Let's Make Robots!

Building the perfect Beast (robot chassis)

2012 may be the year of the Dragon for China but it is the year of the robot chassis for me. I am trying to create a new range of robot chassis's and I'd like to know what features my robot building friends would like to see in a chassis. Obviously low cost and high quality are preferable but what else?

For example size? As far as I can see there is already a range of sizes on the market. Is there a size that's missing? I was looking at some cool wheels that were about 250mm (10 inch). Would you want a huge chassis and for what purpose?

Features? Is there a feature that you want but can never find on a chassis? More mounting holes, built in battery charger or motor driver?

Clutches? many gearboxes, even with metal gears can be damaged through accidental collisions or child abuse (the child abuses the robot).

Encoders? single pulse, quadrature, what is the minimum resolution?

Wheels? big, small, thick thin, mecanum, omni, wheels with retractable claws, what is missing from the online range?

 

To give you some idea of projects I am working on so far:

  • Low cost, miniature 6WD Wild Thumper.
  • New improved QuadBot chassis with clutches on all servos to protect the gear trains.
  • Robot hand/wrist with full range of movement (13 DOF).
  • An advanced balancing chassis with sensors.

Tell me what you want in a robot chassis.

 

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I have seen a similar chassis sold by arexx. it looks like the base for the asuro robot bot has no electronics.
I would certainly buy atleast one of the Propaxxo style robots if they where made.
Tom J 

Yese DAGU /Arexx produce a few similar chassis's. The base for the Picaxxo robot was designed specifically for picaxe chips but now I think perhaps we need a propeller version.

My one bugbear with the Prop is th lack of an analog to digital converter. if you redesign the chassis would there be a built in ADC?
Tom J 

I have got over this lack now........

1 or 2 or 4 or 8 x12 bit adcs chips are easy to add and are veryvery fast, and more reliable than Arduinos attempt at ad-hock adc (i cringe each time i see the arduino adc failing "big time" when the speed is wound up....... having adcs integrated into a single atmel chip is asking for trouble - these are my findings)

So separate ADC chips rock......

 

According to the datasheet the Arduino ADC should be able to opperate much faster so I suspect the problem is due to how the Arduino software configures it.

As for the propeller, what is your recomendation for a good ADC chip. I want to include at least 1 on the PCB.

Dropout :- how to explain ......

Well i get this feeling that analogs are only calculated when you send an analog read command (ie the chip seams not to store values in the background in round robin fashion and store them to buffers) all is fine and stable until you start winding the speed up and then the values either drop out or slip into randomness.

My guess is its all down to time_ing.

At least using a dedicated adc chip - the values are categorically stored ..... so wysiwyg.

This is the family i use :-

The MCP3202,3204,and 3208 will work in the range from 2.7V to 5V. This ADC’s serial interface allows you to minimize microcontroller I/O pin usage while still delivering sampling rates of up to 100 ksps. The MCP A to D chips are economically priced compared to the other A to D chips. 

The Microchip Technology Inc. MCP3204/3208 devices are successive approximation 12-bit Analog-to-Digital (A/D) Converters with on-board sample and hold circuitry. The MCP3204 is programmable to provide two pseudo-differential input pairs or four single-ended inputs. The MCP3208 is programmable to provide four pseudo-differential input pairs or eight single-ended inputs.

 Features:

  • 12-Bit Resolution
  • SPI serial interface (modes 0,0 and 1,1)
  • Analog inputs programmable as single-ended or pseudo-differential pairs
  • Up to 100ksps sampling rate (50ksps for 2.7v, 100ksps for 5v)
  • 16-Pin Narrow DIP

Key Specifications:

  • Power requirements:  2.7V to +5.5 VDC
  • Communication:  SPI serial interface (modes 0,0 and 1,1)
  • Dimensions: .750 X 0.310 X .130 in  (8.65 X 6.00 X 1.25 mm)
  • Operating temp range: -40 to +185 °F (-40°C to +85 °C)
I have not used a propeller yet but I am aware it lacks certain features such as ADC. If I develop a PCB based propeller chassis then ADC would be mandatory.

I finish my degree in a couple of months so i would be more than willing to draw up some schematics for the propeller with an ADC chip for you.

Tom

I appreciate the offer but it will depend on what ADC chip is cheapest. I cannot tell you which one. Speed and resolution are also important factors. Schematic diagrams are not a big issue. I've drawn them since I was 12, and our PCB engineer is also fairly good.