OspreyGozo

According to the specs, the Heng Long TK7.1 is meant for 390 motors on a 1:16 tank. I would like to use the board with a larger 1:10 that uses 540 motors. Is there some kind of (current) amplifying device that would sit between the outputs of the TK7.1 and the motors so that it can supply the necessary power to drive the motors? Some kind of MOSFET device, perhaps? My insistence on using the TK7.1 instead of just using dual ESCs is because I would like to take advantage of the sound features along with (hopefully) better steering mixing (especially for making on the spot turns). Other people have suggested other boards like Elmod or Clark but they are way overkill for me and too complicated. I just need an all in one, ready to run package to which I attach the two motors, two servos and a speaker.

RichJohnson

It will very likely work straight from the 7.1. They are made for up to like 12 volts and a lot of current output draw. So just get one and drive it hard to test it out. They are quite robust. They run the dynamic tranys for 1/16 which have 540 motors.

tankme

Personally, if I was running dual 550s off a 7.1 I would probably find some small heatsinks to use on the mosfets and mount a fan on it just to be on the safe side. If all the years of electronics work I did taught me anything at all, heat is the enemy.

Being that the 7.1 is an all in one solution, not really any good documentation or schematics of it and therefore not any viable way to modify the board. You are kinda stuck with it as is. The HL unit is small to fit in small tanks. A 1/10th scale tank has a lot of space. My larger tanks may end up getting a Benedini sound system and some RC switches when I run out of Open Panzer TCB boards (not available anymore).

OspreyGozo

Just to be clear, I am not asking about modifying the board itself, but to add something that takes in the output wires of the board and boosts the output.

borealis

It might work with 540 motors as described above.
Anyway, aren't CH3 and CH4 a signal output for throttle and steering which you might connect to a more powerful external ESC?

OspreyGozo

I did not know that. I do not yet have the board in hand since I am still deciding what the best option is and haven't read the full capabilities. Using external ESCs would definitely solve my problem, and also open up the possibility of using brushless motors. Thanks!

skyowa

TK 7.1 is spec'd at 180 amps IIRC, you should be fine. As far as stepping up the output from a 7.1, as far as I know, that could be done with some kind of solid state step up device, whether practical I couldn;t say.

OspreyGozo

It turns out the TK7.1 exposes the outputs of channels 3 and 4. I believe that can be use to drive ESCs that can, in turn, drive higher power motors or even brushless ones. I ordered the board yesterday and will wait and see if this is doable once I receive it in about a months time.

tankme

No way it can handle that. It says it, it can't. 180A at 12V is over 2000W which is over a 2.5HP motor. That maybe rated for both channels combined as a quick spike of 90A on each channel, but even that is suspect. Reality would be more like 20A continuous.

OspreyGozo

Thought as much and that is why I was looking into a way to drive the motors with external ESCs in the first place.

skyowa

You'll have to take that up with Heng Long, I just stated what they spec them at.

tankme

Chinese companies are famous for overstating the current handling capacity of their ESCs. Since I'm speaking from background in both AC and DC theory coupled with 30 years of experience repairing electronic devices/computers of all kinds, I was just trying to help the OP avoid blowing up a device and wasting money.

skyowa

I run a full metal bulldog with a red motor all day on a 3S with no issues with the controller even getting hot so I have a little more faith in them I guess, on the other hand I had an early career in music production, back when you could roll into your local Kmart and buy a Kraco "40 watt sound exploder" so yeah, puffery has a long distinguished history that continues today in more than just chinese esc's.

borealis

Anyway, isn't the stall current of each motor the maximum absorption it should get? That value should give an idea about where your system is working in limit conditions, compared with the nominal handling capacity of the board.

skyowa

There's also the battery current capacity and discharge rate to throw in the pudding,

tankme

So there are two different ways an ESC handles or should I say fails to handle stall current of a motor. The first is by implementing overcurrent protection. In that scenario, the ESC is rated to withstand X amps for a number of seconds before causing damage. It gives the user some time to remove throttle on a stalled motor. The second way is not building in a delay in the hardware which means if the motor hits maximum stall current of the ESC, damage occurs.

If you are concerned that a particular ESC can't handle the max stall current of your motor, the simple solution is to install an inline fuse (or breaker) on the positive(+) motor wire to limit the current. So in the case of my larger 1/6th scale tanks, I typically have a breaker set to say 70A coming from the battery or to whatever current I think my batteries can safely provide. Then I will add breakers to each motor at like 40A even though my ESC may be rated for 60A continuous. In that scenario, even if both motors are drawing 40A, the batteries are protected and the ESCs. A motor that can draw 20A continuous can easily stall at over 100A. If you draw too much current from an ESC, it will damage it if it has no overcurrent protection. If you draw too much current from your batteries, you can cause internal damage to them and in the case of LiPo batteries...fire.

Bottom line, when in doubt current limiters like fuses or breakers are your friend. I like to use breakers like these on my motors:

tankme

And then breakers like these between my distribution block and my batteries:

skyowa

Oddly I was looking for something like that for our camper, just ordered a couople.

OspreyGozo

*** UPDATE ***
I finally got my TK7.1 and I can confirm that you can drive external ESCs using CH3 and CH4. Unfortunately, in my eagerness to test it, I did not bother to properly insulate the connections to the power switch which accidentally got in contact with the battery terminals (also not 100% isolated) which resulted in a puff of smoke coming out of the TK7.1 unit. Now it is another month of waiting from one to arrive from Ali Express

tankme

Nice to know. Were there any setting changes that you had to make in order to activate them or did they just work when you hooked up the external ESCs?

OspreyGozo

The ESCs were previously connected to a regular receiver and programmed to go forwards and reverse (as opposed to forward and brakes like in race cars). Previously I had connected the 540 motors directly to the TK7.1 board. They worked but I did not dare drive them for more than a few seconds bursts. Then I plugged the motors back to the original ESCs and connected the ESCs to the board and it worked, albeit the motors were switched. It is when I attempted to switch the ESC cables that I made the f*** up and shorted everything.

skyowa

You can get a TK 7.1 on fleabay shipped from the US if that's where you are, be a lot faster than Allie

Tankhobby

Check the PCB, sometimes when shorts like that happen a trace vaporizes because a lot of current is shorted through it. That will create a nice puff of smoke but if only the trace is damaged the electronics may still work if the trace is repaired. A long shot but worth trying.

heavyaslead

Just for reference, the Tamiya Leopard 2A6 uses 540 motors and the ESC is rated 30 amps per channel (one for drive , one for steer)