Subject:
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Re: Robot base
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 12 Feb 1999 21:49:51 GMT
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Original-From:
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Chuck McManis <cmcmanis@mcmanis+ihatespam+.com>
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Viewed:
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986 times
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Don't do it.
Unfortunately the volumes of robot building do not support building and
selling robot bases, the base price for a "good" robot base ends up being
about $500 list. The reasons are manyfold, but I'll enumerate some of them
here so that you can perhaps avoid mistakes of the past:
Good DC gear motors are $150 EACH. That is if
you have to buy them new. They are $30 each if you buy them
surplus however if you make a "product" counting on surplus
parts you will run into a situation where you cannot meet
demand and then you will get sued and/or go bankrupt.
Fabricating parts is quite expensive in small quanties. Sticking
with straight cut pieces like Lynxmotion does helps as you can
crank these things out on a CNC type device.
Defining what a "base" is can be problematic. In the "deluxe"
category it includes motors, wheels and motor drivers and motion
feedback (either optical encoders or tachometers), in the "economy"
category it might be just a couple of motors mounted to plastic.
Some specific feedback:
> base geometry: circular or rectangular/ single or double decker.
Circular. It is harder to get stuck in corners with a round
robot. It is easier to build a bumper system for it.
> base dimensions: 9", 10" or 12" or larger
10", that leaves you a circumscribed square that is the size
of a PC-104 type computer.
> drive train configuration:
> differential steering or combined drive and
> steering or front wheel drive rear wheel steering.
Differential drive is the easiest to solve the inverse kinematics
for.
One steered wheel and two driven wheels is the easiest one to
get to go straight.
One combined drive and steering wheel is the cheapest to build.
(see the Hero-1, Hero-Jr)
Three steered and driven wheels gives you the most flexibility
and benefit (see the CMU rover papers)
> drive wheel diameter: 2.75", 3" or 3.25" or larger
3.82" wheels for the following reasons:
- Larger diameter gives better results over uneven
terrain.
- 3.82*pi = 12" circumference. 1 rotation == 1 foot
of travel.
Optionally 7.64" wheels
> base material: plastic, aluminum or fiberglass (PCB material)
Plastic (Polycarbonate aka Lexan) and aluminum. Alum for
toughness and plastic that is easily worked, structurally
sound and reasonably light.
> accessories: turret, extra deck
Extra deck that is a turret, slip coupler between the top deck
and the mid-deck for signals.
Anyway, it will cost about $300 to produce, it won't go up stairs and it
won't include batteries and no one will buy it because it can't compete
with a R/C on closeout from Radio Shack. :-(
--Chuck
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Message is in Reply To:
 | | Robot base
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| Hi I have been following this mailing list and the comp.robotics.misc news group for quite a while now and I did notice that there seems to be a lack of good quality and reasonably priced robot bases. All the ones I saw where way overpriced or way (...) (26 years ago, 11-Feb-99, to lugnet.robotics.handyboard)
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