Hi !
I have a little driver board designed for a little robot . The driver can just control 2x little direct drive dc motors and has 8 transistors (4 for each motor) , 1x 1000uF capacitor , some resistors and an LED . Now I wanted to 'upgrade' it , so :
1- it would deliver more power to motors (better transistors) ;
2- it could work with higher currents ;
3- (I'm not sure if it's possible) I could connect it to an arduino UNO .
It's designed to work with little micro-controllers that are on other little boards , then they would be connected to this driver and control it .
I don't know a lot about these , so I didn't know WHAT transistors to put instead of these , and what else can I do to improve it ?
There are S8050 and S8550 transistors .
(picture)
Thanks in advance !!
The Arduino Uno needs 5V to run. What voltage are the batteries ?
It makes a big difference if the motors run on the same voltage as the Arduino (5V) or not.
There are so many drivers, but most of them are for voltages of 5V and above.
Are you willing to spent some money on mosfet drivers ?
4 transistors suggests an H-bridge driver.
There's really no way to upgrade it unless you switch to MOSFETs and MOSFETs don't generally come in that size.
(and the ones that do come in that size aren't high current).
Peter_n:
The Arduino Uno needs 5V to run. What voltage are the batteries ?It makes a big difference if the motors run on the same voltage as the Arduino (5V) or not.
There are so many drivers, but most of them are for voltages of 5V and above.
Are you willing to spent some money on mosfet drivers ?
I want to just change the transistors without destroying the boards .
It would be preferred to spend less money but if the only way to upgrade it would be using mosfets then I would .
Can I just use any mosfet ? Or it has to be a special number ?
And can I put 4 mosfets and 4 other transistors would remain untouched ? Because the robot rarely (perhaps , never) goes reverse so the reverse transistors don't really matter .
If you only want "forwards" then you can replace 4 transistors with a single N-channel, "logic level" MOSFET.
Either:
a) Bridge (short circuit) S1 and put the MOSFET at S4
or
b) Bridge (short circuit) S3 and put the MOSFET at S2
The difference between (a) and (b) is forwards/backwards.
We don't know the details of that board so you'll have to grab a multimeter and figure out the details yourself.
Read that page carefully, all the information is in there.
OTOH, if you're going to do that then trying to hack your PCB is pointless. It will be much easier to get a piece of perfboard and start from zero.
The robotics competition does not allow any other boards than that , but they never did mention about UPGRADING that board .
Although at higher levels that is not limited to one company , like city / province / country I'd never use these stuff , but I would use a ready made H-bridge and Arduino .
I'm not so professional , so unfortunately I understood little to nothing :~
So Can I just place 8 MOSFETs in place of the 8 normal transistors ? Or should I use decreased amounts of MOSFETs ?
And by the way , what MOSFET would you suggest ?
Thanks for helping 
I'm not so professional , so unfortunately I understood little to nothing smiley-confuse
So Can I just place 8 MOSFETs in place of the 8 normal transistors ? Or should I use decreased amounts of MOSFETs ?
And by the way , what MOSFET would you suggest ?
I'm not against bending rules but I think prizes should go to people who manage to bend them all by themselves.
The robotics competition does not allow any other boards than that , but they never did mention about UPGRADING that board .
The concept of upgrading is more of a software one than a hardware one.
If they do state you have to use that board then I guess they do not mean for it to be tamped with. After all once you replace parts it is no longer that board but another one.
So Can I just place 8 MOSFETs in place of the 8 normal transistors ?
No not really. Transistors turn on with 0.75V on the base and FETs take above 4V (logic level ones). Also the design of the base / gate resistor value is different. For a FET it needs to be low for a fast switch on, for a transistor it needs to limit the base current to the right value.
Well it's not cheating and it's fine , because almost everyone make tweaks in this competition (I've seen the robots ) . Usually they put better transistors and maybe for line following robots they'd put better photo transistors .
Well let's say I pick 4 of the transistors and replace them with MOSFETs . 4x 0.75 for 4 normal transistors and 4x 4 for the MOSFETs .
It becomes 19 volts . So I'd use 19v ac/dc converter and I'm done ? If it would be something like this it would be very cool .
Can you read the part numbers of the existing transistors? Are they NPN or PNP
or both?
If you want a high-performing NPN transistor I can recommend ZTX851 or STX724,
and STX790A for PNP.
MarkT:
Can you read the part numbers of the existing transistors? Are they NPN or PNP
or both?If you want a high-performing NPN transistor I can recommend ZTX851 or STX724,
and STX790A for PNP.
Hi , thanks , there are 4x 'S8050' and 'S8550' 4x .4 are PNP and 4 are NPN . I did guess that but a google search did prove it .
