Need Some Help With Dc Motors And This Motor Controller For The Bb-8 Build

 
#1

Hello all, hope your all are having a great holiday season. I need to reach out to you guys for some help with my BB-8 1:1 scale build. Im at the stage of purchasing the dc motors and controllers to work with the v4. I have had bad luck in the past with dc motors stripping on me when I was building LeXI and I need to avoid that this time around. So what im asking is for a good recommendation for hi torque dc motors ( I need 2, working opposite each other moving a weight of say 100 lbs) to move the BB-8 droid. Being a ball which will roll very easily, i still want the added torque strength for reverse ramping for stopping and ramping for start up. I also need the motors to have the shaft dead center not off to the side for the way in mounting them in the ball. Im using a 12v 9 amp power source just to run the 2 motors. Now as for the controller I saw the following on Ebay and would like to know if 1) If its a good choice and 2) if it will work with the V4. My budget for the motors is not to go over $30 each if possible. Below I have posted the Controller link and have added pics of the frame that the motors will be used in. That you all in advance for your help.
Motor Controller



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#2

That controller is for stepper motors. You are unlikely to find steppers for $30, and probably don't want them for this kind of project anyway.

Best thing for picking an H-bridge is to pick the motors first, then match the amperage requirements (max draw at stall plus some overhead).

Alan

#3

@thetechguru Ok when picking out the dc motors what to look for when i need high torque 12v motor. I see some with 8rpm and others 330rpm. High or low?

#4

Usually you get hi torq slow rpm, you lose torq when you add rpm. Try and find a split in the middle. Robot shop has some good ones. Because of limited space look for 90 degree gear motors. And use h bridge to control.

#5

@fxrtst 90 wont work since the motor in the axel. What about these specs on a dc motor i am looking at.

Specifications:

Product Name Gear Motor
Rated Voltage DC 12V
Rated Current 150mA
Rated Torque 20.9Kg.cm
Rated Speed 10 RPM
Shaft Size 15 x 6mm/0.6" x 0.2" (L*D)
Motor Body Length 87mm/3.4"
Motor Body Diameter 37mm/1.5"
Thread Diameter 3.4mm/0.13''
Mounting Size 33 x 33mm/1.3" x 1.3" (L*W)
Total Length 117mm/4.6"
Material Metal, Electronic Parts
Color Silver Tone
Weight 352g
Package Content 1 x Gear Motor

#6

It has the torq but that's a slow and tired BB-8. What's the circumference of the wheels?

#7

Take either the circumference of the wheel or figure circumference by taking the diameter of wheel and x 3.14. Then take that and multiply the rpm to tell you how far it will go in a minute.
As example: a wheel is 3 inches in diameter so, 3 x 3.14=9.42 inches in circumference. Now multiply that times rpm of motor (10) in this case. Or 94.2 inches a minute. So bb8 will only move about 8 feet a minute or 1.5 inches a second.. At full speed.

#8

Anthony,

Regarding the motor controller, consider the reverse current developed when you are "braking" the speed of the ball. You will develop a regenerative current which will pump back into the motor controller. This current could exceed the locked rotor current of the motor. Someone else verify this as my brain gets numb.

By the way Best wishes to you and all the members, for a Happy New Year !

Ron R

#9

@Ron, good point. Despite the cost, a Sabertooth or Roboclaw may be the best option since it can dump that excess enrgy back into the battery safely.

Alan

#10

So if the diameter of the ball (wheel ref) is 20" x 3.14 = 62.8" in circumference. Now my second choice was:

• Powerful 12V motor with a 43.7:1metal gearbox
• Gear motor with integrated quadrature encoder
•Rated torque @ 12V: 1.5 kg*cm
• Encoder resolution: 64CPR(motorshaft)/2797CPR(gearbox shaft)

The 12V DC Motor 251RPMw/Encoder is a Gear Motor w/Encoder. It is a powerful 12V motor with a 43.7:1 metal gearbox and an integrated quadrature encoder that provides a resolution of 64 counts per Revolution of the motor shaft, which corresponds to 2797 counts per Revolution of the gearbox's output shaft. These units have a 0.61'' long, 6 mm-diameter D-shaped output shaft. This motor is intended for use at 12V, though the motor can begin rotating at voltages as low as 1V. This motor is an ideal option for mobile robot projects.


so that makes 1576 or 1313 ft per min?