How long should a VEX IQ Battery Run?

VEX IQ General Discussion IQ Technical Discussion
1

I am a mom asking a question for my daughter. She is heading to worlds and has built a fast bot using six motors she asks me to time her while she drives. The battery dies after about a min of use. She takes it out and lets it cool while she uses a different battery. It seems like it is working fine to me but she says no, “It’s not going fast enough I want it as fast as it will go.” But is what she is doing making the battery die faster? Should she be running it longer or is one min intervals ok? I guess the question is what is the best way for a driver to practice at speed without killing the battery?

2

@Cbmary1
A few questions:

  1. Her robot has six motors, can you tell us the config? (ie 4 motors on the drive base, one for each wheel.
  2. How old is the battery?
  3. Is she bringing the battery up to full charge (ie the charger is green), before she uses it again?
  4. When she says “not going fast enough”, what does she mean? At full RPM the motors don’t turn that fast so some gearing (bigger gear on the motor to a smaller gear on the driven shaft) will help the speed.

Thanks!

3

Hi thanks for getting back to me,
Two motors on the drive base
two motors make claws go up and down that drag hubs and then two motors run a big claw at the top that they use to stack and hang.

She is bringing it to full charge.

She has a brand new battery she likes the way that runs through their strategy once.

They use a chain around a big gear to two little gears that the wheels are on.
They believe the difference in speed is the battery. Is it possible that the battery is being drained by claws that are not being used?

4

@Cbmary1

So the drive base is going faster since they have a big sprocket attached by chain to a smaller sprocket. So she is going the right way to get speed in the base.

It’s possible that the claws are being drained, but they would have to be keeping them closed at 100% speed. That would stall the motors out when the claw faces meet and that would draw a lot of current. For that to happen they would have a button that they press to “open” the claw and a button to press to “close” the claw. They would have code like this (psudo code since I don’t know what they are coding in)

if open_button_pressed then motor(100);  // open the claw
if close_button_pressed then motor(-100); //close the claw

They never say to stop moving the motor. Once you start a motor moving it stays moving until you tell it it to stop.

if open_button_pressed then motor(100)  // open the claw
else if close_button_pressed then motor(-100) //close the claw
else motor(0);  // stop the motor, no buttons being pressed

With six motors you should easily get 5-6 runs without noticing a difference in speed.

You’d need to get her to post the code here for us to see if it’s code related.

1 Like
5

Thanks a bunch for this information. I mentioned this yesterday but they only had a short time to practice they did not want to address it, but they did use an old battery. They said that they are holding the claws down at full so the hubs don’t pop up and the motors are working when the claws are up they use parts to stop the claws from going all the way back. I bet you are right and it is draining the battery to have 4 motors working that hard.

6

@Cbmary1

They might find that holding them down at a lower value (30??) would achieve the same function with a much lower battery usage. Likewise on the uplift.

Are they using the brake option to have the motor hold in place?

Assuming RobotC look here

http://help.robotc.net/WebHelpVEX/index.htm#Resources/topics/VEX_IQ/ROBOTC/Motor_Commands/setMotorBrakeMode.htm

Good luck!
Foster

1 Like
7

Excellent , I have no idea what you are talking about. However the 11 year old and 12 year old working this problem probably will as they won the programming part of regionals. So when they get off the bus I will show them your advice.

8

IMG_6651
IMG_66513000×2250 2.13 MB

Hi Foster,

They are back at it- here is a picture of the code. Any thoughts?

Mary

9

File Transfer: IMG_6652.jpeg
This is the right one . Rylee just sent me this picture and said this is the right one and the motors are hot. She asked me again to ask you if they can fix their program.

Thanks,
Mary

10

@Cbmary1
Your second picture did not post, so I’m going to go off the first one.

So it appears that clawArm and ClawArm2 are on the same claw, are they on the same shaft? Does one of them have the reverse box clicked?

Using the armControl functions/blocks meas you shouldn’t need the stopMotor on line 15.

What are they trying to do in lines 6-10? it says to me
“Stop the robot from moving (7) now move the two claw motors at full speed for 30 seconds)” which seems a really weird thing to do.