Connecting 12V Motor to 9V RC Motors

[FGMatt]

I'm planning on using 12V tracks to run a very long and heavy train, so I want to use multiple motors. I don't want to use multiple 12V motor units because:

1. They're eye-wateringly expensive
2. It will be difficult to use electrically-separate sections of track, as the motors will all be picking up whichever section they're in (unless I modify the aforementioned vastly-expensive motors)

So it seems like a simple solution to use the very cheap RV 9V motors, create a 12V-connector-to-9V-plate wire and then either:

1. Run the whole thing at a maximum of 9V
2. Run the whole thing at 12V and hopefully not blow up the 9V motors
3. Make a special brick (probably from machined brass) containing a 9V regulator as part of the adaptor

Does anyone have any thoughts - or even better experience - with doing anything relevant? One thing I'm wondering is whether there's any significant speed differential between the RC and 12V motors when running at the same voltage; I don't really want the back half of the train trying to overtake the front.

[Andy Glascott]

My guess is the 9v motors will cope with 12v of power. I asked a similar question a few years ago and it’s safe to run a PF motor at that voltage so it may well be ok for the RC ones too. 

[FGMatt]

Well that would certainly make things simpler!

 

Thanks

[ivanlan9]

I've run my 9v motors for years using an HO MRC throttle with sound with no harmful side-effects.  I will say that I never ever run them at the full 12v, because at that speed it takes only a second or two of high-speed running to derail.  Plus it's not at all prototypical--running most HO locos at full throttle results in them flying along at three hundred MPH (480KPH).  I'd imagine that if you did the math to figure out Lego scale speed it'd work out roughly similarly.

[zephyr1934]

I'd suggest using a dead 12v, or one of the 12v power pickups, or a custom pickup to draw the power and then use the modern PUp motors since they are the easiest and cheapest motors you can get (in case you burn a few out).

In terms of friction, 12v era wheel sets > 9v era wheel sets > roller bearing wheel sets. You will be able to pull a lot more with roller bearings at the same effort than you will with any of the other alternatives

How long, how heavy, how many curves, and what radius. R120 are a lot friendlier than R40, but if you are using standard 12v you are stuck with R40. 15+ years ago I was running 40+ car trains in the 9v system. Usually 3 motors was sufficient to move any train on relatively flat surfaces (with 9v wheel sets) before other factors started limiting the length. The first thing to go is the magnetic couplers, fix that with rare earth magnets (or technic links), the next thing to go are the cars stringlining the curves, I never did fully fix that problem but putting the heaviest cars first definitely helped. I had all of the motors at the front though, these efforts were on tables at shows and I did not want the rear of the train pushing a stalled front of the train off the tables. If you are running on the floor or some other safety zone to the edge of tables or simply don't care, distributed power will essentially let you make the train as long as you want but coordinating control potentially becomes a big problem

Curves will be your enemy, not only stringlining but also varying the effort to pull your train. I had one layout with very long straights and then two closely spaced 90° curves. The power needed to get the heavy train moving slowly through the two curves was enough for it to speed up so much on the straight that it would shoot off the track at the next curve. So making a roughly square layout that is like 2.1 times longer than your train (i.e., just after the rear of the train leaves one curve the front starts into the next) will balance the drag from the curves and make your life easier.

Starting a really heavy train, especially on 9v track where you will have dead spots- not just due to dirt also to rail joints and switch frogs, is an art unto itself. Being able to use the "hand of god" just behind the engines helped a lot getting up to speed.

Delivering enough power to the rails is also an issue. At a minimum you will want multiple power connections to the track. I've never used 12v track but with 9v there are a few ohms resistance in the track joint. No big deal with city trains, but draw a lot of current across N rail joints and 9v-N*iR starts to be significant. In other words, as the power demand increases so too does the voltage drop at each rail joint.

It does not sound like you plan to use 9v controllers, but since I've gassed on so long about 9v why stop now? 9v controllers can only really deliver power for up to two 9v motors (I THINK that was Lego's spec, and in my experience they would drop out when I ran three motors for more than a little while). So for the long trains I would connect two or three 9v controllers around the loop, with NO isolation. Probably not good for the controllers but at the time Lego would include one controller with each set so we had plenty of surplus. I don't think I'd do that now.

If you are using 12v track, the teeth on the rails will help you a lot, though I do not know how compatible they are with the narrower treads on the modern motor wheels, so you might need to experiment there to make sure you have enough contact.

