Jaguar Amperage Flow

Hello my name is Harrison, but you can call me Verrazano. I am from FRC team 3512.

currently I am researching Jaguar amperage flow and control, Last year we ran into a major problem we burned out several Jaguars during competition due to pushing against other robots and frying the motor controllers.

through my research I found that there are two possible ways to control the flow of amperage through the Jaguars.

  1. Wire the connection between the Jaguar and motor with a resetting breaker.

  2. Writing code that receives the amperage flow value then shuts down the motor temporarily until the flow is normal.

The easiest of the two ways being to do it using code, which falls into my hands as software lead. seeing as I am unsure of an existing function to get the amperage flow it would be a little difficult.

It would be greatly appreciated if anyone could help us, by giving us some pointers on code or if they have any knowledge of this.

Thank you for you time in reading this and your input.



A question and a few comments:

Which Jags are you talking about here, the Tan or Black ones? The newer ones are supposed to have functioning built-in overcurrent thermal protection. They shouldn’t burn out.

If you use CAN to control the Jag, you can read the current.

If you are using PWM instead of CAN, you can get the current by using an analog input to measure the voltage drop across the Jag’s input power lead on the ground side.

You will have to heavily filter the signal to prevent false positives. Finding the right balance between protecting the Jag and allowing large current surges when necessary may be tricky.

You should look for the root cause. Your drivetrain may be geared improperly (not geared down enough).


We are using the black new jaguars. we are not using CAN, measuring the voltage drops across the power lead to the jaguar sounds like it requires extra equipment which is what we are trying to avoid.

As for the drive train I agree that it was likely to have been geared incorrectly as we just hooked the motors from a chain directly to the wheels. can you think of any other way that doesn’t require my electrical counter parts to hook anything new up.

It does not require extra equipment. The cRIO has analog inputs.

As for the drive train I agree that it was likely to have been geared incorrectly as we just hooked the motors from a chain directly to the wheels.

No gearbox?


Last year we decided that it would add to much weight. This year we are using stripped down and modified super-shifters. I just talked to the electrical team and mechanical team on this matter. The mechanical team agreed with the gearing statement as that being the main reason for our burn outs. They also said that the new gearing will mostly likely eliminate the problem. The supers-shifters also have a rpm instrument on them that we might utilize. I try out the analog reading option with CRio.

Thanks for the help it’s greatly appreciated.

I am a little confused by this part of the question. Breakers are required. The unfortunate thing about them is that they are meant largely, to protect the wiring and prevent fires. They do very little to protect the motors or the controllers.
As to the chain to wheels, there are other components to this arrangement that provide from some reduction ratio between motor and final drive. However, teams that chose this approach must use additional bearings as the bearing assembly in the CIM motor is not designed for the kind of side loading normally encountered in this type of chain drive. It is possible that a correct reduction was designed into your robot such that normal motor operation was expected. The side loading presents very high friction loads to the motor, resulting in significantly increased current. If you had coupled this to a normal tank drive with high friction wheels, then you likely were putting the motor at or near rated stall current of 133 amps. The Jaguar cannot handle this current for long. The newer Jaguar design has current capability of 90-100 amps and repeated demands above this point result in failure of the device. The Jaguar does have internal protections for this and will try to enter a current protection mode before damage can occur. However, repeated high current demands can destroy the Jaguar or Victor for that matter.

As Ether has hinted, measuring the voltage drop across the power wiring feeding the Jaguar will give you an idea of the current each device is delivering. Using #10 wire, 100 amps will drop 0.1 volt per foot. While this requires some special circuitry, it is possible to do so with the analog inputs to the Crio. Remember that the current flowing to the Jaguar on the positive lead is also flowing away from the Jaguar on the negative lead. Low impedance current monitoring is legal under the 2011 rules and will likely also be legal in 2012 as a custom circuit (see 2011 R43).