Mid-drive torque limiter / slipper clutch -> help please!

[planky81]

Hello,

would be nice to get some help/advice

First my setup:
Motor: Astro 3215 T6
Battery: 48V LiFePo4 Pack
Gearing: Neugart PLE 32:1

I will connect the output shaft of the motor with a belt to the input of the Gearing.
My concern is the huge torque when i open up the throttle from 0km/h. Is this concern legit?
I was reading that people had problems with the belt, the drive train and the Frame.
so i found some nice Torque limiter for the motor shaft.

My Problem: i should pick one and the problem is i don´t know which one because i don´t know the torque range (Nm).

Has anyone any experience in that?
A estimated value would help.

additional data:
max rpm of motor will be around 7000
Tooth wheel diameter on the motor shaft is 56mm (here i want to install the torque limiter)
Tooth wheel 56mm diameter on the gearing input
from the output of the gearing i will use a chain with a freewheel to the cranks.
In the end i have a nuvinci gearing hub at the rear wheel.

help or advice would be really great
Thanks
greetings from Hilly Austria
Planky

 

[motomoto]

Read some threads. Particularly Matt Shumaker threads.

 

[Miles]

planky,

I think you should start by re-examining your overall concept.

You have a (1:1) belt drive solely to get the motor torque into the Neugart......

1 belt drive + 2 stage planetary + 2 chain drives + Nu Vinci = a lot of wasted torque........

The efficiency of your drivetrain alone will be less than 70%. Including motor losses, it will be less than 60%.....

On top of that, you want to burn off excess motor torque in a clutch.....

 

[planky81]

Thanks Miles,

Between the Motor shaft and the neugart gearing the belt connection is 1:1 so the RPMs at the cranks are not to high, i want to be able to peal along.
Is there another option to connect this two elements more efficient? i want them to be parallel so they fit between the cranks.

Do you have any suggestion what my build should look like?

Thanks
Planky

 

[planky81]

thanks Motomoto,

i have read Matt Shumaker´s threads. What info should i find there?
maybe you have a link for me.
i saw he uses a plate that puts pressure on the outside of the toothed belt wheel nut whats on the inside?

thanks in advance

greetz
Planky

 

[Miles]

Between the Motor shaft and the neugart gearing the belt connection is 1:1 so the RPMs at the cranks are not to high, i want to be able to peal along.

If there was a ratio in the 1st stage, it would be underdriven rather than overdriven, so the rpm at the cranks would be lower, not higher..... Every stage adds to losses, so to have a "redundant" stage in order to access a 2-stage gearbox seems a bit of a waste......... You could make the belt drive into a reduction and use a single stage Neugart?

 

[Miles]

Slipper clutches have been used in the past because of the lack of control over the stock RC controllers. Better options are now becoming available with the possibility to exercise control over the effective phase current, and hence torque. Better not to create excessive torque than to turn it into heat....

 

[planky81]

Hello Miles,

i have a optical Hall sensor in the Motor and use a Lyen controller in combination with a CA.
Is there a possibility to limit the torque there (e.a. thru the Current)?

so your advice is to get another gearbox e.a. 16:1 (with less stages) instead of a 32:1 and make a reduction after over the belt, right?


thanks
Planky

 

[Miles]

You have some control (indirectly) over the phase current via the CA.

I think that would be preferable. 16:1 gearbox would still be 2 stages, though.

You want about 70 rpm at the cranks?

 

[planky81]

i was thinking about 120-140 at max rpm of the motor, so i can pedal along in normal/daily speed and if i go for high speed i can´t. i thought that it would be better at high speeds to focus on the street than on pedaling along.

i=8 and i=10 would be 1 stage.

attached my ratio calculation.

Update: whats your opinion?

 

[planky81]

regarding the toothed Belt wheel: From a company which makes Packaging machines i got the info i should use big wheels because if i use smaller one i have more torque on less tooth. thats the reason why i was planing to use nearly 1:1. As i like the drive to fit between the cranks i would like to prefer not a wide toothed belt drive.

What´s your experience on that?

Thanks for your help, again.

regards
Planky

 

[Miles]

regarding the toothed Belt wheel: From a company which makes Packaging machines i got the info i should use big wheels because if i use smaller one i have more torque on less tooth.

It's true - up to the point where you exceed the max. span loading of the belt.

