Increasing Rx18 power output

[Alstone]

To be honest I'm not sure all I know is there the ones supplied with the heavy duty gearboxes, they look like black cap 400s?.

With the standard metal gearboxes and motors fitted doing a spin turn on grass blew the Rx18 box. With the new boxes it has more power but still struggles to do a spin turn on grass to the point of stall, but the Rx18 box handles it ok, I do have a 5 amp fuse fitted in the main supply and so far it hasn't blown, when I used a 4 amp fuse it did blow twice. I did try a resettable push button 5 amp circuit breaker but the reaction time was to long so I took it out.

I find that provided I don't do spin turns on grass (which requires both motors on full power) I can do anything no problem on any type of terrain. I do find that the better gear boxes put more power on to the ground than the standard ones, I think this is because they run smoother plus the tank handles more naturally. 

Al

Although I haven't got a fan fitted to my RX-18 board (Yet), I do have a 5amp fuse fitted in the main supply. I also have a 3 amp quick blow fuse installed  in two in-line fuse holders, these are fitted to the positive side on each of the 3-1 motor/gearboxes.   With a fan fitted as in your excellent mod and my 3 fuse set up, I feel you would have the ultimate protection for the RX-18 board. Some people may say its overkill, but I say paying for a fuse once in a while is better than paying for a £20 board. I have went through plenty of RX-13s in my time !!.  In 3 solid months running I have blown one of the 5 ampers   (turning on grass ) and not one of the in line motor fuses. 

Thanks for the comments on cooling the RX18 fets, you can't have two many fuses.

[Wight]

This is an interesting thread as I am considering purchasing a new Heng long tank with RX18.
I have a first generation pershing that was 2 speed and no s&s,it ran about an hour before one side drive blew.
Therefore I have been concerned with buying another Heng Long and was hoping the rx18 is more reliable.

I also mess about with smale scale rc cars (Kyosho mini z's and Xmods) which can also burn fets with too powerful a motor.
The way to get around this on these cars is to stack more fets on top of the originals or replace with better fets also stacked.
In fact this is such a common mod that Kyosho's latest pcb for these cars has a double set of fets already installed.

In the picture on the first post of this thread the fets look the same configuration as those on my cars.
Is it possible that this is a mod that could also be performed to the RX18 pcb?
Adding a set of identical fets stacked on top of the originals should double the current carrying capacity,therefore generating less heat.
If this is so I would be a lot more confident in buying an rx18.

Cheers,Steve.

[koomairoo]

Very good & clear way to cool down RX-18.
I got the same gearbox and do sure to take this tip.
Thanks.

[Joat]

This is an interesting thread as I am considering purchasing a new Heng long tank with RX18.
I have a first generation pershing that was 2 speed and no s&s,it ran about an hour before one side drive blew.
Therefore I have been concerned with buying another Heng Long and was hoping the rx18 is more reliable.

I also mess about with smale scale rc cars (Kyosho mini z's and Xmods) which can also burn fets with too powerful a motor.
The way to get around this on these cars is to stack more fets on top of the originals or replace with better fets also stacked.
In fact this is such a common mod that Kyosho's latest pcb for these cars has a double set of fets already installed.

In the picture on the first post of this thread the fets look the same configuration as those on my cars.
Is it possible that this is a mod that could also be performed to the RX18 pcb?
Adding a set of identical fets stacked on top of the originals should double the current carrying capacity,therefore generating less heat.
If this is so I would be a lot more confident in buying an rx18.

Cheers,Steve.

I started a thread here asking the same?
http://www.rcgroups.com/forums/showthread.php?t=1117613

[Saxondog]

Al,I did not realize their were pictures so detailed when I posted,this is your mod and I edited my pictures out as they are in another thread,your pictures have fine detail and your idea of venting is a smart solution to the overheating issues. Cheers Blake

[Alstone]

Hi all I have re-placed the missing photos for anyone who wants to do the mod.

PS: Some of the photos may not be in the right place.
Al

[margandy]

Hi

Many thanks for your time and pics to explain

cheers

margady

[xrad]

Stacking FETS:

BAsic electronic laws still apply

1) In series, resistance changes can affect the gate operation
2) input voltage needs to be divided equally for best effect (stack two FETS = square power output)

So don't expect maximum power handling.Be very careful how you solder them up.

PDF pics of HL FETS, you can look up the specs online.

Here is what you really need to do. Add one of these bidirectional motor power supplies to the HL system:

http://www.pololu.com/catalog/category/82

I have blown a 5 amp fuse firing the flash/recoil/track motion at same time. Tracks themselves likely draw around 5amps max, but I have not measured. Two of these high power bidirectional brushed DC motor controllers would work great. Just have to figure out how to wire to board. I would directly wire them to battery power via batt switch and not run them through the HL board.

If you pop your HL board out, on the back you will see where the motor driver board is soldered. Easy to identify the motor output pins(four of these). Easy to identify the power and ground pins. Easy to identify the control pins (four..for proportional speed forward and reverse for each motor). NOT easy to determine the driver frequency/voltage. I guess I could just try it some day and see if the HL board produces a driver frequency/voltage within the parameters of the Pololu boards........

[Saxondog]

Seems like an expensive component to be testing,although your knowledge in these matters is above average I was thinking maybe Phil(Blitz)may have experience with these types of power supplies? Sax

[xrad]

I am always up for a cheaper and easier alternative!

Especially one that someone else has figured out!