I've got an old Rebound RC car that I've gutted. I'm controlling the motors with an ATmega168 and a dual H-Bridge, all with a 6 V battery pack. The problem is when power on both motors, one runs at full speed and the other runs very slowly. When I power them by themselves they both run at full speed.
Does anyone know why that would happen? If you need any code or pictures just ask.
Thanks very much!
are they in a series or in
are they in a series or in parallel?
I’m not sure, how would I
I’m not sure, how would I know?
Based on this test - https://www.robotshop.com/letsmakerobots/node/5725 (the one where you hold one wheel and the other one speeds up if they’re in series) I’d guess that they aren’t in series. So would they be in parallel then?
"in a series" means they are
"in a series" means they are hooked up like old-fashioned christmas lights, in a string. “in parallel” means they are hooked up, each separately, between the negative and positive.
since you are using an h-bridge, they are probably in parallel, I missed that.
What are the motors rated for? what is the output current for your battery?
also try checking the internal resistance of each battery if you have a multimeter.
are they new motors or salvaged? one could be burnt out.
do you have pets? check if hair is wrapped around one of the shafts. It’s happened to me before.
What H-Bridge are you using?
What H-Bridge are you using? Are there any specifications printed on your motor? It’s just a guess, but perhaps your motors are asking for more power than your H-Bridge can supply.
Also, perhaps you can provide a picture or drawing of how you have everything hooked up to help with troubleshooting.
its the rebound RC car !
skid steer , each motor is controlled on its own , i suspect an error in PWM control . check that the rate is the same for both , each motor should be controlled on its own to steer , go forward etc…
perhaps
perhaps its an error in the H-bridge , in the end its transistor based , and it can malfunction , switch the wiring , left motor to right , and right motor to left , does the problem move the the other motor ? if yes ( it should be ) then you have a faulty H-bridge .
Well I tried that and the
Well I tried that and the problem did move to the other motor, but then I tried a different H bridge and the same thing happened. Do you think I just happen to have two faulty H bridges?
The important limit to be
The important limit to be considered is not the voltage, but rather the current. More correctly, the amount of current at a given voltage. A standard 9V battery is clearly more voltage than a 6V motor. However, it might not supply enough current for a large 6V motor, because the motor will try to draw more current from the battery than it is possible for it to supply.
The same thing goes for your H-Bridge. According to the link you provided, it “can drive 4.5V up to 36V at 1A continuous output current”. The H-bridge’s VCC1 voltage will be used to supply the internal logic. Whatever voltage you hook up to VCC2 (4.5V to 36V) will supply the outputs to the motors. So what do you have connected to VCC2 (pin 8) on the H-bridge?
Do you own a multimeter? Set it for measuring current and place it in-line with each of your motors while you are powering them with whatever supply/battery you are connecting to VCC2. What is the maximum current you see from each motor under no load and with some load? You can also physically restrain the motor shaft and check the stall current.
What will this tell you? If your motors are trying to draw more than about 1A under load (not stall) then they are probably overloading the H-Bridge. In this case you will need either different motors or a different way to drive them. If the two motors have drastically different current draws under the same conditions, then something may be wrong with one of your motors. Maybe it runs fine connected directly to a battery, but under load with the h-bridge, it is drawing too much current.
Are the 6V batteries you are
Are the 6V batteries you are using fresh and fully charged? See if the voltage from the battery drops when run the h-bridge and motors. If the battery is dropping voltage, it may be low on charge.
are you using a 9v battery
are you using a 9v battery or 6v? what are you using for the 6v? there are a lot of different combinations. If you’re using AA, you might be okay, but AAA put out 1.5 v each too at less current. What powered the original RC? I suspect that you do not have enough current.
I was using 4 AA batteries,
I was using 4 AA batteries, but the charge dropped too much so I switched to a 9V. It was orignally powered by 4 AA batteries.
did they run on the 4 AA? 9v
did they run on the 4 AA? 9v have notoriously low current.
