Speedometer

[Jpwcamel]

Hey,

Been running into an issue with my ebike where the speedometer takes a while to work, from what I can tell it takes like 15-20 rotations with the pedals before my display will show the speed I’m driving, the speed will never show up if I’m just using my throttle, I need to use PAS for it to work.

The speedometor will also drop to 0 almost instanty if I stop pedalling, but if I use my throttle and stop pedalling the speed will decrease gradually until I hit 6kmph (my throttle can only make my bike go 6kmph)

The bike uses a bafang hub motor (RM G060) combined with a KT controller, I’ve tried changing the display with no success.

Anyone have any idea what the issue might be?

 

[amberwolf]

Did it ever work differently?

If so, what happened between the time it worked that way, and the time it changed to what it does now?


(fwiw, it sounds like you have the PAS connected to the speedo input instead of the speedo sensor, or it's now using a motor hall sensor instead of the speedo sensor).

 

[Jpwcamel]

Did it ever work differently?

If so, what happened between the time it worked that way, and the time it changed to what it does now?


(fwiw, it sounds like you have the PAS connected to the speedo input instead of the speedo sensor or a motor hall sensor).

Yeah it worked differently a couple weeks ago, the speedometer would react instantly.

My bike fell over due to wind, and my throttle broke, so I sent it to a bike mechanic and had the throttle replaced.

It’s basically been having this issue since it fell over.

 

[amberwolf]

Since it fell over, or since the bike mechanic fixed it?

If the former, then something else is still wrong, probably something disconnected or wire broken inside it's insulation somewhere, probably near where any parts impacted the ground/etc. It's pretty common for the axle wiring to get damaged.

if the latter, then it could be anything the BM did during the repair, and you should try to find out what *exactly* they did (since it wouldn't *just* be a throttle replacement in that event).


For geared hubmotros, many of them have a separate speed sensor wire, if that's damaged perhaps the system was "fixed" by the BM to instead use a motor hall. if so, it won't read any speed unless the motor is running.

Some systems have an option in the display settings for which sensor is used for speed, if both are present.

 

[docw009]

What model display are you using? If you don't know, post a picture of it. If it is a KT display. maybe the shop changed some of its settings,

 

[Jpwcamel]

What model display are you using? If you don't know, post a picture of it. If it is a KT display. maybe the shop changed some of its settings,

It’s a kt-lcd8 display, I’ve tried changing the display with no luck. Yesterday I looked into the motor to see if a magnet had gone lose or fallen off, and thats not the case either.

 

[Jpwcamel]

Since it fell over, or since the bike mechanic fixed it?

If the former, then something else is still wrong, probably something disconnected or wire broken inside it's insulation somewhere, probably near where any parts impacted the ground/etc. It's pretty common for the axle wiring to get damaged.

if the latter, then it could be anything the BM did during the repair, and you should try to find out what *exactly* they did (since it wouldn't *just* be a throttle replacement in that event).


For geared hubmotros, many of them have a separate speed sensor wire, if that's damaged perhaps the system was "fixed" by the BM to instead use a motor hall. if so, it won't read any speed unless the motor is running.

Some systems have an option in the display settings for which sensor is used for speed, if both are present.

A little while after it fell over but before I sent it to the mechanic. I’ve looked at motor cable and from what I can tell there’s no damage to the wire, I had a look inside the motor yesterday and it looked fine, no apparant damage / loose wires.

 

[amberwolf]

You may not see any damage, but there can still be wire damage inside the cable.

If this motor has an 8-pin connector to the controller, then it only has 3 thick phase wires and 5 thin hall wires for motor operation and speed/position sensing. If it has a 9-pin connector, it may have (probably does) have a separate speedo sensor on the 9th pin. This sensor is usually mounted on the hall sensor board insde the motor as a small black device facing the side of the motor casing somewhere near the axle area. Then there will be usually six little buttonsized magnets embedded into the side of the motor casing itself to line up with it. Sometimes there are six holes for them but only one installed.

If it has this separate speed sensor, that's what needs to be used for the system to read a geared hubmotor's speed.

There is a tiny possiblity that the system has a separate external wheelspeed sensor, with a magnet on the wheel and a little "bar": or other device attached to the frame where the magnet passes, and a wire from it to the controller.

If it doesn't have one of these separate sensors, or it isn't used but instead a motor hall is used, then it will have the problem you describe.

So, either there is a setting in the display that has been changed for which speed sensor is used, or the sensor has failed or magnet came off, or the wire from it to the controller is damaged or broken somewhere, or disconnected (possibly even within the controller casing itself).

Perhaps some other thing is wrong, but those are the only ones I can think of that would cause the problem you see, and *only* that problem.

 

[docw009]

Put a meter on the speed sensor wire, it's the white one in the motor cable. Power up the controller and see if it toggles between 5V and ground when you rotate the wheel. You can pick it at the connector, if it;s the 2x3 white connector. If it's the molded nine pin, you have to pick it up inside the controller.

KT controllers often have a separate speed sensor input. That would be red/white/black. The white is in parallel with the same white in the motor connector, so you may not have to go inside the controller if the motor cable uses the molded connector,.