Hitec H-322HD Servo + 3.6 lbs of metal = success?

[Mikhail_Pham]

We were wondering if a Hitec H22HD servo could swing a 3.6 arm in a circular fashion in a side to side motion with any success. We're kind of at a loss at how to calculate it. The specifications are:


Control System: +Pulse Width Control 1500usec Neutral
Required Pulse: 3-5 Volt Peak to Peak Square Wave
Operating Voltage: 4.8-6.0 Volts
Operating Temperature Range: -20 to +60 Degree C
Operating Speed (4.8V): 0.19sec/60° at no load
Operating Speed (6.0V): 0.15sec/60° at no load
Stall Torque (4.8V): 42 oz/in (3.0 kg/cm)
Stall Torque (6.0V): 51 oz/in (3.7 kg/cm)
Current Drain (4.8V): 7.4mA/idle and 160mA no load operating
Current Drain (6.0V): 7.7mA/idle and 180mA no load operating
Dead Band Width: 5usec
Operating Angle: 40 Deg. one side pulse traveling 400usec
Direction: Clockwise/Pulse Traveling 1500 to 1900usec
Motor Type: Cored Metal Brush
Potentiometer Drive: 4 Slider/Direct Drive
Bearing Type: Top/Resin Bushing
Gear Type: Heavy Duty Resin
360 Modifiable: Yes
Connector Wire Length: 11.81" (300mm)
Dimensions: 1.57" x 0.79"x 1.44" (40 x 20 x 36.5mm)
Weight: 1.52oz (43g)

Any help as to how we would calculate the feasibility of such an application would be very much welcome.

Thank you in advance.

[jgannon]

Torque = Force * Distance. You have a stall torque of 51 oz-in. Assuming that the mass of your arm is uniformly distributed, then the absolute maximum length that your arm could be is 1.77 inches. I'm guessing that that's not going to work for your application.

[dtengineering]

I believe we are also allowed to use VEX continuous rotation motors this year as well, are we not? You could gear a vex motor (essentially a continuous rotation servo) down many, many, times and get a slow movement, perhaps.

If you want a servo style motor hookup take a look at the FP and Banebots motors in the KOP and consider a banebots planetary transmission for them. Plug a variable resistor into the output shaft, so as the shaft moves, the resistor turns. Read the voltage of the resistor with an analog input on the RC and then program the motor to move the resistor to the desired setting.

Or just use lots and lots and lots of the servos... I believe the rule says "unlimited numbers" doesn't it?

Jason

[dlavery]

Or just use lots and lots and lots of the servos... I believe the rule says "unlimited numbers" doesn't it?
True, but there is a finite number of PWM ports on the Robot Controller, and you can only connect servos to the PWM ports (Rule <R62>), so....

-dave


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[Alex698]

True, but there is a finite number of PWM ports on the Robot Controller, so....

-dave


.
make use servo PWM Y-Cables! ;)

All we need now is a Servo-driven shifting gearbox.

[dlavery]

make use servo PWM Y-Cables! ;)

All we need now is a Servo-driven shifting gearbox.

And given that the total combined current supplied from all 16 Analog and 18 Digital +5V Power header pins on the Robot Controller is 1 Amp, and each VEX servo can pull up to 1.5 amps, how many times can you get away with that? :)

Using multiple VEX servos and VEX motors is certainly within the rules. But the capabilities of the system hardware makes the number of possible configurations somewhat self-constraining.

-dave



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[mneary]

In the ifirobotics FAQ (December 2004), they state that "The total combined current that can be supplied from all 16 PWM Output +7.2V header pins is 4 Amp. This current is supplied from the Backup Battery."

Earlier the stall torque was used to calculate the force you can use... operating a motor in stall for more than a second or so will often let the magic smoke out.

[AdamHeard]

What do you need this motion for? There is probably a better way to actuate it.