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Sean Plummer's 2.3m Extra 330 Build Thread - Page 1

These pages chronicle the interesting conversion of Sean Plummer's Comp-ARF 2.3m Extra 330 to electric power.

Sean is President of Hacker Brushless USA, Inc.

You can visit their website at


Over to Sean.........


For quite some time I have been planning on converting a Large scale aerobat for IMAC type of flying. I chose the 2.3m EXTRA 330L. The Model was ordered with custom paint applied in the mold. This model is all composite construction and beautifully painted. I will do my best to detail the conversion online, as time permits.

I plan on using 2 x
Hacker C50 Direct Drive motors and the newest Inner demon drive gear reduction for power that is larger and features a Teflon Coating on the ring gear and pinions. I hope this model will be capable of many flights, before gear drive parts need to be changed. Total watts target is 4200 input. I will use 2 sets of 10s3p Thunder Power.




I started with the motor mounting as this will need to be in place prior to the battery tray installation. I usually do this so a C/G location can be defined early in the conversion allowing all components to be located correctly. This model has a moulded motor dome type of firewall, that has the proper thrust angles built in. Using the mould marks as a reference the thrust centreline can be determined as shown in mm. Next a piece of 5/8" thick Aircraft Plywood is used to form the Gearbox mount. Please note the holes drilled into the gearbox mount and motor dome must be square using a tilting table drill press and level. I also used a small 3mm allen screw as a centre reference before the Gearbox mount holes are drilled. The Gearbox mounting holes and motor wire slots are now added.




Next the 10/32 Blind Nuts are installed (Supplied with the Inner Demon Gearbox- Using the Gearbox mounting feet/tubes from the Inner Demon Gear box, Spacers are fabricated to provide the proper Prop Hub spacing for the spinner/prop and cowling clearance. 10/32 Allen cap screws and Ny-loc nuts are used to mount the Gearbox Plate to the Motor Dome




Next the pinions must be installed onto the motor shafts. Following the the Inner demon -32 instructions, the Pinions are pressed into position using a drill press. Please note the 3mm allen cap screw is used to press the back of the shaft of the motors (Note: the label on the Hacker motors must be cut/removed to directly access the shaft as shown). Be sure to use the supplied "Green" loctite to help secure the pinions to the motor shaft.




The Gearbox mounting plate is now secured to the Motor dome using the spacers and 10/32 allen caps. The Hacker C50 16XL motors are now mounted to the Gearbox/mounting plate. Double check the spacing to the front of the cowling to ensure proper clearance for the spinner/prop.

Shown is the New Inner Demon 32-TEF Gear drive, This has been developed for these large high power applications (4000 watts!) Available at

This mounting method is very strong, and will allow the model to be flown in freestyle/3d fashion. One of the most common mistakes in large aerbatic electric conversions is improper motor/gearbox mounting. The g-forces during spins and tumbles are huge. Saving an ounce here or there is just not worth it on these large models.




The cowling is mounted next as per the instructions. I am using the Tru-Turn Light spinners I used 3.75 inch "P-51" spinner for lower weight, although the instructions recommend 4" diameter.

I have also installed the 26x15 APC-E prop These props are relatively new and provide huge amounts of thrust for electric applications.



Next move to the landing gear as these will have substantial affect on the C/G. The landing gear are Carbon Fiber. Install into the model, as per the instructions. I used the DuBro 4" "Treaded Lite" wheels. Please note the hole that is drilled into the outside of the wheel pants to aid in tightening the allen cap axle/bolt.



All hinging for the Rudder is pre-installed, simply follow the instructions.The hinges use a steel wire that is removable! and allows the rudder to be removed for transport.

The supplied rudder servo tray is designed for 2 standard servos, I have decided to Use a single New
Futaba Digital S9152 servo This servo weighs 2.6oz. and has 277oz torque. I modified the servo tray as shown, using the parts as supplied in the kit. Be sure to use slow epoxy, and clean all surfaces with alcohol prior to gluing

Also note Large Stock Futaba servo horn. I used the Pull-Pull system as supplied in the kit. The supplied Rudder horn is glued into position as per instructions.




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