4-wheel steer and servo wiring question

[Numbchux]

OK, I searched around, and didn't find anything that answered my question. alot of options for 4WS, but not quite what I want.

Tower hobbies (and I'm sure other sources) sells Y adapters for servos so you can plug 2 servos into the same plug. now the servo wires (typically) have a red, black, and white wire. I'm assuming that they're power, ground, and signal, respectively. correct?

I'm thinking if you put a switch on the white wire for one servo, so with it 'off' the servo would still power up, and center, but remain centered. and with the switch 'on' it would turn with the other servo.

I realize this would not allow you to have any remote rear-steer control....but I'm cheap that way.

I don't want to go cutting up my nice radio system here to find out. if I could find my multimeter....I'd test it...but alas.

[Jeckler]

I've never tried it, but I don't think it will work. The signal wire always has a pulse. It's the width of the pulse that tells the servo where it should be. So if you had power, the servo would be on, but wouldn't know what to do, so it would move all over just by moving the arm.
I do seem to remember there was someone that did something similar to what you want, but it involved a failsafe and a RAM component (RAM35 I think). He used the 3rd channel on his radio to turn it on and off. I'll see if I can dig it up. I think it was on RCMT, but it was 2 or 3 years ago.

[Jeckler]

Found it. It was Hairball that did it. His site is gone, but the Wayback machine has an archive. Some of the pictures no longer work, but give it a shot.
http://web.archive.org/web/200502071...m/hairmods.htm

[Numbchux]

the link is experiencing technical difficulties....hopefully it'll be back on later.

but that sounds exactly like what I want to do! I want to flip a switch and have the rear end be proportional with the front, and flip it off and have the rear center and stay centered. if it was on the controller, that'd be that much better!!

anyway, I think you're right, I did find my multimeter this afternoon, and did a little testing. sure enough, the red and black wires have + and - full power (happens to be 6-volts here) as long as the switch is on. whether the controller is on or not. if the controller is off, the servo does not center. so you're right, there has to be a signal from the signal wire in order for it to center.

[chevellian]

Originally Posted by Numbchux

but that sounds exactly like what I want to do! I want to flip a switch and have the rear end be proportional with the front, and flip it off and have the rear center and stay centered. if it was on the controller, that'd be that much better.

if you have mixing on your radio, you can do exactly what you want.

[Jeckler]

Here is the text of the page, from Google's cache:

On Demand 4WS

With real life Monster Trucks, you get four wheel steering, giving the truck the ability to make tight corners. Now you can do this with the TXT-1 as well, but you'll lose high speed handling. Try to turn at anything faster the five or six miles per hour with four wheel steering and your truck will end up upside down. Not very fun.

Climbing rocks with four wheel steering rules, but driving fast with two wheel steering kicks *** as well. What if I could have the best of both worlds? On the fly selectable four wheel steering? So you can switch between two wheel and four wheel steering with the push of a button? Read on.

There are a number of ways to accomplish this. The first way is to get a fancy radio with channel mixing, and plug the rear servo into the auxiliary channel, and use the radios channel mixing to control the rear servo with the front servo. The JR R-1 can do this with ease. Some whack jobs out there use 4 channel airplane radio systems and use one stick to steer the front wheels, and one stick to steer the rear wheels. You can do some cool crab walking stuff with this, but I just hate the feel of a stick radio (unless I'm flying a plane or a helicopter that is). Its just not right! I happen to use a Ko Propo EX-11 Presto. Its got 4 channels on a pistol grip style radio, and suits my needs perfectly for now. (CH3 for the transmission, CH4 for the 4WS switching). Check out www.kopropo.co.uk if you're interested.

