Day 4: Motor and seat mounts

Today started so terribly.  It was 4:30pm already and all I had was a CAD of a motor bracket. And a partly scrapped attempt at a pair of brackets.

I took a break for 20 minutes, followed by a few minutes of sulking.

Then, 4:55pm, waterjet.

15 minutes after it was done cutting:

waterjet: my sun and stars

This was definitely the boost I needed to get going for the day. The first thing I did was mount the motor, a Turnigy 63-64-A 280Kv 65A Brushless Outrunner (52-30). The drive pulley I am using is steel with 14 teeth, but doesn’t have a hub, so the set screw is really short. Its necessary to have a pretty substantial flat on the shaft so that the set screw clears the pulley grooves.

ground a flat on the motor shaft
really short set screw, 1/4"-20 roughly 0.18" long

For the belt tensioner, I was going to turn a simple idler roller out of delrin, but I came across an even better idea. I found some 1/4″ ID ball bearings, and 4 of them side by side fit really well as a tensioner.  The inner races are just slighly wider than the outer, so even when the bolt is clamped tighly to hold the tensioner position, the bearings spin freely.

tensioner assembly

Overall the geometry worked out really well since the position of the tensioner allows the small pulley to have lots of contact with the belt – less slipage.

Assembled motor mount
top view

The two 1/4″ motor plates on the right clamp to the frame tube, which is one way belt tension can be adjusted. In addition, the tensioner bolt holes are slotted. I thought at first to just weld a motor mount to the frame, but I like the modularity of this way, and the double plates provide added rigidity.

side view

Now onto the seat. I got this off a stool where the seat post screws into the stand to adjust the height. I didn’t really want to deal with these plastic threads. Thankfully, the tube was 7/8″ OD aluminum with plastic molded over it. I took one of those dremel router tools to cut a groove on the plastic, which then just slid off. Although, you can see dimples that were crimped into the tube the retain the plastic before.

dremel router tool

I wanted to mount the seat back as far as possible since the chassis is so short. But the motor mount takes up quite a bit of space, so the seat bracket needed to be extremely compact. I opted for some welded parts and something similar to what you find on a bike.

boring the seat post

I’ve always wanted to ream a hole like this. I just eye-balled the center of the hole, and it actually turned out really well. Below are the two parts of the seat mount that actually clamp to the frame. Here they are aligned in clamps so that the bolt holes can be drilled.

seat bracket frame clamps right before drilling

Just like on a bike, the top of the seat tube is slit so that it can be clamped to the seat post.

slit for seat post clamp

This setup took a while to clamp up before welding. Here a 7/8″ steel rod is used to align the two seat tube halves and two block on either side are used to keep the frame clamps square.

ready to weld seat mounts

The fillets on these were huge. In case the picture doesn’t make that obvious. It took almost 2 feed rods to do these…

another angle
welded seat stuff

The actual clamp on the seat tube is actually just a bike part. The diameters were off, so I bent a thin piece of sheet metal as a shim to go between the clamp and the seat tube I welded.

seat assembly, 3/8" threaded rod clamps everything together

One final touch before I finish for today: a board to mount electronics. By this point I was tired of setting up stuff on heavy machinery, so it felt great to just zip through some 1/8″ polycarb on a bandsaw. The I just sharpied some holes and drilled them out with a hand drill so I could fit some zip ties to hold it in place. Quick. Easy.

electronics board

I am going to mount one battery pack on each side, with a controller in the middle. The clear bottom should let me mount lights in the center, too. So I can look cool.

In summary:

side view



This leaves me with one final day to do electronics. Thankfully, Charles is graciously helping build battery packs, and helping to mount sensors on the motor. I’ll figure out wiring, and some kind of throttle.





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