Electrical advice needed

[Meathead316]

Hi

Im planning on building a ride on tank for my 2 year old son. I plan on using 2 cordless 12v drills to drive it (1 drill per track)

Thing is as my son is only young im not sure he will be able to drive it yet, so i want to incorporate an r/c system

Now this is a budget build so im hoping to use a cheap r/c car and remote, and NOT buy seperate parts.

Ive recently bought an rc impreza from argos for

[RussH]

Get yourself a BEC. Basically it is a DC to DC converter. 12v in, 5v out & around 2 to 3amp capability. 

Edited June 19, 2013 by RussH

[XV Pilot]

Cheap Argos toy-grade models almost exclusively make use of 27MHz AM radio gear. This is very prone to interference from multiple sources. I would strongly advise against using it to control a vehicle that is to be occupied by a child, even if it is a relatively slow one.

 

In the interests of your child's safety, rather get hold of a hobby-grade 2.4GHz radio set. You don't need anything fancy - a basic set costing under 30 quid should do the job nicely, and will be far safer. It will also likely be easier to integrate with the vehicle's manual control system.

[Meathead316]

Sorry if i wasnt clear in my original post, i still wasnt the motors running at 12v but would somehow need the r/c side of things to not be burnt out by such a high voltage.

Please tell me more about this

[XV Pilot]

Yes, we understand. A BEC will allow you to do that. People use them in cars that have high-output LiPo drive batteries, to bring down the voltage to safe levels for the RC gear.

Don't know about Ebay, but if you have a look on Modelsport.co.uk in the RC Equipment section, you'll see that Abysma, Ansmann, Etronix and Tamco all have radio sets in the sub-30-quid price range.

The radio set comes with a transmitter and a receiver. How to install and use it will depend on your plans for the manual control system for your ride-on tank. You might use a pair of electronic speed controllers, or you might use a pair of servos pressing on microswitches. You might also want a tank mixer.

Let us know more about your intended control system, and we'll see what we can suggest in terms of rigging it for radio control.

Edited June 20, 2013 by XV Pilot

[Meathead316]

Manual control systems, speed controllers, tank mixer??? Its all starting to sound a little complex...

Yes im sure there is a super cool, hi-tech way of doing this, but im after the most basic way.

So my plan if i understand the parts correctly is:

- build tank

- 1 x 12v cordless drill powering each track (just the motor and gearbox)

- 1 x 12v nimh battery to power it all

- this r/c gear:

http://www.modelsport.co.uk/core-rc-code-2.4ghz-2-channel-fhss-sport-stick-combo/rc-car-products/38218

- r/c module in tank with both drills attached

- r/c remote will be able to be mointed inside the cockpit so that my son can drive it (will look into some sort of kill switch later)

- no speed control, just all or nothin...

So very basic, and this is based on my understanding that the 3 channels are basically slots for 3 servos? (Of which i need 2)

Also, can i rotate the right anolog stick so that it moves up and down rather than left and right? (Surely you can just unscrew and rotate it...)

Thanks again for your advice

[Meathead316]

Oops forgot to ask, is the r/c set i posted a link to ok with a 12v nimh? Whats the min and max operating voltages?

Also worth noting i do not wanna use lipos as i already have a nimh charger i usr for airsoft and intend on keeping this simple an cheap!

[Shudson]

Your easiest option is to set up a mounting for your servos so that you can mount a couple of micro switches on each servo to control the motors. Alternatively, if you could source a couple of old (pre ESC) mechanical speed/reverse controllers which are almost purpose made for what you want (I dare bet nearly everyone on here will have some in their "junk" box and would probably part with them cheaply).

Either will isolate your 12v power from your radio gear. You then have the choice of powering the radio from your drive battery, via a BEC, or independently from dry batteries.

I suspect that you will need to suppress your motors (a couple of small capacitors each) as cheap drill motors will no doubt be quite "dirty".

[Meathead316]

So i cant just use the drills in place of a servo?

I think i understand the micro switch idea. Have normal servos have the arm hit a switch to make the drill go, the drill will essentially be a seperate circuit. Do the servos go back to their start position as soon as you release the trigger?

Surpress the motors? "Dirty"????

Also why does a servo have 3 wires? + and - is obvious, but whats the yellow signal wire all about?

[bbadger]

The three wires are Positive Negative and Signal.      The signal wire tells the servo how far to turn and where to centre, it is not just a case of reversing the current to change the direction of a servo, you need to be able to get it to rotate to a certain point so the signal wire sends a series of pulses that the servo interprets as a position.

[NuttyProfessor]

Reading this thread, the problem you will have is that you would have to switch both motors on at the same time because channel 2 on a reciever is the throttle on a standard setup. Im guessing you will want each track to move independent for steering it so a aircraft transmitter is your best bet so you can have 2 throttles, left track on the left stick and right track on the right stick.

Speak to DeadMeatUK, he has made ride on vehicle's for his kid that go quite well.

Edited June 20, 2013 by NuttyProfessor

[Meathead316]

Riiiight, sounds complicated O_o but do servos know how to do all this clever stuff on thier own or do they need to be told?

Do you "need" a signal wire? Is there not a way to just reverse the current?

[Meathead316]

So i cant use a standard transmitter (say for a car)?

[NuttyProfessor]

It needs the signal to tell it what to do. Not complicated, just need to figure out which channels will do what, easier to use a stick controller. I had an RC car years ago called a Fast Traxx by Tyco that had tank tracks, had a stick type controller so instead of up and down on the left and left and right on the right, both were up and down so each track moved independent.

I bought a stick type controller on Hobbyking for like

Edited June 20, 2013 by NuttyProfessor

[Meathead316]

Ah cool.

