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I recently bought 10254 Winter Holiday Train and wanted to get it running around the provided circle of track. I was wondering if there is any way to do this without incorporating the IR receiver and speed remote? My understanding is that if I were to simply connect a battery box to the motor and switch it on it would run too fast and de-rail.

I suppose my question is ultimately; is there a way to limit the speed without using the speed remote? The train will only ever go around a perfect circle of track so I have no desire to alter the speed for straights/corners. I don't have a huge knowledge of electronics but can use a soldering iron and am willing to get my hands dirty.

I also understand that the rechargeable battery box has a variable speed output (which does sound ideal) but was wondering if there is a cheaper option?

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There is a fairly easy and cheap way to do this since you don't want real variable speed control. As you noted, connecting the AAA battery box directly to the PF train motor technically works, but the motor runs too fast.

The default AAA battery box provides 9v from 6 AAA cells. Lowering this voltage will lower the speed of your motor. If you'd like to get your hands dirty, you can modify the AAA battery box or buy a battery box that supplies another voltage and connect this up to the C0 and C1 lines of your motor.

However, the simplest solution I can think of is to purchase (or possibly build) AAA dummy batteries and use a few of these in the AAA battery box in conjunction with regular batteries. These look like AAA batteries, but are actually just metal conductors internally. By using a number of these in the battery box, you can have it provide 1.5v, 3v, 4.5v, 6v, 7.5v, or 9v.

Philo has a nice breakdown of speed vs voltage for PF train motors:

3V = 135 rpm (2 AAA batteries, 4 dummies)
4.5V = 468  rpm (3 AAA batteries, 3 dummies)
6V = 792 rpm (4 AAA batteries, 2 dummies)
7.5V = 1107 rpm (5 AAA batteries, 1 dummies)
9V = 1458 rpm (6 AAA batteries, 0 dummies)

You can make adjustments in 1.5 volt increments by adding or removing batteries from your setup to hopefully find a speed that works for you.

It's a bit more complicated/expensive to get proper variable speed control, but if you just want a constant speed that is slower than the default PF full speed, this is the simplest method I can think of.

  • This is exactly the kind of solution I was after, I've found some very cheap dummy batteries online, thanks so much for your help! – Matt Nov 7 '16 at 22:45
  • Don't you mean AAA batteries? Battery box 64228 rather than 58119 (see this page for example) – Móż Nov 8 '16 at 21:47
  • That's a great point. I've changed this to AAA since that battery box is a better fit for trains. The math is the same for both, and either one should technically work. – jncraton Nov 8 '16 at 23:33
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LEGO train motors get powered using a 9V cable. Philo (who also visits this site) has an excellent site with all the features and characteristics about the PowerFunctions motor system, which includes trains. This site is located at http://philohome.com/tech.htm.

The speed of the train is regulated using PWM (Pulse Width Modulation) on the inside two wires (C0 and C1) of the power functions connector. If you feel adventurous, you can cut a PF cable and put electronics in between (an Arduino perhaps) to give the train a constant speed (perhaps read the speed from a pot-meter, this is how the rechargeable battery box works).

For reference, I've done something similar in my RFID controlled train, see my video on Flickr. Just a word of warning, unless you know what you're doing you're probably spending a lot of time on this and just forking out $50 for the rechargeable battery (plus either $30 for LEGO's adapter or $10 for a generic adapter (assuming you can regulate the voltage and the polarity of the pin)) might be the easiest and most cost-effective option.

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    Thanks very much for your suggestion, I loved your video, looks so fun! – Matt Nov 7 '16 at 22:49
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Easy solution. Use 3 dead batteries, 3 new batteries. Achieved perfect speed.

Dead batteries are easy to find in kids toys :)

  • That's not a bad solution - you may want to mark the "known" dead ones to help you replace the real ones when they go flat ;) – Zhaph - Ben Duguid Nov 28 '17 at 12:27

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