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User avatar
By BMWi8
#145895
This thread will review upgrades to the Avigo (Aria Child) BMW i8 6V electric powered car. Note that a 12V version does exist, but I am not familiar with it.

PHASE 1 - BATTERY RUN TIME UPGRADE
The first thing I noticed was insufficient "run-time". After about 20 minutes of use, the i8 sounded different and was visually slower. Sure enough, checking the LED "power meter" showed only the red LED illuminated. There are 2 main factors which affect this run-time, that being load on the motor and battery capacity (amp hour rating). I cannot easily change the load on the motor, as this is determined by weight of the operator and resistance (both slope and rolling resistance). I can however change the battery to a higher Ah rating!

The battery tray appears to be designed for several different sizes. After taking some measurements I went with the 6VDC 12Ah sealed lead-acid battery by Keyko Japan.

Supplies
1. Wire stripper & terminal crimp tool
2. 2x 1/4" female spade connectors (for 12 gauge wire)
3. 6VDC 12Ah replacement battery by Keyko
4. Phillips screwdriver
5. Rubber bumpers
6. Electrical tape (optional)

Procedure:
1. Remove original battery, 2x phillips screws and black battery cap
2. Cut off red (positive) and black (negative) terminals as close as possible to their ends
3. Strip 1/4" of insulation off each wire and crimp on 1/4" female spade connectors
4. Add rubber bumpers as needed to reduce battery vibration (vibration can shorten battery life). I did the underside of the hold down bar and one end of the battery
5. Install, cover terminals with electrical tape, charge and enjoy over 50% more runtime!

PHASE 2 will be upgrading from 1WD (the factory installed motor drives only the right rear wheel) to 2WD.
Attachments
Battery Upgrade 1.jpg
Battery Upgrade 2.jpg
Battery Upgrade 3.jpg
Battery Upgrade 4.jpg
Battery Upgrade 5.jpg
Battery Upgrade 6.jpg
Last edited by BMWi8 on Wed Feb 07, 2018 5:35 am, edited 2 times in total.
User avatar
By BMWi8
#145901
PHASE 2 - UPGRADE FROM 1WD TO 2WD
If the BMW i8 attempts to climb the valley between the street and driveway at an angle, the single drive wheel can loose traction and the car gets "stuck". The ability to go through grass is a struggle and use in light snow or ice is non-existant. Time to upgrade to 2WD!

You can purchase replacement motors ($15) from http://rollplay.net/products/view/6v-bmw-i8-silver
I chose to wire the 2nd motor in parallel with the existing motor. As such, the 6VDC battery will see half the resistance and output twice the current. There is risk the relays (HF3FF) on the original control board will not be able to handle this additional current, and overheat. The relay data sheet says version "1C" is rated to 10 Amps at 28VDC or 280W. If I divide 280W by the battery voltage of 6 VDC that gives me almost 47 amps... using a DC clamp meter I did record a very brief spike of up to 36 amps from the battery when stalling both motors, so maybe it will be fine?

Supplies
1. Wire stripper & terminal crimp tool
2. male and female connectors and / or solder
3. stranded wire
4. replacement drive motor and gearbox
5. Pry tool & needle nose pliers

Procedure:
1. Cut the majority of wire harness off from new motor, strip and crimp connectors to wire ends
2. Pry off center BMW cap, use pliers to remove cotter pin, remove outer washer and wheel
3. Remove black 1.5" long plastic spacer, ensure inner washer is in place, install new motor and gearbox assembly, re-install wheel, outer washer and cotter pin
4. Use several zip ties (or one long one) to secure gearbox in same manner as original gearbox
5. Depress metal tabs inside original motor harness connector, remove both contacts, solder stranded wire and re-insert contacts
5. Connect wires, noting that the white wire from the new motor needs to connect to the blue wire of the original motor to allow both motors to operate in the same direction (otherwise you'll spin in a circle)

Observations:
The extra torque handles "heavier" riders easier. Runs through the grass better. Does make a louder noise during turns, as the outside wheel needs to spin faster than the inside... which the motors aren't set up to do.

PHASE 3 will be upgrading to a 12 VDC ESC system... in about a month
Attachments
2WD 1.jpg
2WD 2.jpg
2WD 3.jpg
2WD 4.jpg
2WD 5.jpg
2WD 6.jpg
2WD 7.jpg
Last edited by BMWi8 on Tue Feb 06, 2018 8:57 pm, edited 1 time in total.
User avatar
By Masterjosh
#147654
was just curious if u had any update on your project. I have a 6v Rollplay chevy police truck and the inside guts looks insanely close. everything looks identical, so i went on a whim and just ordered the gearbox as i believe its prob the same, however its odd that on the parts page for the truck my son has it doesn't list the motor/gearbox as a part you can purchase..so i went to the 6v truck non police version and it was there. also curious in what the difference would be if u wired the motors in series instead of parallel as you did? was just curious how things were holding up for you.
User avatar
By BMWi8
#148444
Masterjosh wrote:was just curious if u had any update on your project. I have a 6v Rollplay chevy police truck and the inside guts looks insanely close. everything looks identical, so i went on a whim and just ordered the gearbox as i believe its prob the same, however its odd that on the parts page for the truck my son has it doesn't list the motor/gearbox as a part you can purchase..so i went to the 6v truck non police version and it was there. also curious in what the difference would be if u wired the motors in series instead of parallel as you did? was just curious how things were holding up for you.