I also have a Ko Propo EX-1 Mars that I tried first, but no matter how cool this radio is for all my racing models (I love it to death), its 3rd channel operation sucks ***. You can't adjust the 3rd channel, its on and off only, so be advised. My advice is to make sure the radio has the features you want and they work the way you want them to before you buy it. The JR R-1 and Ko Propo EX-11 are good to go. The Airtronics M8 would work fine, just a little tricky because of the way it makes use of the 3rd channel. The Futaba high end models like the 3PJS and such I'm told will work perfectly, but I have no experience with them. The new Multiplex radios (the 3 to 7 channel pistols) would most likely work, but I think they're ugly, and holding one is even worse. I think the JR XR3 would probably work as well, but I've never used one, so I couldn't tell you. I'm sure there is at least a dozen more radios that I haven't mentioned here that will probably work. I just named the big ones that everyone seems to have these days. And, if you can afford a TXT-1, I'm assuming you'll have a high-end radio to go along with it.

Besides, a little research never hurt anybody.

Step 1 - Figure out a way to enable and disable a servo with the push of a button. What?

This requires a lot of thinking (And yes it hurt). I'll go into the details later. After consulting quite a few people online, and some experimenting myself, I came up with this -



With the simple push of a button on my transmitter, I can switch from two wheel steering for high speed driving, or to four wheel steering for ultra maneuverability in those tight spots. The best of both worlds.

Step 2 - Lets go shopping!

You're probably looking at this saying to yourself saying one of two things. "What the **** is all that crap" or "How much did that cost"? The most expensive part was the second high torque digital servo. And that wasn't too bad really. Now if you want to do this to your rig, you'll need the following items.

Another servo for the rear (Duh) - I use Hitec HS-5925MG Digital servos. They have AWESOME holding power, and more than enough torque to move those big wheels. The only drawback is that they make this weird noise when they aren't centered (which is all the time). If you don't understand what a digital servo is exactly, don't worry about it, all you need to know is its very good. ~Thanks for the recommendation Todd~

Cirrus "Y" Harness with servo reverse - (You can use a standard "Y" harness without the reverse feature, but then you have to use Tamiya's crappy rear servo mounting setup that is really weak, with the reverse feature you can just mount the rear servo exactly as the front servo, and it works great, plus you can center the rear servo independently from the front servo, saving extensive linkage adjustments to make the truck drive straight) ( Hobby People stores carry them if your local shop doesn't have it)

RAM 35 Solid State Switch - (go to Tower Hobbies and search for "RAM 35" and you'll find it)

Fail Safe Unit - (I used a Ko Propo Unit, because everything else on the rig is Ko. I'm assuming you can use just about any brand fail safe unit and be fine, just make sure its the inline type. The built into the receiver type JR uses will not work, the reason for this is you have to fake out the fail safe into think that its lost radio signal, not an easy task if the fail safe is built into the receiver).

6" Servo extension cable (At least one) - (I'd buy two in case the first one gets screwed up, you're going to have to do a little cutting on this guy)

Small shrink tubing - to patch up the extension cable after hacking it up. Use can use electrical tape as well, but I WOULD NOT RECOMMEND IT. If you don't know what shrink tubing is, go your nearest Radio Shack (or whatever) and ask. Its about $2 a pack. USE IT OR DIE! Oh, and a hair dryer can be used to shrink it once its in place, or be a man and use a lighter or match. You'll get the hang of it after melting a few pieces.

Soldering Iron - If you need to ask what this is, or what its for, stop reading here, and forget about any dreams of selectable four wheel steering. (Once again, Radio Shack if you don't have a clue, and you'll need some rosin core solder as well).

A whole bunch of tie wraps - that is unless you want you rig looking like a bomb hit it and its guts are all hanging out everywhere.

Step 3 - How / Why it works

I'm going to go into the how and why this circuit works. If you don't care HOW it works, and just want to MAKE it work, skip on to step 4.

