Community Question

I'm making my first wheeled robot using the ez robot v4. I recently connected an h-bridge to my ezb v4 without a problem. The directions were clear and concise. Operating the motors through the ez builder was easy.

My question is this, why does it appear that the motors are running slower than they can? It's a fairly slow rotation. As a test of the set up, I''m running the FingerTech "Gold Spark" 16mm Gearmotors.

Here are the motor specs:
Operating Voltage: 3V - 18.5V (>10V decreases motor life)
Nominal Voltage: 6Vdc
No Load RPM: 11530rpm
No Load Current: 0.09A
Stall Current: 1.3A
Stall Torque: 0.0461kg-cm (0.64oz-in)
Kt: 0.0352kg-cm/A (0.49oz-in/A)
Kv: 1573rpm/V
Peak Efficiency: 52%
RPM @ Peak Eff: 9100
Current @ Peak Eff: 0.34A

As a check, i connected a 9v DC 25 motor (I dont have amp info) and it's speed was similar to the more nimble gold spark motor.

Is there something I'm missing (no doubt)? Is there a different way to set-up the hbridge to increase the motors speed?

Thanks for your help.

DJ Sures
Commented December 2017
Is it very noticeable speed difference? That hbridge might not be efficient and that’s the best it can do.
Commented December 2017

troubleshoot your h-bridge (alone):

User-inserted image

If you use 3 dip switches jumpers, you should have the motor on max speed.

Other variables:

1) Power

6 x AA (Alkaline batteries) = 6 x 1.5v = 9 v
6 x AA (Rechargeable batteries) = 6 x 1.2 = 7.2 v

2) H-Bridge chip L298N

Although is very easy to source and very cheap is not very efficient, the chip drops almost 2 volts. If you power the h-bridge with 7.2 v only 5.2 volts are delivered to the motors.

Check all the details and let us know your findings.

Edit 1: Correction Dip Switches i meant Jumpers

Edit 2: if you are powering the H-Bridge with more than 12 v, you will need to remove the Jumper JP1 and provide a 5V for the H-Bridge logic.
Commented December 2017


** The driver comes with a 5v linear regulator supply. The 5v supply is enabled with a jumper. If your motor supply is higher than 12v it’s recommended that you remove the jumper and use an external supply. The 5V supply is enabled with a Jumper./

Your answer is right there. Remove the jumper to take the 5v regulator out of the circuit. In your picture, the jumper is on the left, next to the green motor connector block.


Commented December 2017
JD - there is a noticeable speed difference b/t a direct connect to the battery and the HB. It's a 185 rpm motor. Connected to the battery directly I'm getting approximately - 180 +/- RPM. Connected through the Hb I'm getting 120 +/- rpm.

PTP - Jumpers = Check!
Power = 6 x AA (Alkaline batteries) with an output of 8.7v. It's powered through ezb v4.

Thetechguru - I removed the jumper and there was no descernable difference. The motor was operating at around 120 rpm.

I think, based on the discussion on this thread, I'm going to buy another, different hbridge and give that a try for comparison. For now, this hbridge will work ok to get the my robot moving.

Thanks again for your help!

Happy New Year!
DJ Sures
Commented December 2017
Of course we recommend using the ezrobot hbridge, bexause it always works :)
Avatarby ggr_scott
Published Friday, December 29, 2017