The other thing to bear in mind is the input speed to the gearbox. Is 7000 rpm ok for the PLE version that you intend to use?

 

[planky81]

no problem max. rpm of the gearingbox is 13000.

Would you recommend less RPM at the cranks?

attached new calc

 

[Miles]

Would you recommend less RPM at the cranks?

Yes.

I don't have a fixed ratio between motor and cranks on my bike but, from the feedback on here, having a ratio that isn't in step seems problematic. 100 rpm is much better.

10t is too few teeth at the motor. 18t is more reasonable. Make up the difference in the stage between the gear box and cranks....

 

[Miles]

How about:

Belt 18t to 45t (2.5:1)

gearbox 8:1

Chain to cranks 3.5:1

Total reduction 70:1

 

[planky81]

Thanks Miles,

i go for your advice

Regards from Austria
Planky

 

[Miles]

An 18t to 45t 5M HTD drive 15mm wide would have a rating (for industrial use) of about 6Nm at the driver pulley.

That's 420Nm at the cranks. Divided by three is 140Nm at the back wheel, which is the rating of the Nu Vinci...

 

[planky81]

hello Miles,

spinningmagnets told me that you are using a roller clutch instead of a freewheel.
what are the pros and cons of that solution?
what would you recommend?

thanks
regards
Andreas

 

[panurge]

How about:

Belt 18t to 45t (2.5:1)

gearbox 8:1

Chain to cranks 3.5:1

Total reduction 70:1

Hi Miles
That's a good plan similar to what I had in mind when obtained my PLE80 8:1. the problem I had, not mentioning weight and price, is that, as obvious, for an increase of reduction among the same stage count serie, corresponds a decrease of the torque rate, so for instance a PLE80 i:8 that's a single stage, has a nominal output torque rate of 50Nm, and 80Nm as max output....
So looking at my math :wink: I concluded that with a single stage 8:1 model, 1:1 on the belt is the only reliable option.....
indeed, 6Nm at the driver means 6*3.5*8=168Nm output, and none of the PLE80 is alble to handle this torque nominally, and only those with the lower "i" (reduction) among the same Z (stages) are able to handle it, but really close to their max torque rate. I have made only 2 "table" runs with the Astro and the Neugart just to test the gearbox was working good and in no load conditions, so I'm talking mostly starting from Neugart's datas... I was missing something?

Andreas, I have an i:8 PLE80 sitting here (Italy) if you are interested, it has some years but is in great conditions and works good, I think It's perfect for a cheap try :wink: , also, you have a smaller motor than my 3220 4t. this could help a lot.

If I well remember someone around here has given a try to the PLE80 and a member named RonZ, works with and sells E-kits made by small Astros coupled axially with a PLE60 and a custom freewheel setup featuring a phase current regulation. Maybe you can search or ask advices from him and his posts.

 

[Miles]

Hi Jules,

Good point.

Planky's first stage belt is 2.5:1, so max. torque out from the gearbox would be 120Nm that's 50% over the rated maximum for the PLE 80 i:8. It might not last as long as is expected...

Capping output torque at 5Nm (which happens to be the peak rating for the Astro 3215..) would reduce that to 100Nm.

Changing the first stage reduction to 2:1 would bring that down to 80Nm - meeting the specification of the gear box. The final stage, to the cranks would then need to be 4.375:1. Maybe 14t to 60t of #219 chain?

 

[Miles]

spinningmagnets told me that you are using a roller clutch instead of a freewheel.
what would you recommend?

Hi Andreas,

You will need a ratchet freewheel on the cranks.

If you reduce ouput torque of the gearbox to 80Nm, you could use a CSK25 sprag clutch at the driver pulley of the chain stage.

 

[panurge]

Planky's first stage belt is 2.5:1.....

Yes....sorry, I mixed the stages.... but as you figured, also with 2.5:1 torque still remain, on the paper, too high....
But assuming that 5Nm should be an occasional peak, with a 2:1 belt reduction, yes, it could match well the peak output of the Neugart (Neugart nominal rates are known to be reasonably undersized).
Also, To keep in mind is that Neugarts have an emergency stop at 2*nominal torque rate so 100Nm for the 8:1, this safety stop could be performed around 1000 times.....
However, the declared efficiency loss for the second stage is only around 2%,
so a 2 stage i:9 could be the best one with his 130/208 Nm rates, I have not found one for a reasonable price though...