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[DPRG] Big Robot Base Advice Please.

Subject: [DPRG] Big Robot Base Advice Please.
From: Jonathan szarzynski at earthlink.net
Date: Mon May 22 17:45:01 CDT 2006

Hello DPRG,

It's 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 Parallax's 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 parallax's 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 25's are too small, then I have to spend about $200 more to jump up to two Victor 883's or something like the Vantec RDFR23 Dual Controller, or two of the OSMC's.  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-25's, 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 25's 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 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.

I have money burning a hole in my pocket and lots of time on my hands.

Thanks for your time,




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