The previous month I have worked a lot with the throttle. Most of the machining is done, and I have tested that the sensors work with the motor and controller. In addition, I had another go at machining the bracket that holds the throttle and I recieved the tube that will be the main body for the DPV.
The body tube is a high density polyethylene (PE 100) intended for industrial use. This particular tube has an outer diameter of 225 mm and SDR (standard dimension ratio) of 17. This means that the wall thickness is 225/17 = 13.24 mm. The tube was kindly donated from Eurofusion AS (www.efas.no) because they liked my project. Thank you!
Once all the parts are finished, I will measure the weight of everything so that I can calculate how much bouyancy I need. Neutral bouyancy will then be acceived by cutting the tube to exact lenght. Preliminary calculations have showed that the tube needs to be around 520 mm long.
This is the cross-section of the throttle mechanism. The knob on the top controls speed, and the lever on the bottom is for on/off operation.
The first machining operations on the throttle was to face the end, turn the outer diameter to 60 mm and cut grooves so that I could reach in and turn the middle section down to 40 mm before knurling.
I was not sure what diameter the grip needed to be in order to get a good knurl, but I was able to calculate the pitch of the knurl by using the method described by Conrad Hoffman here. I concluded that the diameter needed to be 40.54mm.
The knurling was performed at 90 rpm using manual feed. Coolant was used to prevent chips from building up in the knurl.
The finished knurl. Im quite happy with it as this was my first try at knurling. It's not perfect, but it provides plenty of grip.
Once all the turning was done, the next operation was milling the sides flat, as well as drilling holes for the shaft that the finger trigger will pivot around. I also drilled and threaded the hole for the waterproof cable gland.
Here I am using an edge finder to locate the center of the knob that will be used to regulate the speed of the DPV. Next, 8 slots were cut to increase the grip of the knob.
After many hours of machining, this is how the handle came out. I still have to make the lever for on/off operation, but all the machining on the handle itself is done. I'm very pleased with how it turned out, and really looking forward to trying it on the finished DPV!
Just before christmas I got some help machining the bracket that holds the throttle, but the results were poor. Last weekend we tried again using a new tool path and a different endmill. I had ordered a 3-flute, 6mm endmill from Ebay that was specifically designed for roughing aluminium, so we were quite optimistic. However, the new endmill lasted about 5 seconds before it gummed up and broke. We concluded that there was insufficient room for the chips to clear with such a small endmill, so we tried a 2-flute 10 mm endmill instead. This worked much better, and we were finally able to get a good part.
Here is how the part came out. Some creative workholding was needed to keep the part from moving on the final passes.
I made a short video of the finishing pass of the milling. The milling was performed in two passes per depth step in order to get a good finish. You can hear the endmill being blasted by compressed air to clear away the chips.
Testing the motor and controller. From the left you can see the motor, speed control knob, reed switch and motor controller. The hall effect sensor is mounted to a breadboard next to the throttle.
Here I am demonstrating how the motor will be controlled from the handle of the DPV. On/off operation is triggered by a reed-sensor connected to the brake circuit of the controller, and speed is adjusted by moving two magnets across a hall-effect sensor.