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erco
Registered Member

Date Joined Mar 2008
Total Posts : 664

Posted 11/1/2009 6:04 PM (GMT -8)

I'm starting a new diff-drive robot platform in the 15-pound category. This will be my biggest autonomous bot yet. I'm using two surplus gearmotors & wheels, and I've tracked extras down online for ~$10 each at http://www.mpja.com/prodinfo.asp?number=17971+MD and http://www.allelectronics.com/make-a-store/item/DCM-351/24-VDC-GEAR-MOTOR-W/-TURNTABLE/1.html . My wheel is slightly different, but the motor number & specs match, so I'm ordering more.

These are unusually nice 24V gearmotors in a sealed metal case with bushings and spur gears w/minimum backlash. Excellent efficiency, no worm drives here. Motor is a small China-made RS-380SH. Operates nicely at 12V, which is what I plan to use, a big cheap gel cell. Stall current is only half an amp at 12V! No-load speed on the wheel provided is a stately ~8 inches/second, ~ 22 RPM. A bargain at $10.

My long range goal is a large boe-bot/scribbler type BS-2 platform with collision avoidance using encoders and such from the Scribbler encoder project.

"If you build it, they will come."

Post Edited (erco) : 11/10/2009 5:24:19 PM GMT

Whit
Registered Member

Date Joined Mar 2007
Total Posts : 1137

Posted 11/3/2009 12:43 PM (GMT -8)

erco said...

My long range goal is a large boe-bot/scribbler type BS-2 platform with collision avoidance for transporting ba..., er, cargo from room to room, using encoders and such from the Scribbler encoder project to enable supervised navigation. It's very precious cargo I'm hauling. smile

I think sleep deprivation is beginning to set in. smilewinkgrin

I really like the motors. Great price!

Whit+

"We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney

SRLM
Registered Member

Date Joined Jul 2008
Total Posts : 2720

Posted 11/5/2009 4:00 PM (GMT -8)

I saw one of these in action today. The guy in the lab was running it at 40v, and it didn't even get hot...

erco
Registered Member

Date Joined Mar 2008
Total Posts : 664

Posted 11/6/2009 3:56 AM (GMT -8)

The only problem so far with these drive units are the tires. They are an O-ring in a shallow groove, and they are not a super tight fit. The product descriptions list this as a "friction drive" to move something else, as opposed to being a ground-based rolling tire. When I did a one-motor turn, the O-ring on the stationary tire came off, since it was rotating/scrubbing in place. It stayed on fine for a two-motor turn in place. I can live with that, but I suspect that the O-ring will slip on the wheel somewhat in normal use, which will kill odometry efforts. Can't really glue the thin O-ring to the nylon wheel, so I may have to come up with different tires.

Nov 13 edit: I did find a smaller OD O-ring that fits much tighter, it stays in place perfectly for one-motor turns.

"If you build it, they will come."

Post Edited (erco) : 11/14/2009 4:12:27 AM GMT

erco
Registered Member

Date Joined Mar 2008
Total Posts : 664

Posted 11/15/2009 3:05 PM (GMT -8)

My encoders aren't functional yet, but the motorized platform drives very nicely! BS2 controller board is driving programmed s-turns, squares and figure 8's at 2 speeds and looks quite promising. Next I'll finish the encoders and add IR control & proximity sensors for collision avoidance.

"If you build it, they will come."

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