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[DPRG] Big Robot Base Advice Please.

Subject: [DPRG] Big Robot Base Advice Please.
From: Glenn Pipe ggpipe at yahoo.com
Date: Mon May 22 22:43:04 CDT 2006

I have built a middleweight battlebot from scratch so I know the kind of bucks that can take. If all you care about is moving around at the speed of a person (walking?) then it sounds like the $200 option may do the trick as long as you don't try skid steering as that takes alot more power. Also as another person said it depends alot of the surface that you travel on and the kind of tires you use. You only have to accelerate up to speed and maintain that speed, overcoming the force of friction.

For my MW battlebot, I had 2 1 HP motors in a skid steer arrangement. When it was in a drivetrain only config (no weapons or armour, about 40 lbs) it drove around great and was really zippy, but when I added the extra weight of the armour and weapons it started to have problems turning on rough concrete because the wheels I had dug into the concrete so well. It ran straight great though. To fix that problem, I changed two of the wheels to a harder rubber compound which helped some. Also the competition was held on a slicker steel floor so that wasn't as bad. I used IFI 883s, with 1 HP motors in a chain, sprocket reduction. Sprocket and chain worked OK, but you have to make sure everything is lined up well, and have chain tensioners. Even then you can have the occasional chain break or slip off. If I did it again I would use gear boxes or timing belts.



----- Original Message ----
From: Jonathan <szarzynski at earthlink.net>
To: dprglist at dprg.org
Sent: Monday, May 22, 2006 5:45:01 PM
Subject: [DPRG] Big Robot Base Advice Please.

        Hello DPRG,
 Its time to start buying parts for my big robot and I would really  appreciate some advice.  The big  question I have is whether 2x a parallax HB 25 motor controller driving a  350W scooter motor will get the job done, or will I have to drop $700 building a  middleweight battlebot?  Or are there better options than these  two?
  The only requirement is that the robot must be able to move around ~100  lbs at ~the speed of a person.  I  dusted off some old textbooks and figured that two ¼ - ½ hp motors should do it.  
 I already own a bunch of sensors and a basic stamp set-up.  My next purchase is going to be motors,  motor controllers and batteries.   And here there is a big fork in the road.  One fork costs ~$700 and the other fork  is well under $200.
 I plan on using a tripod base with two independently-driven wheels and a  castor.
 Motor Controllers:   
 I want to use Parallaxs new HB-25(amp) motor controllers. (http://www.parallax.com/detail.asp?product_id=29144) It can control a motor up to ½ Hp.  They are relatively inexpensive and I  like parallaxs products, but I am having a hard time finding motor/gearbox  combos that are close to ½ Hp.  Any  suggestions here would be fantastic.
 If the 25s are too small, then I have to spend about $200 more to jump  up to two Victor 883s or something like the Vantec RDFR23 Dual Controller, or  two of the OSMCs.  Going down this  route is going to put me way over budget, and as a result, in the  doghouse.
 Motors and Gearboxes:
 I think I have two main options here.  Either wheelchair motors or electric  scooter motors.  Wheelchair motors  are a sure thing  they will work, but they are expensive and I cant use the  HB-25s, because the wheelchair motors pull too many amps. (the ones I have  found)  Ebay usually has 2 x 560W  motors for sale just under $200.   (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=9522159868&ssPageName=ADME:B:EF:US:1)
 Scootor motors are cheap and they come in the 350W size - so the HB 25s  should work.  Ebay usually has these  little motors for $15.  Apparently  they are reversible and they use a sprocket and chain type drive.  Has anyone used these for  robots?
 Frame Fabrication:
 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  shouldnt 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.
 I have money burning a hole in my pocket and lots of time on my  hands.
 Thanks for your time,

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