April 2012

High-speed Romo Modification

A couple weeks back I got Romotive's Romo cell bot from a project I sponsored on Kickstarter. Cell bots use an onboard cellphone as their controller. As with other cell bots I've built, audio out is used to communicate with the robot platform. Some of the earlier cell bots actually directly controlled servo motors using the audio out. Romotive executed this far better with their robot base and it's the best such small cell bot I have. The assembly was straight-forward and with a pre-assembled board, no soldering was required. The only slight detraction was that the power switch on the circuit board came broken off and email to the Romotive team via both Kickstarter and their own support email has gone unanswered. It's fairly minor though since the switch can be forced on or off with a screwdriver but it would have been nice to hear from them. The Romo supports both IOS and Android phones and tablets (phones for the controller on the Romo itself). The devices vary in both camera placement and whether the screen is rotated which can make the wrong combination awkward to use. I'm sure this will be resolved in time. I've tried the Romo with iPhone and iPod Touch and control with iPad, Xoom, and iMac. For my array of devices, I found it's best to have the iPhone onthe Romo and control works best with iPad and iPod Touch. The small size of the robot and the traction afforded by the treads make it fun as it can move through some pretty confined spaces. Remote exploration is easy with ability to see remote real-time video from both front and rear facing cameras on the phone mounted on the Romo.  As seen in the photo below, the Romo is very expressive with various emotive settings controllable from the remote.

The phone mounts very securely on the base. The front also has three accessory ports which could be utilized by various effectors (but probably not sensors unless other connections to the phone are utilized).

Romotive took advantage of alot of Pololu parts in designing the robot. Quite literally why re-invent the wheel (or track) when Pololu's got some excellent parts including the tracks, motors, and motor mounts. I think the original motors are probably the 100:1 #992 motors from Pololu.  The Romotive guys also said they required about 10 oz-in of torque and that the limit on the H-bridges was about 1 amp as reported in this thread.  The original Romo actually moves kind of slow and I thought speeding it up might be nice.  I couldn't quite find another micro gear motor on the Pololu site that met the specs.  But one of the posts on the previous thread mentioned a nice 56:1 gear motor that met the specs.  So I decided to give it a try.  I used a couple of JST connectors and wires I had around (since the Romo uses JST connectors for the motors) and I soldered the new motors onto the leads.  After installing, the result is a much higher-speed Romo as shown in the video below.This operates the Romo a bit faster than the original software was designed for.  It would be nice to get some enhancements to the default applications to support this.  For instance, better motor speed control would be nice or at least a mode where it slows down for turning in place.  Also the Romo may more easily sense that it's been shaken and makes a noise and a confused expression -- but this happens much more often at high speed and it would be nice to turn it off.  I also somehow ended up with the motor polarities on the new motors exactly backwards even though I carefully mirrored the way the wiring was done with the other motors.  This could obviously be a quick fix with a motor polarity software setting but unfortunately there's no such setting in the app.  The Romo is a lot of fun and the high-speed version will certainly speed up my exploring.