Hello everyone,
My team and I are trying to determine the current drawn by the motors during the standard operation of the robot. We were looking at the spec sheet online (Antigravity 4004 KV300 - 2PCS/SET_Antigravity Type_Motors_Multirotor_T-MOTOR Store-Official Store for T-motor drone motor,ESC,Propeller) and we are having trouble figuring out the max expected current that the motors would use based on the 20 gauge recommended wire for the motors. This is in part due to the specifications being provided in relation to the propeller type. Any information would be helpful.
Hello Revant,
we typically limit the maximal motor current to 15A.
That produces a torque of about 2,7Nm at the output.
Please note that this current can only be applied for short durations of time.
In contrast to quadcopters there is no cooling from the propellers and the motor windings can heat up quickly.
During standard operation the motors require much less current.
Pierre-Alexandre shared data logs of the Solo12 robot performing a trot.
Best. Felix
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Hello @mahajanrevant ,
The link to download the data logs on the other topic is expired. If you want to have a quick look at the torques here is a new link : Download link
Logs contain measured position and velocity of actuators, estimated linear and angular velocities of the base as well as torques measurements. We get torques directly from motor currents with a reduction ratio of 9 and a torque constant of 0.025. Be careful in one of the experiments (the 2nd one I believe) I put the wrong data in the baseLinearVel field…
Tomorrow I will upload more complete logs with motion capture data so that the recordings are easier to understand and analyze (and with data in the correct fields).
Best,
Pierre-Alexandre Léziart
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Hi, I’m one of Revant’s teammates. We’re more concerned that 20 gauge wire is not enough to handle the power requirements of the motors for our use case. So another question would if in your experience, have you had any cases where the motor drew more power than the 20 gauge wire would be rated for? We were thinking of replacing the 20 gauge recommendation with 16 gauge which we’re more comfortable with.
I understand that with brushless motors having 3 phases, its not like brushed motors where its constant current being applied through one cable so higher gauge wire can be used. However, in the case of something like standing in place where the motors are stalled, would this not be applying constant current through one or multiple wires? This is where we’re most concerned with the 20 gauge wire.
Hi,
Indeed, having too small wires for periods of time when the robot is applying a high torque could damage the wires. But as stated by @fgrimminger, for this application, the motors are not cooled, so we can not apply high current for a long period. If we did, the motor phases winding would simply burn.
To minimize the total weight of the robot and the volume taken by the wire, we want to have the motor winding and the phase wires to be in the same order of magnitude.
Of course, you can go with bigger phase wire without problem. But remember that the weak point is really the motor itself.
In a future version of the motor controller, we plan to monitor online the resistance of each phase to have an estimate of the motor winding temperature and protect them from overheating.
Hope this helps,
Best, Thomas.
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Dear all,
I have uploaded the recordings I was talking about yesterday on this online repository : https://github.com/paLeziart/solo12-recordings
Details about the logs are explained in the README.
Best regards,
Pierre-Alexandre
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