Direct Drive vs Geared Hub

[Blunderbuss]

I have just changed my 1000w DD for a 500w GH (thanks to anotherkiwi, Nealh and d8veh for educating me on the “way of the watt”)

Because of the rubbish weather over the weekend I only got to do a couple of miles.

The first thing of note is the weight difference is massive – the GH is nearly half of the DD, and that notices on handling.

There is a tiny bit of gear noise, but hardly noticeable and it is much smoother when pulling away (my controller is square wave) compared to the DD.

The display was showing the same watts in each of the assist levels, and it is difficult to be accurate on such as short test, but there is certainly more “pulling power” from standstill.

You can also feel less drag when pedalling without using the motor.

I will hopefully be able to do a longer run soon to get a better feel for the difference and to try and make a direct comparison as I have kept the controller settings the same.

But I think I will need to change one of the settings on the KT-LCD3 as the MPH is reading over double and goes to zero when I stop pedalling – or I have got one of the signal wires connected wrongly – any thoughts welcome.

 

[Deleted member 4366]

The controller is getting its speed signal from the motor halls. Does your motor have a separate speed sensor in it? If not, you need an external one.

The noise that most people think is gear noise is in fact commutation noise. If you use a sine wave controller, it'll go away.

If you see the same watts in each PAS level, your controller is set to speed control rather than current control.

 

[Nealh]

Let us know the GH hub used.
For correct odo reading you may have to adjust P1 to suit the motor characteristics and P2 will probably need to set to 1.

 

[Blunderbuss]

The controller is getting its speed signal from the motor halls. Does your motor have a separate speed sensor in it? If not, you need an external one.

The noise that most people think is gear noise is in fact commutation noise. If you use a sine wave controller, it'll go away.

If you see the same watts in each PAS level, your controller is set to speed control rather than current control.

I have connected all the signal wires so presume the motor does not have the speed sensor (pic below), are there any which you can recommend?

http://dillengerelectricbikes.co.uk/spares/bafang-8fun/bbs-speed-sensor-by-bafang.html

 

[Nealh]

P1 set to 87 for near correct mph read out for most Bafang's.
IIRC D/D hubs are set for P1 46 which will see over speed with a GH.
For odo reading try P2 + 6 to read correct when freewheeling.

For my sensored Bafang CST I used P2 + 6 for odo reading when free wheeling.
For my other hubs it is P1 + 1.

 

[Blunderbuss]

P1 set to 87 for near correct mph read out.
For odo reading try P2 + 6 to read correct when freewheeling.

For my sensored Bafang CST I used P2 + 6 for odo reading when free wheeling.
For my other hubs it is P1 + 1.

Thank you - i will pop those in when i get home from work (still raining of cousre!).

Looking at the noise (which is so slight it does not bother me) are there any other advantages of the sine wave controllers.

 

[Deleted member 4366]

Do the settings first. Unfortunately, there's no way to check whether the motor has the speed sensor or not unless you make a special test lead, like I did today, for which you need the female motor connector and a 3 x AA battery pack.

You can use any speed sensor off an old cycle computer or buy one of these cheapo ones:

https://www.ebay.co.uk/itm/KEUK-Cycling-Bike-Bicycle-Cycle-Computer-Odometer-Speedometer-Waterproof/253522313252?epid=1988634049&hash=item3b071b8024:g:44kAAOSw~P9auduQ

Cut the sensor wire (2 core) at the head unit, mount the sensor on the frame/fork, the magnet on the spoke and join one core to the white wire on the motor hall connector at the controller and the other core to ground. Sometimes, you have to connect the second core to any 5v instead of ground. It depends which way round the controller works. No damage will occur if you get it wrong, so try each way until it works.

 

[Blunderbuss]

Just tried the P settings and P1 at 87 feels spot on , but I only get a reading when P2 is at zero (I tried all the P2 settings) and I still get nothing when freewheeling.

 

[Blunderbuss]

I have done a decent ride (30 miles) with the new GH on exactly the same route i have used the DD a number of times, so i can make some meaningful comparisons.

I really noticed the torque, up the hills i was using one setting lower on the pedal assist. On one particular very steep bit i had the DD on 5 and with my pedaling it would hold speed, but with the GH on level 4 i was picking up speed.

Through a couple of short stretches where the mud was deep i use the throttle to keep me going, with my feet off the pedals ready to stop me falling, and i noticed that it is much better graduated (the DD was all or nothing). If i pushed the throttle all the way (through the mud i am only going about about 5 MPH) the rear wheel would spin in the mud - once I realised it did that i could not resist it, childish but fun

When i got back the battery indicator had just lost its second bar, on the DD it was three bars gone (voltage at rest was 48.7v, - wish i would have measured the DD).

All the above is really good, but the biggest difference is between assist 1 and 0, ignoring downhill there were few occasions when i could pedal without some assistance with the DD. But the GH is a world away (at least for my legs!) I don't know what the resistance/drag is from a 1000W DD with no power applied (and its extra weight), but I must have trebled the distance i pedaled without assistance. Of my 30 miles that may only be an uplift from 1 to 3 miles without assistance, but add that to using a lower assist for the steeper hills and the extra distance on my battery should be quite noticeable

I am now considering a smaller battery, may be a 15AH which will reduce weight further, but give me about the same distance as the DD did with my 20AH, the piggy bank is looking scared!

Thanks again to those of you for introducing me to the GH as an option - its great.

 

[Deleted member 4366]

I have done a decent ride (30 miles) with the new GH on exactly the same route i have used the DD a number of times, so i can make some meaningful comparisons.

I really noticed the torque, up the hills i was using one setting lower on the pedal assist. On one particular very steep bit i had the DD on 5 and with my pedaling it would hold speed, but with the GH on level 4 i was picking up speed.

Through a couple of short stretches where the mud was deep i use the throttle to keep me going, with my feet off the pedals ready to stop me falling, and i noticed that it is much better graduated (the DD was all or nothing). If i pushed the throttle all the way (through the mud i am only going about about 5 MPH) the rear wheel would spin in the mud - once I realised it did that i could not resist it, childish but fun

When i got back the battery indicator had just lost its second bar, on the DD it was three bars gone (voltage at rest was 48.7v, - wish i would have measured the DD).

All the above is really good, but the biggest difference is between assist 1 and 0, ignoring downhill there were few occasions when i could pedal without some assistance with the DD. But the GH is a world away (at least for my legs!) I don't know what the resistance/drag is from a 1000W DD with no power applied (and its extra weight), but I must have trebled the distance i pedaled without assistance. Of my 30 miles that may only be an uplift from 1 to 3 miles without assistance, but add that to using a lower assist for the steeper hills and the extra distance on my battery should be quite noticeable

I am now considering a smaller battery, may be a 15AH which will reduce weight further, but give me about the same distance as the DD did with my 20AH, the piggy bank is looking scared!

Thanks again to those of you for introducing me to the GH as an option - its great.

You've found out what many did before you. Many are tempted by the very cheap price, and they think that they're going to get four times the power of a 250w one, when they actually get less where they need it.

Those motors do come to life if you increase the current to 40 amps, but then you need an expensive battery and controller, and a bike that can cope with that sort of power.