Has anyone modified a Minn Kota trolling motor?

I have inherited a pair of MK trolling motors that have been modified to the point that they doin't work any more. The pevious owner wanted to make them remote control, so he attached a receiver from an RC car and an electric gear motor was attached to the end of the throttle handle.  I think the soft rheostat has been damaged, so now it doesn't work anymore. In the attached picture we have a white soft rheostat with a cable to the controller. I believe the controller is okay. I think I want to attach a new potentiomoter to the cable to run the two motors. Has anyone worked on one before?

Please don't ask me to ask Minn Kota. They are less than helpful. The board containing teh ribbon cable is no longer made. And the newer versions have one ribbon cable rather than two.

Picture of Has anyone modified a Minn Kota trolling motor?
sort by: active | newest | oldest
rickharris5 years ago


Case II. Motor fails to operate.
Step 1. Check to ensure proper voltage and polarity at battery (red +, black -). Inspect all battery
connections, trolling motor plug (if installed), and any butt splice connections in battery leadwire for
corrosion and security.
Step 2. Check to see if all wires are securely attached to the proper control board terminals. Check for
corroded connections.
Step 3. Check to see if lower unit operates.
A. Connect battery lead wire to battery.
B. Disconnect the black battery lead from the control board and connect it directly to the black
brush lead.
C. Disconnect the red battery lead from the control board and touch it directly to the red brush
lead. The motor should run.
C-1. If motor does not run, a problem exists in the lower unit. Check the lower unit for
voltage at the brushes, water in the lower unit, worn brushes, or an open or shorted
C-2. If the motor does run, go to Step 4.
Step 4. Check control board.
A. Remove soft-pot from handle assembly and ensure actuator pin and actuator spring are
making proper contact on the silver conductor layer of the soft-pot. Visually inspect soft-pot
for collapsed dome switches and excess wear on silver conductive layer of soft-pot. If
Hand-Control w/Control Board Repair Manual 01/20/04
2- 2
necessary, solder on replace soft-pot (P/N 2364005) and test motor for proper operation (per
the procedure shown in Service Bulletin dated 1/12/99).
B. Operate control board manually (without handle assembly actuators). With battery and brush
leads attached to proper terminals of the control board, activate switch in upper right hand
corner and run fingertip around silver conductive layer. The motor should be varying in
speed as you apply pressure to the forward speed portion of the soft-pot. (As per Service
Bulletin dated 1/12/99)
B-1. If there is no control board output (motor not running), replace control board.
B-2. If there is control board output, but the soft-pot is worn or either of the dome
switches is bad, replace the soft-pot (solder on replacement soft-pot, P/N 2364005, per
the procedure shown in Service Bulletin dated 1/12/99). When reassembling the
handle pay close attention to ensure that the actuation spring and pin are correctly
installed and making contact with the soft-pot. With the new soft-pot and handle
reassembled, re-test motor for proper operation.
A. After rechecking that all wires are securely attached to the proper connections with proper
voltage, verify the control board is defective:
A-1. Check for control board output by hooking up a test light (or V.O.M. probes) to
board output terminals (consult appropriate wiring diagram). Remove handle
assembly (with handle pivot and magnet rod) off potentiometer. (The magnet rod
needs to be away from the on/off reed switch.) Connect battery leads to proper
voltage. Vary the potentiometer by turning potentiometer’s stem. The test light
should vary in intensity from off to bright. If there is no control board output, the
main control board is defective.
vectorges (author)  rickharris5 years ago
Wow. That is great. (Notice the phrase "soft pot) popping up in here.

The soft pot is at the end of teh throttle handle and (I assume) send a resistance to the main PCB which is translated to the outbound voltage or PWM signal. The original owner removed the controller from the top of the shaft and mounted it under a lazarette at the stern. The soft pot is still inline with the original controller housing. I want to replace it with a "normal" pot and move the pot away from the controller. to make navigation easier.

As a separate thought, have you ever used an electronic variable resistor? I assume you send some kind of signal to this component which varies hte resistance of it. Like a solid state rheostat?

Thanx for this excellent write up.
The electronic resistor is a digital device you send a "number" and it will act like an appropriate resistance. Personally I would go for a simple mechanical hookup with the speed pot wherever I needed it connected by wires to the motor controller - they don't need to be close and this avoids the complexity of getting some kind of remote working.

Old Post but i try it anyway, since it is very related to a project I am working on. I have 3 Monn Kota 36v / 112Lbs trolling motors that i want to control in parallel.

