GrayK's RC Mid-Drive (Deathbike)

GrayK

GrayK

1 mW
Joined
Jan 4, 2018
Messages
18
I have been using CAD so much more recently and decided it was time to make a crazier bike than my old Denzel motor. When I had the fund I started to work on an extremely compact solution. I am using 3 VESC all in a CAN array powering 200kv 6384 sensored motors. Pictures do most of the talking. I was extremely lucky and had a friend of mine waterjet the plates for me. I can hit 40mph on 1st gear and its so much power I worry that I will break the controllers. Still building confidence on it. If there is a big enough demand for these motor assemblies I might start selling them. They are super compact and still can output 100Nm of torque at the drive sprocket. The hardest part now is finding batteries that will be happy to push out 240+ amps so, for now, its 12s Lipo. I also can't get FOC to work on VESC because of a "Flux leakage"
 

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That's quite the build!
Have you considered putting a chain guard over the mid-drive chainsaw mechanism?
 
Hahaha thats so funny yeah kinda have been busy recently with school but for now i'm wearing shorts and tucking in laces
 
Great project!
Do you have some videos to share with us?
I can see some LG 18650 cells, is this your backup power to get you home when you run out of lipo power??
 

They arent 18650s they are large Caps I think you are talking about the VESC noise protection but im not sure. I will post videos soon
 
GrayK said:
I can hit 40mph on 1st gear and its so much power I worry that I will break the controllers.
Click to expand...
I'd worry more about breaking the chain/cluster. That's a lot of torque for a bike chain designed for ~250 watts.
 
billvon said:
GrayK said:
I can hit 40mph on 1st gear and its so much power I worry that I will break the controllers.
Click to expand...
I'd worry more about breaking the chain/cluster. That's a lot of torque for a bike chain designed for ~250 watts.
Click to expand...

I put a torque curve on the motor controller for that reason. It ramps up the power from 10% to 100% in a given time independent from the position of the throttle.
 
GrayK said:
I put a torque curve on the motor controller for that reason. It ramps up the power from 10% to 100% in a given time independent from the position of the throttle.
Click to expand...
That doesn't sound like it limits the torque, just reduces the ramp rate.
 
billvon said:
GrayK said:
I put a torque curve on the motor controller for that reason. It ramps up the power from 10% to 100% in a given time independent from the position of the throttle.
Click to expand...
That doesn't sound like it limits the torque, just reduces the ramp rate.
Click to expand...

Yeah its a current ramping limit. Basically a torque limiter
 
That's a really good frame to run as left hand drive since the rear drop out is 150mm. With a 40mph first gear that's all your need. That would also let you run more of the reduction on the rear wheel via 219 chain.
Plus your be able to pedal and chain breakage is much less likely.

I bet it sounds wild!
 
GrayK said:
Yeah its a current ramping limit. Basically a torque limiter
Click to expand...
But it doesn't limit the torque; just limits how fast it rises. Your powertrain still has to withstand all the torque the motor can put out.
 
I disagree since Torque generated = (60 * K * I * flux)/ 2pi where K is the armature torque constant and I is the current. The torque generated is directly proportionate to the current being fed into them.
billvon said:
GrayK said:
Yeah its a current ramping limit. Basically a torque limiter
Click to expand...
But it doesn't limit the torque; just limits how fast it rises. Your powertrain still has to withstand all the torque the motor can put out.
Click to expand...
 
GrayK said:
I disagree since Torque generated = (60 * K * I * flux)/ 2pi where K is the armature torque constant and I is the current. The torque generated is directly proportionate to the current being fed into them.
Click to expand...
Agreed. So if you limit the current, you limit the torque. If you let the current ramp up to maximum, then you ramp up to maximum torque.
 
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