Servo's work on a signal pulse from the receiver. The red and black wires provide power to the servo, while the white wire (sometimes blue) tells it what to do. If the receiver sends out say a 1.5v signal on the signal wire to the servo, it turns to say 120 degrees. Change the signal to say 1.3v and the servo will turn to 90 degrees. (these are just numbers, the actual signal voltages are probably different, but the theory is the same). This is where the fail safe unit comes into play. The whole purpose of a fail safe unit is so that if the model loses radio signal (goes out of range or something) the fail safe will turn the servo to a preset position (that you set) until radio signal is restored. For example on a gas powered car, a fail safe may be used on the throttle servo, so if the model goes out of range, the fail safe just shuts the engine off to prevent it from going out of control. This is where the RAM 35 solid state switch comes into play. What it does is temporarily "cut" the signal wire (the white wire in most cases) going to the rear servo, and makes the inline fail safe unit *think* that the model has lost signal from the transmitter and locks the rear wheels into the straight position (or any position tell it to set it too, although I don't see the point in anything but straight). In reality, the model is still very much in control, and the rear servo is just holding the rear wheels straight.

Why do I need a fail safe? Couldn't I just cut the signal wire with the wheels straight? No. Although this would work at first, with nothing *telling* (the fail safe's job) the rear servo what to do, it could go out of control and twitch, or lose all holding power and let the rear wheels do whatever they want. Not good.

If that doesn't make sense, email me and I'll try and clear it up. Be sure to label the email subject something like "4WS wiring questions", or I may not get to it for awhile.

Step 4 - Installation

STOP!

BEFORE DOING ANYTHING, READ THIS ENTIRE SECTION TO THE END, THEN GO BACK AND DO IT STEP BY STEP. If you have questions about this, or need additional help with it EMAIL ME! I'd rather you drive me nuts asking a zillion questions then do something wrong and burn up a bunch of expensive equipment hooking something up wrong. Please refer to the step number you're stuck at, so I have a better idea or where your at.

Now you can be cool like me and copy my radio tray layout, or come up with something of your own. The sky is the limit. I was a bit restricted due to my E-Maxx tranny shifting servo location, so I had to work around that. If you're using the stock tranny, it will be simpler. (Or if you mount your servo somewhere else). For this I'm assuming that your radio system uses WHITE for the signal wire color. Older Ko Propo and Airtronics servos use BLUE for the signal wire. If all else fails, consult your radio equipments manual, or just call them if you don't have the manual. I've seen orange used in this place as well. And wiring this stuff up, I suggest that you print out this whole write up. That way you can see exactly what I'm talking about while hooking things together.

**Note** You can use butt connectors (the ones you'd use in a car audio installation) instead of soldering the wires in the above steps, its just soldering them looks so much nicer, and gives a much cleaner connection.

Step 1 - The first thing you have to do is cut the WHITE wire on the 6" servo extension cable right about half way through (3" from either end of the cable). DO NOT CUT THE BLACK OR RED WIRES! If you do, you'll have to patch them up (or use the second extension cable I recommended buying before). *Peal* the white wire away from the other wires about 1/2" in both directions. If you did it right it should look something like this -



Step 2 - Now using the soldering iron and shrink tubing, connect one of the WHITE wires to the YELLOW wire coming out of the RAM 35 unit (solder then together), and the other WHITE wire your *pealed* back to the BLACK wire that is twisted up with the YELLOW wire (solder them together as well) from the RAM 35. It should look something like this -



Step 3 - There are two more wires coming out of the RAM 35 unit as well. A RED and BLACK pair of wires twisted together. You'll need to connect these together (Solder the black to the red wire, in a loop you could say). Just but a small piece of shrink tubing over the solder joint to protect it. See below. Please excuse my lousy drawings. But I think you'll get the idea.



** The purpose of the red and black twisted wires is to hook up an external power source (like a small battery separate from the main battery packs and receiver pack (if used), so that when the circuit is closed, the battery would provide power to the yellow and black wires to power up an accessory like external lights on a plane or something, but this is not what we want it to do) for what ever you may be switching with the RAM 35. **

Since we don't need an extra power source in this circuit, just connect them together. If you don't, it won't work. Trust me on this one. It took me a good half an hour to figure out why the thing wasn't working at first, then I tried just holding the two wires together (the red and black twisted pair) with my fingers an BINGO, everything started working exactly as I had hoped for.

**Note #2** The Orange wire on the Cirrus "Y" harness is the signal wire, so it should be where the white wire is normally. I have no idea why Cirrus picked such a weird color scheme, but that's just the way it is.

