Merlin: $53 robot with Sparkun's Magician chassis and Quickstart
Here's our first entry into the budget robot arena.
It's the $14.99 Magician chassis from Sparkfun together with Parallax Quickstart Board.
We've come up with a little controller board called Merlin that plugs into the Quickstart.
Merlin has a dual-motor controller and also headers for servos and sensors, etc.
Merlin also accepts a 5..9 VDC power supply.
The Magician battery pack plugs right in.
We've also come up with some $5 proximity detectors with a range of ~1 inch.
These are good for keeping the robot from hitting walls:
Watch Merlin robot use optical sensors to avoid hitting the wall:
http://www.youtube.com/watch?v=N-JmOayldJ4
Note robot programmed to go full reverse when sees something, so it looks like it bounces off the wall, but
it doesn't touch it!
Some simple micro-switches would be a lower cost route than these optical sensors though.
We're also going to try the Quickstart+Merlin out on a $14.99 Ardbot chassis and see how that goes.
That might be better since it uses servos instead of motors to drive it...
But, it'll cost more because the servos aren't included...
The Merlin board can also be used to convert your BoeBot to Quickstart:
It's the $14.99 Magician chassis from Sparkfun together with Parallax Quickstart Board.
We've come up with a little controller board called Merlin that plugs into the Quickstart.
Merlin has a dual-motor controller and also headers for servos and sensors, etc.
Merlin also accepts a 5..9 VDC power supply.
The Magician battery pack plugs right in.
We've also come up with some $5 proximity detectors with a range of ~1 inch.
These are good for keeping the robot from hitting walls:
Watch Merlin robot use optical sensors to avoid hitting the wall:
http://www.youtube.com/watch?v=N-JmOayldJ4
Note robot programmed to go full reverse when sees something, so it looks like it bounces off the wall, but
it doesn't touch it!
Some simple micro-switches would be a lower cost route than these optical sensors though.
We're also going to try the Quickstart+Merlin out on a $14.99 Ardbot chassis and see how that goes.
That might be better since it uses servos instead of motors to drive it...
But, it'll cost more because the servos aren't included...
The Merlin board can also be used to convert your BoeBot to Quickstart:
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Comments
Vienna, VA? I grew up in Woodbridge. Fond memories of NoVa.
Merlin does not really have a A/D converter...
But, there is a solderless breadboard where one could hook one up...
Also, the Quickstart has unpopuled SMT pads for doing sigma-delta ADC using P8 and P9.
The Merlin board is really sqeezed tight, so I don't see getting one in.
But, perhaps I could make a different version that has an ADC chip instead of motor controller...
Make that $15.99, as of this morning. Price had to go up because I need to have these made by an outside CNC shop, and they charge way too much for small runs. My machine is on its last legs -- or mill, or router spindle, or whatever marks the final days of a CNC.
Small consolation is that servos won't have the robot make as many unintended turns.
-- Gordon
I think the Ardbot looks great, even at $15.99. I have one and I'll be testing it soon with Merlin.
I think you're talking about how the Magician doesn't always go straight, right?
That's a very good point. The problem is the gear train makes the motors have very little torque.
Problem gets worse as speed goes down.
But, it does have optical chopper wheels installed. If you add a couple optical leds and photodiodes, you can tell how fast each wheel has gone.
Or, there is a 3-axis gyro module that can plug into the EEPROM socket and maybe that could be used to make it go straight.
I'm interested in the concept of a gyro as a go-straight odometer. Has the math been done on this yet? I'd be interested in looking at it.
The chopper disc they include is not very opaque to IR (already being red, no less), so you have to either paint it, or reduce the LED output, or reduce the phototransistor sensitivity (or all three). I haven't yet bothered with it because I don't have an optical switch wide enough for the 1/8" plastic they use, at least not without more precision mounting. I'd have to fashion something and I'm getting too old for that!
One of the designers at DAGU indicated the correct motors for the Magician have a much higher torque, and don't exhibit this problem. He sent me samples, and they indeed have a higher gearing of about 150:1. They don't veer as much. The ones I got with my Magicians from SparkFun were 1:50.
-- Gordon
Regarding that 1:50 gearmotor, I trust I have made my feelings known adequately in previous posts on undergeared plastic robots!
I think I can fit the MCP3202 (2-channel, 12-bit) ADC in it's place and use the same stencil.
Don't see an easy way to run it at 5V and talk the the Prop, so I'll probably do it at Vdd=3.3V.
Was worried about getting a signal from the sharp IR proximity sensors, but it looks like they output less than 3.3V, so it should be OK.
That might be better for BoeBot and ArdBot that don't need motor drivers...
BTW: We've put Merlin up for sale for $12.99.
So, you can make now a robot for $14.99 + $12.99 + $25 = $52.98