Overview:
Project is based around 60KG Robot Servos, controlled from Arduino configured as Custom Serial Device in SimHub. It is relatively easy to assemble, works quite well and cost is moderate (compared to other options).
Robot Servos: Project utilizes 60KG robot servos. They are pretty strong and fast enough for such application. Be careful not to drive them at full lock - they use up lot of juice in full lock and generally can hurt you! They have decent travel (mine are 180 degree) and it is more than enough for a belt tensioner.
Seatbelt: Preferably use 5 or 6-point harness. Four Point Harness is possible but does not work well - when servos pull it on top it just moves around - does not tighten your shoulders. Harness should be fixed from the bottom of the buckle so it remains static and actually have the compression effect - thus at least 5 point.
Supercapacitors: They are optional but recommended part. They smooth out the servo response by profividng constant current. Servos operate faster and quieter with the supercaps
Power Supply: Be careful with the PSU - this type of servo is rated at 6.2A on full lock and this is a lot of power. Preferably drive them at 8V, limit is 8.4V without supercaps. More on this topic further down...
There are several options based on complexity and accessories to build this Project:
Basic Setup:
Includes 2x Robot Servos + Arduino controller + PSU. This is the most simple and basic setup, works well enough and does the job. Be careful with the power supply - these servos pull about 3.5-4A on full lock, you will need properly sized PSU.
Supercapacitor Extension:
You can add 3x automotive Supercapacitors in series (best approach is to buy pre-soldered component with integrate balancer circuit). The supercaps smoot out servo operation by providing constant power on surges. What you get at the end is smoother, faster and quieter servo operation. This also unloads the PSU by removing the peak drains.
Offload circuit (button or relay operated):
As supercaps store a lot of energy they take considerable amount of time to unload themselves. If no load is connected mine would take up to 10 minutes. As a safety precaution I decided to add and offload circuit. First one was automotive headlight bulb connected in parallel with a switch - when shut down the PSU I switch the circuit on and drain the Supercaps.
Later extended this with Automotive Blinker Resistor + LED indicator to operate as off-load. I added Automotive Relay to make this switch automated (always wanted to build central console with relay on it). utilizing the relay also decouples galvanically both circuits - when switched off capacitors are connected directly to Offload circuit and PSU is disconnected.
Keep in mind this circuit is not needed, I added it just for precaution and extra satisfaction.
Parts List
- 1. Robot servos 2x, 60KG, 180deg - preferably buy the ones with metal bracket. Do not bother with weaker servos - they burn fast.
- 2. Seat belt - 5 or 6-point harness, 4 does not work well
- 3. Arduino Nano/Pro Micro - maybe others work but I have not tested them
- 4. Super Capacitor High Current 2.7V 100F, 16V 16.6F - cheapest and easiest option is to buy Double Row 6 piece capacitor assembly and cut it in half. These capacitors require ballance circuit for charging and this would be the easiest option to go for.
- 5. DC-DC Buck Converter Step Down Module - I used 300W, 20A peak (15A constant) - needed to step down to 8V
- 6. Power Supply - 12V are the most common and accessible units. I am using 24V as it is also powering my Bass Shakers. Be sure to have adequate current rating.
- 7. Additional parts - automotive fuse and holder (10A), power switch by choice, connectors, cables, digital voltmeter
- 8. Offload circuit - automotive relay if you wish it automated, automotive blinker resistor (1-2.5 OhM), indicator light (LED) by choice
3D Printed Parts
- 1. Seat Belt rollers - ball bearing, remove friction in belts to provide much better experience
- 2. Enclosure for the Step Down Buck Convertor
- 3. Enclosure for supercaps/arduino
- 4. PSU Control Unit for additional extras you want (offload circuit, relay, etc.)
Software
- 1. Arduino Pro Micro + modified SimHub Arduino Sketch - Servo Belt Tensioner on GitHub
- 2. Original BluePill Arduino Sketch if preferred - Blekenbleu on GitHub
- 3. SimHub - Official SimHub Page
Power Considerations
- 1. Servos are rated 6.2A at full lock. I measured mine on Full-Lock at about 4A (ranging from 3.8-4.2A). On "Normal-Lock" (meaning my shoulders do not huirt) it consumes about 2.2A. Stil times 2 both servos will consume almost 5A continuous
- 2. Servos are rated at 8.4V, but Supercaps are 2.7V each - total 8.1V for the three of them. Operationg them at about 8 ensures good performance/longevity balance
- 3. If you cannot find direct PSU at 8 V you will have to add the Step Down DC-DC module
- 4. Servo cables look thin but they are not. For the rest of the circuit I used 16AWG and 18AWG wire (compute PSU grade). You will be powering two servos at about 8V 5A constant at times - be careful with cabling!
- 5. If you add the supercaps you can get away with lower rated StepDown (6A should be fine). If you skip supercaps opt for at least 8A Step down.
- 6. With SuperCaps you can limit your StepDown to 4-5A if it supports it for safety. Without Supercaps this will underpower the servos so use proper rating StepDown.
- 7. Use proper 12V PSU. With Supercaps 5A at 12V should be enough. Without supercaps you need full power realtime, this translates to 5.33A - go for at least 6A 12V PSU
Price Estimate
All these prices are current at the time of writing the article. They are calculated with shipping in Europe. Aliexpress links constantly change and are hard to maintina but searching by component name shoudl give you the part.
| Core Components | Supplier | Price | Count | Total |
|---|---|---|---|---|
| Robot Servo 60KG, 180DEG, Metal Bracket | AliExpress | 33.36 EUR | 2 | 66.72 EUR |
| Arduino Pro Micro | AliExpress | 4.52 EUR | 1 | 4.52 EUR |
| 5-Point Harness | Race-Shop.com | 56.20 EUR | 1 | 56.20 EUR |
| DC-DC Buck Converter Step Down Module 300W 20A | AliExpress | 4.85 EUR | 1 | 4.85 EUR |
| LED Power Supply adapter 12V 5A minimum with SuperCaps, 8A without | AliExpress | 13.78 EUR | 1 | 13.78 EUR |
| Electrical Wire Black-Red - 18AWGx2 (0.75x2), 5m | AliExpress | 3.63 EUR | 1 | 3.63 EUR |
| Illuminated Led Toggle Switch With Safety Aircraft Flip Up Cover Guard 12V20A | AliExpress | 1.79 EUR | 1 | 1.79 EUR |
| Car Blade Fuse with Holder 10A | AliExpress | 0.71 EUR | 1 | 0.71 EUR |
| SubTotal | 152 EUR | |||
| Extended Circuit | Supplier | Price | Count | Total |
| Super Capacitor High Current 2.7V 100F Double Row 6pcs 16V 16.6F | AliExpress | 18.19 EUR | 1 | 18.19 EUR |
| Aluminum Power Metal Shell Case Wirewound Resistor 50W-1R | AliExpress | 1.07 EUR | 1 | 1.07 EUR |
| Automotive Relay JD1914 12V 40A 5p | AliExpress | 2.2 EUR | 1 | 2.2 EUR |
| 6mm LED Waterproof Metal Indicator Light Signal Lamp 12V | AliExpress | 0.75 EUR | 1 | 0.75 EUR |
| SubTotal | 22 EUR | |||
| Total | 174 EUR |
Comments
0 # jaz2