darknrgy's blog

6WD Robot - test build of drive train

 

6WD Robust Robot Platform - Design Phase

I've been planning a 6WD robot. Two cordless drill motors transmit power through #25 pitch chain to each side individually, giving it a tank track drive system. The base material is acrylic with various parts coming from mcmaster carr and other online stores.

 

This is an older version I built as proof of concept to get the microcontroller, pwm motor controls, etc all to work. I had a friend control this robot from a different state as a final test and it worked great. 

Here is some of the parts list for the new bot. 

roller chain ansi #25, 6 feet

http://www.mcmaster.com/#6261k286/=7rla4d

18+ bearings

http://www.vxb.com/page/bearings/PROD/Kit223

3' steel shafting 1/4" 

http://www.mcmaster.com/#1327k66/=7rln9e

8 1/4" smallest drive sprockets (9)

http://www.mcmaster.com/#2737t1/=7rlrhm

2 drive sprocket 3/8" 12 tooth

http://www.mcmaster.com/#2737t102/=7rlstj

2 large sprocket

http://www.mcmaster.com/#2737t151/=7rlzcv

16 1/4" shaft collars

http://www.mcmaster.com/#9414t6/=7rm193

2 wheels (test idea first)

http://www.robotmarketplace.com/products/0-HPI4456.html

http://www.robotmarketplace.com/products/0-HPI3048.html

http://www.robotmarketplace.com/products/0-HUB12.html

 

EDIT: A few more parts I've ordered:

12V 5A 200 oz-in 150 RPM 67:1 Gear Motors X2

http://www.pololu.com/catalog/product/1445

Brackets for mounting these motors:

http://www.pololu.com/catalog/product/1084

Dual 5A H-Bridge motor controller, PWM; very simple, not current limited, needs heat sinks

http://robokits.co.in/shop/index.php?main_page=product_info&products_id=15

More info on this kind of circuit:

http://www.bobblick.com/techref/projects/hbridge/hbridge.html

http://www.ikalogic.com/H_bridge_old.php

 

 

Here are some of my notes on assembly. I have a lot of work to do: 

- assemble frame rail test platform

    - come up with distance between wheels

    - measure out and build chain for this distance

    - determine hole position using chain with sprockets

    - assemble two wheels, 2 sprockets, chain, shafts

    - come up with minimum height of assembly based on sprocket + chain 

- design final drive assembly based on wheel separation, height

- test 5/8" bearing hole

- cut shafts

- build chains (4X)

- cut all pieces

    -4 frame rails 

- height determined by previous step

- length determined by wheel separation, leave room for end pieces (1/2")

    -4 end stops

- height same as rails

- length TBD by guesstimate on strength needs

    -1 main platform

- length is exact same as frame rail

    - sawing order

- set saw for frame rail and main platform length

- cut big enough piece to get all frame rails - should be at least (frame rail height) X 4

- cut one additional rail to be cut up into end pieces

- cut big enough piece to become main platform

- set saw for frame rail and end piece height

- cut 4 frame rails from previous set

- cut out bottom shield pieces

 

- stack all frame rails and adhere with something temporary

- drill bearing holes 5/8" X 3

- glue frame rails to end pieces, take extreme care to line up properly

- lightly glue bottom shield

- drill the holes for the main bolts, count TBD, size TBD

- attach bottom shield

- assemble drive train

    - possible order:

- wheel -> shaft collar  -> washer -> bearing -> washer -> shaft collar -> (sprocket or shaft collar) -> bearing

- wheel -> drive sprocket -> shaft collar -> etc

    - attach wheel to one end of bearing

    - slide shaft through shaft collar, washer, outter frame bearing, etc

    - wrap chain around sprocket(s) before inner frame bearing

    - tighten all collars and sprockets