Dyne's Treadwell

[Dyne]

I know from Paul's build log that Treadwells can be quite power hungry due to the friction of the treads.  I'm wondering whether going the (more efficient) brushless motor route would be help with the power draw.  I know they aren't cheap, but I'll have to run numbers.

Following up on this, I've compiled a spreadsheet with some variants, really more as a summary of information scattered around Astromech than any new analysis.  I'm not including shipping in any of my prices here, as it depends on too many variables, but I record it in my spreadsheet if it's unusually high (motors, belts).

Firstly, as a baseline, I added up the brushed scooter motors and ESC that Paul6700 was using, even though this specific ESC is discontinued (I found a few sources that gave this price):

• Scooter Motors @ $23.16 x2
  
• Roboteq AX2550 @ $495 x1
  
• Total: 541.32
  

The RoboteQ ESCs that Oliver Steeples and others use with the Q85s (see the ESC section later) are perhaps the nearest equivalent, and cost about the same.


Oliver also posted his alternative to the Jaycar motor setup on astromech.net for a styrene R2:

• Banebots 16:1 P60 gearbox @ $54.50 x2
  
• Multistar 268kv brushless motor @ $40.24 x2
  
• HobbyKing 45 brushless motor controller @ $21.37 x2
  
• Scorpion Power Systems HK-2208 Shaft Kit @ $4 x2
  
• Hobbyking programmer @ $6.58 x1
  
• Total: $246.80
  

He mentioned considering the lower 30 amp version of this ESC, because it doesn't have a fan and thus runs quieter.

Only issue with this Jaycar alternative setup is that I've no idea if it would be sufficient for a styrene Treadwell or not.  The treads make the droid different than the R2 this was designed for, while the styrene+brushless motors make the weight and power output different than Paul's Treadwell.  

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Moving on to other setups, I've split the options up into the motors and the ESC.  Mostly the ESCs.

Motor Considerations

The Jaycar alternative works for styrene droids, which are usually fairly light.  The current favorite brushless motor for heavier R2 units is the Q85 ebike hub motor.  These cost around $80 each, and require modification so that the droid can reverse.  Premodified motors are available for $190 each.  I'd need 2.  

The entire motor rotates on its axle and these have LOTS of torque -- even one motor is quite capable of carrying an adult human (which is, after all, the intended function) ... or bending a bicycle fork, which is why they require a fairly hefty mount.  

I have my doubts this motor would be a good fit for Treadwell, not only due to the excessive torque for a styrene droid, but also due to the physical size and mounting considerations.  

After modification (turning or bandsawing most of the spoke flanges away), I think the motor with no tire ends up being around 4.25".  Treadwell's drive wheels are 4", so the Q85 could only be used directly as the center idler wheels (which are 1/16" larger than the motor).  It wouldn't have as much grip on the treads there.  Even worse, Treadwell's setup needs two 1.25" thick wheels with a gap in between, while the tire mounting portion of the Q85 is about 1.5" wide and the motor casing extends beyond that.

Not only does the Q85 need a beefy mount, but since the motor itself spins, you are really meant to support both ends of the axle.  Not sure how necessary that is, but it really wouldn't work with a standard Treadwell layout.  So I think the easiest way you could use this motor would be to turn the drive wheels indirectly using gears and a chain, like a Senna R2 drive system.

If you aren't set on screen accuracy, you could add a track carrier, kind of like the two Mountain State Treadwells in the foreground below, but at that point you can modify the treads however you like:

Mountain States Droid Builders

There are a variety of other brushless motors one could get.  Unfortunately, I don't know much about sizing brushless motors, so I'm going to have to think about this before listing any.  (Frankly, before I built Artie, I didn't know much about sizing brushed motors either, and originally bought a pair of these woefully anemic things.)

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ESCs

On the original thread about the Q85 on Astromech, Oliver listed the Roboteq SBL1360 ESC @ $275 x2.  Some people favor the SBL2360 @ $495 instead, slightly cheaper since you only need one.  Oliver also mentioned the Turnigy TrackStar 200A 8s as a cheaper alternative.

Experiments have been done with these ESCs

• Turnigy TrackStar Gen II @ $87.03 x2 (poor low speed performance)
  
• a chinese ESC referred to as JYQD_V7.3E (pretty cheap @ $12.33 x2, but it lacks braking and has a noticable delay before reversing direction)
  
• Alien Power Systems 120A @ $89.16 x2.  
  
• James Bruton has recently been making use of the O Drive speed controller for his brushless motors in OpenDog Project, after initially mentioning it in his Exosuit build.  A dual channel 24v controller with connectors is $129.
  
• I think people were planning to test the VESC open source controllers (which James used in his exosuit video), but I don't know the results.
  

So depending on the specific options, a brushless motor setup could run anywhere from about $170 (using the $12 ESC) to over $700 (dual SBL1360).

Assuming that I can't get away with Oliver's Jaycar setup on a Styrene treadwell due to increased friction, I'm leaning most toward the O Drive, assuming it works with whatever motors I select.