Mindsensors GlideWheel-M PF Motor Controller
I have received a pair of Mindsensors' GlideWheel-Ms, Power Functions Motor Controllers to Beta-Test. The GlideWheel-M is a motor controller for Power Functions (PF) Motors that allows you to connect Power Functions Motors to NXT Motor Ports. Using the built in encoder, the GlideWheel-M, allows rotational control of Power Functions Motors.
The GlideWheel-M is connected to the NXT Motor Port via NXT a NXT style cable. The Power Functions Motor’s power is derived from connecting the GlideWheel-M via a Power Functions style cable to the Power Functions Motor.
Attachment of the GlideWheel-M to the Power Functions motor allows the GlideWheel-M encoder to turn proportional to the motor’s rotation. You can mount GlideWheel-M directly on to the Power Functions motor and insert an axle through the GlideWheel-M encoder to the motor, or Mount GlideWheel-M else where along the motor's drive-line.
You need to remember to match the final drive output direction with the Power Functions Motor's direction of rotation when attaching the GlideWheel-M Power Functions Motor Controller. If this is not done, it will complicate your coding unnecessarily. The front of the GlideWheel-M has both positive and negative direction of rotation marked on it.
After some initial tests using the GlideWheel-M with the Power Functions M-Motor (58120cx1 or 8883-1), I discovered (as Mindsensor notes in their User Guide) that for accuracy, it is best not to connect the GlideWheel-M directly to the M-Motors output. This due to the M-Motor's output speed causing errors from the GlideWheel-M's encoder.
The arrangement below which uses a Worm Gear to drive a Technics Turntable, and with the GlideWheel-M's input from a 12 Tooth Double Bevel Gear results in less than a "5 Degree" of inaccuracy. The 12 Tooth Bevel Gear rotates 4.667 times for every full Turntable rotation. The total final gear ratio is 1:11.999. That is one full GlideWheel-M axle rotation for every 12 full axle rotations of the M-Motor.
The GlideWheel-M can be connected directly to the Power Functions XL-Motor (58121c01 or 8882-1), with the XL- Motor's output directly driving the GlideWheel-M's Encoder. The errors associated with the Power Functions M-Motor, are not an issue with the XL-Motor.
I have been pestering all the after market sensor makers to produce such an item for several years now. Well done Mindsensors!
Not only can the GlideWheel-M be used with [powerfunctions] Motors, but you can dust off your old RCX Type Motors (71427c01) and use them. You will need a Power Functions Extension Wire (8886-1), to adapt the Power Functions plug on the GlideWheel-M to the RCX Motors power lead.
I have noticed a couple of (minor) technical issues in regards to the GlideWheel-M's attachment to LEGO Technic elements:
- The axle holes a very tight. When I went to insert a 'Blue Technic Axle Pin' into one sensor, one of the laminations began to separate. When working with Rotacaster Australia with their Holonomic wheels, this proved to be an expensive fix. Like all LEGO related tolerances, if it is in 1/1000 of an inch either way, it just doesn't work properly.
- The second issue is due to the thickness of all the sensor laminates are less than the width of a standard Technic Beam. I found trimming off the end of the 'Blue Technic Axle Pins' which connect the GlideWheel-M to the 'Large Power Functions Motor' only solved half the problem. If you wish to connect to the non-motor side of the GlideWheel-M, and also wished to use the 'XL-Motor's' side pin holes, you still end up with alignment issues. These issues are only a problem when the GlideWheel-M is inserted in the drive-line (in series with other Technic parts).
Hopefully when the GlideWheel-M goes into production these little issues will be rectified.
An alternate work around for the GlideWheel-M's thickness problem, is to cut a Technics Half Bush in half. The Half Bush halves can then be place in between the Power Functions XL-Motor and the GlideWheel-M. As shown in the two photographs below, this solves the alignment issues mentioned above.
Perhaps Mindsensors might consider a second version of the GlideWheel-M with a NXT type Socket in preference to the NXT Fly-lead for use as an Encoder at the end of a drive-line. The primary reason being it allows the use of any length of NXT Cable between the GlideWheel-M and the NXT, without the need for a Extender to join two cables for the required length. It is a real pity that an inline NXT type Sockets is not available commercially, but Mindsensors Extender for NXT Cables is a great work around.
I'm very, very impressed with the GlideWheel-M from Mindsensors. As regular readers know, I hate the design of the standard NXT Motors, and often use Power Functions Motors in preference where encoder feedback isn't required. I honestly don't know what the LEGO Designers where on when they decided to lumbers us all with the NXT Motor. Yes, they were primarily designed to be legs for Alpha One Robot in theNXT Kit . But most of us want to do more than build Alpha One.
With the Mindsensors GlideWheel-M, we now have the freedom to use non-NXT LEGO Motors in our creations. The GlideWheel-M also allows one to use third party 9 volt motor with the same ease.
So save up your penny's, as you will want more than just one Mindsensors GlideWheel-M in your sensor kit. I can see a lot of NXT Motors gathering dust as a result of this sensor.