Introduction: Modular Drive Pod Using VEX Components

Build 1 of 2 drive units, for a tank style drive application. Designed for robotic combat/fighting, so an emphasis on strength and ease of part replacement.


You will need


  • Drill bits
    • 5/32" or 4.5mm
    • 3/16" or 5mm
    • 6mm
  • Imperial Hex keys
    • 9/64 (for #8 bolts)
    • 5/32 (for #10 bolts)
    • 3/32 (for shaft collar and motor drive shaft coupler grub screw)
  • Metric Hex keys
    • 4mm (for M5 shoulder bolt)
    • 3mm (for M4 cap head bolts)
  • Stepped bit (or equivalent) 35mm
  • Imperial Sockets/Spanner
    • 11/32 (for 8-32 nut)
  • Metric Socket/Spanner
    • 8mm (for M5 nut)
  • Hacksaw
  • Soft mallet
  • Centre punch
  • File and counter sink bit for deburring
  • Scribe or ultra fine pen


  • Lithium grease
  • Loctite 222
  • Superglue (or equivalent)


  • 1 x M6x25mm Nylon Spacer
  • 1 x M5 6mm dia shoulder bolt x 50mm (6x50)
  • 1 x M5 nyloc (or equivalent) nut
  • 2 x #10-32 x 1.750" UNF cap head bolt
  • 1 x 1/4-20 x 0.375" UNC button head bolt
  • 1/4" washer

VEX Components:


a360 Gallery and Download

Step 1: Assemble the Gearbox and Motor

  • Assemble the gearbox as per the instructions from VEX
  • Do a dry run before greasing and thread locking the unit to ensure correct construction.
  • Also pictured are the 2 x #10-32 x 1.750" UNF bolts that will later mount the gearbox to the frame.
  • You can also add a connector to the motor at this point
  • Tip: Use transparent heat shrink so you can inspect the solder joints.

Step 2: Cut the Frame

  • Cut a 281mm length of the frame. Leave even spacing between pre-drilled holes and the ends of the frame.
  • Follow the attached design PDF to drill the holes in either side.
  • Take care to note which side you're working on, and the orientation of each side.
  • Use the face bearing mount (4183 / bearing carrier plates) as guides for your holes. Place them on the frame as per the distances marked on the design and hold in place with some thin tape.
  • Drill out all 4 corner holes around each larger bearing hole. Use a pillar drill and drill through both sides of the frame in one go to ensure the holes line up with each other.
  • Remember, the holes for the Gearbox need to be the larger 5mm ones. You'll also need to drill out the carrier plate holes to 5mm, but only where the gearbox attaches.
  • You can find the centre of the larger holes by scoring/marking the hole onto the frame using the mount as a guide. Then using the centre line already found on the frame, measure the centre point with a ruler and mark/punch.
  • If using metric bits to drill the mounting holes they'll come up slightly large. This isn't an issue, and can compensate for any inaccuracies in the hole placement. It can also ease bolt insertion.
  • Use the stepped bit to drill out the 35mm holes. You can make these holes larger to ensure the bearing will clear the edge, just don't go any larger than the surrounding smaller holes.
  • When you're done, deburr the whole frame and remove any remaining swarf.

Step 3: Add Bearing Carriers and Bearings

  • Cut 2 face bearing mounts in half to give you 3 single mounts (and 1 left over)
  • Mount them using the #8 bolt and 8-32 nuts. Take care to attach the nut on the correct side
  • The double mount is partly held in place with the #10 bolts that also mount the gearbox, so only bolt the half closer to the middle with #8 bolts.
  • The bolts, at 1.500", are slightly too long and will foul on the timing pulleys (added later). So with the hacksaw cut them flush to the ends of the bolts. File off any burrs.
  • Now insert the bearings, they'll just press into place with your fingers. Take care to insert the bearing with the hexagonal centre into the mount that'll have the gearbox shaft protruding from it.
  • Once you're sure the assembly is correct, add a dab of glue to hold the bearings in the mounts. This'll stop them falling out as you assemble the rest of the pod.

Step 4: Assemble Axles

  • Start by cutting the hex stock (which will be our axles) to length. Each one needs to be 126mm long.
    • Don't worry about cutting them too long, this is easier to fix than if you do it too short!
    • If using a vice to hold the hex bar, be sure to use some soft jaws, as any fouling of the bar surface will make pressing on the bearings very difficult.
  • Once cut, use a file to de-bur and round the edges.
  • Now assemble the axles, Clamp > Pulley > Spacer (make sure the clamp is right at the end of the axle)
  • Fix the clamp onto the axle end by tightening the inserted bolt.
  • Push the axle right the way through the 2 bearings in our frame until the bearing touches up against the spacer.
    • Don't worry about interference, the spacer touches up against the rotating part of the bearing.
  • Make sure the pulleys are on the side with 2 bearing carriers.
  • The bearings are a tight fit over the axles, so don't be afraid to 'persuade' gently with a rubber mallet.
  • Also don't be surprised if the bearings pop out of their carriers, just place them back in. The complete assembly will hold them in place.

Step 5: Add Wheels and Spur Gear

  • First mount the motor/gearbox assembly.
    • Thread lock bolts #10 that hold the gearbox onto the frame.
  • Place a 1/8" spacer and the smaller spur gear over the end of the gearbox output (in that order), which should protrude from the bearing.
  • Hold these in place with the 1/4" washer and bolt. Threadlock the bolt.
    • The 1/4" bolt must be of type button head, otherwise it'll foul on the wheel which is coming next.
  • On the closest axle add another 1/8" Spacer > Large Spur gear > Wheel > Clamp.
    • They may also need a little 'persuading' by gently tapping with a mallet.
  • Tighten the axle clamp
  • Now complete the other axle by pushing on the 1/16" spacer > Wheel >Clamp (tap on with mallet if needed)
  • Tighten this axle clamp
  • Ensure all the components are pressed up against each other, if not then your axle won't be along enough, check for any gaps.

Step 6: Fit Belt and Tensioner

  • Now finish off by adding the belt. It is intentionally too large so should be easy to get over both pulleys.
  • If you want you can add a belt tensioner, this is done by:
  • Drill a 5mm through both sides of the frame. The hole position needs to be 10mm from the top of the frame and central to both pulleys.
  • Now widen the hole on the pulley side to 6mm. (This side only!) deburr as required.
  • Grease the shoulder of the shoulder bolt (just a little) and slide over the nylon spacer.
  • Pull the belt down below the level of the hole and hold in place, while you...
  • Press the shoulder bolt through the 6mm hole and the threaded end out of the 5mm hold.
  • Secure in place with the M5 nyloc nut. (Other shake proof nuts are available...)
  • The bolt and nylon spacer will take the slack out of the belt.

You're done!

If you did a dry run assembly, then now check that everything is correct and is running freely. If happy; add grease to the gearbox and threadlock all the bolts (except those with nyloc nuts).

Now connect a power source or ESC and run in the gearbox, you want half power in both directions for a few minutes.