Monday, May 10, 2010

Wheels and Motor Controller Attached

Once the motor controllers were given one last test, I screwed on the protective black covers and mounted the motors. I ran the new encoder signal cables through rubber grommets and holes through the side of the main bucket. The signal cables were left coiled up for hookup to a microcontroller later.

I had to shim one motor a bit to get the wheel in vertical alignment -- it was leaning in a bit while the other is straight. A few washers on the inboard bolts helped make it match the left side. Hopefully this will help it track straighter.

I cut some sheet aluminum to fit over the battery charger area and bolted it down using an existing hole in the bracket.

The motor controller is a Sabertooth 2x25 that's mounted on top of this plate with a few small bolts. I think it has enough contact with metal to keep it cool.

I want to protect this area more as additional parts are built on top, but for now this should be good to test the motors.

The front terminal strip on the motor controller has six connections. The middle two are for the battery power, which comes via a cable scavenged from the wheelchair base.

This previously plugged into the wheelchair motor controller, which I couldn't easily interface to and found a new home on eBay. I don't have the matching connector, but I think I can make something that will work. I could just cut the cable, but like the idea of having something easier to disconnect.

Two spade connectors from the hardware store fit in the connector snugly, so I built a short pigtail set of wires that are secured to the controllers terminal screws on one end and plug into the batter cable on the other.


This is now hanging out in the open, so I'll have to figure out a way to mount the connection solidly and make certain it can't be pulled out by all the vibration when this thing is bouncing around.

I grafted a similar pair of connectors onto the wire coming from the battery charger.

The charger has a 3rd wire (in addition to the +27v power and ground) that I'm not sure of what it does. Originally this plugged into the wheelchair motor controller, not directly to the batteries.

It passed the basic smoke test when I plugged it in, then the current soon dropped to a trickle, which seems good since the batteries are fully charged.

I'll wire the charger directly to the batteries, before the kill switch. That way I can cut the power feed to the motor controller, then plug in the charger and feed the batteries while the rest of the circuit is isolated.

I measured the current feed from the batteries back into the charger and it was less than one milliamp, so it should be OK to leave it in the circuit during normal usage.

The next step will be wiring the motors to the controller.

2 comments:

  1. I'm doing something similar here with the same motors, for a R/C lawnmower. Also chose the Sabertooth 2x25 - what a sweet unit.

    I also bought the 24 V charger from the same wheelchair, but have no clue as to what the polarity of the 3 wires on the 24 Volt side are. Could you tell me which of the three ( brown / yellow-green / blue ) are positive and negative? thanks

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  2. Hi, are you still working on this ?

    matt

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