In series would result in each motor seeing half the voltage... so top speed would be almost half, but you would have 2WD and more rimpull or torque to drive in rougher ground (higher rolling resistance) like grass. So far, no issues with the extra current going through the relays... but I didn't run more than 2 months and removed the factory relay board to run a 12 VDC setup through my own relay.
Last edited by BMWi8 on Wed Feb 07, 2018 5:38 am, edited 1 time in total.
User avatar
By BMWi8
#148445
vtjballeng wrote:
BMWi8 wrote:PHASE 2 - UPGRADE FROM 1WD TO 2WD

PHASE 3 will be upgrading to a 12 VDC ESC system... in about a month


So, how has the durability been? Did you upgrade to 12V?


No issues for the 2 months running higher current through the factory relay board. Yes, I upgraded to 12 VDC. Hope to post results this month!
User avatar
By BMWi8
#148446
PHASE 3 - PART 1 - Adding 12 VDC battery
Since the dashboard, steering wheel sounds, lights and aux audio input with amplifier all rely on 6 VDC, I decided to leave the 6 VDC battery and add a 12 VDC battery. I went a bit overkill with 18Ah, which adds extra weight, but I suspect it will take at least a hour of operation to run this battery down to where you would notice lower power.

Supplies:
1. 12 VDC AGM battery, 18Ah or less
2. 1/2" by 1/2" aluminum angle (3 foot long pieces are at most hardware stores)
3. 1/8" aluminum pop rivets
4. 2x 3/16" carriage bolts + 2x nuts

Procedure:
1. Measure and cut the aluminum angle per the dimensions of your battery, allowing extra length to rivet the ends
2. Drill holes in each "corner" and rivet to make a 4-sided aluminum frame
3. Drill 2x 3/16" holes mid-way on the left and right side of the frame, along with matching holes in the plastic car body
4. Trim out the car body holes to a square shape to match the square underside of the carriage bolt
5. Install battery, frame, bolts and tighten down nuts

Observations:
The extra weight at the rear may help traction, but the car is heavier to pick up and move around. The last photo shows the black battery mounted against the back wall at an angle. This is a sealed AGM battery, so the angle won't affect operation or battery life. You need a battery shape that doesn't stick out far enough to interfere with installation of the seat - keep this in mind as some battery designs may be too "thick".

... next will be the ESC and new foot throttle to make use of the 12 VDC battery (you can see the silver cased ESC in the last photo)
Attachments
Battery 1.jpg
Battery 2.jpg
Battery 3.jpg
Last edited by BMWi8 on Wed Feb 07, 2018 5:43 am, edited 1 time in total.
User avatar
By BMWi8
#148447
PHASE 3 - PART 2 - FOOT PEDAL REPLACEMENT
I went with an $8 Foot Pedal I found on eBay. It uses a 49E Hall Effect semiconductor which according to a generic datasheet allows 3 to 6.5 VDC input and varies the voltage output from 0.86 - 4.21 VDC based on the strength of the magnetic field it sees. When I applied 4.5 VDC to the pedal, the maximum output voltage (pedal fully depressed) was about 3.8 VDC on the green wire. When I applied 6.0 VDC, the maximum output voltage (pedal fully depressed) was about 5.2 VDC on the green wire... which is greater than what the spec sheet indicates. This should work well with a ESC designed to be controlled by a hall effect sensor and eliminate the "whiplash" from the factory's almost instant on design.

UPDATE 2/7: My notes were off on how I attached the spacer plate, corrected below plus a photo of the 49E sensor

Supplies:
1. Foot Pedal w/ integrated hall effect sensor (eBay search for "Foot Pedal Electric Car Vehicle Throttle")
2. 1/8" thick ABS plastic sheet
3. Plastic adhesive
4. #10 x 1" pan head sheet metal screw

Procedure:
1. Pry out old pedal and note plastic car body has a slight depression about 1/8" deep
2. Trace old pedal (after removing the switch) on 1/8" ABS sheet and cutout a spacer plate in the same shape
3. New pedal has 3 tabs which stick out from the bottom. Cut 1 notch and 2 slits in the ABS plate for these 3 tabs, then make a center cutout to allow the pedal to be fully depressed
4. Use plastic adhesive to secure the spacer plate into the depression
5. Remove the two top screws and drill a single hole down through the BMW floor. A #10 x 1" sheet metal screw was used to secure the new pedal.

Observations:
Fabricating the adapter plate was time consuming, but the fit is solid. I applied some plastic adhesive to help keep it in place, but this may not be the best permanent solution.
I noticed the pedal was difficult to depress all the way down. The rubber boot doesn't collapse very well, so I removed the 2 top screws, swung open the pedal and cut off the top 1/2 of the rubber boot. It may not protect the hall sensor from water as well, but you can fully depress the pedal much easier. All the attached photos show the rubber boot removed for clarity.

Next will be the ESC to make use of the new foot pedal...
Attachments
Pedal 1.jpg
Pedal 2.jpg
Pedal 3.jpg
Pedal 4.jpg
Pedal 5.jpg
Pedal 6.jpg
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