Segway RMP 50 Omni Review

One of the newest offerings from Segway is the RMP 50 Omni, a trimmed down version of the RMP 400 Omni. This platform has mecanum wheels which give the base the ability to drive forward, backward, right, left, and turn independently. It is a capable mobile base in a sleek and low profile package, but this product doesn't come with all the features one would expect from a $21,000 platform.

The platform evaluated for this review was purchased to facilitate research on healthcare robotics at the Georgia Institute of Technology (to which this author belongs).

Segway RMP 50 Omni

The RMP 50 Omni brings the holonomic advantages of the RMP 400 Omni to environments where space is even more constrained. The capability for differential motion in three degrees could greatly simplify many tasks for service robots and altogether enable other tasks.  The key feature of the RMP 50 Omni is its smaller footprint. By trimming upto 12in. off the RMP 400 Omni, Segway gave the RMP 50 Omni the ablity  to negotiate many doors commonly found in homes and offices. Since the platform and standard wheelchairs have very similar dimensions, it is well suited for use as an assistive robot platform. This video shows the platform being controlled using a wireless gamepad:

 


Hardware

 

Segway RMP 50 Omni Top View

 

The RMP 50 Omni is built from two RMP 50's connected with 80x20 as seen below. The 8in diameter mecanum wheels are only slightly larger than the gear housings that drive them, giving the Omni only 9mm of ground clearance. It has no suspension, so flat ground is imperative. Slight changes in the floor's planarity or surface friction can have adverse affects on the robot's motion. Approaching surface transitions perpendicularly can reduce the degree to which the robot suffers from this drawback.  Because the RMP 50 is a cost engineered platform, the Omni only uses 2 NiMH batteries although it has 4 battery bays. It is possible to get a payload power module for each of the empty bays. The module can supply payload electronics regulated power or raw 60V from the battery rated for about 3 Amp-hours.

 

Segway RMP 50 Omni with 80x20 visible

 

Many people have probably seen the leaked footage of the RMP 400 Omni doubling as a holonomic surfboard leaked at Robobusiness 2008 (see video below). Unfortunately, the RMP 50 Omni has a lower payload of 150lbs--I guess this means many of us will have to shed a few pounds before we can mount-up. The payload is quite sufficient for most service robot applications, but with a full payload the platform would weigh in at 280lbs. During an entirely unintentional test in the lab, we found that it is possible to move furniture (a bookshelf) with this platform.

 

 


Software

Because the RMP 50 Omni is based on the  RMP 50, the same drivers can be used to control it. However, there are several key features that are omitted from the RMP Omni's API. The most conspicuous difficulty arises from the inability to coordinate motion between the two RMP's. Additionally, the firmware API lacks commands to specify wheel velocities independently or in a coordinated fashion, both of which are essential for controlling a holonomic platform of this type. By specifying a forward and turning velocity, it is possible to uniquely specify the individual wheel velocities. However, this decomposition is convoluted because RMP's use a different control scheme for low and high forward velocities. Hopefully future versions of the Omni will expose the underlying functionality necessary to directly control the velocity of the wheels through the Omni's API.

 

Summary

This is a functional, solid platform for indoor service robotics. The platform will fit through most doors with at least 3in. clearance on both sides. The platform is heavy, but it is also rugged, powerful, and sports a commendable payload. Driver reuse is possible. The most serious drawback is the inability to ensure synchronized motion between the front and rear RMP's. The API is not tailored to the omnidirectional nature of the platform. There is plenty of room to improve the platform, but it remains an attractive option because it is a moderate cost off-the-shelf holonomic base from a well known company.

 

Comments

Can it climb the stairs ? Which all Segway products can climb the stairs. 
—Abhijeet

@ Abhijeet

No, the RMP50 cannot climb stairs.  Perhaps you were thinking of the iBot

—Travis Deyle

I can see it but for a research toy, but not for a real world applicaton. The Vetex RoboMate has over 6 times the capacity, over 50 Ahrs of power. It is bigger, but fits through most doors, it is rugged enough for commecial and industrial applications, and it works right out of the box. Smaller versions and ROS compliance are comming too.

—Anonymous

@Anonymous,

That may all well be true... but please keep in mind the date on this article: 2008.  This was before ROS was mainstream. In fact, I helped write the ROS drivers for the RMP... though it may have been "pre-ROS" (ie. botherder) -- I can't recall. :-/

I'm curious about the fidelity of the odometry for the RoboMate.  Naturally, swedish wheels rely on slipping for omnidirectional movement, so wheel encoders aren't generally too accurate.  We actually built a custom visual odometry system using downward facing cameras so that we could get millimeter accuracies for mobile manipulation: Visual Odometry and Control for an Omnidirectional Mobile Robot with a Downward-Facing Camera

—Travis Deyle

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