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Ah, a board with R/C PWM servo ports. That's a 1970s interface which should have been replaced by now. There are servos with a bidirectional serial interface, so you can ask what the actuator is doing, but they're overpriced.[1] They're about 5x-10x as expensive as standard R/C servos.

There was an open source project, OpenServo, to do something about this, but it was done by 2008 and seems to be dormant. [2] There's no multi-manufacturer standard for servos above the dumb level.

Annoying things in low-end robotics: 1) motor controllers with significant power handling cost too much, although this is improving, 2) encoders cost too much, although they're simple and every mouse wheel has one, and 3) encoders are usually fragile plastic add-ons to motors with strong metal cases, instead of being integrated inside the motor case.

[1] http://www.trossenrobotics.com/c/robotis-dynamixel-robot-ser... [2] https://openservo.org/

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The core problem with the dynamixels is cost. I'm hesitant to use them in any situation they could get trashed because they are so expensive. Add on that they are harder to control and it's a recipe for a niche product.

Having used them I loved them, but they aren't a tool I reach for at first. But now that you've brought them up I kind of want to use them for something.

But why this board has RC PWM Servo ports? Because it's a cheap easy way of interfacing with things. More importantly, it let's you hook Brushed/Brushless ESCs up fairly easily to get things moving with motors that draw more than 1 amp.

1) DC Brushed - Spark ESC https://www.amazon.com/SPARK-Motor-Controller-REV-Robotics/d... (Disclaimer - I know the owner of Rev, he's a friend) 2) This is really a function of scale more than anything. But yes, they are expensive. 3) With the advent of 3d printing it's at least manageable to put something around them

But I agree with you that most of these are incredibly annoying.

Spark Revs are nice :) we just had your friend come out and replace one on our practice robot

Speaking of big motors and big torques its interesting to consider CNC machine tool conversion technology ... Admittedly continuous use, industrial level indestructibility and temperature levels means expense, but if you want 400+ oz=in of torque for a wheel perhaps, you could do worse than CNC controller hardware perhaps driven by something other than CNC software. At some point you have a 5 volt TTL interface thats as simple as direction and step. You'll be spending maybe $200 per axle but you look at the price of 400+ oz-in servos or gear motors plus drive circuitry and suddenly its not that bad. 1000+ oz-in is not out of line for the larger machine tool conversions. Standard NEMA motor mounts etc. You take 200 steps/rev stepper and add 10-step microstepping driver like a geckodrive and theres 2000 steps/rev at 400+ oz/in with a simple TTL interface for maybe $200 (plus power, and steppers are hungry beasts)

Could you provide a link to some of these $200 devices for reference?

Something like a geckodrive G251 single axis stepper driver for $89 good to 3.5 amps combined with a NEMA 23 stepper one of the lower current 1.8 amp "long" types $48 on amazon for 340 oz/in torque. That's about $140. That's 68% of budget for 85% of specified torque.

Its easy to find a NEMA 34 with over 600 Oz/in for $60 on amazon but it'll probably draw 6 amps at 600 oz/in and you'll need a more expensive controller. Something like a geckodrive G201X is rated to 7 amps at $127 which just barely makes spec.

The worlds cheapest stepper paired with the worlds fanciest most indestructible controller is probably unrealistic.

The dynamixels are fairly priced when compared to equivalent servos. Compared to the weakest slowest servos with lots of dead band slop the dynamixels are quite expensive. However those servos are quite useless of course, and compared to servos of similar built quality the added cost of a dynamixel is minimal.

Look at something like an AX12W dynamixel which costs $25 more than an equivalent Futuba S3003, roughly same torque and speed. Given the control capabilities of the AX12 I don't see the point of buying the Futuba product.

Or a Futaba S9452 is about $90 for 130 oz-in of torque or Dynamixel AX-18A for $95 for 255 oz-in torque. Eh an extra $5 for twice the torque, not that ridiculous.

There obvious scaling problems where putting a vary fancy controller on piece of junk mechanicals doesn't make economic sense so you'll probably never see something with the control features of a dynamixel on sale for $5 each.

Dynamixel servos are expensive for sure, but there are a couple of low-end models which are pretty reasonably priced given their (excellent, as you note) capabilities. The XL-320[1] is only $22. They're puny, but I've had fun with them.

[1] http://www.trossenrobotics.com/dynamixel-xl-320-robot-actuat...

> motor controllers with significant power handling cost too much, although this is improving

There are more than a few h-bridge ICs out there that can easily control many amps of current; Infineon's BTN89xxx line is fairly popular, but there are others. Many can be found as "breakout boards" on Ebay and other places. They'll usually control 12-24vdc @ 40A and more; they are MOSFET devices (n-channel, integrated high-side pumps, etc). These boards are fairly cheap.

Now, an h-bridge of course doesn't make a motor controller, but it is the most difficult piece of the puzzle, and perhaps the most expensive part (in terms of electronics hardware and developing one - because frying MOSFETs or IGBTs in the process of development can add up quickly). The rest is monitoring and code (basically using a microcontroller to interpret control signals and feedback signals from current, encoders, etc - implement PID as needed for speed or other control, overcurrent monitoring, etc).

Of course, none of this will match the capabilities of a Roboteq or Vantec motor controller - but you won't be spending several hundred dollars, either. These lower end devices and designs (and there are other companies that make lower-end controllers, like Dimension Engineering and others) are more than enough though to control electric wheelchair motors (but if you want proven "bulletproof" controllers, spend the money).

And if you are really cheap or want to experiment? Pick up some cheap logic-level high-amperage N-channel mosfets off ebay (or other places), parallel them together for more current handling (of course, there may be issues with capacitance load), then build a simple "h-bridge" from 40A Bosch relays scavenged from a pick-ur-part (most of those places give 'em away), and put the mosfet pack on the low-side connected to ground. A couple more mosfets to control the relay switching, and you have a (somewhat) cheap (though large) 40A PWM-capable hybrid h-bridge (just don't switch the relays while PWM'ing!).

I guess all of this is to say that there are plenty of inexpensive options out there that aren't "old-school" L293 or L298 solutions (though honestly, for their application, such h-bridge controllers still work well, provided you pair them properly - that is, larger motors running at 12 volts or a tad more off of gel-cell or similar batteries, when efficiency isn't as great a deal).

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