Looking at the gripper they are selling in the shop it states that it has a HD servo motor installed not a micro servo. After reviewing the specs on EZ Robots HD servo I don't think you'll find one as reasonably prices at $12 USD. The closest one I can find to EZ Robot' s HD servo is a Futaba BLS-172SV at servo City for $219 USD. I'm not sure but if you go with a different brand then EZ Robot you may find they move at different speeds. You may need to adjust your scripts it compensate. This is just a guess as I don't own any of the revolution robots and haven't messed around with how they work yet.

Servo City / Futaba BLS-1725v

Control System: +Pulse Width Control 1520usec Neutral
Required Pulse: 3-5 Volt Peak to Peak Square Wave
Operating Voltage: 6.6V ~ 7.4V Volts
Operating Temperature Range: -20 to +60 Degree C
Operating Speed (6.6V): 0.12 sec/60 degrees at no load
Operating Speed (7.4V): 0.11 sec/60 degrees at no load
Stall Torque (6.6V): 472.3 oz/in. (34 kg.cm)
Stall Torque (7.4V): 513.9 oz/in. (37 kg.cm)
Operating Angle: 45 Deg. one side pulse traveling 400usec
Continuous Rotation Modifiable: No
Direction: Counter Clockwise/Pulse Traveling 1520-1900usec
Motor Type: 3-Pole Motor
Potentiometer Drive: Indirect Drive 
Bearing Type: Dual Ball Bearing
Gear Type: Metal Gears
Connector Wire Length: 12"
Dimensions: See schematics
Weight: 2.61oz. (74g)

EZ Robot's HD Servo:

Operating speed: 0.24sec/60degree (7.4V)
Stall torque: 15.0kg-cm/529 oz-in.(7.4V)
Temperature Range: -20C to +60C
Operating Voltage: 4.8V to 7.4V
3 pole ferrite
Dual ball metal bearing
All metal gears
connector wire length: 32cm
Futaba 3f (25 teeth) for driving spline/shaft
6.2mm spline (including teeth

My mistake. I should have been clearer. I have the grippers that came with Roli. It's an HD, metal gear micro. But thanks for the other info. It may come in handy one day

The grippers do use the micro servo. I don't know the brand or anything but am monitoring this as I too have one that I need to replace.

Any HD Micro servo which can handle 8.4v max will do.

Dimensions of the EZ-Robot micro HD servo are

Length: 29.11mm (not including tabs) Width: 13.75mm Height: 30.40mm (not including spindle)

Thanks Rich. I'll look to see what I can find.

Doing some interneting I've found that the Hitec HS-85MG Metal Gear Micro servo is the closest match at 1.14" x 0.51" x 1.18". It's just a couple mm smaller overall.

They are a bit pricey so if someone finds an alternative that works in the claw I'd like to know.

Thanks again guys.

The HS-85MG is only rated for up to 6vdc according to ServoCity's chart. However it is an analog servo. The HS-5070MH is rated for 7.4vdc but is digital and even more expencive then the HS-85MG. Digital is good but they are a little noisy when trying to hold position. Either way you'll want the HiTech C1 standard spline and both these have that.

15kg cm is 208.2oz in torque. Just gotta remember to convert cm to inches. So yea there are a handful of servos with that power. Like a power HD , 240 Oz in @ 6 volts. The EZ-Robot HD servo is strong and a great price! It is not as strong as a couple of these posts implied.

Hy,

the ez-shop indicate a standard micro servo for the grippers with 44.4 oz-in of torque : https://synthiam.com/Shop/AccessoriesDetails.aspx?productNumber=13

I think 15kg/cm of torque is a mistake, 44.4 oz/in make 3.19 kg/cm for me.

Maybe Turnigy TGY-S310 could make the job. (google it )

(I use many of HS-85MG in my rc sailplane )

Thanks for all of the info guys.