Torque arms, shoddy disc brakes and a new CA

[nonlineartom]

Right then, my eBike is coming along nicely, I'm still very much a N00b but slowly learning everything. Having a few doubts and questions I wanted to run past everyone here any hopefully get a bit of help so bear with me

I recently moved to a 750W rear motor and got a new Specialzed hardrock, problem is the specalized has really shallow dropouts. I knew I needed torque arm but was reluctant to pay 40 quid with the shipping and then wait 6 weeks for them to arrive (to the UK) I tried to make a home made torque plate out of an old kickstand that just butted up against the frame in an attempt to stop the axle from destroying the frame. I've ridden about 100 miles over a variety of terrain, took it off today to find this...

I consider myself very lucky! A few more miles and it probably wouldn't have been very pretty, it seems to have just steadily worked it's way out, no regen on this controller but the motor has plenty of torque. Luckily my overpriced scraps of steel, dropouts arrived today so I went about fitting them, realised I couldn't mount them on the motor wire side without cutting and re-soldering cables to thread it over the wire so decided to use just one on the other side (is that ok?) This is my application, I can't decide if it's upside down or whether the forces are going to tear it apart or do more damage...

The axle is seated as low in the dropout as it can and the torque arm is tied down with the supplied U bolt and plate, tightened really tight but no threadlock. I take this bike on "black" level MTB trails with some fairly big drops so this setup will take some heavy impacts.

As you can see in this picture I'm using the supplied disc brake and mounting, which is absolutely awful. There is a worrying about of play in the mounting and it screeches and squeeks like a swine unless it's set up perfectly, then as soon as you set off it goes out of calibration and is rubbish again, and the stopping power is 1/10th that of the standard Tektro budget brake I've got on the front. I would used the standard Tektro on the back on those currently unused brake mounts but the callipers are too deep and conflict with the motor casing, It's the screw on type disc rotor so I can't seem to space the disc out further away from the hub. Anyone got any words of wisdom on this? The motor is from an eBay seller called "SannyKung" It looks identical to my old Conhismotor 500W front motor but it's a lot lot quieter and smoother.

*takes breath* and finally, I just got a CA so I can actually tell when I'm going to be stranded with a dead battery. Spent a frustrating evening with a toy soldering iron trying to wire in the shunt resistor. Plugged it in to my freshly charged battery ( conhismotor 36V 15ah Lipo4 gaffer pack A123) and this is the screen I was greeted with

45 Volts, is that right?! and is it normal to be always using 2W when stationary? I took it for a quick test ride and noticed at full throttle on the flat I was pulling 1100 to 1200W not 750W that the motor / controller was purchased as, is that normal? I've blown the 13amp fuse 3 or 4 times when going up very steep hills.

well yes there we go, my quest to build the ultimate super-commuter / weekend trails hybrid continues, I've got some Maxxis 2.5 tires riding in the mail that should be here any day and a few other bells and whistles to go on. Thanks for reading and I await the great wisdom of ES

 

[wesnewell]

Don't worry about the 1200W draw. I draw over 1500W on my 500W motor under heavy loads. That's normal. I'd get a hacksaw and/or file and deepen those dropouts so the axle fits deeper into them. I'd also do something about the way the torque arm connects to the swing arm. The brackets that attach to the swing arm look like they would slip easily. I'd use solid brackets with just one hole that would match to the hole in the swing arm and bolt it that way. Or make it triangle shaped and use both holes in the swing arm for added strength. And I'd use both torque arms even if I had to cut the wires and add more connectors. Almost forgot, get a bigger fuse, 15-20A.

 

[dogman dan]

Yep, deepen the dropouts enough to get the center of the new axle same as the old one. Usually about 2 mm does it.

 

[nonlineartom]

Thanks for the help, a few more things to note:

The battery just died at 13ah, it's a 15ah battery, is this normal?

I've just blown my THIRD innertube, the rim tape looks intact, each blowout as been a tear in the innertube on the inside of the tube, any ideas?

 

[The Mighty Volt]

I like that brake-disc arrangement, did you get that from Conhismotor??

I have been having no end of brake disc issues.

 

[The Mighty Volt]

Thanks for the help, a few more things to note:

The battery just died at 13ah, it's a 15ah battery, is this normal?

I've just blown my THIRD innertube, the rim tape looks intact, each blowout as been a tear in the innertube on the inside of the tube, any ideas?

For the tube, check the tire. There may be a bit of a nail or a tack or a thorn broken off inside the tire that is shredding the tubes as you fit them. Make sure also you are not pinching the tube.

As for the battery, dying at 13Ah is normal if the battery is new, and is not balanced. Bring it back to full charge and discharge it 80% and then recharge it. In due course you should start to get closer to the 15Ah capacity.

 

[nonlineartom]

Thanks for the feedback. The battery is about 4 months old, always has the BMS so balances itself, It's usually discharged about 50% and then charged, 5 days a week, every week. It's a nice battery otherwise, very little voltage sag, its an A123 pack ( I think )

The disc brake is from a different eBay seller but is identical to the one conhismotor sell. It's good because the turning force is on the axle not the frame, and I think it's made from old warship it's designed the last. Just a shame I can't get the callipers to bite, and god knows where I will get spare pads from

 

[AussieJester]

Just a shame I can't get the callipers to bite, and god knows where I will get spare pads from

Those brake calipers look pretty much identical to what ChoppersUS sell IIRC they also carry the pads for them.

KiM