7 réponses à ce sujet

[TNERA]

Hi all!

 

Inspired by the successful Quadruped builds at TRR, I'm eager to try another build. From the posts that have been made recently, I've learned about the importance of stronger servos, better batteries, and lighter weight. In my previous builds, I encountered issues with weak servos and excessive robot weight.

For my next project, I'm seeking advice on the servo/distribution/battery aspects. For an 8 or 12 DoF robot, I will need a lot of servos, and suitable battery. Hopefully, I could find the magical affordable servos with a torque of 40kg/cm and a speed of 0.1 s / 60°!

Regarding the electrical requirements, I need help calculating the required current flow and determining the appropriate battery capacity (C value). Should I assume that the stall current multiplied by the number of servos represents the maximum requirement? Or is there a larger requirement due to the combined impulse of all the servos?

I'm also rethinking power distribution. Would a custom board be necessary, considering the possibility of expanding the design to a 12DoF configuration?  This is obviously beyond the capabilities of a PCA9685.

 

Thanks!

 

[Oracid]

The battery Parick used for Felin is this one (TATTU LiPo Batterie 2300mAh 11.1V 45C 3S), https://www.amazon.f...1zcF9hdGY&psc=1

 

The most the C value is high, the most the battery can delivers high intensity instantly. Drone batteries seem to be the best fit.

I dont know if the PCA9685 will stand 8 or 12 servos with that intensity. That's one of my next test.

For information, I will start using a shield, not a PCA9685.

 

In my opinion, it will be very difficult to find a low cost servo with 40kg.cm torque and 0.10s/60° speed.

[Oracid]

Here, for you. https://www.robot-ma...0kgcm/?p=118850

[pat92fr]

I have used this battery for the TRR for 12V servo : https://www.amazon.f...product_details

 

The overall current should be less than about 3 x STALL_CURRENT with a 12 DOF quadruped, but the power supply must be able to support inrush/peak current (start up sequence, touch down torque..). Do not use switched BEC or DC/DC converter between battery and servo.

 

Good luck !

[TNERA]

Thanks both,

question, slightly off topic, does anyone have recommendations for the charging devices for these types of batteries? I know it needs to be LiPo, and there are different qualities of chargers out there, some with discharge capability and certainly with ability to view across the cells while charging. DroneBot Workshop had a great tutorial on this. but my question is ... any favorite devices here in Europe?

[pat92fr]

This one ! I have got two devices, both charging two batteriy packs. 

[TNERA]

Thanks for the recommendations.  The charger is quiet nice and now part of my workshop. 

The battery is much lighter than I expected, I see now how 'you all' are able to keep the weight of the quadrupeds down.

 

From an electrical perspective, using 11.1V for 12V servos makes sense. 

I will take your advice:
"Do not use switched BEC or DC/DC converter between battery and servo."

 

I need to upgrade my servos to 12V, next step.  and get a 7.4V for my mg995 servos.

 

thanks!

[Oracid]

I need to upgrade my servos to 12V, next step.  and get a 7.4V for my mg995 servos.

In my opinion, the MG995 servo is too heavy for a small quadruped and has not enough torque for a big quadruped.

For a small quadruped like I done till now, I suggest MG92B servo.

For a big quadruped like Patrick has done or which I am making in to day project, I suggest 40kg.cm torque servos.

 

https://www.robot-ma...-2023/?p=118550

https://www.robot-ma...upede/?p=118867

https://www.robot-ma...-race/?p=117037

 

A cheap 40kg.cm torque servo :

https://www.robot-ma...0kgcm/?p=118850