[Jeckler]

...continued

Step 4 - Next, hook up everything as laid out in the schematic above (no more soldering is needed, just plug everything in using the connectors supplied). Plug the RAM 35 servo leads into your receiver's 3rd channel (or 4th in my case).

Step 5 - Next, plug the male end of the Cirrus "Y" harness into channel 1 on the receiver, then the front steering servo into one of the "Y" harness's leads, and the male end of the modified 6" extension cable (the one you hacked up earlier in step 1 and soldered the wires to) into the other.

Step 6 - Now plug the FAIL SAFE unit into the female end of the 6" extension cable. Now plug the rear servo into the FAIL SAFE unit.

Step 7 - Confused yet? Here is the catch. With the truck on, and 4WS engaged (The LED on the RAM 35 unit should be on), adjust the small adjustment potentiometer on the Cirrus "Y" harness so that the rear wheels are straight. Now move your steering wheel (or stick) to make sure all four wheels turn (if only the front or wheels turn (NOT BOTH) then the RAM 35 is active and cutting off one of the servos, adjust your transmitters 3rd channel to make sure this is not the case). If the adjustment moves the front servo, you need to switch the FRONT SERVO LEAD with the 6" SERVO EXTENSION CABLE on the "Y" harness. Only one of the outputs on the "Y" harness is reversed, but the plugs are not labeled (Why there are not labels is what I want to know). I labeled then with an hobby knife by scratching an "R" for rear on one, and a "F" for front on the other once I figured out which was which.

Step 8 - Now hit the Channel 3 button (or switch or knob or whatever) on your transmitter to activate the RAM 35 (the little light should go out) and your FAIL SAFE should take over the rear servo and you should only be able to steer the front wheels. Use the potentiometer adjustment on the FAIL SAFE to make the rear wheels straight.

The little light on the RAM 35 does nothing except tell you if the circuit is working, and my fail safe unit (Ko Propo) also has a light on it that lights up when signal is lost. So in 4WS mode, the red LED on the RAM 35 comes on, and in 2WS the green LED on the fail safe comes on. Groovy.

Step 9 - You may have to make some adjustments on your transmitter to get the RAM 35 switch to work right, but it should only take a second. Read the instructions that accompany the RAM 35 and the Fail Safe unit if you have any doubts. Basically, your should set the end point adjustments to MAX on channel 3. with the 3rd channel on it should be for example +100 (or whatever your transmitter reads in) and -100 with the 3rd channel off. If you are using an old analog transmitter without digital adjustments are all you've got is two little "pots", turn one all the way to the left (counter-clockwise) and turn the other all the way to the right (clockwise). If you don't have any adjustments for your 3rd channel (like on the Ko Propo EX1 Mars), you may have to hold the 3rd channel button with your figure when you want 4WS, and release it when you want 2WS. If that's not the case, you're on your own. Sorry, I can't please everyone. My only advice is call your radio manufacturer and seek there guidance.

END - IF YOU FOLLOWED THE DIRECTIONS, GO BACK TO STEP 1 AND START WIRING EVERYTHING TOGETHER

Optional Stupidity - Now, if you really wanted too, you could leave out the RAM 35 electronic switch, and just wire in a standard small electronic switch and A) Drive the truck over to yourself and hit the switch with your hands (boring) or B) Rig up another servo to hit the switch for you (complicated, and not much cheaper than just buying the RAM 35 switch, plus you'd be adding more moving parts and things to go wrong).

[Numbchux]

wow, thanks. link works now :-P

[Jeckler]

It keeps going up and down. I'm trying to get all the pics, but they're not really necessary.
Plus, I wanted to post the text here so that it doesn't get "lost".

[MafiaxB]

that link is awesome - i hope we can have it immortalized as a tech article - it's a great little thing to be able to do if you dont have a mix radio (i do )

[bcooper]

Wouldnt A Momentary On/ Off/ Momentary On Switch Do The Same Thing, Like What Comes With The Tq3 From The Crawler Store For Like 65.00 With Swich Installed?