Im still confused with the servo. I want it to just go one way when i press up and the other when i press down and to stop when i dont press...

Cant i take the brain (signal wire etc) from a servo and splice it to a drill?

I msg deadmeatuk, hopin he gets back to me

[Meathead316]

Waaaaait a minute

Arent servos used for steering cars??

Shouldnt i be lookin at using a drill to replace the cars drive motor?

[NuttyProfessor]

Right, a normal rc car uses channel 1 for steering and channel 2 for throttle, because you will be using 2 channels for just throttle (one for each track) you will need a controller that can do it. If you want to go just forward and back with no steering, by all means go for a switch and a servo to kick the power on. A servo board will only handle about 50ma so using it as a direct drive switch will kill it especially for a ride on, you would need a relay to switch up the power.

[NuttyProfessor]

Waaaaait a minute

Arent servos used for steering cars??

Shouldnt i be lookin at using a drill to replace the cars

drive motor?

Servo's are used for anything that needs mechanical movement like steering etc. Because you are using tracks, its not a conventional steering setup, you need to spin each track independent of each other to provide the steering

[Meathead316]

Ok right i think i get it...

So running 12v through it is a no no

Connecting drive motors (drills) to it also a no no

So the switch method it is

A few more queries if i may.

Can i use a steering servo in channel 1 and another steering servo in channel 2? If i can then i can see how it will work

Do these servos re centre them selves one i releasr the control stick thus it will stop pressing the switch powering the drill

Do i "need" a special controller? Or will an up/down left/right one work?

[NuttyProfessor]

You can use the 12v for the drills but need 5-6v for the reciever. Only other way is to get proper esc's to drive the motors. Problem using a bog standard wheel type controller is the wheel is used to steer but you will basically need 2 triggers instead of one trigger and a wheel hence why I said get an aircraft stick type so you have 2 separate sticks, one for each motor so you are

using 2 throttles, one for each track so it can steer. Problem is with a 2 channel stick controller is the obvious problem of one stick goes up and down and one goes left and right, you really want both to be able to go up and down.

Do the drills variate the speed on how hard you pull back the switch?

Edited June 20, 2013 by NuttyProfessor

[NuttyProfessor]

http://www.hobbyking.co.uk/hobbyking/store/__8337__Hobby_King_2_4Ghz_4Ch_Tx_Rx_V2_Mode_1_.html

Both the sticks move in all directions so you have up and

down on both sticks. Just need to change a spring round internally so both sticks centre due to aircraft not needing a self centre throttle.

Edited June 20, 2013 by NuttyProfessor

[Shudson]

Yes, you've got it. As far as the drill wiring/connections are concerned, just imagine you were doing it without radio and the switching you would use. All you would be doing by adding radio is to replace those manual switches with ones operated by servos.

For what you are wanting, a servo is a servo, full stop. There is no difference between a steering and a throttle servo for your purposes, as you do not need extra power or speed or accuracy. You just need the cheapest you can find.

The servos are "dumb" - they do exactly what the controls on the transmitter tell them to do. So as far as them centring themselves is concerned, if the sticks on the transmitter are sprung and return to centre when they are released, then their respective servo will return to centre as well.

It is possible to construct simple circuits that will replace the servos with relays but, and I don't mean this disrespectfully, with your limited knowledge of electronics, I would leave that alone unless anyone does ready made units.

There is actually a lot to be said for using the old fashioned electric R/C car speed controllers I mentioned previously, as these usually include reverse and would give some measure of speed control as well (go for the two or three speed, rather than the variable speed ones, bearing in mind the likely voltage and current). Sourcing suitable micro switches might not be easy, as they would need to double pole changeover (assuming you want to be able to reverse - unless you use two batteries) and quite a high current rating (I would guess at least 10 amps, depending on the motors, gearing and weight of your child).

I might add that I do actually have experience of this sort of thing as I built from scratch and adapted from large toys various ride-ons for my young brother about 40odd years ago.

By the way, does it have to be a tracked vehicle, because there are electric ride-on cars with R/C control/over-ride available commercially.

[Meathead316]

I wasnt lookin at a trigger and wheel receiver, i was lookin at this one:

http://www.modelsport.co.uk/core-rc-code-2.4ghz-2-channel-fhss-sport-stick-combo/rc-car-products/38218

As for the drill being variable speed, im not sure as i havent bought it yet, but if thats a problem i could just wire the power directly to the motor

That link to the reciever is no good to me im afraid as it doesnt seem to be a UK stockist... Thanks anyway

To begin ill use what ever reciever i can get cheap, and once working, try to find a more suitable one

Im still unsure whether or not servos self centre when you release the trigger.

And whether both channels (with the reciever i linked) can be a servo (as opposed to a servo and a drive motor)

[NuttyProfessor]

Im really sorry fella but if you havent grasped that a reciever is basically just a signal point irrelevant to if its a servo or esc plugged into it, you shouldnt tackle something this difficult because all you will do is spend a load of money, get annoyed that it wont work then chuck it to one side. Ive spelt everything out and you still aint grasping it. Sorry to be so blunt but its the truth.

[Shudson]

Im really sorry fella but if you havent grasped that a reciever is basically just a signal point irrelevant to if its a servo or esc plugged into it, you shouldnt tackle something this difficult because all you will do is spend a load of money, get annoyed that it wont work then chuck it to one side. Ive spelt everything out and you still aint grasping it. Sorry to be so blunt but its the truth.

Whilst I probably wouldn't go quite as far as Nutty Professor, and I don't think that what you are contemplating is particularly difficult, it is clearly not as straight forward as you perhaps first thought. Certainly, there is no straight forward "plug and play" solution and you would have to be prepared to "tinker" to get things working right. With this in mind, its your choice.