Make sure there is enough weight on each motor so the wheels do not slip (too much)

Good luck and post pictures/video if you do so in brick

[wannes_dn]

12V

[FGMatt]

On 8/20/2023 at 3:30 PM, zephyr1934 said:

I'd suggest using a dead 12v, or one of the 12v power pickups, or a custom pickup to draw the power and then use the modern PUp motors since they are the easiest and cheapest motors you can get (in case you burn a few out).

In terms of friction, 12v era wheel sets > 9v era wheel sets > roller bearing wheel sets. You will be able to pull a lot more with roller bearings at the same effort than you will with any of the other alternatives

How long, how heavy, how many curves, and what radius. R120 are a lot friendlier than R40, but if you are using standard 12v you are stuck with R40. 15+ years ago I was running 40+ car trains in the 9v system. Usually 3 motors was sufficient to move any train on relatively flat surfaces (with 9v wheel sets) before other factors started limiting the length. The first thing to go is the magnetic couplers, fix that with rare earth magnets (or technic links), the next thing to go are the cars stringlining the curves, I never did fully fix that problem but putting the heaviest cars first definitely helped. I had all of the motors at the front though, these efforts were on tables at shows and I did not want the rear of the train pushing a stalled front of the train off the tables. If you are running on the floor or some other safety zone to the edge of tables or simply don't care, distributed power will essentially let you make the train as long as you want but coordinating control potentially becomes a big problem

Curves will be your enemy, not only stringlining but also varying the effort to pull your train. I had one layout with very long straights and then two closely spaced 90° curves. The power needed to get the heavy train moving slowly through the two curves was enough for it to speed up so much on the straight that it would shoot off the track at the next curve. So making a roughly square layout that is like 2.1 times longer than your train (i.e., just after the rear of the train leaves one curve the front starts into the next) will balance the drag from the curves and make your life easier.

Starting a really heavy train, especially on 9v track where you will have dead spots- not just due to dirt also to rail joints and switch frogs, is an art unto itself. Being able to use the "hand of god" just behind the engines helped a lot getting up to speed.

Delivering enough power to the rails is also an issue. At a minimum you will want multiple power connections to the track. I've never used 12v track but with 9v there are a few ohms resistance in the track joint. No big deal with city trains, but draw a lot of current across N rail joints and 9v-N*iR starts to be significant. In other words, as the power demand increases so too does the voltage drop at each rail joint.

It does not sound like you plan to use 9v controllers, but since I've gassed on so long about 9v why stop now? 9v controllers can only really deliver power for up to two 9v motors (I THINK that was Lego's spec, and in my experience they would drop out when I ran three motors for more than a little while). So for the long trains I would connect two or three 9v controllers around the loop, with NO isolation. Probably not good for the controllers but at the time Lego would include one controller with each set so we had plenty of surplus. I don't think I'd do that now.

If you are using 12v track, the teeth on the rails will help you a lot, though I do not know how compatible they are with the narrower treads on the modern motor wheels, so you might need to experiment there to make sure you have enough contact.

Make sure there is enough weight on each motor so the wheels do not slip (too much)

Good luck and post pictures/video if you do so in brick

Cheers, very thorough!

It's going to be an exceedingly large layout, so the power supply will all be customised rather than using any Lego components. I'm planning to keep corners relatively to a minimum; no more than 90 degrees within the train length, and I'm also thinking of making a larger radius by alternating pieces of curved with straight track.

[zephyr1934]

On 9/26/2023 at 8:31 PM, FGMatt said:

Cheers, very thorough!

Excellent

 

On 9/26/2023 at 8:31 PM, FGMatt said:

I'm also thinking of making a larger radius by alternating pieces of curved with straight track.

Test it before jumping head first to make sure it works for your needs. It will give you larger radii, but if you are at the limits of your pulling power and using cars with bogies it might create more drag than the normal R40 curves. Each time a bogie transitions between straight and curved it has to rotate and that rotation creates resistance for the engine to overcome. I'm not saying it won't work, I'm just saying you might want to make sure there are no nasty surprises after you make a big investment.

[FGMatt]

21 hours ago, zephyr1934 said:

Excellent

 

Test it before jumping head first to make sure it works for your needs. It will give you larger radii, but if you are at the limits of your pulling power and using cars with bogies it might create more drag than the normal R40 curves. Each time a bogie transitions between straight and curved it has to rotate and that rotation creates resistance for the engine to overcome. I'm not saying it won't work, I'm just saying you might want to make sure there are no nasty surprises after you make a big investment.

Cheers, will bear that in mind