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I am currently working on an exoskeleton. The exoskeleton is going to help kids with cerebral palsy learn to walk 4 years sooner than traditional therapy. Currently we are using 2 Ame 226-3003 with the roboclaw 2x60A motor controller controlled by an Arduino mega. The Ame 226-3003 motors are not powerful enough. In addition the Ame 226-3003 has a worm gear thus the motor cannot be moved when the motor is turned off. Our position feedback system is a gear attached to the shaft of the motor which spins a gear on a potentiometer. The two gears have a 1:1 ratio.

In order to better understand the project, please see the video: https://www.youtube.com/watch?v=NL_aCwJSRiE&feature=youtu.be

The Ame 226-3003 catalog page: http://www.amequipment.com/wp-content/uploads/2013/02/801-1071-web.pdf

We need a new drive system:

  • more powerful than the Ame 226-3003 motor. We do not have an exact torque spec but we believe any drive system that is 70-100% more powerful than the Ame 226 - 3003.
  • We like the rpm range of the Ame 226-3003.
  • The drive system must be able to spin freely when the motor is not in use.
  • We need a way to get position feedback, the potentiometer system we are using seems to work, however it adds to much extra hardware(more stuff to break), (ie) the gear on the potentiometer and the gear on the shaft have to mesh constantly and we have to zero the potentiometer every time we put the leg together so the potentiometer doesn't over spin. * We would prefer to have an optical encoder inside the motor.
  • We need to have the drive system be at a right angle.

I need help designing a drive system that will meet the requirements.

I think I might have found a motor that will work:

The amp flow G43-500

http://www.ampflow.com/standard_motors.htm

I like the G43-500 because it can run at 24 v, thus it will take less amps than 12v. Will that motor get the job done?

I need to gear this down to around 80rpm. What type of gear box would work best?

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closed as too broad by Ian, Andrew Aug 6 '14 at 17:51

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For your question on position feedback, this brand, among others, are used in actual commercial/industrial systems.

Has small and big size.

Absolute gives actual angle, says 256 steps per 360 degrees. This may best suits you.

Incremental is to give, says, 500 pulses per revolution. However, you need other sensor to sensor the 'starting angle'. May not suits you, in this case.

http://www.ia.omron.com/products/category/sensors/rotary-encoders/incremental/index.html

http://www.ia.omron.com/products/category/sensors/rotary-encoders/absolute/index.html

For man-rated system, safety is very important, especially when powerful motor is used. You may want to use some sort of force sensor to ensure motor auto stop in case of hardware/software error/ equipment failure, etc. so as to protect the human. Case noise etc. cause errors. Optical isolation may be more safe.

Hope it helps.

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  • $\begingroup$ Safety is our number one concern. We have a plethora of shut off switches and we are adding a mechanical stop as well $\endgroup$ – Joel Jul 28 '14 at 18:08
  • $\begingroup$ Have you ever tried to interface those encoders with an Arduino? If not, do you know of a forum post or a place I can go to figure out how to interface them? $\endgroup$ – Joel Jul 28 '14 at 18:09
  • $\begingroup$ For example, choose a rugged unit (better for man-rated system, for safe with solid construction IP65 and EMC spec.) ia.omron.com/product/item/e6c31034m/index.html. Best to choose 5V, as same as Ardu. with2 meters cable. See 'output circuit diagram tab' on the web page. Has 2.4k ohms pull up resistor inside. Hence, good resistance to noise. Connect Shield pin to system ground for EMC protection (reduce error due to noise). Program ardu as 8 DIGITAL INPUT pin as 'connected spec chart tab'. Read data as binary number for 256 steps. see 'timing chart tab". $\endgroup$ – EEd Jul 28 '14 at 19:32
  • $\begingroup$ To test, rotate slowly. See 'timing chart tab". The output will change as binary number from 0 to 255 when rotate a full 360 degrees. Interfacing is typical and straight forward for someone with suitable hardware education/experience/background. Check voltage output from the encoder with multitester, oscilloscope or simple LED, as needed. best to test the encoder, with just 5 voltage power and not yet connect to Ardu to ensure correct understanding of the spec. Take time to do it slowly. No big difficulty. $\endgroup$ – EEd Jul 28 '14 at 19:39
  • $\begingroup$ Education material in ia.omron.com/support/faq/5/34.html ia.omron.com/support/guide/34/overview.html $\endgroup$ – EEd Jul 28 '14 at 19:42

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