R.C. conversion of a GP7 using parts from RC car, several questions.

[Boyd]

I bought a R.C. tank 18 months ago. A cheaper one that cost about $100. It didn't really impress me much and I've only ran it about 2-3 hours. It uses a 7.2v rechagable battery pack. It has left and right sticks for the drive. But its only one speed and not digital proportional. The engine I'm thinking of powering it from is a Lionel Northern Pacific GP20 with dual DC motors which I would use for pusher service or switching. The single speed would be a drawback for sure. Would 7.2 volts be enough power to make it move or would it be fast or slow or??? I took measurements of the electronic board and it would just fit in a box car along with the battery pack.
At Wal Mart wednesday night I saw a "BIG" RC Range Rover marked for clearance at a cheap $30.00. It runs a 12 volt battery pack but has 2 speeds in each direction. I would have to buy it, take it apart to measure the controll board on it but I'm guessing I could find a box car to mount it in. A basic RC car with digital proportional speed would be the best donor but I don't see them often.
Tips, thoughts, ideas anyone?

[FJ and G]

Hi Boyd,

7.2v should be enough, but you can always harness another battery up to it with a harness yoke. I forget which it is, series or parallel, but one way will increase the voltage and the other way will increase the run time (more battery reserve). You also can hook up an Electronic Speed Control unit.

I'm powering my Williams dual-motor on 7.2v and will be running tests this weekend on steep grades with a bunch of freight cars. I'll post results next week.

[lionelsoni]

Series for more voltage, parallel for more charge.

[FJ and G]

Thanks, Bob. One other question regarding this, and I believe the other day when I visited your cool layout, you answered it but if you were to use battery power instead of A.C. to the full-bridge rectifier, would reversed polarity (incorrectly hooking up the positive and negative leads) damage the unit? My guess is "no" it wouldn't, b/c the A.C. entering the bridge rectifier is pulsating + and - anyway, so nothing would happen. So, you'd simply reverse the leads to get the circuit to function.

This question is sort of related to R/C operations. Thus far, I've only powered the motors, avoiding the circuitry b/c of my ignorance of electronics. I believe the only way to damage the circuits would be to input too much current.

[lionelsoni]

A bridge rectifier would be a very good way to protect the circuitry from a reverse-polarity battery. The only downside is that you would lose about 1.5 volts in the rectifier. A compromise alternative would be to use a single rectifier diode in series. This would prevent any damage from reversed polarity; but, instead of working with either polarity, it would just stop working if the polarity was wrong. The advantage is that it loses only half the voltage that the bridge does.

If you supply the proper voltage to the circuits that you are using, they will draw whatever current they need. Whether the battery can supply more than that doesn't matter and won't damage the load. Except for protecting the battery and wiring in case of some abnormal load, like a short circuit or other failure, which is why one would use a fuse or circuit breaker.

[Boyd]

This tank has a few other things that will add to the engine. Directional lights for each side, controlls for a rotating turret, gun barrel goes up and down, gun barrel fires. I was thinking of using the mechanism for rotating the gun turret for a turntable. I love modifiying stuff. Woohoo!

[FJ and G]

Thanks, Bob.

Boyd, be sure to post photos with details on the mods!

[MikeSanta]

Is 7.2 volts enough? I think you need more juice than that.

[FJ and G]

Mike,

Perhaps. We shall see during some trials this weekend, but preliminary results show the Williams going at about 70 smph+ with 2 cars in tow on level track and 3% grade. Gonna add steeper grades and more cars (did same using DCS variable (conventional) at 7 volts).

When you start adding lights, sounds, speed control and other stuff tho, it perhaps consumes more current. Later I'll be testing MTH. Please be patient and stay tuned, as I'm rather slow at gettin round to things.

