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[DPRG] Big Robot Base Advice Please.

Subject: [DPRG] Big Robot Base Advice Please.
From: Chris Jang cjang at ix.netcom.com
Date: Mon May 22 20:19:39 CDT 2006

> My plan is to purchase all my parts and then use CAD to design a frame, 
> take the frame drawings somewhere and have them charge me a ridiculous 
> amount of money to build it.  I did this type of work for a couple of 
> years, (as a mechanical design engineer) so this shouldn't be a problem 
> (except for the money part.)  I plan on the design being very 
> simple/cheap.  I live in the DFW area, so some of you might have a 
> specific recommendation.

This is only my advice. I've never built anything that large. And I'm not 
a mechanical engineer.

Watch out for ground pressure. The torque required to roll on a prepared 
surface is much lower than on grass or dirt. Also, a steel frame can 
easily become heavy unless it is built like a decent mountain bicycle with 
cro-moly tubing. Consider aluminum tubes as you start out with a big 
weight advantage. If you don't know what battery configuration will be on 
the robot, then that is a big unknown that could put the robot overweight. 
Expect it to come out heavier than expected. Weight makes everything more 
difficult.

Here's a datapoint. My robot weighs 40 pounds and uses two 18 V Panasonic 
drill motors. In low gear, it accelerates up to 6 mph or so on level 
pavement. I don't know the power rating of the motors. But the NiMH 
battery packs are 3.5 Ah each. However, the weak part is the clutch and 
drivetrain more than the motors. For your robot, make sure the drivetrain 
is strong.

Also, I have an old issue of RC Driver (September 2004) that has an 
article about the piezo gyro used to stabilize Shredhead (spinner combat 
robot). It uses an elevon mixer to two ESCs with a Futaba GY240 to offer 
negative feedback. For your large differentially steered robot, this is 
probably the simplest way to get stable driving. You can use COTS RC radio 
gear and then hook in a microcontroller/SBC later.

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