Building the Recbot

Hi, folks.

I am new to teaching robotics with VEX, and have been working with my class to build the Recbot from the parts included in the EDR Super Kit. I decided to go with the Recbot, rather than the Clawbot, because it’s a bit simpler mechanically, and it is the bot shown in all of the Cortex Video Trainer videos.

I have been encountering ALL KINDS of issues with the build! If anyone has tips for the Recbot build, I would love to hear them!

To start, the 10,000 steel parts in the “Super” Kit don’t include the 2x2x15 chassis bumpers needed to construct the Recbot, and VEX doesn’t sell those parts except as part of an expensive and wasteful chassis kit, so I bought a bunch of extra 2x2x35 angles and cut them down.

Second, the motors in the Recbot instructions are older, three-wire motors, which seem to have clutches pre-installed. No problem- the Cortex Video Trainer included a link to a pdf showing how to use the motor controller 29 with the two-wire motors, and I found the clutches in the Booster Kit and figured out how to install them.

Third, the entire drivetrain of the Recbot seems to be full of glitches. When attaching shaft encoders to the chassis, protruding pop rivet heads kept the encoder from sitting flush against the chassis rail, so we added nylon washers and used a longer #8 screw to attach the encoder to the chassis. The 3" shafts seem too short for attaching the wheels- to be fair, the instructions do say that 3" shafts are the minimum useable length- so we wanted to replace them with 4" shafts. We need one 4" shaft per wheel, but we could only find two 4" shafts in the kit (the Super Kit contents online list 4x4" shafts, but we can’t find the other two). Of course, VEX doesn’t sell the 4" shafts except as part of the Booster Kit (yes, I know that I can hack 12" shafts apart, but not my idea of a fun time). Finally, the wheels are held onto the shaft by a shaft collar on the outside, but there is no spacer or collar shown between the wheels and the outer chassis rail, meaning that the only way to eliminate slop in the shaft would be to snug the wheels down to against the chassis rail, introducing LOTS of friction. There’s room for a spacer if you use 4" shafts, but there’s no hope of adding a spacer on a 3" shaft.

I’m sure I’m in for more excitement as we finish the build! Do any of you build the Recbot regularly, and if so, do you have tips for overcoming these problems? What are the issues I have yet to hit with my class?



A few students in my class are attempting to build the recbot as well…and we don’t have any shaft encoders. Did you order those separately, or were they supposed to be in the super kit? The students are just blocking off the space with some collars to hold the gears in allignment. Is there a list of extra items required for the build? I would like to know what to order for next year.

@rhesse Though I never made the recbot, I made the clawbot once, never having done robotics before, and I can say that it is sufficiently simple for a beginner. But anyways, here are some tips:

  1. You don’t need clutches for the 2 wire motors, they have metal internals & clutches were to protect the old plastic internals from 3 wire motors
  2. IDK if the kit comes with washers, if it doesn’t you can make some easily, but you can use those instead of spacers to reduce friction and they don’t take up much space.
  3. Cutting shafts isn’t too hard, if you need to then do it
  4. Try to not use pop rivets whenever you can, they are unreliable
    If you have more questions I am willing to help
    @brigittegudz the Super kit should contain 2 encoders