One of the motors is a bowmount RT112/ST and this will work as a "Master" to the other 2 motors which is RT112/SF. As far as I understand the control board on the "ST" motor generates a PWM Signal to the motor for speed control. The SF motor however is controlled by a pot meter through a grip handle assembly and then again converted to a PWM to the motor for speed control. To make a easy as possible hook up between the motors, my plan was to find a unit to "listen" to the PWM singal in the ST motor and then convert this PWM signal to a analog voltage to replace the Pot Meter installed on the SF motors..

Does any of you have any thoughts and comments on this solution ?

I have just received the motors so I have not had a chance to start measuring the Signal requirements yet.

magnetik4 years ago
Look for a true pwm motor controller (more efficient than standard pots) and throw all of the rest into the trash. You should have + and - coming straight out of the motor.. you can either build one yourself or just buy one at the usual spots. Make sure you get a slightly beefier version with higher amperage ratings than your trolling motor. Then you can move the controls wherever you want. I did this when ripping apart one for my kayak.

this is all assuming the lower unit is in working order.
vectorges (author)  magnetik4 years ago
The pot isn't the controller. The pot sends the signal to the rest of the electronics behind it, which is a true pwm controller. What I am trying to avoid is reinventing the pwm if I already have one.
vectorges (author) 5 years ago
Well Rick, apparently your 28 years in electronics didn't include any work with Minn Kota, which is what I was looking for. I used the term "soft rheostat "because that is what Minn Kota calls it. It is a variable resistance device (or possibly two) that has a soft, circular section upon which pressure is applied to set the resistance. The ribbon cable has three contacts, just like a rheostat. I assume the three would attach just like a normal theostat, but I was hoping someone knew that for sure.\

The throttle handle was attached to a plunger that applied pressure around soft arc of the rheostat. I think this change in resistance is what

The brown PCB on top is a RC receiver and has nothing to do with the analysis.

I should have been clearer on the pic. The white cylinder attached to the aluminum cylinder has been detached and turned over. It is the original throttle handle.
Nope I was right the device is a 3 terminal potentiometer a rheostat is a different 2 terminal beast - and Rheostat is a very old fashioned name!

No idea what the "soft gel" part is - All Pots I see are hard and anything.

It is possible they use the pot as a center off device so the controller can go forward or reverse.

You should check the output of the control on the PCB to see if the resistance changes - and check with power on to see if the voltage on the center pin changes.

Beyond that fault finding depends a lot on having a really good look and investigating the circuit board to try to divine what the parts do and then try to find some part that works and go back from there towards the control handle.

Looking at the various diagrams in the manuals I am guessing the controller board looks something like this
rickharris5 years ago
After over 28 years in electronics I have no idea what a soft rheostat is!

Technically a Rheostat is a variable resistor and will have 2 leads so the resistance can be varied between 0 and full resistance.

A Potentiometer - also a variable resistor has 3 connections - to make it the same as the Rheostat you need to connect one end to the middle of the 3 pins.

You need to know the value of the existing resistor and find a similar potentiometer.

Looking at the picture it is hard to see what is connected where and you can do this much better than me - BUT it looks like what is labeled "soft rheostat" is in fact simply a flexible connector to the PCB the ribbon wire is connected to.

The PCB looks like it may be a switch rather than a variable resistance - perhaps switching it various fixed resistors on the main PBC.

I Don't know from what I see.

Does the throttle turn the internal mechanism at all now?

vectorges (author)  rickharris5 years ago
I misspoke. It is a pot, not a rheostat. So the three wire ribbon cable makes sense. The "soft-pot" has three parts in the picture. At the top the ribbon cable attaches to a board. The back side of the board has the pot, which has a soft, squishy arc that feels like a Dr Scholl's gel pad. (Except at this point I am definitely not gelling). The white plate at an angle is just a guide that forms the arc for a little plastic pin to follow.The white cylinder is holds the pin and turns around its center shaft. This section originally was flipped over and attached (badly) to that motor on the right side of the picture. The motor replaced the original manual throttle handle.

I think the tow ribbon cables are coming from two parts of the soft-pot arc, and one is for forward and one for reverse. My end goal is to use a small stepper motor instead of the big gear otor and provide a manual backup in teh event that anything weird happens with the RC part.
rickharris5 years ago
Several manuals here http://www.fish307.com


what model is it?
vectorges (author)  rickharris5 years ago
It is a Minn Kota Riptide 101. 36 volts, 47 (??) amps
rickharris5 years ago

Sell spares and legacy replacement PCB for $75 ish
vectorges (author)  rickharris5 years ago
Except this is a 101 pound thrust at 36 volts, and none of these parts comply.