thumb wheels allow more accurate adjustment of output speed levels -- in part due to amplified auditory and tactile feedback.





The black knobs (Technic balls, later red) effectively put the controller's built-in red kill buttons right under your thumbs when using the thumb wheels. Quick kills are essential for both fast MOCs and those involving finnicky adjustments.





The side grips (i) add rigidity to the thumb wheel mounts, (ii) place adult thumbs directly over the thumbwheels, and (iii) make the controller much easier for AFOL hands to hold comfortably in operating position.

The kinda good news: You can still work the channel selector by coming at it from the front with a thumb.

The kinda bad news: You'll need something pointy to work the polarity switches, but polarity changes usually represent a tiny fraction of the typical SCH workflow.

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The LEGOŽ remote control system of my dreams

The PF system ain't it.

For a host of reasons, the non-Mindstorms remote control system of my dreams would revive the RF signalling last seen more than a decade ago in the RC Race Buggy and related products.

For starters, RF technology would (i) extend the PF system's pathetic range, (ii) eliminate its crippling line-of-sight restriction, and (iii) do away with the interference by sunlight and bright incandescent lighting, both of which are loaded with the IR wavelengths used by the PF system. The last problem makes the PF system all but unusable outdoors during the day.

My dream receiver would be a heck of a lot smaller and lighter than the RC Race buggy receiver, seen below in a friend's powerboat.



My dream handset would have hard stops at full forward and full reverse with reliable, well-marked, and widely spaced click-stops at the power levels in between.

I'd keep the panic buttons for emergencies but widen the no-power zone relative to the others to make it easier to find. (Gradually ramping the power down to zero is very much hit and miss with the SCH.) I'd also add a switch to turn the auto-stop feature on or off as desired.

Just add money.

The good news: The third-party PF-compatible Bluetooth-based sbrick has many of my dream features, and the iPhone and Android apps seem are working reasonably well as of March, 2017.

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Specifications

Overall dimensions:76 x 128 x 88 mm in LxWxH
Overall weight:0.169 kg (0.37 lb)
Construction:Studless
Thumbwheels:36-tooth double bevels with 1:1.5 overdrive
Angular separation between dial click-stops:26°
Electrical power:3 rechargeable AAA NiMH batteries
Modified LEGOŽ parts:None
Non-LEGOŽ parts:None
Credits:Entirely original feature package

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Comments

 I made it 
  July 2, 2016
Quoting Pedro Damiao Where Do I find instructions or a list of the pieces you used to make it?
Sorry, not available.
  July 1, 2016
Where Do I find instructions or a list of the pieces you used to make it?
 I made it 
  May 4, 2015
Quoting White Shapes Excellent description, as always. I have read 90% of this page, to include the comments :) V 1.3 of the android Sbrick app works with my simple configuration (1 Sbrick controlling cars with various features), but it's still a beta for sure ! Marc
Thanks for the kind words and sbrick update, Marc. Interesting that Android's giving them so much trouble.
Jeremy McCreary
 I like it 
White Shapes
  May 2, 2015
Excellent description, as always. I have read 90% of this page, to include the comments :) V 1.3 of the android Sbrick app works with my simple configuration (1 Sbrick controlling cars with various features), but it's still a beta for sure ! Marc
 I made it 
  February 18, 2015
Quoting Walter Lee Very very nice! I too have lost control of my PF IR creations more than once - sunlight really limits the effective distance of its IR system to a few feet. I also been playing around with Lego's RC Racer system but they use batteries quickly and lack an on-off button on the transmitter or motor-receiver which makes conserving power difficult.
Thanks, Walter. Agree, all LEGO RC solutions have serious issues. The third-party sbrick looks to be our best bet for the foreseeable future. Can't wait till they get the Android software working.
 I like it 
  February 17, 2015
Very very nice! I too have lost control of my PF IR creations more than once - sunlight really limits the effective distance of its IR system to a few feet. I also been playing around with Lego's RC Racer system but they use batteries quickly and lack an on-off button on the transmitter or motor-receiver which makes conserving power difficult.
 I made it 
  February 16, 2015
Quoting Giorgio Ferrannini It's pretty late now so I admit I haven't read the whole text, but I get the point of this mod and I will certainly build and try it. Tomorrow, maybe.
Giorgio, please let me know if you find ways to improve it. And don't worry -- nobody reads even 10% of my pages. They're all way too long.
 I like it 
  February 16, 2015
It's pretty late now so I admit I haven't read the whole text, but I get the point of this mod and I will certainly build and try it. Tomorrow, maybe.
 I like it 
  March 20, 2014
I think I needs to gets me one of them. Perfect for chasing a pet, reaction time you know. ;) Clever design!
 I like it 
  March 18, 2014
good idea!
 
By Jeremy McCreary
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LEGO models my own creation MOCpages toys shop Yet another PF speed control modTechnic


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