CrunchyFrog

Can your standard (if there is such a thing) 75 MHz board run DC motors, in lieu of servos digital or analog?

I've got a half-dozen DC motors, essentially free. I can't afford servos at $8 apiece, and instead I use a motor in the "wet" to operate my rudder. The linkage I made stops the rudder at end-of-travel each direction.

I may burn up a motor once every four to eight months, not bad for free--I just roll in a new motor. Can't afford to burn up servos. Dirt-cheap is the only way I can have a hobby.

So, does every r/c board that runs servos have the ability to do DC motors in their stead ?

cyclops2

I am not sure what you want. But.

Can I run a dc motor with a servo PC board ? YES. Have done it many times.

If I read you correctly, you want the motor to be driven into a left or right mechanical stops of the rudder ?

Yes again. I have 4 cheap RC cars that are built that way for simple steering. They have a centering spring setup to always return to neutral.
They will be used in 4 ....48" RC freighters.
Bought each car for $8 each with working RC setups. I remove the RC guts, steering, motor & put them in each boat.

Big problem is to make sure the STALLED in the stops, motor, does not pull so much current that it burns out the servo PC board amplifier.

I know electronics well and can put in a resistor to allow enough power to STALL and not kill the PC amplifier.

CrunchyFrog

>Can I run a dc motor with a servo PC board ?

That's sort of my question. I mean, if I go down to the hobby store and buy a typical 75MHz r/c car setup--where they've packaged servos with it--is it likely I'd be able to run DC motors instead ? Sounds as though I might actually have to take apart the servo and reappropriate the leads off the PC board of an individual servo. I was hoping I might be able to do it just by reappropriating the servo leads from the servo's plug on the pc board.

>If I read you correctly, you want the motor to be driven into a left or right mechanical stops of the rudder ?

> I have 4 cheap RC cars that are built that way for simple steering. They have a centering spring setup to always return to neutral.

Right...27 or 49 MHz, right? But I'm considering 75MHz (now that GreenAce got me started thinking), since if I blow a channel I can probably order a 75MHz board by itself--not so for a 27MHz or 49MHz board (in a size that would fit my watertight compartment, that is).

Wow...freighters? How do you find a powerful enough cheapie car to push a four-foot freighter? Do you use the size battery cells that were stock for the car, or "up-gun" it a bit?

cyclops2

Crunchy.

Do not take this wrongly. You have the right ideas. But you need a guy like me next to you to do the job right.
Do it wrong and $ 8 servos ARE MUCH cheaper. ..... I feel I will help you more by telling you to save up for a servo as you can and steer with them.
I read your post as ... you ARE RUNNING motors in the "wet" . Stay with what is working.

I really wish I could do more.

GreenAce92

Hey crunch, i kinda have to say with the servos its the best idea because the 75mhz's i think all have 3wire hook ups, this way you dont need a spring to stop the servo in travel directions. Let me see what you can do.

heres a nice 4ch tx
http://www.servocity.com/html/laser_...d_systems.html

proportional controls n' what not. I thought you had a WTC? So shouldnt those keep your stuff dry, if nothign else you could use those rubber end things for pushrods which is kept water tight but the shape of the rubber part is like those thigns the music people compress and have a piano on the side, do you know what im talking about?

CrunchyFrog

I really do appreciate this info ! I haven't owned anything more modular than "toy" r/c vehicles (where I ripped out the innards to configure my sub, as you've done with your freighters). I've been trying to get an idea of what options are available if (when) I burn out a channel on my current setup and look to replace it.

The 27 and 49MHz cheapie donor cars have decent power, but I am looking at more modular (and they're always servo-based) systems because I'm getting tired of scavenging cars to remove the board; I'd rather just buy the circuit board itself. Plus it would be nice also to buy a modular board with plugins instead of a throwaway board--I'm no artisan with soldering. But most of all, I can never be sure what size of board is inside the car I'm buying--I just hope it will fit my setup !

When my current board goes, then, I will probably look for 75MHz. I've heard servos can be run wet with tool dip, though I'll have to see who has been doing that. Thanks for your input !

GreenAce, yes I do have a WTC. The DC motors I use as servos are outside in the water--so I can pull out my WTC lakeside without affecting the rudder linkage or bowplane setup, all I have to do is unbolt the propshaft. If see leaking water inside the clear-wall WTC, it's nice to be able to yank out the WTC and pop it open for drain-and-dry on the spot.

>if nothign else you could use those rubber end things for pushrods which is kept water tight but the shape of the rubber part is like those thigns the music people compress and have a piano on the side, do you know what im talking about?

Sounds intriguing but I have no idea what you're describing !

GreenAce92

Ok heres a drawing of what im describing i cant find them they are hard to find, but im short people like Captain nemo and others know where they are, i dont even know what there called, but basically its a rubber thing hooked up to the pushrod and the WTC cap so that it allows the pushrod to go out and back and its waterproof.

CrunchyFrog

Oh, I see ! A bellows-type pushrod seal. Thanks.

I'm going to try to keep the servos out in the wet, though, and avoid having to align the rudder rod when I insert the WTC. When there's leakage, I like to be able to pull the innards right out in one convenient piece (I use quick connectors on the wires), and that way ensure all the electronics are quickly exposed to dry. Also, if I stop using wet motors, then having to do alignment also means more intricate ship-in-the-bottle work inside the WTC that I don't enjoy. So for the beginner (or at least, me), there's quite a few advantages to running motors wet. It's crude and quick. I'm no model master.

The drive motor's the one motor inside the WTC--dynamic divers gotta have their speed. It's probably worth putting it there so it doesn't have to push against water that would otherwise seep inside it.

Captain Nemo12

Using RC-car boards is a trade-off, Price vs Longevity.

I remember during my Stingray conversion, I had the WTC and boards all insulated well (I used a balloon to keep the board dry, space was a problem). However, just as everything seemed right, a transistor must have blown out and the whole board poof![:@] I'm no expert in circuitry so I've never really gotten to fixing the thing. Since then the Stingray project pretty much went belly up.[&:]

@Crunchy: I'm not sure if you can find any cheap RC-car boards that carry the 75Mhz frequency, since most hobby-grade equipment use it. Radioshack cars mostly run on 27 or 49mhz. The RC-tank boards I posted on the other thread seems to be pretty reliable, as long as you add a heatsink and cool it well. A never version is available via a dealer in the US, the transmitter should be compatible as long as you use the same crystals.

The bellows GreenAce mentioned do their job well, I bought a set myself to use in my U-boat.

Hope everything works well!

cyclops2

Only 1 way I know of, to make a servo water RESISTANT. For a while. Russian Roulette.
Take the bottom & top covers off CAREFULLY with the servo ALREADY at 0 degrees first.
Then gentily smear a little Vasaline grease on all the surfaces & the output arm shaft. Try not to move the gears or drop them. I press down on the output shaft enough so the gears stay meshed As I carefully raise the cover. This can be very difficult on the micro sizes. Do it wrong & you can re-mesh gears many times to get it right.
ORR.
You can just remove the servo output arm pack grease around the white shaft, messy is OK, put the arm back on.
Either way, above only stops 1 of 3 leaky areas.

2 &3 rd leaks are the bottom cover and the bottom screws. Carefull not to get carelees with the top cover falling off also.
Grease the sealing edges & pack a little blob under each screwhead just before you push them down & tighten.