Propeller driven Lego car.

Lego Technic is perfect for creating quick prototypes of pretty much anything, combine this with RC stuff and you can create really fun stuff. One simple example is the robot i describe in this post:
Sunday afternoon robot

My old Lego is usually stuffed away in a box in the basement, but when we have kids visiting we usually bring it up to the apartment. I suspect I’m the one enjoying it most and this time I built a RC lego car

Lego Propcar 1
From the side
Lego Propcar 2
The motor and propeller us used as a pusher
Lego Propcar 3
The battery, ESC and receiver is secured with a rubber band
Lego Propcar 4
I use a HXT900 servo to steer

After a few testruns I added a propeller protection bar to minimize the risk of running into something with the propeller.

Lego Propcar 5
Propeller protection

Runs great, I’ll probably update this post with a video when I’ve recorded one.

Battery bag for my E-Bike

Last weekend we borrowed a sewing machine to make new curtains for the apartment. When I was sewing the curtains I realized that It wouldn’t be very difficult to make a custom battery bag for my e-bike. I would like a bag that I could mount in the frame triangle and have room for 4 Turnigy 6S 5Ah batteries. Doing some measurements, calculations and drawing I came up with this design

Battery bag drawing
An outline of the battery bag, the red triangle is the frame, the blue rectangles are batteries and the gray rectangle is the controller mounted on the frame.

I went to the fabric store and found a black nylon fabric that had a PVC layer on one side. This should be fairly water resistant and I plan to spray it with some textile waterproofing spray as well. I was recommended to use a thread for furniture which is much stronger than ordinary thread as well. A couple of hours thinking, cutting, and sewing later:

Battery bag
I use some Depron in the bottom, and some foam in the two corners to protect the batteries and fill out the bag.
Zipper
The zipper has a bit of fabric folding over it for water protection
Hole for cable
The hole for the cable is also waterproof since the side of the bag overlaps ~10 cm where the cable comes out.
Cable
I'm using the cable I made for the E-Puch. This cable is for two turnigy batteries in series and two in paralell with a 60A fuse. The LEGO part is just for size reference.
Packed
Everything fits nicely inside the bag

The bag fits perfect on the bike!

Battery bag on bike
Battery bag on bike
Battery bag in frame
Battery bag in frame

Pleas write a comment if you think I should make some kind of drawing and description on how to make a bag like this.

Have somebody seen my magic smoke?

A little while since the last post, this is maybe old information if you have read my posts on Endless Sphere or the Swedish Electronics Forum. We played around for the whole weekend with the moped until the motor got enough. My guess is that several hard accelerations during a short period of time heated the stator enough for the insulation to melt.

The black insides of a BLDC motor
The black insides of a BLDC motor

Not pretty! I’m afraid I’ll have to torment my hands with another rewind. A member on SEF is good enough to donate a large roll of 1,5 x 2,5 mm flat copper wire to me which I will use for the rewind. I have three different actions to prevent this from happening again.

  • Increase the gear ratio. Less torque on the motor means less current.
  • Increase kv, one less turn of copper wire will increase kv to match the higher gear ration and reduce the resistance. It will also leave more room for air to flow through the motor
  • Forced cooling, I’ll put a fan in one end of the motor to force more air through.

I’ve also ordered a spare motor from china. The 80-100 is very hard to get nowdays, but I found a 80-85 motor with the same mounting profile and axle. But i’ll keep a close watch on the stock of the 80-100 motor.