[Jim Duda]

Each cell (NiCd or NiMh) outputs 1.2volts...so you can build your packs in those increments...1.2, 2.4, 3.6, 4.8, 6.0. 7.2, 8.4, 9.6, 10.8, 12.0, 13.2, 14.6, etc. I bolded the ones I think will prove best for an R/C application. We'll have to wait for Dave's testing to progress...

Remember, the voltage you supply (or think you're supplying to the rails) is probably not what the DC can motor is getting from the electronic E-Unit...connecting two 7.2V car battery packs with a series Y-harness will be WAAAY TOO FAST!

[dwiemer]

Interesting ideas. What about charging the battery (ies)? Can you charge them with track power, or would it be possible to use one or more of the new battery replacement units that will charge off track power? As to the turntable, that would be a good idea, if you can have it to do the fine movement to match the tracks. Please keep us informed of your progress and / or failure that we may learn from your experiences or add to your ideas.
Thanks
Dennis

[Jim Duda]

Dennis - In Vergun's application, there will be no track power...that's the reason for going R/C and supplying the power from batteries. The track can be rusty just like protypical operations, without the hassle of electrical conductivity and good connections. The track serves merely to guide the train - the quintessential essence of prototypicality...(wink)

To answer your question, yes...a battery charger could be designed to charge off the track AC...MTH does that now, only the battery is of smaller capacity (mah) than what the R/Cers use. But why would you want to do that? NiCd/NiMh chargers are cheap and readily available. When your batteries are exhausted, simply unplug them from the battery car, plug in a new pack, and you're running again for several hours. The exhausted battery is plugged into an AC/DC charger and is completely recharged in less than 30 minutes.

[Boyd]

If I don't use the gun turret for the turntable, I have a similar mechanism from a toy fire truck that rotates, tilts and extends the ladder.

[FJ and G]

Thanks, Jim for explaining.

Boyd,

I guess when it comes to R/C, the sky is the limit. One could, I suppose, tinker with all sorts of off-the-shelf R/C trucks, cars and other stuff, gut the components, and incorporate them into some aspect of toy trains.

The coolest thing to me about R/C is not having to rely any more on transformers, wiring, track power, DCS signal strength. And, the power one gets from the extremely strong transmitter signal is incredible. I will not even need to uncoil the antenna! Will be doing some more tests this weekend.

[Boyd]

A simple brainstorm gave me this shortcut idea: I touched 2 power wires off of the track to the hookups on one of the 7.2 volt power packs, with the intended engine on the track with 6 scale cars behind it on a basically flat table. It took off going pretty fast. Not much faster and it would be flying off the 48" curves on my layout. Electronics class was over 20 years ago. I remember what series and paralell are but don't remember thier workings. After I fix the truck on my 2nd NP GP20 I could wire them together and hopefully slow them down. Possibly I could hook up the wiring for one of the other controlls to a motor that could controll a rheostat and then I could have variable speed.

[FJ and G]

BOyd,

Very interesting! Nice experiment. When you use a battery car or place the battery inside the shell of the loco, you are simply doing the same thing that you did. The loco doesn't care whether the battery power comes from the track or from the battery car.

I found it interesting that this morning, just as I concluded testing, I saw your post and your results are exactly the same as mine. 7.2 V is MORE than adequate power.

I'll be testing 2 locos (4 motors, 2 each), at a later time.

I'll be looking at this post in future with much interest!

BTW, my transmitter allows me to slow down the train (fortunately)

Well, BB the beagle and I are gonna run the train some more as I'd like to see it eventually run out of power. (one could hook the batteries up in parallel to make them last even longer, as my battery harness yoke came in the mail)

[Jim Duda]

Dave - be careful...I believe the Y harness you got puts the batts in SERIES which will throw 14.4 volts at your motors! The train will become a missile and break the sound barrier...(and maybe your patio door)...

Have your neighbor get some of those Tamiya connectors and make a Y-harness IN PARALLEL like shown below...

(Click to enlarge)

[FJ and G]

Thanks for the warning Jim. I'm now wiring up a 2nd loco. So, we shall see...