S8050 is NPN and S8550 is PNP .
. Now I wanted to 'upgrade' it , so :
1- it would deliver more power to motors (better transistors) ;
2- it could work with higher currents ;
Higher power transistors are NOT going to automatically provide more power to the motors. Transistors don't "provide" power, they switch/control power.
The power & current depend on the applied voltage, the characteristics of the motor, and the ability of the power supply to supply the power. For example if you increase the voltage and/or use a bigger motor, the transistors might burn-up. If that happens, you need higher-power transistors. But, if the transistors don't get fried, bigger transistors aren't going to make any difference.
With MOSFETs you'll typically get less voltage-drop across the drivers so you might get one more volt to the motors, and they will typically run cooler. But, there are easier ways to get more voltage and if you need more voltage you probably want more than one additional volt.
3- (I'm not sure if it's possible) I could connect it to an arduino UNO .
Probably, but I don't have the specs for the driver board. Of course if you modify it, you'll change the specs. 
DVDdoug:
Higher power transistors are NOT going to automatically provide more power to the motors.[/b]
Better BJT transistors should have less collector-emitter voltage drop, yes? Looking at VCE(sat) on the datasheets, a 2N2222 drops 1.0V at 500mA Ic, The S8050 drops 0.5V at 500mA Ic, and a ZTX1049A only drops .045V at 500mA Ic. I would think that by presenting less voltage drop, all else being equal, better BJTs will improve motor performance.
It may be argued that the improvement will not be significant (why bother if it's only 0.1% gain), which point I'll concede since we have no data on the batteries or motors being used.
Anyway. A BJT may not be able to compete with a MOSFET, true, but not all BJTs are created equal.
Well . I actually thought transistors do differ in power delivery , performance , heat generation and destruction voltage , and I think a MOSFET would be better than a normal transistor in these ? The motors are those little 1.5 v ones , although if I do manage to get the gear attached to them I'd rather use 12v motors . So let's say 24v is going to pass through this , transistors would burn to destruction , the capacitor would MELT (it works on max. 6.3 v) and there wouldn't be any robot . So I need a capacitor that would withstand 24v , transistors that switch 24v , preferably those with little heat sinks attached to their heads . What transistors would you recommend to me ? 
thanks in advance
Whether your transistors need heat sinks is entirely dependent on the amperage you are passing through them, not the voltage. We would need to know either the stall current rating @ what voltage of your motors, or their Ohm value so that stall current can be calculated for a given voltage.
tylernt:
DVDdoug:
Higher power transistors are NOT going to automatically provide more power to the motors.[/b]Better BJT transistors should have less collector-emitter voltage drop, yes? Looking at VCE(sat) on the datasheets, a 2N2222 drops 1.0V at 500mA Ic, The S8050 drops 0.5V at 500mA Ic, and a ZTX1049A only drops .045V at 500mA Ic. I would think that by presenting less voltage drop, all else being equal, better BJTs will improve motor performance.
It may be argued that the improvement will not be significant (why bother if it's only 0.1% gain), which point I'll concede since we have no data on the batteries or motors being used.
Anyway. A BJT may not be able to compete with a MOSFET, true, but not all BJTs are created equal.
So I guess I can upgrade it without the need for MOSFETs ?
The board itself says 6v , some guide for that robot says 9v is ideal ( and there is a 9v battery snap with the robot which proves this ) but as one of the keys to make robots perform better , they tell us to use more current - they say use 12 v 2.5 Amp . But they tell us NOT to give more - the board will get destroyed . So , I need tougher parts ! And some person who had been in the competition showed his driver -- newer transistors ! Unfortunately , I didn't see what transistors they were , just understood the fact that they where that sort of transistors with little heat sink pads on their heads .
Currently , I am feeding them with un regulated 9v battery , but soon , I am going to use 2.5 Amps .
In my opinion, yes, upgrading the transistors to better BJTs will let you achieve your goal of using higher voltages and currents.
However, I do not claim to be an EE expert.
Also, we would need a schematic to make sure that the transistors are connected up in such a way that a 3.3V/5V Arduino pin can operate them properly at high voltages.
but soon , I am going to use 2.5 Amps .
How?
You can only increase the current by increasing the voltage or reducing the motor windings resistance.
Grumpy_Mike:
but soon , I am going to use 2.5 Amps .
How?
You can only increase the current by increasing the voltage or reducing the motor windings resistance.
No , made a mistake . I'll be using regulated 9v 1 amp which unregulated 9v batteries do deliver too , so there won't be any difference in the power supply at all . So would you recommend using a better BJT or switching to MOSFETs (considering power source is going to be the same) ?
And thanks everyone !